Cooperia curticei in Sheep: Small Intestine Nematode and Periparturient Rise

Introduction

Cooperia curticei is a trichostrongylid nematode parasite that inhabits the small intestine of sheep and, less commonly, goats. As part of the complex of gastrointestinal nematodes (GIN) affecting small ruminants, C. curticei contributes to production losses through subclinical enteropathy, reduced weight gain, and impaired reproductive performance. The phenomenon of periparturient rise (PPR) in fecal egg counts (FEC) is especially relevant for this species, as it amplifies pasture contamination around lambing. This article provides a comprehensive reference on the etiology, epidemiology, clinical pathology, diagnostic approaches, treatment options, and control strategies for C. curticei infection in sheep, with an emphasis on the periparturient period.

Etiology and Morphology

Cooperia curticei belongs to the order Strongylida, family Trichostrongylidae. Adults are slender, reddish worms measuring 4–6 mm in length. The anterior end is slightly swollen, with a small buccal capsule and no pronounced lips or teeth, a feature distinguishing it from the larger Haemonchus species. Males possess a prominent copulatory bursa with two long spicules. The eggs are thin-shelled, oval, and measure approximately 70–90 × 30–40 µm, morphologically indistinguishable from other trichostrongylid eggs (e.g., Teladorsagia, Trichostrongylus) on routine fecal flotation. The cuticular synlophe (longitudinal ridges) pattern is a key feature for species identification using scanning electron microscopy or nemabiome sequencing [1].

Life Cycle

Cooperia curticei follows a direct life cycle typical of trichostrongylids. Adult females in the small intestine produce eggs that are shed in feces. Under favorable environmental conditions (temperatures above 10°C, adequate moisture), eggs hatch into first-stage (L1) larvae, which molt to second-stage (L2) and then to infective third-stage (L3) larvae within 7–14 days. L3 larvae migrate onto herbage and are ingested by grazing sheep. After ingestion, exsheathment occurs in the rumen or abomasum, and the larvae penetrate the small intestinal mucosa, undergoing two more molts (L4 to L5) before emerging as adults. The prepatent period is approximately 14–21 days. Unlike some abomasal species (e.g., Haemonchus contortus), C. curticei does not undergo extensive hypobiosis (arrested development) under temperate conditions, although some seasonal inhibition may occur.

Epidemiology

Prevalence and Geographic Distribution

Cooperia curticei is a common component of the ovine GIN community in temperate regions of Europe, North America, and Australasia. In a large-scale nemabiome survey of UK sheep farms, C. curticei was detected in the majority of flocks, often co-infecting with Teladorsagia circumcincta, Trichostrongylus spp., and Haemonchus contortus [1]. A slaughterhouse survey in Upper Bavaria revealed that C. curticei was present in a substantial proportion of sheep, with moderate worm burdens [2]. The species can also infect cattle experimentally, but natural cross-infection is limited due to host specificity [3].

Transmission Dynamics

Transmission is driven by pasture contamination. Infective L3 larvae can survive overwinter on pasture in temperate climates, providing a source of infection for lambs born in spring. The periparturient rise in FEC in ewes is a critical epidemiological driver, as it synchronizes with the emergence of L3 larvae on pasture when naive lambs begin grazing [4, 5]. Factors influencing transmission intensity include stocking density, pasture management, climatic conditions (especially temperature and rainfall), and host immunity.

Periparturient Rise (PPR) in Ewes

The periparturient rise is a well-documented phenomenon in which fecal egg counts in ewes increase sharply around lambing and during early lactation. This occurs due to a temporary relaxation of acquired immunity, mediated by hormonal changes (e.g., elevated prolactin and glucocorticoids) and the nutritional demands of pregnancy and lactation [6, 7]. Although PPR has been most intensively studied for Teladorsagia circumcincta and Haemonchus contortus, Cooperia curticei also contributes to the overall egg output during this period. Studies using nemabiome sequencing have confirmed that C. curticei is one of the species whose relative abundance increases in periparturient ewes [1, 4].

The magnitude of the PPR is influenced by ewe body condition score, nutritional status, and lambing season [8, 9, 10]. Protein supplementation during late pregnancy and lactation can reduce the PPR [11, 12]. Ewes with higher genetic resistance to nematodes exhibit lower FEC during the periparturient period [13, 14]. The PPR is not merely a statistical artifact; it has real consequences for lamb infection risk and subsequent pasture contamination [4, 5].

Clinical Signs and Pathology

Pathogenesis

Cooperia curticei adults reside in the proximal small intestine, where they cause villous atrophy, crypt hyperplasia, and a mild inflammatory infiltrate. The pathological changes are less severe than those caused by Trichostrongylus colubriformis or Nematodirus battus, but heavy burdens ( > 10,000 worms) can lead to protein-losing enteropathy, reduced digestive efficiency, and impaired nutrient absorption. Diarrhea is uncommon unless co-infection with other pathogens exists.

