Sheep Pox and Goat Pox Differential Guide

Overview and Taxonomy of Capripoxviruses: Differentiating Sheep Pox Virus, Goat Pox Virus, and Lumpy Skin Disease Virus

The genus Capripoxvirus (CaPV), within the subfamily Chordopoxvirinae of the family Poxviridae, comprises three of the most economically devastating viral pathogens affecting livestock production across Africa, Asia, and the Middle East: Sheep pox virus (SPPV), Goat pox virus (GTPV), and Lumpy skin disease virus (LSDV) [1, 3, 6]. These large, double-stranded DNA viruses share a remarkable degree of genetic and antigenic homology, with nucleotide sequence similarities reaching up to 97% across the three species [2, 4, 7]. This extraordinary genetic conservation presents profound challenges for differential diagnosis, vaccine selection, and disease surveillance, particularly in regions where multiple capripoxviruses circulate sympatrically [3, 5]. The World Organisation for Animal Health (WOAH) classifies sheep pox, goat pox, and lumpy skin disease as notifiable diseases due to their transboundary nature and capacity to cause catastrophic economic losses, and the Food and Agriculture Organization (FAO) has prioritized their control within global livestock health frameworks [1, 5, 10].

Taxonomic Classification and Genomic Architecture

The taxonomic framework of the Capripoxvirus genus is rooted in both serological cross-reactivity and genomic phylogeny. Historically, classification relied upon host species specificity: SPPV was considered the causative agent of disease in sheep, GTPV in goats, and LSDV in cattle [1, 3]. However, contemporary molecular characterization has revealed that this host restriction is not absolute, and cross-species transmission events, particularly involving GTPV infecting sheep and SPPV infecting goats, are well-documented [4, 6]. The genome of capripoxviruses is a linear, double-stranded DNA molecule ranging from approximately 145 to 150 kilobase pairs, encoding over 150 open reading frames [9]. The central core region is highly conserved among the three species, encoding essential genes involved in replication, transcription, and virion assembly, while the terminal inverted repeat (ITR) regions exhibit greater variability and have been exploited for species-specific diagnostic targeting [3, 4].

Phylogenetic analyses based on the P32 gene (encoding a major envelope protein) and the RPO30 gene (encoding the RNA polymerase subunit) consistently resolve three distinct clades corresponding to SPPV, GTPV, and LSDV [4, 6]. The P32 gene, in particular, has served as a cornerstone for molecular epidemiological studies, as its sequence divergence is sufficient to differentiate the three species while maintaining enough conservation for universal capripoxvirus detection [6, 7]. Importantly, the high degree of homology within the P32 protein explains the extensive serological cross-reactivity observed among capripoxviruses, complicating efforts to develop species-specific serological assays [2, 7]. As noted by Saidi et al. (2023), phylogenetic clustering of Moroccan SPPV isolates within the SPPV clade confirmed the utility of P32-based genotyping for guiding vaccine selection, emphasizing that homologous vaccines (i.e., SPPV vaccines for sheep) provide superior protection compared to heterologous GTPV-based vaccines in endemic settings [6].

Biological and Pathological Distinctions

Despite their genetic similarity, SPPV, GTPV, and LSDV exhibit distinct biological behaviors that manifest in differential host tropism, clinical presentation, and epidemiological patterns. Sheep pox and goat pox are characterized by generalized pox lesions affecting the skin, mucous membranes, and internal organs, with morbidity and mortality rates that can exceed 80% in naive populations, particularly in young animals [1, 5]. The clinical syndromes are virtually indistinguishable between sheep and goats, presenting with pyrexia, lymphadenopathy, multifocal papular to pustular skin lesions, and respiratory distress due to pulmonary involvement [1, 3]. This clinical ambiguity necessitates molecular differentiation, as serological methods cannot reliably distinguish SPPV from GTPV infection [3, 4].

Lumpy skin disease, in contrast, is primarily a disease of cattle and water buffalo, although recent evidence suggests that LSDV can infect certain wildlife species and, under experimental conditions, small ruminants [2, 4]. The disease is characterized by firm, circumscribed skin nodules (hence the name "lumpy skin"), severe lymphadenopathy, edema of the limbs and brisket, and a pronounced drop in milk production [2, 7]. While LSDV shares the same generalized pox pathology as SPPV and GTPV, the nodular lesions in cattle are typically larger and more deeply seated than the superficial papules seen in small ruminant pox [1, 2]. Importantly, the economic impact of LSDV extends beyond mortality; affected cattle suffer from permanent hide damage, reduced fertility, and secondary bacterial infections that can lead to chronic debilitation [2, 7].

Host Specificity and Cross-Species Transmission

The traditional paradigm of strict host specificity within the Capripoxvirus genus has been increasingly challenged by molecular epidemiological data. Wang et al. (2021) explicitly noted that "Capripoxvirus are not strictly host specific," a finding that has profound implications for disease control strategies [4]. Field reports have documented GTPV causing clinical disease in sheep and SPPV infecting goats, particularly in regions where mixed flocks are common and vaccination practices involve heterologous strains [3, 4]. Furthermore, the widespread use of attenuated GTPV and SPPV vaccines to protect cattle against LSDV, a practice born from the serological cross-protection afforded by their genetic similarity, has created a complex immunological landscape where vaccinated animals cannot be serologically distinguished from naturally infected ones [2, 7].

This cross-protective phenomenon, while economically advantageous in resource-limited settings, has introduced a critical diagnostic dilemma. Yuan et al. (2024) highlighted that "available serological testing methods cannot accurately differentiate cattle vaccinated with GTPV from those infected with LSDV, posing a significant risk for disease spread" [2]. The development of DIVA (Differentiating Infected from Vaccinated Animals) strategies has therefore become a priority for capripoxvirus control programs. The identification of LSDV-specific genomic sequences, such as the synthesized gene described by Yuan et al. (2024), has enabled the development of indirect ELISAs that detect antibodies unique to LSDV infection without cross-reacting with GTPV or SPPV vaccine-induced antibodies [2]. Similarly, Chang et al. (2025) successfully generated monoclonal antibodies targeting the P32 protein of LSDV that do not cross-react with SPPV or GTPV, establishing a double-antibody sandwich ELISA capable of distinguishing LSDV from its small ruminant counterparts [7].

Molecular Diagnostic Approaches for Species Differentiation

The inability to differentiate capripoxviruses clinically or serologically has driven the development of molecular diagnostic tools that target species-specific genomic regions. Zhao et al. (2014) pioneered a loop-mediated isothermal amplification (LAMP) assay targeting the ITR sequences of SPPV and GTPV, achieving 100% detection rates for GTPV and 98.8% for SPPV in preserved epidemic materials [3]. This method offers significant advantages for field deployment in endemic areas, as it requires only a simple heat block (62°C for 45–60 minutes) and eliminates the need for expensive thermocyclers [3]. The LAMP assay demonstrated no cross-reactivity with other pathogens causing similar clinical signs, including orf virus, foot-and-mouth disease virus, and various bacterial and protozoan agents [3].

Multiplex real-time PCR has further refined the diagnostic arsenal. Wang et al. (2021) developed a system employing universal capripoxvirus primers combined with species-specific probes for LSDV, SPPV, and GTPV, achieving a limit of detection of 10² copies of target genomic DNA [4]. This assay successfully differentiated viruses from ovine (sheep and goat) and bovine samples, with results consistent with RFLP-PCR analysis of the P32 and RPO30 genes [4]. The ability to simultaneously detect and differentiate all three capripoxviruses in a single reaction represents a significant advancement for surveillance programs, particularly in regions like the Thrace region of southeastern Europe, where multiple capripoxviruses have historically entered and where rapid differential diagnosis is critical for outbreak containment [5, 10].

Epidemiological Context and Global Distribution

The global distribution of capripoxviruses reflects historical trade routes, livestock movement patterns, and ecological niches. Sheep pox and goat pox are endemic across northern and central Africa, the Middle East, the Indian subcontinent, and parts of Central Asia, with sporadic incursions into southeastern Europe [1, 5, 6]. Lumpy skin disease, historically confined to sub-Saharan Africa, has undergone a dramatic expansion since 2012, spreading through the Middle East, Turkey, the Balkans, Russia, and into parts of Asia, including China and Southeast Asia [2, 4, 7]. The introduction of LSDV into Europe via the Thrace region of Greece, Bulgaria, and Turkey exemplifies the vulnerability of high-risk border areas to capripoxvirus incursions [10].

In the United States, sheep pox and goat pox are classified as foreign animal diseases, and the USDA Animal and Plant Health Inspection Service (APHIS) maintains rigorous surveillance protocols to detect potential introductions [1]. Simpson et al. (2023) emphasized that US-based practitioners must maintain a high index of suspicion for capripoxviruses when encountering dermatologic lesions in small ruminants, as the clinical presentation can mimic endemic diseases such as orf (contagious ecthyma), ulcerative dermatosis, bluetongue, and dermatophilosis [1]. The authors stressed that "any cases involving unusual dermatologic lesions associated with high morbidity and/or mortality warrant reporting to governmental authorities including USDA APHIS or state regulatory veterinarians" [1].

The economic burden of capripoxviruses in endemic regions is staggering. In the Somali Region of Ethiopia, a participatory epidemiological study ranked sheep and goat pox as the fourth most important livestock disease, accounting for 11.0% of disease prioritization across five districts [8]. The study revealed that disease outbreaks peak during spring and autumn, coinciding with livestock congregation around water sources and increased vector activity [8]. The authors noted that "CCPP and PPR were perceived as the most severe and transmissible, particularly during the summer season," but sheep and goat pox remained a persistent threat due to its high morbidity and the lack of effective vaccination coverage in pastoral systems [8].

Implications for Vaccine Development and Control Strategies

The genetic and antigenic relatedness of capripoxviruses has shaped vaccine development strategies for decades. Live attenuated vaccines derived from SPPV or GTPV have been widely used to protect against homologous infection in small ruminants and, importantly, to cross-protect cattle against LSDV [2, 7]. However, the inability to serologically distinguish vaccinated from infected animals has hampered eradication efforts, particularly in regions transitioning from control to elimination phases [2]. The development of LSDV-specific diagnostic tools, including the synthesized gene antigen described by Yuan et al. (2024) and the monoclonal antibody-based ELISA reported by Chang et al. (2025), represents a critical step toward implementing DIVA-compatible vaccination programs [2, 7].

The choice of vaccine strain also carries implications for disease emergence. The use of attenuated GTPV vaccines in cattle has been associated with the selection of recombinant LSDV strains in some regions, raising concerns about vaccine-driven evolution [2]. Furthermore, the recent expansion of LSDV into new geographic areas has highlighted the need for rapid, field-deployable diagnostic tools that can differentiate vaccine-derived immunity from natural infection [4, 7]. As Radojičić et al. (2025) emphasized, "the veterinary service must quickly identify suspected cases, provide accurate diagnoses, and implement emergency measures to control outbreaks," particularly in the context of emerging infectious diseases of small ruminants [5].

