# [Internal Parasites of Sheep](/knowledge/parasites/livestock-parasites/internal-parasites-sheep-gastrointestinal-nematodes): Worms, Diagnosis, and Management ## Key Takeaways - Internal parasites, primarily nematodes like *Haemonchus contortus* and *Teladorsagia circumcincta*, significantly impact ovine productivity through subclinical losses, clinical disease, and mortality, particularly in lambs and periparturient ewes. - Diagnosis relies on a multi-faceted approach including fecal egg counts (FEC) using methods like McMaster or Mini-FLOTAC, Baermann sedimentation for lungworms, and sedimentation for liver fluke eggs, complemented by hematological assessment (e.g., FAMACHA system for anemia) and serological tests (ELISA for *Fasciola hepatica*, *Toxoplasma gondii*). - Anthelmintic resistance is a critical global threat, necessitating strategic drug use and monitoring via fecal egg count reduction tests (FECRT); available drug classes include benzimidazoles, macrocyclic lactones, imidazothiazoles, salicylanilides, amino-acetonitrile derivatives, and spiroindoles. - Integrated Parasite Management (IPM) is paramount, combining targeted selective treatment (TST) based on FEC or FAMACHA scores, strategic grazing management (pasture rotation, mixed-species grazing), genetic selection for parasite resistance, and robust biosecurity measures like quarantine drenching. - Clinical signs vary by parasite, with *H. contortus* causing anemia and hypoproteinemia, *T. circumcincta* leading to abomasal inflammation and diarrhea, and *Fasciola hepatica* inducing acute or chronic fasciolosis with liver damage and anemia. --- ## Introduction Internal parasites represent a major constraint to ovine productivity and welfare globally [1, 2]. The term "[worms sheep get](/knowledge/bacteria/livestock-parasites/worms-sheep-gastrointestinal-nematode-control)" encompasses a diverse assemblage of helminths and protozoa that inhabit the gastrointestinal tract, respiratory system, liver, and other tissues [1, 3]. These infections cause subclinical production losses, clinical disease, and mortality, particularly in lambs and periparturient ewes [4]. The economic impact arises from reduced weight gain, decreased wool production, impaired fertility, and costs associated with treatment and control [4, 5]. Understanding the biology, epidemiology, and pathophysiology of these parasites is essential for designing effective diagnostic and management programs [6, 7]. ## Etiology and Classification The [internal parasites of sheep](/knowledge/parasites/livestock-parasites/internal-parasites-sheep-gastrointestinal-nematodes) are taxonomically diverse and include nematodes (roundworms), cestodes (tapeworms), trematodes (flukes), and protozoa [1, 8]. ### Nematodes Nematodes are the most prevalent and economically significant [internal parasites of sheep](/knowledge/parasites/livestock-parasites/internal-parasites-sheep-gastrointestinal-nematodes) [1, 9]. The major genera include: - **[Haemonchus contortus](/knowledge/parasites/livestock-parasites/haemonchus-contortus)**: The barber's pole worm, a blood-feeding abomasal nematode [1, 10]. - **[Teladorsagia circumcincta](/knowledge/parasites/livestock-parasites/teladorsagia-circumcincta-sheep-abomasal-worm-anthelmintic-resistance)**: The brown stomach worm, an abomasal parasite causing type I and type II ostertagiosis [1]. - **Trichostrongylus spp.**: Including *T. colubriformis* and *T. axei*, small intestinal and abomasal parasites respectively [1, 11]. - **Nematodirus spp.**: Including *N. battus* and *N. filicollis*, [intestinal parasites](/knowledge/parasites/pet-parasites/intestinal-parasites-dogs-cats-identification-treatment) with a unique egg development requirement [1]. - **Cooperia curticei**: A small intestinal nematode [1]. - **Oesophagostomum columbianum**: The nodule worm, a large intestinal parasite [1, 9]. - **Chabertia ovina**: A large intestinal nematode [1]. - **Dictyocaulus filaria**: The large lungworm, a bronchial parasite [1]. - **Protostrongylus rufescens** and **[Muellerius capillaris](/knowledge/parasites/livestock-parasites/muellerius-capillaris-sheep-goat-lungworm-protostrongylid-diagnosis)**: Small lungworms residing in lung parenchyma and bronchioles [1]. ### Cestodes Cestodes of sheep include: - **Moniezia expansa** and **Moniezia benedeni**: Intestinal tapeworms requiring oribatid mites as intermediate hosts [1]. - **Taenia multiceps** (larval stage: *Coenurus cerebralis*): Causes gid or sturdy, a neurological disease [1]. - **Echinococcus granulosus** (larval stage: hydatid cyst): A zoonotic cestode forming cysts in viscera [1]. ### Trematodes Trematodes include: - **Fasciola hepatica**: The liver fluke, causing fasciolosis [1, 12]. - **Dicrocoelium dendriticum**: The lancet fluke, a bile duct parasite [1]. - **Paramphistomum spp.