Clinical Signs

In lambs, moderate to heavy infections manifest as ill-thrift, reduced weight gain, and a slightly rough coat. Clinical signs are often subclinical, especially in well-nourished animals. In ewes, the PPR is usually asymptomatic but contributes to the overall FEC that perpetuates pasture contamination. Severe infections can cause mild anemia (though C. curticei is not a blood-feeder), hypoproteinemia, and reduced milk production. The combination of C. curticei with other GIN may exacerbate clinical disease [6].

Diagnosis

Traditional Methods

Routine diagnosis relies on fecal egg count (FEC) using modified McMaster or FLOTAC techniques. Because trichostrongylid eggs are morphologically identical, quantitative FEC cannot differentiate C. curticei from Teladorsagia, Trichostrongylus, or Haemonchus. Larval culture followed by morphological identification of L3 larvae is possible but requires expertise and is time-consuming. C. curticei L3 larvae are distinguished by their small size and characteristic tail sheath.

Molecular Diagnostics

The application of nemabiome sequencing using the internal transcribed spacer 2 (ITS-2) region of ribosomal DNA has revolutionized species identification. The ITS-2 rDNA nemabiome assay validated for ovine GIN allows simultaneous quantification of C. curticei along with other co-infecting species from fecal samples [1]. This method is high-throughput, accurate, and suitable for large-scale epidemiological studies. Pooled PCR approaches for anthelmintic resistance detection (e.g., for benzimidazole resistance) have also been applied to C. curticei, though less commonly than for H. contortus or T. circumcincta.

Differential diagnosis from other small intestinal nematodes such as Trichostrongylus colubriformis (see Trichostrongylus colubriformis: The Bankrupt Worm of Sheep and Cattle – Pathogenesis and Pasture Management) and Nematodirus spp. is aided by molecular methods.

Treatment and Anthelmintic Resistance

Anthelmintic Classes

Several anthelmintics are effective against C. curticei:

• Benzimidazoles (e.g., thiabendazole, fenbendazole): Broad-spectrum activity. However, resistance has been documented. Kerboeuf et al. [15] demonstrated that in a benzimidazole-resistant isolate, adult C. curticei were localized more distally in the small intestine after treatment, suggesting a behavioral resistance mechanism.
• Macrocyclic lactones (e.g., ivermectin, moxidectin): Ivermectin is highly effective against C. curticei at the recommended dose [16]. Long-acting moxidectin formulations have been used to suppress PPR in ewes [17, 18].
• Imidazothiazoles (e.g., levamisole): Also effective, though resistance may emerge.

Anthelmintic Resistance

Anthelmintic resistance in C. curticei is less frequently reported than in H. contortus or T. circumcincta, but it does occur. Resistance to benzimidazoles has been documented in sheep and goats [15, 19]. The faecal egg count reduction test (FECRT) remains the field standard for detecting resistance, but molecular detection of single nucleotide polymorphisms (SNPs) in the β-tubulin isotype 1 gene can confirm benzimidazole resistance. Integration of C. curticei into resistance surveillance programs is recommended given its contribution to overall FEC.

Control Strategies

Integrated Parasite Management

Control of C. curticei must be part of a comprehensive GIN management program rather than species-specific.

Pasture Management

Reducing pasture contamination through rotational grazing, mixed-species grazing (e.g., with cattle or horses), and prolonged rest periods can lower L3 availability. Because C. curticei has a relatively short survival on pasture compared to some other species, strategic grazing of low-risk pastures for lambs is beneficial.

Nutritional Interventions

Protein supplementation during late pregnancy and lactation reduces the magnitude of PPR and improves immunity [11, 12]. Ewes with adequate body condition exhibit lower FEC around lambing [8].

Genetic Resistance

Breeding for nematode resistance, as measured by low FEC, has been applied in several sheep breeds. Studies in Katahdin sheep have shown that ewe periparturient FEC is heritable and genetically correlated with lamb FEC and body weights [14, 10]. Selection for resistant ewes can reduce overall egg shedding and PPR [13].

Biological Control

Nematophagous fungi such as Duddingtonia flagrans, administered as chlamydospores in feed, reduce L3 numbers in feces. Field trials in periparturient ewes have demonstrated efficacy against H. contortus, and likely impact C. curticei [20]. Tannin-rich forages (e.g., sainfoin) have shown promise against both H. contortus and C. curticei in lambs [21].

Targeted Treatment

Selective treatment based on FEC thresholds or indicators (e.g., dag score, FAMACHA) helps preserve refugia and slow resistance development. For C. curticei, which does not cause anemia, FAMACHA is not directly applicable; thus FEC-based decision making is preferred.