Conclusion of Taxonomic and Diagnostic Considerations

The taxonomy of capripoxviruses, while firmly rooted in genomic phylogeny, continues to evolve as new molecular data emerge. The three recognized species, SPPV, GTPV, and LSDV, represent distinct genetic lineages with overlapping host ranges and cross-protective immunity, yet they retain sufficient biological differences to warrant species-specific diagnostic approaches [3, 4, 6]. The development of molecular tools targeting ITR sequences, P32 gene polymorphisms, and LSDV-specific genomic regions has revolutionized the differential diagnosis of capripoxvirus infections, enabling rapid and accurate species identification even in resource-limited settings [2-4, 7]. As global livestock trade intensifies and climate change alters vector distributions, the ability to differentiate these viruses will remain paramount for effective disease surveillance, vaccine selection, and outbreak containment [5, 10]. The continued integration of genomic, serological, and epidemiological data will be essential for refining our understanding of capripoxvirus taxonomy and for developing next-generation control strategies that can adapt to the dynamic landscape of transboundary animal diseases.

Molecular Pathogenesis and Genetic Basis of Host Specificity in Sheep Pox and Goat Pox

The genus Capripoxvirus (CaPV), family Poxviridae, subfamily Chordopoxvirinae, comprises three genetically and antigenically related species: sheep pox virus (SPPV), goat pox virus (GTPV), and lumpy skin disease virus (LSDV) [2, 3, 9]. These viruses are the etiological agents of economically devastating diseases in small ruminants and cattle, respectively, and are classified as notifiable diseases by the World Organisation for Animal Health (WOAH) due to their transboundary potential and severe impact on livestock production [1, 5, 8]. While the clinical presentations of sheep pox (SP) and goat pox (GP) are remarkably similar, characterized by fever, generalized papular and nodular skin lesions, lymphadenopathy, and respiratory distress, the underlying molecular mechanisms governing host restriction and pathogenesis remain a subject of intense investigation [3, 4]. The high degree of genomic homology (approximately 96–97% nucleotide identity across the core genome) between SPPV, GTPV, and LSDV belies their distinct, though not absolute, host preferences [2, 7]. This section delves into the molecular architecture, viral gene functions, and host–virus interactions that underpin the pathogenesis and host specificity of SPPV and GTPV, drawing upon comparative genomics, transcriptomics, and advanced diagnostic molecular tools.

Genomic Architecture and Conserved Virulence Factors

The CaPV genome is a linear, double-stranded DNA molecule ranging from approximately 145 to 155 kbp in length, characterized by a central core region encoding essential replication and structural proteins, flanked by variable inverted terminal repeats (ITRs) that contain genes involved in host range and virulence [3, 9]. The high genetic similarity among CaPV species has historically complicated differential diagnosis and vaccine development, as attenuated GTPV strains are frequently employed to vaccinate cattle against LSDV, and cross-protection between SPPV and GTPV is well-documented [2, 4]. However, subtle yet critical genetic differences, particularly within the ITR regions and specific open reading frames (ORFs), dictate host tropism.

The P32 gene (also known as the ortholog of vaccinia virus H3L gene), encoding a 32-kDa envelope protein, is a cornerstone of CaPV molecular characterization and serodiagnosis [6, 7]. This immunodominant protein is highly conserved across the three species, yet it harbors species-specific single nucleotide polymorphisms (SNPs) that allow for phylogenetic clustering of isolates into distinct SPPV, GTPV, and LSDV clades [6]. Phylogenetic analyses of the P32 gene from Moroccan sheep isolates, for example, unequivocally placed them within the SPPV clade, confirming the utility of this marker for molecular epidemiology [6]. The P32 protein is a key target for neutralizing antibodies, and its structural integrity is essential for viral entry and cell-to-cell spread. Monoclonal antibodies (mAbs) raised against the LSDV P32 protein have demonstrated exquisite specificity, failing to cross-react with SPPV or GTPV in double-antibody sandwich ELISA formats, thereby enabling serological differentiation of infected from vaccinated animals (DIVA) in cattle [7]. This specificity, despite the high overall homology, underscores the presence of unique conformational epitopes on the P32 protein of each virus species, likely arising from minor amino acid substitutions that alter surface topology.

Another critical genomic region for host specificity resides within the ITRs. Zhao et al. (2014) exploited sequence variations in the ITR regions to design loop-mediated isothermal amplification (LAMP) primers capable of unequivocally distinguishing GTPV from SPPV [3]. The ITR regions are known to harbor genes encoding ankyrin repeat proteins, chemokine-binding proteins, and other host-range factors that modulate the innate immune response. The differential amplification patterns observed with these LAMP primers suggest that the ITR sequences contain species-specific insertions, deletions, or substitutions that are stable across diverse geographic isolates [3]. This genetic variability in the ITRs is a primary driver of host adaptation, as these regions are under less selective constraint than the core genome and are more permissive to evolutionary change.

Molecular Mechanisms of Host Restriction and Cellular Tropism

The traditional dogma of strict host specificity, SPPV infecting only sheep, GTPV only goats, and LSDV only cattle, has been challenged by recent molecular and epidemiological evidence [4, 9]. While SPPV and GTPV generally exhibit a strong preference for their respective natural hosts, cross-species infections are documented, particularly under conditions of high viral load or immunosuppression. The molecular basis for this host restriction is multifactorial, involving interactions between viral entry proteins and host cell receptors, evasion of species-specific innate immune pathways, and differential replication kinetics in ovine versus caprine cells.

Comparative RNA sequencing (RNA-seq) analyses of CaPV infections in an immortalized bovine endothelial cell line (hTERT-bOEC) revealed that LSDV, SPPV, and GTPV induce remarkably similar transcriptomic profiles, with shared upregulation of genes involved in inflammatory signaling, apoptosis, and interferon (IFN) response pathways [9]. This suggests that the core replication machinery and the host cell response to infection are largely conserved across the three viruses. However, subtle differences in the magnitude and kinetics of gene expression were noted, particularly among the top five up- and down-regulated differentially expressed genes (DEGs) [9]. These DEGs may encode viral antagonists of host restriction factors that are species-specific. For instance, the ability of SPPV to productively infect sheep keratinocytes and dermal fibroblasts, while GTPV may replicate less efficiently in these same cells, could be attributed to variations in the viral IFN-modulating proteins. Poxviruses are masters of immune evasion, encoding a plethora of proteins that inhibit IFN signaling, chemokine activity, and apoptosis. The ankyrin repeat proteins encoded within the ITRs are prime candidates for host-range determinants, as they interact with host ubiquitin ligase complexes to degrade antiviral proteins such as NF-κB and IRF3. A single amino acid change in such a protein could dramatically alter its affinity for ovine versus caprine orthologs of these signaling molecules.

Furthermore, the viral entry process itself may impose a barrier to cross-species infection. While the specific cellular receptor(s) for CaPVs remain incompletely characterized, it is hypothesized that they utilize ubiquitous cell surface molecules, such as glycosaminoglycans or integrins, similar to other poxviruses. The high susceptibility of hTERT-bOEC cells to all three CaPV species suggests that the primary receptor is conserved across ruminant species [9]. However, post-entry blocks, such as inefficient uncoating or suboptimal viral DNA replication in non-permissive cells, are more likely to account for host restriction. The development of a multiplex real-time PCR assay targeting the RPO30 gene (encoding the viral RNA polymerase subunit) and the P32 gene has further enabled the simultaneous detection and differentiation of SPPV, GTPV, and LSDV, confirming that these viruses can be present in mixed infections or in non-traditional hosts [4]. This molecular tool has been validated on clinical samples from both sheep and goats, demonstrating that the host range is more fluid than previously appreciated [4].

Genetic Basis of Differential Pathogenicity and Tissue Tropism

The clinical severity of sheep pox and goat pox varies considerably depending on the viral strain, host breed, age, and immune status. Some SPPV strains cause a mild, localized disease, while others induce a fulminant systemic infection with mortality rates exceeding 50% in lambs [1, 5]. The genetic determinants of this differential pathogenicity are beginning to be elucidated through comparative genomics of field isolates. The P32 gene, while useful for species identification, does not correlate with virulence [6]. Instead, virulence factors are likely distributed across the genome, including genes encoding viral growth factors (e.g., epidermal growth factor-like proteins), serine protease inhibitors (serpins), and inhibitors of the complement cascade.

The tissue tropism of SPPV and GTPV is primarily epitheliotropic and lymphotropic. The virus initially replicates in the dermal macrophages and fibroblasts at the site of inoculation, followed by dissemination via the lymphatics to regional lymph nodes, where massive viral replication occurs. Secondary viremia leads to widespread infection of vascular endothelial cells, resulting in the characteristic papules, nodules, and pustules in the skin and mucous membranes [1, 9]. The severe respiratory form of the disease, often fatal, results from viral replication in the pulmonary epithelium and alveolar macrophages, leading to interstitial pneumonia. The molecular basis for this pneumotropism may involve the expression of specific viral proteins that facilitate entry into type II pneumocytes or that subvert the pulmonary innate immune response.

The development of a synthesized gene unique to LSDV for DIVA serological applications highlights the potential for identifying species-specific genetic signatures [2]. This approach, which involved the expression of a recombinant protein that is absent from GTPV and SPPV, successfully differentiated LSDV-infected cattle from those vaccinated with attenuated GTPV [2]. The converse approach, identifying SPPV- or GTPV-specific antigens, could be applied to develop serological tests for small ruminants, enabling the differentiation of natural infection from vaccination with heterologous strains. The high diagnostic specificity (100%) and sensitivity (93.3%) of this LSDV-specific iELISA underscore the feasibility of such an approach [2].

Implications for Differential Diagnosis and Disease Control

The molecular pathogenesis and genetic basis of host specificity have profound implications for the differential diagnosis of sheep pox and goat pox. Clinically, these diseases are indistinguishable from each other and from other vesicular and pustular conditions such as contagious ecthyma (orf), bluetongue, ulcerative dermatosis, and dermatophilosis [1, 5]. The high morbidity and mortality associated with sheep and goat pox, coupled with their status as foreign animal diseases in many countries (e.g., the United States), necessitate rapid and accurate laboratory confirmation [1]. Molecular diagnostic tools, including real-time PCR, LAMP, and RFLP-PCR, have become indispensable for differentiating SPPV from GTPV and for distinguishing them from LSDV [3, 4]. These assays target conserved genes (e.g., P32, RPO30) for pan-CaPV detection and species-specific regions (e.g., ITR sequences) for differentiation [3, 4, 6].

The genetic similarity between SPPV and GTPV also complicates vaccine development and serological surveillance. Live attenuated vaccines, often derived from one species, are used to protect against both diseases due to cross-protection. However, this practice makes it impossible to differentiate vaccinated from infected animals using standard serological tests [2, 7]. The development of DIVA-compatible vaccines and companion diagnostic tests, such as the LSDV-specific ELISA, is a critical priority for control programs [2, 7]. The identification of unique genetic markers in the ITR regions and in specific ORFs encoding host-range factors provides a roadmap for the rational design of such tools.

In conclusion, the molecular pathogenesis of sheep pox and goat pox is a complex interplay of conserved poxviral replication mechanisms and species-specific adaptations encoded primarily within the variable regions of the genome. The high genetic homology between SPPV and GTPV, particularly in core genes like P32, necessitates the use of advanced molecular techniques for definitive diagnosis. The subtle genetic differences in the ITRs and in genes encoding immune evasion proteins dictate host range and pathogenicity, explaining the observed, though not absolute, host specificity. The continued application of comparative genomics, transcriptomics, and proteomics will be essential to fully unravel the molecular determinants of host restriction and to develop next-generation vaccines and diagnostics for these economically devastating diseases.

Global Epidemiology, Transmission Dynamics, and Foreign Animal Disease Status of Sheep Pox and Goat Pox

Global Distribution and Endemic Burden

Sheep pox (SPP) and goat pox (GTP), caused by sheeppox virus (SPPV) and goatpox virus (GTPV) respectively, represent two of the most economically devastating transboundary viral diseases affecting small ruminant production systems across Africa, Asia, and the Middle East [1, 5, 6]. These diseases, together with lumpy skin disease virus (LSDV), belong to the genus Capripoxvirus within the family Poxviridae, and share nucleotide sequence homology approaching 97% at the genomic level [2, 7, 9]. This extraordinary genetic similarity underpins the profound challenges in differential diagnosis, vaccine selection, and serological surveillance that confront veterinary authorities globally.

The endemic geography of SPP and GTP extends across a vast longitudinal swath from northern Africa through the Sahel, the Horn of Africa, the Middle East, the Indian subcontinent, and into central and East Asia [1, 5, 6]. In these regions, capripoxviruses impose chronic production losses through morbidity rates that can exceed 75% in naive populations and mortality rates ranging from 10% to 85%, depending on the virus strain, host breed, age, and nutritional status [1, 8]. Participatory epidemiological investigations conducted in the Somali Region of Ethiopia, a quintessential pastoral production system, identified sheep and goat pox (SGP) as the fourth most important livestock disease, accounting for 11.0% of disease burden prioritization across five surveyed districts, trailing only contagious caprine pleuropneumonia (14.2%), peste des petits ruminants (13.0%), and hemorrhagic septicemia (12.0%) [8]. These data, derived from consensus-based community scoring with high inter-district agreement (W = 0.886, p < 0.001), underscore the profound livelihood impacts of capripoxviruses in resource-limited settings where veterinary surveillance and reporting infrastructure remain nascent.

Seasonal epidemiological patterns demonstrate distinct temporal clustering, with SGP outbreaks peaking during spring and autumn in the Horn of Africa, coinciding with periods of livestock congregation around water sources and heightened animal movement for transhumance [8]. This seasonal forcing reflects the interplay between viral transmission dynamics, host population density, and vector activity, though the role of arthropod mechanical vectors in SPP and GTP transmission remains less well-characterized than for LSDV. Critically, the World Organization for Animal Health (WOAH) classifies sheep pox and goat pox as notifiable diseases, and their presence in a previously free country triggers immediate trade restrictions that can devastate national livestock economies [1, 5].

Transmission Dynamics and Risk Factors

The transmission ecology of SPPV and GTPV encompasses multiple routes, reflecting the broad tissue tropism of capripoxviruses. Direct contact between infected and susceptible animals constitutes the primary transmission mechanism, with viral shedding occurring from ruptured skin nodules, ocular and nasal discharges, saliva, and contaminated scabs [1, 5]. Infected animals can shed virus for extended periods, scabs may retain infectivity for months under ambient environmental conditions, particularly in shaded, dry environments, creating persistent fomite reservoirs on contaminated bedding, feeding equipment, transport vehicles, and personnel clothing [1, 5]. Aerosol transmission over short distances (<10 meters) has been demonstrated experimentally, contributing to rapid within-flock spread, particularly in confined housing systems where stocking densities are high and ventilation is poor [5].

The role of subclinically infected or convalescent carriers in maintaining transmission chains warrants particular attention. SPPV and GTPV can persist in skin scars and lymph nodes for weeks to months following clinical resolution, and recrudescence under stress, such as parturition, nutritional deprivation, or intercurrent disease, has been documented [1, 5]. This carrier state complicates eradication efforts in endemic zones and heightens the risk of reintroduction into disease-free areas through apparently healthy animals. The 97% genomic identity between capripoxviruses further complicates epidemiological tracking, as SPPV and GTPV can cross-infect heterologous hosts, blurring species boundaries and challenging traditional diagnostic assumptions [2, 4, 9].

Indirect transmission via contaminated fomites represents a particularly insidious pathway for long-distance spread. The stability of capripoxviruses in the environment allows contaminated wool, hides, and animal products to serve as vehicles for transboundary movement [1, 5]. In the Thrace region of Greece, Bulgaria, and Turkey, a recognized high-risk corridor for capripoxvirus incursion into southeastern Europe, multiple factors converge to amplify transmission risk: mixing of small ruminant herds with bovine and backyard production systems, limited biosecurity awareness among pastoralists, and incomplete clinical surveillance in remote flocks [10]. Expert elicitation studies in this region revealed that awareness of clinical disease, reporting procedures, and biosecurity measures significantly affected the early stages of disease reporting, particularly in small ruminant herds and mixed production units identified as having lower reporting sensitivity [10]. This surveillance gap creates an epidemiological blind spot, where incursions may propagate undetected for weeks before formal notification, by which time regional spread may be irreversible.

Molecular Epidemiology and Phylogenetic Considerations

Molecular characterization of circulating capripoxvirus strains provides critical insights into transmission networks, vaccine mismatches, and emergence risks. Phylogenetic analysis based on the P32 gene, a major envelope protein encoding a key immunodominant antigen, has become the gold standard for genotype assignment [3, 6]. Studies of Moroccan SPPV isolates, for example, confirmed that all sequenced field strains clustered within the SPPV clade, phylogenetically distinct from GTPV and LSDV, guiding veterinary authorities toward homologous vaccine selection [6]. This distinction is not merely academic: vaccine mismatches, where a GTPV-based vaccine is deployed against SPPV or vice versa, can result in suboptimal protection, breakthrough infections, and continued transmission [2, 4, 7].

The development of molecular diagnostic tools capable of discriminating between SPPV, GTPV, and LSDV has advanced dramatically over the past decade. Loop-mediated isothermal amplification (LAMP) assays targeting the inverted terminal repeat (ITR) regions of the capripoxvirus genome have demonstrated 100% detection rates for universal and GTPV-specific primers, with 98.8% sensitivity for SPPV, while showing no cross-reactivity with orf virus, foot-and-mouth disease virus, Mycoplasma mycoides subsp. capri, or various hemoparasites [3]. Similarly, multiplex real-time PCR systems utilizing specific probes for each capripoxvirus species have achieved limits of detection as low as 10² copies of target genomic DNA, with complete concordance to RFLP-PCR analysis and gene sequencing across 557 clinical samples from China and Ethiopia [4]. These advances are transforming diagnostic capacity in endemic regions, enabling rapid genotype assignment that informs vaccine selection and outbreak response.

Foreign Animal Disease Status and Surveillance Imperatives

For nations currently free of sheep pox and goat pox, the specter of incursion represents a continuous threat that demands robust surveillance architecture. In the United States, SPP and GTP are classified as foreign animal diseases (FADs) by the United States Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) [1]. The clinical presentation of capripoxviruses, fever, multifocal cutaneous papules progressing to umbilicated pustules, lymphadenopathy, and respiratory distress, overlaps substantially with endemic conditions such as orf (contagious ecthyma), ulcerative dermatosis, bluetongue, and dermatophilosis [1, 5]. This differential diagnostic challenge places frontline veterinarians in a critical sentinel role: any case involving unusual dermatologic lesions associated with high morbidity and/or mortality must be reported immediately to state regulatory veterinarians or USDA APHIS for herd/flock investigation [1]. The economic stakes are staggering, an FAD incursion into the US small ruminant sector would trigger immediate trade embargoes, mass depopulation, and multi-year eradication campaigns costing hundreds of millions of dollars.

The European Union faces a similar calculus, with SPP and GTP listed as notifiable diseases under EU animal health law. Recent epidemiological analyses have highlighted the Thrace region, spanning Greece, Bulgaria, and Turkey, as a high-risk gateway for capripoxvirus entry into Europe, given its proximity to endemic zones in Anatolia and the Levant [5, 10]. The European Food Safety Authority (EFSA) and the European Commission for the Control of Foot-and-Mouth Disease (EuFMD) have invested substantially in capacity-building initiatives to strengthen disease reporting sensitivity in this corridor, recognizing that early detection is the single most cost-effective intervention [10]. Training exercises using expert elicitation and scenario tree modeling have revealed that small ruminant herds, mixed bovine herds, and backyard production systems exhibit the lowest disease reporting sensitivity, driven by limited clinical awareness, weak biosecurity practices, and insufficient veterinary outreach [10].

The 2023–2025 epizootic situation in Europe has been characterized as “increasingly challenging” by regional veterinary authorities, with peste des petits ruminants, sheep pox, goat pox, and foot-and-mouth disease posing imminent threats to the continent’s livestock sectors [5]. Given that outbreaks of these diseases have occurred in geographically proximate regions, “every omission, even the smallest, always costs millions of euros” [5]. This stark assessment underscores the need for integrated surveillance strategies that combine passive clinical reporting with active molecular surveillance, including environmental sampling at livestock markets, border checkpoints, and slaughter facilities, to detect incursions at the earliest possible moment.

Serological Surveillance and the DIVA Challenge

The high genetic and antigenic homology between SPPV, GTPV, and LSDV (up to 97% nucleotide identity) presents an intractable challenge for serological differentiation [2, 7]. Standard enzyme-linked immunosorbent assays (ELISAs) based on whole-virus antigens or recombinant structural proteins, such as the P32 capsid protein, cannot discriminate between antibodies elicited by SPPV, GTPV, or LSDV infection, nor between natural infection and vaccination with live attenuated capripoxvirus vaccines [2, 7]. This conundrum has direct implications for the use of goat pox vaccines as cross-protective immunogens against lumpy skin disease in cattle, a practice widely adopted in China and other LSD-affected nations [2]. When cattle vaccinated with GTPV-based vaccines are serologically tested, they produce antibodies that are indistinguishable from those of LSDV-infected animals, rendering traditional serosurveillance useless for DIVA (differentiating infected from vaccinated animals) purposes [2].