Decision Tree for Integrated Control

The following Mermaid diagram summarizes a decision framework for managing C. curticei within a flock, emphasizing the periparturient period.

graph TD
    A[Start: Pre-lambing ewe assessment], > B{Body condition score < 2.5?}
    B, Yes, > C[Improve nutrition: protein supplement]
    B, No, > D[Fecal egg count (FEC) at lambing]
    C, > D
    D, > E{FEC > 500 epg?}
    E, Yes, > F[Consider targeted treatment with macrocyclic lactone or benzimidazole (if resistance confirmed)]
    E, No, > G[No treatment; monitor lambs]
    F, > H[Perform FECRT 10-14 days post-treatment to assess efficacy]
    H, > I{Reduction < 90%?}
    I, Yes, > J[Suspected resistance; switch anthelmintic class, implement refugia]
    I, No, > K[Continue monitoring]
    J, > L[Submit samples for nemabiome & resistance genotyping]
    L, > M[Adjust pasture management: avoid contaminated paddocks, use sainfoin silage or D. flagrans]
    G, > N[Graze lambs on low-risk pasture; monitor FEC in lambs at 8-12 weeks]
    K, > N
    M, > N
    N, > O[End of season evaluation: FEC, growth, pasture contamination]

Conclusion

Cooperia curticei is an often overlooked but epidemiologically significant small intestinal nematode of sheep. Its role in the periparturient rise in FEC makes it a key contributor to pasture contamination and subsequent infection in lambs. Accurate diagnosis now benefits from nemabiome sequencing, allowing species-specific surveillance without the need for larval culture. Anthelmintic resistance is emerging, necessitating integrated control strategies that combine pasture management, nutritional support, genetic selection, and targeted treatment. Understanding the biology and epidemiology of C. curticei is essential for sustainable nematode control in sheep flocks.

References

[1] Redman E, Queiroz C, Bartley DJ, et al. Validation of ITS-2 rDNA nemabiome sequencing for ovine gastrointestinal nematodes and its application to a large scale survey of UK sheep farms. Vet Parasitol. 2019. URL: https://pubmed.ncbi.nlm.nih.gov/31606485/

[2] Rehbein S, Kollmannsberger M, Visser M, et al. [Helminth burden of slaughter sheep in Upper Bavaria. 1: Species spectrum, infestation extent and infestation intensity]. Berl Munch Tierarztl Wochenschr. 1996. URL: https://pubmed.ncbi.nlm.nih.gov/8694743/

[3] Borgsteede FH. Experimental cross-infections with gastrointestinal nematodes of sheep and cattle. Z Parasitenkd. 1981. URL: https://pubmed.ncbi.nlm.nih.gov/7245840/

[4] Hamer K, McIntyre J, Morrison AA, et al. The dynamics of ovine gastrointestinal nematode infections within ewe and lamb cohorts on three Scottish sheep farms. Prev Vet Med. 2019. URL: https://pubmed.ncbi.nlm.nih.gov/31479849/

[5] Falzon LC, Menzies PI, Shakya KP, et al. A longitudinal study on the effect of lambing season on the periparturient egg rise in Ontario sheep flocks. Prev Vet Med. 2013. URL: https://pubmed.ncbi.nlm.nih.gov/23333408/

[6] Fthenakis GC, Mavrogianni VS, Gallidis E, et al. Interactions between parasitic infections and reproductive efficiency in sheep. Vet Parasitol. 2015. URL: https://pubmed.ncbi.nlm.nih.gov/25577675/

[7] Beasley AM, Kahn LP, Windon RG. The influence of reproductive physiology and nutrient supply on the periparturient relaxation of immunity to the gastrointestinal nematode Trichostrongylus colubriformis in Merino ewes. Vet Parasitol. 2012. URL: https://pubmed.ncbi.nlm.nih.gov/22503385/

[8] González-Warleta M, Castro-Hermida JA, Mezo M. Gastrointestinal nematode egg counts throughout the reproductive cycle of breeding ewes: Relation to body condition, FAMACHA and dag scores. Vet Parasitol. 2025. URL: https://pubmed.ncbi.nlm.nih.gov/41005127/

[9] Höglund J, Carlsson A, Gustafsson K. Effects of lambing season on nematode faecal egg output in ewes. Vet Parasitol Reg Stud Reports. 2021. URL: https://pubmed.ncbi.nlm.nih.gov/34879944/

[10] Notter DR, Burke JM, Miller JE, et al. Factors affecting fecal egg counts in periparturient Katahdin ewes and their lambs. J Anim Sci. 2017. URL: https://pubmed.ncbi.nlm.nih.gov/28177372/