Recent advancements in DIVA technology offer a promising path forward. The development of a synthesized gene unique to LSDV, encoding a protein not present in SPPV or GTPV, has enabled the construction of an indirect ELISA with diagnostic specificity of 100% (95% CI: 88.43–100) and sensitivity of 93.3% (95% CI: 77.93–99.18) for detecting LSDV-specific antibodies [2]. Application of this assay to vaccinated herds demonstrated zero false positives (0/141), while infected herds showed 33.9% seropositivity (20/59), confirming robust differentiation capacity [2]. Similarly, the generation of LSDV-specific monoclonal antibodies targeting the P32 protein, exemplified by clones 3C10 and 6H3, has enabled a double-antibody sandwich ELISA that shows no cross-reactivity with GTPV or SPPV, providing a second orthogonal DIVA platform [7].

These innovations carry profound implications for global capripoxvirus epidemiology. Without reliable DIVA capability, vaccination programs necessarily compromise serosurveillance sensitivity, leaving health authorities blind to the true extent of field virus circulation. As vaccine coverage expands, particularly in high-burden regions of Africa and Asia, the risk of undetected viral persistence and cryptic transmission increases proportionally. The integration of DIVA-compatible ELISAs into national surveillance programs, coupled with molecular genotyping tools such as LAMP and multiplex real-time PCR, represents the current gold standard for comprehensive capripoxvirus management [2-4, 7].

Gaps in Surveillance Infrastructure and Future Directions

Despite significant advances in diagnostic technology, substantial gaps persist in global capripoxvirus surveillance. In endemic regions of sub-Saharan Africa and South Asia, laboratory infrastructure for molecular testing remains scarce, cold chain logistics for sample transport are unreliable, and trained veterinary personnel are chronically underresourced [8]. Participatory epidemiological approaches, which engage livestock owners, herders, and community leaders in disease prioritization and reporting, have demonstrated effectiveness in bridging these gaps, as evidenced by the Ethiopian Somali Region study [8]. However, the reliance on community-based clinical recognition means that mild or atypical presentations of SPP/GTP, particularly in partially immune populations or heterologous host infections, may go unreported.

The recent availability of immortalized cell lines, such as the hTERT-bOEC line engineered to express human telomerase reverse transcriptase, has opened new frontiers for capripoxvirus research, including transcriptomic profiling of host-virus interactions, vaccine strain characterization, and antiviral screening [9]. RNA sequencing analyses of hTERT-bOECs infected with LSDV, SPPV, and GTPV have revealed conserved and divergent patterns of gene expression and signaling pathway activation, providing molecular signatures that may inform future diagnostic and therapeutic strategies [9]. As these tools transition from research laboratories to field applications, they hold the potential to revolutionize real-time outbreak detection and strain tracking.

The Centers for Disease Control and Prevention (CDC), WOAH, and the Food and Agriculture Organization of the United Nations (FAO) maintain global databases of capripoxvirus outbreaks, but reporting latency and incomplete passive surveillance data limit their utility for real-time risk assessment. Strengthening north-south partnerships for laboratory capacity building, deploying handheld molecular diagnostics to district-level veterinary offices, and integrating syndromic surveillance with mobile health platforms represent priority interventions for reducing the global burden of sheep pox and goat pox. The stakes could not be higher: in the words of one recent analysis, “in the race for first place, the most contagious diseases that cause enormous damage in bordering countries are peste des petits ruminants, sheep pox, goat pox, and foot-and-mouth disease” [5]. For veterinary services worldwide, preparedness begins with understanding the epidemiological landscape, transmission pathways, and diagnostic tools that define this formidable group of pathogens.

Clinical Presentation and Gross Pathology: Differentiating Sheep Pox and Goat Pox from Endemic Dermatologic Conditions

The clinical differentiation of sheep pox (SPP) and goat pox (GTP) from endemic dermatologic conditions represents one of the most formidable diagnostic challenges in small ruminant medicine, particularly in regions where these diseases are exotic or emerging. The capripoxviruses, sheep pox virus (SPPV), goat pox virus (GTPV), and lumpy skin disease virus (LSDV), share nucleotide sequence similarities of up to 97%, and the clinical syndromes they induce are virtually indistinguishable from one another without molecular confirmation [2, 3]. This genetic and clinical homology is compounded by the fact that numerous endemic conditions, including orf (contagious ecthyma), ulcerative dermatosis, bluetongue, dermatophilosis, and even peste des petits ruminants (PPR), can produce cutaneous lesions that mimic the early or atypical presentations of capripoxvirus infections [1, 5]. For the practicing veterinarian, the stakes are extraordinarily high: a missed diagnosis of SPP or GTP in a previously free region can lead to catastrophic economic losses, trade restrictions, and the implementation of costly eradication programs [1, 10]. Conversely, a false-positive diagnosis can trigger unnecessary regulatory actions and erode producer confidence. This section provides an exhaustive analysis of the clinical presentation and gross pathological features that distinguish SPP and GTP from the most common endemic dermatologic conditions affecting sheep and goats globally.

The Hallmark Cutaneous Lesions of Sheep Pox and Goat Pox: A Pathognomonic Framework

The clinical progression of SPP and GTP follows a remarkably consistent temporal pattern, regardless of the host species or viral strain. Following an incubation period of 4 to 14 days, the initial clinical signs are nonspecific: pyrexia (often exceeding 40.5°C), depression, anorexia, serous to mucopurulent nasal and ocular discharge, and pronounced salivation [1, 5]. It is the subsequent development of the characteristic exanthem that provides the first truly diagnostic clues. The cutaneous eruption begins as multifocal, erythematous macules, typically first observed on the sparsely haired or wool-free areas of the body, the perineum, axillae, inguinal region, medial thighs, and the periocular and perioral skin [1]. Within 24 to 48 hours, these macules progress to firm, raised papules, which then evolve into vesicles and, critically, into pustules. The pustules are not the superficial, fragile lesions seen in bacterial pyodermas; rather, they are deep-seated, firm, and often umbilicated, reflecting the underlying dermal necrosis and edema that characterize capripoxvirus pathology.

The gross pathological hallmark of SPP and GTP is the formation of “pox lesions” that undergo a predictable sequence of necrosis, scabbing, and healing. As the pustules mature, they become hemorrhagic and undergo central necrosis, resulting in a depressed, dark-colored eschar surrounded by a raised, hyperemic rim. These lesions are typically 1 to 3 cm in diameter, but in severe cases, they may coalesce to form large, irregular plaques of necrotic tissue [1, 6]. The distribution of these lesions is a critical differentiating feature: in SPP and GTP, the lesions are generalized and bilateral, with a predilection for the ventral abdomen, the perineum, and the mucous membranes of the oral and nasal cavities, the conjunctiva, and the vulva or prepuce. Involvement of the oral mucosa is particularly common and can be severe, leading to necrotic stomatitis, dysphagia, and secondary bacterial infections. The presence of lesions on the coronary bands and interdigital spaces is also frequently reported, causing lameness and reluctance to move [1, 5].

The gross pathology at necropsy is equally distinctive. The skin lesions, when incised, reveal a characteristic “button-like” appearance: a central core of necrotic, caseous material surrounded by a zone of intense hyperemia and edema. Histologically, this corresponds to the pathognomonic “capripoxvirus inclusion body”, an eosinophilic, intracytoplasmic inclusion within keratinocytes and dermal macrophages, known as a Bollinger body [1, 6]. In fatal cases, particularly in young animals or highly virulent strains, the virus disseminates systemically. Gross lesions are consistently found in the respiratory tract, including the nasal mucosa, trachea, and lungs. Pulmonary lesions manifest as multifocal to coalescing, firm, gray-white nodules (so-called “pox pneumonia”), which on cut section exude a caseous, necrotic material. Similar nodular lesions may be observed in the liver, spleen, kidneys, and abomasum, reflecting the viremic phase of the disease [1, 5, 6]. The presence of these systemic, necrotic nodules in multiple organ systems is a powerful discriminator from most endemic dermatologic conditions, which are typically confined to the skin or have a different pattern of visceral involvement.

Differentiating from Orf (Contagious Ecthyma): The Parapoxvirus Challenge

Orf, caused by the parapoxvirus Orf virus (ORFV), is arguably the most common and clinically confusing differential diagnosis for SPP and GTP in endemic areas [1, 5]. Both diseases produce proliferative, scabby lesions on the lips, muzzle, and oral mucosa, and both can cause significant morbidity in young animals. However, several key clinical and pathological features allow for differentiation. The lesions of orf are typically more localized and superficial than those of capripox. Orf begins as erythematous macules that rapidly progress to papules, vesicles, and then thick, brownish crusts or scabs. These scabs are characteristically exophytic and “wart-like,” often forming large, friable, proliferative masses that can bleed easily when manipulated. In contrast, the pox lesions of SPP and GTP are deeper, more necrotic, and have a distinct umbilicated or depressed center [1].

The anatomical distribution is another critical discriminator. Orf lesions are overwhelmingly confined to the mucocutaneous junctions of the lips, muzzle, nostrils, and, less commonly, the eyelids, teats, and coronary bands. While severe cases of orf can involve the oral mucosa and cause necrotic stomatitis, the lesions rarely extend to the ventral abdomen, perineum, or axillae, sites that are almost invariably affected in generalized capripoxvirus infections [1]. Furthermore, orf is rarely fatal in immunocompetent adult animals; mortality is typically limited to lambs and kids that are unable to nurse due to painful oral lesions, or to cases complicated by secondary bacterial or fungal infections (e.g., Dermatophilus congolensis). In contrast, SPP and GTP can cause mortality rates of 50–100% in naive flocks, particularly in young animals, and death is often due to systemic viral dissemination and secondary pneumonia [1, 5].

The gross pathology at necropsy provides additional clarity. In orf, the internal organs are typically unaffected. The lesions are confined to the skin and oral mucosa, and the characteristic systemic nodules of capripoxvirus infection, particularly the pulmonary and gastrointestinal nodules, are absent. Histologically, orf is characterized by marked epidermal hyperplasia (acanthosis) and ballooning degeneration of keratinocytes, with eosinophilic intracytoplasmic inclusion bodies that are smaller and less distinct than the Bollinger bodies of capripoxvirus. Importantly, orf virus can be differentiated from capripoxvirus by electron microscopy (orf virions are ovoid and crisscrossed, while capripoxviruses are brick-shaped) or by molecular methods such as PCR or loop-mediated isothermal amplification (LAMP), which have been specifically designed to distinguish SPPV and GTPV from ORFV [3, 4].

Differentiating from Ulcerative Dermatosis: A Clinically Overlapping Syndrome

Ulcerative dermatosis (UD), caused by a yet-to-be-fully-characterized virus (historically associated with a parapoxvirus or a capripoxvirus variant), presents a particularly vexing differential diagnosis. UD is characterized by the development of ulcers, crusts, and scabs on the lips, nostrils, eyelids, and, notably, the external genitalia of both sexes [1]. The genital lesions, ulcerative vulvitis in females and balanoposthitis in males, are a hallmark of UD and can be severe, leading to adhesions, phimosis, and secondary infections. This genital involvement is a key feature that can overlap with SPP and GTP, as capripoxviruses also frequently cause lesions on the vulva and prepuce [1].

However, there are critical differentiating features. UD lesions are typically more superficial and ulcerative than the deep, necrotic, nodular lesions of capripox. The ulcers of UD have a clean, punched-out appearance with minimal surrounding inflammation, whereas capripox lesions are raised, firm, and have a central necrotic core. Furthermore, UD is rarely associated with systemic signs. Affected animals may show mild pyrexia and inappetence, but the severe depression, high fever, and respiratory distress characteristic of SPP and GTP are absent. Mortality from UD is low, and the disease is typically self-limiting within 2–4 weeks [1]. At necropsy, UD lacks the systemic visceral nodules that are pathognomonic for disseminated capripoxvirus infection. The presence of pulmonary, hepatic, or splenic nodules should immediately raise suspicion for SPP or GTP rather than UD.

Differentiating from Bluetongue: The Orbivirus Impostor

Bluetongue (BT), caused by the orbivirus Bluetongue virus (BTV) and transmitted by Culicoides midges, is another critical differential diagnosis, particularly in sheep [1, 5]. BT can produce severe oral lesions, including hyperemia, edema, ulceration, and necrosis of the oral mucosa, tongue, and dental pad, findings that can closely mimic the necrotic stomatitis of SPP and GTP. Additionally, BT causes coronitis (inflammation of the coronary bands), leading to lameness, and can result in muscle necrosis and torticollis, which are not typical of capripoxvirus infections [1].

The key differentiating features lie in the nature and distribution of the lesions. In BT, the oral lesions are primarily hyperemic and edematous, with a characteristic cyanotic (“blue”) appearance of the tongue in severe cases. The lesions are typically superficial ulcers and erosions, not the deep, necrotic, nodular lesions of capripox. Furthermore, BT does not produce the characteristic cutaneous papules, pustules, and scabs that are the hallmark of SPP and GTP. The skin lesions of BT, when present, are more likely to be secondary to photosensitization or pressure necrosis in recumbent animals, rather than primary viral exanthems [1]. The absence of generalized skin nodules on the ventral abdomen, perineum, and axillae is a powerful discriminator. Additionally, BT is a seasonal disease, closely linked to Culicoides activity, whereas SPP and GTP can occur year-round and are transmitted through direct contact and fomites [1, 5]. At necropsy, BT is characterized by widespread hemorrhage, edema, and serous effusions in body cavities, along with characteristic myocardial necrosis (leading to “heartwater” in some descriptions). These findings are distinct from the necrotic, nodular lesions of capripoxvirus infection.

Differentiating from Dermatophilosis: The Bacterial Masquerader

Dermatophilosis, caused by the actinomycete Dermatophilus congolensis, is a common cause of exudative, crusting dermatitis in small ruminants, particularly in humid or wet conditions [1]. The disease presents with matted, crusty scabs that adhere firmly to the skin, often forming a “paintbrush” or “lumpy wool” appearance. These crusts can be extensive and may involve the dorsum, flanks, and face, leading to a superficial resemblance to the scabbing phase of SPP and GTP.

However, several features distinguish dermatophilosis from capripoxvirus infections. The crusts of dermatophilosis are superficial and can be easily peeled away to reveal a moist, erythematous, and exudative surface. In contrast, the scabs of SPP and GTP are firmly adherent to the underlying necrotic dermis and, when removed, leave a deep, punched-out ulcer. Dermatophilosis is not associated with systemic signs such as high fever, depression, or anorexia, unless there is extensive secondary bacterial infection. The lesions are not nodular and do not undergo the papule-vesicle-pustule sequence characteristic of poxvirus infections [1]. Furthermore, dermatophilosis does not involve the mucous membranes or internal organs. The absence of oral, nasal, or genital lesions, and the lack of systemic visceral nodules at necropsy, effectively rules out SPP and GTP. A simple Gram stain of a crust smear will reveal the characteristic “railroad track” or “zigzag” filaments of D. congolensis, providing a rapid, point-of-care diagnosis.

The Critical Role of Lesion Distribution and Systemic Involvement

Across all differential diagnoses, the single most important clinical and pathological discriminator for SPP and GTP is the combination of generalized cutaneous nodular lesions and systemic visceral involvement. The endemic conditions discussed, orf, ulcerative dermatosis, bluetongue, and dermatophilosis, are either confined to the skin and mucous membranes (orf, UD, dermatophilosis) or produce a different pattern of systemic pathology (BT). The presence of firm, 1–3 cm, umbilicated nodules distributed bilaterally on the ventral abdomen, perineum, axillae, and medial thighs, in conjunction with pyrexia, depression, and respiratory signs, should immediately trigger a high index of suspicion for capripoxvirus infection [1, 5]. The finding of similar nodular lesions in the lungs, trachea, liver, spleen, and gastrointestinal tract at necropsy is virtually pathognomonic for SPP or GTP and should prompt immediate notification of regulatory authorities, as these diseases are reportable to the World Organisation for Animal Health (WOAH) and are considered foreign animal diseases in many countries, including the United States [1, 10].

The Imperative for Laboratory Confirmation

Given the profound clinical overlap between SPP, GTP, and the endemic conditions described, it is essential to emphasize that clinical and gross pathological examination alone is insufficient for a definitive diagnosis. The consequences of misdiagnosis are too severe. Any case involving unusual dermatologic lesions associated with high morbidity and/or mortality, particularly in a previously free region, warrants immediate reporting to governmental authorities, such as the USDA APHIS in the United States or the relevant state regulatory veterinarians [1]. Confirmatory laboratory testing is mandatory. Molecular techniques, including multiplex real-time PCR and LAMP assays, have been developed that can simultaneously detect and differentiate SPPV, GTPV, and LSDV with high sensitivity and specificity, and can distinguish them from ORFV, FMDV, and other pathogens [3, 4, 6]. These assays target specific genetic markers, such as the P32 gene and the inverted terminal repeat (ITR) sequences, and can provide a definitive diagnosis within hours [3, 4, 6]. Serological methods, including ELISA, are also available but may be less useful in the acute phase of the disease and can be complicated by cross-reactivity between the capripoxviruses [2, 7]. The development of DIVA (Differentiating Infected from Vaccinated Animals) strategies, such as the use of LSDV-specific synthesized antigens, represents a significant advance for serological surveillance in endemic areas where vaccination is practiced [2, 7]. Ultimately, the integration of meticulous clinical observation, thorough gross pathological examination, and rapid, specific molecular diagnostics is the only reliable approach to navigating the complex differential diagnosis of sheep pox and goat pox.

Differential Diagnosis of Sheep Pox and Goat Pox: Comparative Lesion Analysis with Orf, Bluetongue, Ulcerative Dermatosis, and Dermatophilosis

The clinical differentiation of sheep pox (SPP) and goat pox (GTP) from other dermatologic conditions of small ruminants represents one of the most formidable challenges in veterinary diagnostic medicine, particularly in regions where these diseases are not endemic or where co-circulation with endemic pathogens occurs [1, 5]. The causative agents, sheep pox virus (SPPV) and goat pox virus (GTPV), belong to the genus Capripoxvirus within the family Poxviridae and share up to 97% nucleotide sequence homology with each other and with lumpy skin disease virus (LSDV) [2, 7]. This genetic proximity translates into clinical syndromes that are virtually indistinguishable from one another at the individual animal level, yet the lesions produced by SPPV and GTPV must be meticulously differentiated from those caused by orf virus (contagious ecthyma), bluetongue virus (BTV), the poorly characterized agent of ulcerative dermatosis, and Dermatophilus congolensis (dermatophilosis) [1]. The stakes of misdiagnosis are extraordinarily high: as noted by Radojičić et al. (2025), "every omission, even the smallest, always costs millions of euros" [5]. The World Organisation for Animal Health (WOAH) classifies SPP and GTP as notifiable diseases due to their transboundary nature and devastating economic impact on sheep and goat production systems, and any suspicion of these diseases in disease-free regions must trigger immediate reporting to national authorities such as the USDA APHIS in the United States [1]. This comparative lesion analysis provides a systematic framework for distinguishing these conditions based on lesion morphology, anatomical distribution, progression, and associated systemic findings, drawing upon the most current molecular, epidemiological, and clinical evidence.

Comparative Lesion Characteristics: Orf (Contagious Ecthyma) versus Sheep Pox and Goat Pox

Orf, caused by the Parapoxvirus genus, represents perhaps the most frequently encountered differential diagnosis for capripoxvirus infections in small ruminants, particularly in young animals and in flocks where the virus is enzootic [1, 3]. The lesion distribution serves as a primary distinguishing feature: orf typically manifests as proliferative, scabbed, and sometimes papillomatous lesions confined almost exclusively to the mucocutaneous junctions of the lips, muzzle, nostrils, eyelids, teats, and coronary bands [1]. In contrast, SPP and GTP produce a generalized, systemic exanthem that extends far beyond these anatomical boundaries. The poxvirus lesions of SPP/GTP evolve through a predictable sequence beginning with erythematous macules (1–3 days post-infection), progressing to firm, raised papules (3–5 days), then to vesicles and pustules that undergo central umbilication, culminating in thick, adherent scabs that may persist for 2–4 weeks [1, 6]. Histopathologically, the hallmark of capripoxvirus infection is the presence of large, eosinophilic intracytoplasmic inclusion bodies (Borrel bodies) within ballooning degeneration of epithelial cells, a feature absent in orf lesions, which instead demonstrate characteristic eosinophilic intracytoplasmic inclusions that are smaller and more uniform [1].

The zoonotic potential of orf further complicates the clinical picture. Orf virus is readily transmissible to humans through direct contact with infected animals or fomites, producing painful, erythematous nodules on the hands, arms, and face of handlers [1]. The WOAH and the Centers for Disease Control and Prevention (CDC) recognize orf as an occupational zoonosis of shepherds, veterinarians, and abattoir workers. In contrast, SPPV and GTPV are not considered zoonotic, though their high contagion among ruminants necessitates strict biosecurity measures [1]. Molecular diagnostics provide definitive differentiation: the loop-mediated isothermal amplification (LAMP) assay developed by Zhao et al. (2014) using primers targeting the inverted terminal repeat (ITR) regions of capripoxviruses demonstrated no cross-reactivity with orf virus, foot-and-mouth disease virus (FMDV), or a battery of other endemic pathogens [3]. Similarly, multiplex real-time PCR systems capable of simultaneously detecting and differentiating SPPV, GTPV, and LSDV have shown no cross-reaction with orf virus, providing a robust confirmatory tool [4]. Clinicians must therefore maintain a high index of suspicion when lesions extend beyond the typical mucocutaneous distribution of orf, particularly if accompanied by systemic signs such as pyrexia (40–42°C), depression, anorexia, and lymphadenopathy, which are inconsistent with uncomplicated orf infections [1, 6].