[11] López-Leyva Y, González-Garduño R, Cruz-Tamayo AA, et al. Protein Supplementation as a Nutritional Strategy to Reduce Gastrointestinal Nematodiasis in Periparturient and Lactating Pelibuey Ewes in a Tropical Environment. Pathogens. 2022. URL: https://pubmed.ncbi.nlm.nih.gov/36015063/

[12] Sebastiano RS, Sweeney T, Keady TW, et al. Can the amount of digestible undegraded protein offered to ewes in late pregnancy affect the periparturient change in resistance to gastrointestinal nematodes? Vet Parasitol. 2017. URL: https://pubmed.ncbi.nlm.nih.gov/28215873/

[13] Rose Vineer H, Baber P, White T, et al. Reduced egg shedding in nematode-resistant ewes and projected epidemiological benefits under climate change. Int J Parasitol. 2019. URL: https://pubmed.ncbi.nlm.nih.gov/31585121/

[14] Notter DR, Ngere L, Burke JM, et al. Genetic parameters for ewe reproductive performance and peri-parturient fecal egg counts and their genetic relationships with lamb body weights and fecal egg counts in Katahdin sheep. J Anim Sci. 2018. URL: https://pubmed.ncbi.nlm.nih.gov/29733415/

[15] Kerboeuf D, Hubert J, Alvinerie M. Localization and migration of benzimidazole resistant and susceptible adult Cooperia curticei in the small intestine of sheep after treatment with thiabendazole. Vet Parasitol. 2000. URL: https://pubmed.ncbi.nlm.nih.gov/11027860/

[16] Bogan JA, McKellar QA, Mitchell ES, et al. Efficacy of ivermectin against Cooperia curticei infection in sheep. Am J Vet Res. 1988. URL: https://pubmed.ncbi.nlm.nih.gov/3354973/

[17] Crilly JP, Jennings A, Sargison N. Patterns of faecal nematode egg shedding after treatment of sheep with a long-acting formulation of moxidectin. Vet Parasitol. 2015. URL: https://pubmed.ncbi.nlm.nih.gov/26276580/

[18] Sargison ND, Bartram DJ, Wilson DJ. Use of a long acting injectable formulation of moxidectin to control the periparturient rise in faecal Teladorsagia circumcincta egg output of ewes. Vet Parasitol. 2012. URL: https://pubmed.ncbi.nlm.nih.gov/22647461/

[19] Borgsteede FH, Pekelder JJ, Dercksen DP. Anthelmintic resistant nematodes in goats in The Netherlands. Vet Parasitol. 1996. URL: https://pubmed.ncbi.nlm.nih.gov/8916403/

[20] de la Crúz-Crúz HA, Higuera-Piedrahita RI, Zamilpa A, et al. Using an Aqueous Suspension of Duddingtonia flagrans Chlamydospores and a Hexane Extract of Artemisia cina as Sustainable Methods to Reduce the Fecal Egg Count and Larvae of Haemonchus contortus in the Feces of Periparturient Ewes. Pathogens. 2025. URL: https://pubmed.ncbi.nlm.nih.gov/40005482/

[21] Heckendorn F, Häring DA, Maurer V, et al. Effect of sainfoin (Onobrychis viciifolia) silage and hay on established populations of Haemonchus contortus and Cooperia curticei in lambs. Vet Parasitol. 2006. URL: https://pubmed.ncbi.nlm.nih.gov/16934938/

[22] Borkowski EA, Avula J, Redman EM, et al. Correlation of subclinical gastrointestinal nematode parasitism with growth and reproductive performance in ewe lambs in Ontario. Prev Vet Med. 2020. URL: https://pubmed.ncbi.nlm.nih.gov/33099151/

[23] Teixeira M, Matos AFIM, Albuquerque FHMA, et al. Strategic vaccination of hair sheep against Haemonchus contortus. Parasitol Res. 2019. URL: https://pubmed.ncbi.nlm.nih.gov/31203449/

[24] Leivesley JA, Bussière LF, Pemberton JM, et al. Survival costs of reproduction are mediated by parasite infection in wild Soay sheep. Ecol Lett. 2019. URL: https://pubmed.ncbi.nlm.nih.gov/31111651/

[25] Vargas-Duarte JJ, Lozano-Márquez H, Grajales-Lombana HA, et al. Effect of Moxidectin Treatment at Peripartum on Gastrointestinal Parasite Infections in Ewes Raised under Tropical Andes High Altitude Conditions. Vet Med Int. 2015. URL: https://pubmed.ncbi.nlm.nih.gov/26078913/

[26] Akkari H, Gharbi M, Darghouth MA. Dynamics of infestation of tracers lambs by gastrointestinal helminths under a traditional management system in the North of Tunisia. Parasite. 2012. URL: https://pubmed.ncbi.nlm.nih.gov/23193526/