Bluetongue: Differentiating Vascular Lesions from Poxvirus-Induced Pathology

Bluetongue virus (BTV), an arbovirus transmitted by Culicoides midges, produces a constellation of clinical signs that can mimic the early or atypical presentations of SPP and GTP, particularly in sheep [1, 5]. The key differentiating factor lies in the pathogenesis of the lesions: bluetongue is fundamentally a vascular disease mediated by endothelial damage and disseminated intravascular coagulation, whereas capripoxviruses induce direct epithelial proliferation and necrosis [1]. This pathophysiological distinction manifests in the character and distribution of lesions. In bluetongue, the classic findings include cyanosis and edema of the tongue, lips, and oral mucosa (hence the name "bluetongue"), along with coronitis, laminitis, and characteristic hemorrhagic crusting of the muzzle and oral commissures [1]. The lesions are primarily congestive and hemorrhagic rather than proliferative; they lack the firm, nodular, umbilicated appearance of poxvirus lesions. Furthermore, bluetongue frequently presents with severe muscle necrosis and torticollis due to vascular infarction of skeletal muscle, a finding notably absent in SPP/GTP [1].

The epidemiological context provides additional discriminative clues. Bluetongue exhibits a distinct seasonal pattern correlated with vector activity, typically occurring in late summer and autumn in temperate regions, whereas SPP and GTP can occur year-round in endemic areas and are transmitted through direct contact, fomites, and aerosol routes [1, 5]. As Mohomed et al. (2026) documented in participatory epidemiological studies in the Somali Region of Ethiopia, sheep and goat pox were perceived by pastoralists to peak in spring and autumn seasons, while hemorrhagic diseases (including bluetongue) exhibited different seasonal patterns [8]. Fever patterns also differ: bluetongue often presents with a biphasic fever curve, while SPP/GTP typically produce sustained high fever concurrent with the eruptive phase of the disease [1]. Laboratory confirmation becomes essential when clinical differentiation is ambiguous. BTV can be detected through reverse-transcription PCR (RT-PCR) targeting the NS3 gene segment, viral isolation in embryonated chicken eggs or cell culture, and serological assays such as competitive ELISA for group-specific antibodies. These methods show no cross-reactivity with capripoxviruses [1, 4]. The Food and Agriculture Organization (FAO) and WOAH both emphasize the importance of including bluetongue in the differential diagnosis of any febrile, ulcerative, or vesicular condition in sheep and goats, particularly in regions where both diseases circulate [1, 5].

Ulcerative Dermatosis: A Nodular and Ulcerative Mimic

Ulcerative dermatosis (UD) of sheep and goats, a condition of uncertain etiology sometimes attributed to a virus in the genus Parapoxvirus or possibly a distinct but related agent, presents a particularly vexing diagnostic challenge because its lesions share morphological features with both orf and capripoxvirus infections [1]. UD is characterized by nodular and ulcerative lesions that most commonly affect the lips, nostrils, eyelids, prepuce, vulva, and coronary bands, a distribution that overlaps significantly with the predilection sites of SPP and GTP [1]. However, critical differences exist in lesion progression and histology. In UD, the nodules are typically softer, more friable, and lack the firm, organized structure of poxvirus nodules. They rapidly progress to shallow, well-demarcated ulcers with raised borders that exude serosanguinous fluid and form dry, adherent crusts [1]. Unlike SPP/GTP, UD lesions rarely exhibit true umbilication or the central depression characteristic of poxvirus lesions. Furthermore, UD is generally a milder disease with lower morbidity and negligible mortality compared to the systemic, often fatal course of acute capripoxvirus infections in naive populations [1, 8].

The reproductive system is frequently involved in UD, with lesions on the prepuce and vulva causing dysuria, balanoposthitis, and vaginitis that may be mistaken for the genital lesions of SPP/GTP [1]. In rams, ulcerative dermatosis can cause significant penile and preputial adhesions, leading to breeding soundness issues. Notably, UD does not produce the generalized lymphadenopathy or the profound immunosuppression seen in severe capripoxvirus infections, and affected animals typically remain afebrile or exhibit only mild temperature elevation [1]. The historical presence of UD has been documented primarily in North America, and Simpson et al. (2023) specifically highlight its relevance to United States-based practitioners who must differentiate this endemic condition from the foreign animal diseases SPP and GTP [1]. Molecular characterization of the causative agent of UD remains incomplete, but available evidence suggests it is distinct from both capripoxviruses and orf virus. The multiplex PCR systems designed for capripoxvirus detection show no cross-reactivity with UD lesions, providing a definitive diagnostic pathway in suspect cases [4]. When faced with a proliferative and ulcerative dermatosis in a sheep or goat flock, veterinarians should carefully assess lesion consistency (firm versus friable), the presence of umbilication, systemic signs (fever, lymphadenopathy), and the overall morbidity and mortality pattern to guide initial clinical suspicion before laboratory confirmation [1, 6].

Dermatophilosis: The Crusting Masquerader

Dermatophilosis, caused by the actinomycete bacterium Dermatophilus congolensis, stands as one of the most commonly misdiagnosed conditions in the differential workup for capripoxvirus infections, particularly in environments with high humidity or where animals are exposed to prolonged wetting [1]. The disease produces exudative dermatitis characterized by thick, laminated, crusty scabs that adhere firmly to the underlying skin, often forming columnar or "paintbrush" lesions when the crusts are lifted [1]. In sheep, dermatophilosis typically affects the dorsum, flanks, and back, areas that are less commonly involved in SPP/GTP, where lesions concentrate on the ventrum, axillae, groin, perineum, and mucocutaneous junctions [1]. However, in severe or generalized cases of dermatophilosis, the distribution can become widespread, mimicking the generalized poxvirus exanthem. The critical distinguishing feature is the superficial nature of dermatophilosis lesions: the crusts are composed of matted hair and exudate that can be readily removed with gentle traction, revealing a moist, erythematous but intact epidermis beneath [1]. In contrast, SPP/GTP scabs are adherent to a disrupted, necrotic epithelium, and their removal reveals underlying ulceration, granulation tissue, or purulent exudate [1, 6].

The epidemiology and host factors also assist in differentiation. Dermatophilosis is associated with predisposing factors such as ectoparasite infestation (particularly Damalinia ovis and Psoroptes ovis), prolonged wetting from rainfall or poor shelter, nutritional deficiencies, and concurrent immunosuppressive diseases [1]. It is often observed in younger lambs and kids with poor body condition, whereas SPP/GTP can affect animals of any age and condition, though young animals are typically more severely affected. Importantly, D. congolensis infection is not accompanied by systemic signs such as fever, anorexia, or depression unless there is secondary bacterial infection or extensive skin involvement [1]. Microscopic examination of Giemsa-stained crust smears reveals the pathognomonic "railroad track" or "zigzag" arrangement of branching filaments and coccoid zoospores of D. congolensis, providing a rapid, cost-effective, and definitive diagnostic method that is widely available in field settings [1]. Bacterial culture on blood agar under microaerophilic conditions yields characteristic colonies within 24–48 hours. The absence of intracytoplasmic inclusion bodies on histopathology and the negative results on capripoxvirus-specific PCR [2-4] further confirm the diagnosis. The FAO and WOAH recommend routine acid-fast staining and culture for D. congolensis in any differential diagnosis for generalized crusting dermatitis in small ruminants, particularly in tropical and subtropical regions where dermatophilosis is endemic [1, 8].

Integrative Diagnostic Approach and Clinical Decision-Making

The clinical differentiation of SPP and GTP from orf, bluetongue, ulcerative dermatosis, and dermatophilosis requires a systematic approach that integrates lesion morphology, anatomical distribution, progression over time, systemic involvement, epidemiological context, and rapid deployment of laboratory diagnostics. No single clinical feature is pathognomonic, but a constellation of findings can guide initial suspicion and appropriate sample collection [1, 5]. The following clinical algorithm is proposed based on the synthesis of current evidence:

First, assess lesion morphology and distribution. Generalized, firm, umbilicated nodules distributed across the ventrum, perineum, and mucocutaneous junctions, with progression through defined stages (macule-papule-vesicle-pustule-scab), strongly favor capripoxvirus infection [1, 6]. Lesions confined to the lips, nostrils, and teats with a proliferative, papillomatous appearance suggest orf [1, 3]. Hemorrhagic, congestive lesions accompanied by cyanosis, coronitis, and fever without firm nodules favor bluetongue [1]. Soft, friable nodules that ulcerate rapidly without umbilication

Advanced Molecular Diagnostics and Serological Differentiation (DIVA) Strategies for Capripoxvirus Infections

The clinical and pathological indistinguishability of sheep pox virus (SPPV), goat pox virus (GTPV), and lumpy skin disease virus (LSDV) presents one of the most formidable challenges in veterinary virology. These three members of the genus Capripoxvirus within the family Poxviridae share nucleotide sequence identities of up to 97%, a genetic proximity that renders traditional serological methods incapable of discriminating between infections caused by different species or between naturally infected and vaccinated animals [2, 4]. This genetic homology is not merely a taxonomic curiosity; it has profound implications for disease surveillance, outbreak response, and the implementation of vaccination programs. The World Organisation for Animal Health (WOAH) recognizes capripoxviruses as transboundary animal diseases of critical economic importance, and the Food and Agriculture Organization (FAO) has repeatedly emphasized the need for robust differential diagnostic capabilities to support global eradication efforts. The development and refinement of advanced molecular diagnostics and serological differentiation of infected from vaccinated animals (DIVA) strategies have therefore become central pillars of modern capripoxvirus control programs.

The Molecular Basis for Diagnostic Differentiation

Understanding the genetic architecture of capripoxviruses is essential for designing effective diagnostic tools. The genomes of SPPV, GTPV, and LSDV are linear double-stranded DNA molecules ranging from approximately 150 to 155 kilobase pairs, characterized by conserved central regions flanked by variable inverted terminal repeats (ITRs) [3]. The ITR regions, along with specific open reading frames such as the P32 gene (encoding a major envelope protein) and the RPO30 gene (encoding the RNA polymerase 30 kDa subunit), exhibit sufficient sequence divergence to serve as targets for species-specific discrimination [4, 6]. The P32 gene, in particular, has been extensively characterized and utilized for phylogenetic clustering, with studies from Morocco demonstrating that SPPV isolates consistently form a distinct clade separate from GTPV and LSDV when subjected to P32-based sequencing and phylogenetic analysis [6]. This molecular heterogeneity, while subtle, provides the foundation upon which all advanced diagnostic platforms are built.

The biological implications of this genetic similarity cannot be overstated. The lack of strict host specificity among capripoxviruses further complicates diagnostic interpretation. While SPPV and GTPV have historically been considered host-restricted to sheep and goats respectively, and LSDV to cattle, recent evidence indicates that cross-species transmission events are more common than previously recognized [4]. This phenomenon has been particularly well-documented in the context of lumpy skin disease control, where attenuated GTPV and SPPV vaccines are routinely administered to cattle in endemic regions due to their protective efficacy against LSDV [2]. The resulting serological cross-reactivity creates a diagnostic quagmire: standard serological assays cannot distinguish between antibodies generated by natural LSDV infection and those induced by GTPV or SPPV vaccination, thereby undermining surveillance efforts and complicating the certification of disease-free status for international trade.

Loop-Mediated Isothermal Amplification (LAMP) for Field-Deployable Genotyping

The development of loop-mediated isothermal amplification (LAMP) assays represents a paradigm shift in capripoxvirus diagnostics, particularly for resource-limited settings endemic for sheep and goat pox. Unlike conventional polymerase chain reaction (PCR) methods that require sophisticated thermocycling equipment, LAMP operates at a constant temperature (typically 60-65°C), dramatically reducing the infrastructure requirements and enabling point-of-care testing in field conditions [3]. Zhao et al. (2014) pioneered a LAMP-based approach specifically designed for the differential detection of GTPV and SPPV, exploiting sequence variations within the ITR regions. Their methodology employed three distinct sets of LAMP primers: universal primers (GSPV) capable of detecting all capripoxviruses, GTPV-specific primers, and SPPV-specific primers. The reaction conditions were optimized at 62°C for 45 to 60 minutes, yielding results that could be visualized by simple turbidity assessment or fluorescent dye incorporation, eliminating the need for gel electrophoresis [3].

The analytical performance of this LAMP assay was rigorously evaluated against a panel of 135 preserved epidemic materials previously characterized by restriction fragment length polymorphism PCR (RFLP-PCR). The universal and GTPV-specific LAMP primers achieved 100% detection rates, while the SPPV-specific primers demonstrated 98.8% detection, with no cross-reactivity observed against a comprehensive panel of pathogens including Orf virus, foot-and-mouth disease virus, Mycoplasma mycoides subsp. capri, Chlamydophila psittaci, and multiple hemoparasites [3]. This specificity is particularly noteworthy given the clinical overlap between sheep pox and other vesicular and pustular diseases such as contagious ecthyma (orf), bluetongue, and dermatophilosis, conditions that frequently confound clinical diagnosis in endemic regions [1, 5]. The LAMP assay's ability to function without sophisticated laboratory infrastructure makes it ideally suited for integration into national surveillance programs in low- and middle-income countries, where the majority of capripoxvirus outbreaks occur. Furthermore, the rapid turnaround time, less than one hour from sample collection to result, enables real-time outbreak response, allowing veterinary authorities to implement quarantine and vaccination measures before extensive viral dissemination occurs.

Multiplex Real-Time PCR: High-Throughput Discrimination with Quantitative Capacity

While LAMP offers unparalleled field applicability, multiplex real-time PCR remains the gold standard for high-throughput, quantitative differential diagnosis in centralized reference laboratories. Wang et al. (2021) developed and validated a triplex real-time PCR assay capable of simultaneously detecting and differentiating SPPV, GTPV, and LSDV in a single reaction. The assay design incorporated universal primers targeting a conserved region of the capripoxvirus genome, coupled with species-specific hydrolysis probes labeled with distinct fluorophores (e.g., FAM, HEX, and Cy5) to enable multiplex detection [4]. The analytical sensitivity of this system was exceptional, with a limit of detection (LOD) of 10² copies of target genomic DNA per reaction, a threshold that ensures reliable detection even in samples with low viral loads, such as those collected during the early stages of infection or from animals with mild clinical signs [4].

The diagnostic specificity of the multiplex real-time PCR was confirmed through extensive cross-reactivity testing against a panel of pathogens that produce similar clinical manifestations in small ruminants, including Orf virus, bluetongue virus, and foot-and-mouth disease virus. No cross-reactivity was observed, and the assay successfully identified capripoxvirus species in 557 clinical samples from both Chinese and Ethiopian field settings, with results fully concordant with RFLP-PCR analysis of the P32 and RPO30 genes and subsequent gene sequencing [4]. This level of accuracy is critical for guiding vaccine selection, as the use of homologous vaccines (i.e., SPPV vaccine for sheep pox, GTPV vaccine for goat pox) is associated with superior immunogenicity and reduced risk of adverse reactions compared to heterologous vaccination [6]. The quantitative nature of real-time PCR also provides valuable epidemiological data; viral load quantification can inform estimates of infectiousness, track the progression of outbreaks, and evaluate the efficacy of control interventions. From a regulatory perspective, the ability to definitively differentiate between SPPV, GTPV, and LSDV is essential for compliance with WOAH reporting requirements and for maintaining access to international livestock markets.

Serological DIVA Strategies: Overcoming the Cross-Reactivity Barrier

The most intractable challenge in capripoxvirus serology has been the development of DIVA-compatible assays that can distinguish naturally infected animals from those vaccinated with live attenuated vaccines. This problem is particularly acute in the context of lumpy skin disease control, where attenuated GTPV and SPPV vaccines are widely used due to their safety profile and cross-protective efficacy against LSDV [2]. Conventional serological tests, including virus neutralization tests and whole-virus enzyme-linked immunosorbent assays (ELISAs), detect antibodies against conserved viral proteins that are shared across all capripoxvirus species, rendering them incapable of differentiating vaccine-induced immunity from natural infection. This limitation has profound consequences for surveillance programs, as seropositive animals in vaccinated populations cannot be reliably classified, potentially masking ongoing viral circulation and delaying outbreak detection.

Yuan et al. (2024) addressed this diagnostic gap through an innovative approach: the development of a synthesized gene unique to LSDV for use as a differential antigen in an indirect ELISA (iELISA). The strategy involved identifying genomic sequences present in LSDV but absent from GTPV and SPPV, synthesizing the corresponding recombinant protein, and using it as the coating antigen in an iELISA format. The rationale is straightforward: animals vaccinated with GTPV or SPPV vaccines will not develop antibodies against LSDV-specific epitopes, whereas animals naturally infected with LSDV will mount a humoral response against these unique antigens [2]. The performance characteristics of this iELISA were impressive. Using a cut-off value of 30% sample-to-positive ratio (S/P%), the assay achieved 100% diagnostic specificity (95% CI: 88.43–100) and 93.3% diagnostic sensitivity (95% CI: 77.93–99.18) when evaluated against a panel of well-characterized serum samples. The intra-assay coefficient of variation (CV) ranged from 1.08% to 4.11%, and the inter-assay CV from 0.00% to 8.90%, indicating excellent reproducibility [2].

The true test of any DIVA assay lies in its performance under field conditions. When applied to 200 clinical serum samples from Chinese cattle populations, the iELISA demonstrated remarkable discriminatory power. Among 141 samples collected from herds vaccinated with attenuated GTPV vaccine, none tested positive (0/141), confirming the absence of cross-reactivity with antibodies induced by heterologous vaccination. In contrast, among 59 samples from herds with confirmed LSDV infection, the overall seropositivity rate was 33.90% (20/59; 95% CI: 22.08–47.39) [2]. This differential performance validates the concept that LSDV-specific epitopes can be exploited for serological discrimination, even in populations with complex vaccination histories. The implications for disease surveillance are transformative: veterinary authorities can now conduct serosurveys in vaccinated populations to detect incursions of wild-type LSDV, enabling early intervention before clinical cases become apparent.

Monoclonal Antibody-Based Approaches for Antigen Detection

Complementing the serological DIVA strategies based on recombinant antigens, recent advances in monoclonal antibody (mAb) technology have yielded tools for direct antigen detection that can differentiate LSDV from SPPV and GTPV. Chang et al. (2025) generated two LSDV-specific monoclonal antibodies, designated 3C10 and 6H3, both targeting the P32 protein of LSDV. The P32 protein, a major envelope glycoprotein, is highly conserved among capripoxviruses but contains species-specific epitopes that can be exploited for differential diagnosis. Through hybridoma technology and rigorous screening, the researchers identified mAbs that bound specifically to LSDV P32 without cross-reacting with the homologous proteins from SPPV or GTPV [7].

These mAbs were subsequently used to develop a double-antibody sandwich ELISA (DAS-ELISA), in which mAb 3C10 served as the capture antibody and horseradish peroxidase-conjugated mAb 6H3 as the detection antibody. The DAS-ELISA format offers several advantages over indirect ELISAs, including the ability to detect viral antigen directly in clinical samples (e.g., skin scabs, vesicular fluid, or tissue homogenates) rather than relying on the host antibody response. This is particularly valuable for acute-phase diagnosis, where viral antigen is abundant but seroconversion may not yet have occurred. The assay demonstrated high specificity, showing no cross-reactivity with a panel of common bovine and ovine pathogens, including SPPV and GTPV [7]. The development of such antigen-capture ELISAs represents a significant advancement, as they provide a serological counterpart to molecular methods, offering redundancy in diagnostic capacity and enabling cross-validation of results. Moreover, the ability to detect viral antigen in the absence of detectable nucleic acid (e.g., in degraded samples or following antiviral treatment) expands the diagnostic window and enhances surveillance sensitivity.

Integrating Molecular and Serological Approaches into Surveillance Frameworks

The optimal deployment of advanced molecular diagnostics and DIVA serological assays requires careful integration into existing surveillance and reporting systems. The Thrace region of southeastern Europe, which spans Greece, Bulgaria, and Turkey, provides a instructive case study in the challenges of disease reporting in high-risk areas. This region has historically served as a gateway for the introduction of capripoxviruses and other transboundary animal diseases into Europe, driven by the movement of livestock across porous borders and the presence of diverse production systems ranging from intensive commercial operations to smallholder backyard flocks [10]. Expert elicitation studies have revealed significant variability in the sensitivity of disease reporting across different production sectors, with small ruminant herds, mixed bovine herds, and backyard operations consistently identified as having lower reporting sensitivity due to limited awareness of clinical signs, unfamiliarity with reporting procedures, and inadequate biosecurity measures [10].

The availability of field-deployable LAMP assays and portable real-time PCR platforms can directly address these surveillance gaps by enabling rapid on-site testing by veterinary paraprofessionals, reducing the time between sample collection and diagnostic confirmation. When coupled with DIVA-compatible serological assays, these tools provide a comprehensive diagnostic framework capable of detecting both acute infections (via molecular methods) and past exposure (via serology), even in vaccinated populations. The participatory epidemiological studies conducted in the Somali Region of Ethiopia underscore the importance of community engagement in surveillance efforts. In these pastoralist communities, sheep and goat pox was ranked as the fourth most important livestock disease, accounting for 11.0% of disease burden, behind contagious caprine pleuropneumonia (14.2%), peste des petits ruminants (13.0%), and hemorrhagic septicemia (12.0%) [8]. The high level of agreement across districts (W = 0.886, p < 0.001) regarding disease prioritization indicates that community perceptions align closely with epidemiological reality, providing a foundation for participatory surveillance programs that integrate local knowledge with advanced diagnostic technologies [8].

The transcriptomic insights gained from comparative RNA sequencing analyses of capripoxvirus infections in immortalized bovine endothelial cell models have further refined our understanding of host-virus interactions, identifying differentially expressed genes and signaling pathways that may serve as biomarkers for species-specific infection [9]. While still in the research phase, such biomarkers could eventually be incorporated into multiplex diagnostic platforms, enabling simultaneous detection of viral nucleic acid, host antibody responses, and host transcriptomic signatures. The convergence of molecular virology, immunology, and bioinformatics is driving the next generation of capripoxvirus diagnostics, moving beyond simple pathogen detection toward a systems-level understanding of infection dynamics that can inform predictive modeling and risk-based surveillance.

Prevention, Biosecurity, and Regulatory Reporting Protocols for Sheep Pox and Goat Pox in Non-Endemic Regions

In jurisdictions where sheep pox and goat pox are classified as foreign or exotic animal diseases, most notably the United States, the United Kingdom, Australia, New Zealand, and large portions of Western Europe, the fundamental pillars of disease management rest upon stringent prevention, robust on-farm biosecurity, and a legally mandated regulatory reporting framework. The absence of circulating Capripoxvirus (CaPV) within these regions creates a uniquely vulnerable epidemiological landscape: naïve small-ruminant populations lack any herd immunity, animal health infrastructures are not routinely attuned to the clinical presentation of these diseases, and the economic consequences of an incursion would be catastrophic due to immediate trade sanctions and depopulation measures [1, 5, 10]. Because sheep pox virus (SPPV) and goat pox virus (GTPV) share up to 97% nucleotide homology with lumpy skin disease virus (LSDV) and produce virtually indistinguishable clinical signs, fever, multifocal nodular dermatitis, lymphadenopathy, and respiratory distress, the need for a multi-layered defence strategy that integrates prevention, biosecurity, and rapid, accurate reporting cannot be overstated [2, 4, 7].

Prophylactic Prevention and Import Risk Management

Prevention in non-endemic regions begins far before any animal sets hoof on domestic soil. The primary line of defence is rigorous import control. Live sheep and goats, their germplasm, and any derived biological products (e.g., unprocessed hides, semen, embryos) should be sourced exclusively from countries or zones officially free of SPPV and GTPV under the World Organisation for Animal Health (WOAH) Terrestrial Animal Health Code. Import permits must require pre-export quarantine and negative molecular testing, preferably using multiplex real-time PCR assays capable of differentiating SPPV, GTPV, and LSDV in a single reaction, to intercept latent or subclinical infections [4, 6]. Given that CaPVs can survive for weeks in dried scabs, wool, and contaminated fomites [1], imported materials should undergo mandatory disinfection protocols (e.g., 2% sodium hydroxide or 0.5% citric acid) endorsed by the Food and Agriculture Organization (FAO) for poxvirus inactivation.

Vaccination is intentionally omitted from the prevention toolkit in most non-endemic settings. The use of live-attenuated capripox vaccines, often derived from either SPPV or GTPV strains, carries an unacceptable risk of reversion to virulence, residual pathogenicity in naïve animals, and the creation of serological interference that undermines surveillance [2, 6]. Furthermore, vaccinated animals become seropositive, making it impossible to distinguish them from naturally infected animals using conventional serology unless a DIVA (Differentiating Infected from Vaccinated Animals) strategy is employed, and such DIVA assays currently exist only for LSDV, not for SPPV/GTPV [2, 7]. Therefore, livestock producers in non-endemic areas must rely exclusively on biosecurity, early detection, and emergency preparedness rather than prophylactic immunization.

On-Farm Biosecurity in the Absence of Disease

Biosecurity for SPPV/GTPV in non-endemic regions demands a “prevention mindset” that treats every unexplained febrile dermatosis as a potential foreign animal disease (FAD) until proven otherwise [1, 5]. The cornerstone is segregation and surveillance of high-risk cohorts. Because sheep and goats are often commingled in smallholder or mixed production systems, and because Capripoxvirus can cross the ovine-caprine species barrier when viral load is high [4, 8], any new animal entering a naïve flock must undergo a minimum 28-day isolation period with daily clinical inspections for nodular skin lesions, ocular-nasal discharge, and pyrexia.

Producers and herd veterinarians must be trained to recognize the “red flag” clinical triad of SPPV/GTPV: (1) generalized papular-to-nodular skin eruptions that progress to crusted scabs, particularly on the head, perineum, and udder; (2) high morbidity (>50%) accompanied by significant mortality; and (3) rapid spread within the flock concurrent with systemic signs such as pneumonia or diarrhoea [1, 5, 8]. Any of these signs should immediately trigger a cessation of animal movements, restriction of farm access, and notification of the state or federal regulatory veterinary authority. Environmental biosecurity measures, dedicated clothing and footwear for personnel handling suspect animals, disinfection of vehicles and equipment with virucidal agents, and control of biting insects (though mechanical transmission is less important than direct contact) , must be documented and rehearsed during periodic biosecurity drills [10].

Molecular and Serological Surveillance as a Biosecurity Force Multiplier

Biosecurity is only as strong as the surveillance system that underpins it. In non-endemic regions, passive surveillance (reporting of clinical suspects) must be supplemented by targeted active surveillance in high-risk populations, for example, flocks near international borders, livestock markets, or ports of entry. Advances in molecular diagnostics now allow for same-day confirmation and species-level differentiation. The loop-mediated isothermal amplification (LAMP) assay developed by Zhao et al. provides a field-deployable tool that can distinguish GTPV from SPPV at 62°C within 45–60 minutes, with no cross-reaction against orf virus, foot-and-mouth disease virus, or common bacterial pathogens [3]. This test is particularly valuable in remote or resource-limited settings where real-time PCR platforms are unavailable.

For laboratory-based confirmation, the multiplex real-time PCR system described by Wang et al. simultaneously detects SPPV, GTPV, and LSDV with a limit of detection of 100 genomic copies and 100% specificity against other pathogens causing similar clinical signs (e.g., bluetongue virus, contagious ecthyma, dermatophilosis) [4]. These assays should be incorporated into national veterinary laboratory networks and validated against locally circulating strains. Serological surveillance, while less informative for acute case detection, can be used for retrospective herd-level screening. However, the high genetic homology among CaPVs (≤97%) means that standardized enzyme-linked immunosorbent assays (ELISAs) cannot reliably discriminate SPPV from GTPV unless they employ species-specific antigens [2, 7]. The recent development of monoclonal antibody-based double-antibody sandwich ELISAs that distinguish LSDV from SPPV/GTPV [7] and synthetic protein-based iELISAs for DIVA [2] represent critical progress, but these tools remain primarily calibrated for lumpy skin disease; analogous DIVA platforms for sheep and goat pox in non-endemic regions are an urgent research gap.

Regulatory Reporting Protocols: A Legal and Epidemiological Imperative

In the United States, sheep pox and goat pox are designated as notifiable foreign animal diseases under the authority of the USDA Animal and Plant Health Inspection Service (APHIS). The protocol is unambiguous: any veterinarian, producer, or laboratory personnel who suspects SPPV or GTPV infection must immediately report to the area veterinarian in charge (AVIC) or a state regulatory veterinarian [1]. Similar mandatory reporting frameworks exist in the European Union (EU), where SPPV and GTPV are listed as notifiable diseases under Council Directive 92/119/EEC, and in the United Kingdom under the Animal Health Act 1981. Reporting triggers an immediate epidemiological hold on the premises, an official veterinary investigation, and the collection of diagnostic samples (whole blood, scabs, and lesion biopsy material in viral transport medium) for molecular confirmation [5, 10].

Timeliness of reporting is the single most critical variable controlling outbreak size. The scenario-tree modelling study in the Thrace region of Greece, Bulgaria, and Turkey, a geographic gateway for multiple CaPV incursions into Europe, demonstrated that reporting sensitivity is lowest in small-ruminant herds, mixed bovine herds, and backyard production systems, precisely where clinical awareness of sheep pox and goat pox is poorest [10]. The study identified several modifiable barriers: lack of awareness of reporting procedures, fear of economic repercussions, and poor understanding of biosecurity measures among smallholders. To counteract these, animal health services in non-endemic regions must conduct regular training exercises and tabletop simulations that immerse field veterinarians and producers in the recognition of capripox lesions, the steps of sample collection, and the legal duty to report. Participatory epidemiology, engaging livestock owners in focus groups, matrix scoring, and seasonal calendaring, has proven highly effective in improving disease prioritization and reporting compliance in pastoral communities and can be adapted for the small-ruminant sector in non-endemic countries [8].

Once a report is filed, the regulatory response cascade follows a standard FAD framework: quarantine of the affected premises, tracing of animal and human movements in the preceding 21 days, immediate depopulation of infected and in-contact flocks (with compensation to encourage future reporting), and decontamination of facilities under official supervision. Molecular characterization of the isolate, typically via sequencing of the P32 gene or the RPO30 gene, is essential to confirm the species (SPPV vs. GTPV) and to compare the strain with global sequences to identify the likely origin of introduction [6, 9]. This information informs trade restrictions and guides the international notification to WOAH. Because CaPVs can persist in scabs and contaminated environments for months, a premises may not be restocked until at least 60 days after final disinfection and negative sentinel animal testing.

Integrating Regulatory Reporting with Transboundary Surveillance

No non-endemic region exists in isolation. The regular incursions of sheep pox and goat pox into the Balkans, the Middle East, and parts of southern Asia underscore the porous nature of national borders and the importance of cross-border reporting harmonization. Under the FAO’s Emergency Prevention System (EMPRES) and WOAH’s World Animal Health Information System (WAHIS), any confirmed outbreak of SPPV or GTPV must be reported within 24 hours to prevent trade disruptions and enable neighbouring countries to step up passive surveillance. The recent participatory epidemiological studies in the Somali Region of Ethiopia, where SPPV/GTPV ranks as the fourth most important livestock disease, highlight that even endemic regions struggle with under-reporting; this data should be used by non-endemic countries to update risk assessments for importation from those zones [8].

Finally, the regulatory framework must be dynamic and evidence-based. As new point-of-care diagnostics (e.g., LAMP [3]) and DIVA serological tools [2, 7] move from research pipelines into validation, they should be formally incorporated into national outbreak investigation protocols to reduce the lag between suspicion and confirmation. Regular auditing of reporting system sensitivity, using methods such as scenario-tree modelling and expert elicitation [10], can identify weaknesses in the surveillance chain and guide targeted investments in producer education, mobile veterinary services, and communication infrastructure. In this way, prevention, biosecurity, and regulatory reporting form a cohesive, perpetually improving shield against one of the most economically devastating viral diseases of small ruminants.

References

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