**: Rumen flukes [1]. ### Protozoa Protozoan parasites include: - **Eimeria spp.**: Coccidia causing coccidiosis, primarily in lambs [1]. - **Cryptosporidium parvum**: A zoonotic protozoan causing enteritis in lambs [1]. - **[Toxoplasma gondii](/knowledge/parasites/protozoa/toxoplasma-gondii-lifecycle-neurological-infection)**: A protozoan causing abortion in ewes [1]. ## Epidemiology The prevalence and intensity of internal parasites are influenced by climatic conditions, management practices, host immunity, and parasite biology [2, 13]. Seasonal patterns are well documented, with peak transmission typically occurring during warm, moist periods [13, 14]. In temperate regions, larvae survive on pasture over winter and contaminate spring grazing [13, 15]. In tropical and subtropical regions, transmission may occur year-round with peaks during rainy seasons [2, 16]. Grazing management strategies significantly affect parasite exposure [15]. Mixed-species grazing with cattle can reduce pasture contamination for sheep-specific parasites [15]. Stocking density, pasture rotation, and the use of clean or rested pastures are critical determinants of infection risk [7, 15]. Host factors include age, nutritional status, and immune competence [4, 17]. Lambs are highly susceptible due to naive immune systems [4]. Periparturient ewes experience a relaxation of immunity, leading to increased egg shedding, a phenomenon known as the periparturient rise [1, 4]. Trace element deficiencies, particularly cobalt and copper, have been associated with increased susceptibility to parasitism [17, 18, 19]. ## Clinical Signs and Pathology Clinical manifestations depend on the parasite species, burden, and host factors [1, 4]. ### Gastrointestinal Nematodes **Haemonchus contortus** is a blood-feeding parasite causing anemia, hypoproteinemia, submandibular edema (bottle jaw), and death in severe cases [1, 10]. The pathogenesis is directly related to blood loss, with each worm consuming approximately 0.05 mL of blood per day [1]. **[Teladorsagia circumcincta](/knowledge/parasites/livestock-parasites/teladorsagia-circumcincta-sheep-abomasal-worm-anthelmintic-resistance)** causes abomasal inflammation, reduced feed intake, and protein-losing enteropathy, leading to weight loss and diarrhea [1]. **Trichostrongylus spp.** cause enteritis, diarrhea, and reduced growth rates [1, 11]. **Nematodirus battus** is particularly pathogenic in lambs, causing severe diarrhea and dehydration [1]. ### Lungworms **Dictyocaulus filaria** causes parasitic bronchitis, characterized by coughing, dyspnea, and reduced exercise tolerance [1]. **[Muellerius capillaris](/knowledge/parasites/livestock-parasites/muellerius-capillaris-sheep-goat-lungworm-protostrongylid-diagnosis)** and **Protostrongylus rufescens** are less pathogenic but can cause chronic cough and pneumonia in heavy infections [1]. ### Liver Fluke **Fasciola hepatica** causes acute or chronic fasciolosis [1, 12]. Acute disease results from massive migration of immature flukes through the liver parenchyma, causing hemorrhage, hepatitis, and sudden death [1, 12]. Chronic disease is characterized by bile duct hyperplasia, fibrosis, anemia, and hypoalbuminemia [1, 12]. ### Coccidia **Eimeria spp.** cause coccidiosis, primarily in lambs 3 to 8 weeks of age [1]. Clinical signs include diarrhea (often with blood or mucus), tenesmus, dehydration, and weight loss [1]. ## Diagnosis Accurate diagnosis is fundamental to effective management [20, 21]. Diagnostic methods include clinical examination, fecal analysis, hematology, serology, molecular techniques, and postmortem examination [20, 21, 22]. ### Fecal Examination Fecal egg counts (FEC) are the cornerstone of nematode diagnosis [21]. The McMaster technique is a quantitative flotation method that estimates eggs per gram (EPG) of feces [21]. The Mini-FLOTAC method offers improved sensitivity and is recommended for low-intensity infections [21]. Centrifugal flotation techniques provide higher sensitivity than simple flotation [21]. For lungworm diagnosis, the Baermann sedimentation technique is used to recover first-stage larvae [21]. For **Fasciola hepatica**, sedimentation techniques are required to detect eggs, which are large and operculated [21]. ### Hematology Packed cell volume (PCV) and hemoglobin concentration are useful indicators of anemia caused by **H. contortus** [1]. The FAMACHA system, a clinical scoring method based on conjunctival color, is a practical tool for identifying anemic sheep in the field [1]. ### Serology Commercial ELISA kits are available for detecting antibodies to **Fasciola hepatica** and **[Toxoplasma gondii](/knowledge/parasites/protozoa/toxoplasma-gondii-lifecycle-neurological-infection)** [1]. Coproantigen ELISA tests detect fluke antigens in feces and are useful for diagnosing active fasciolosis [1]. ### Molecular Diagnostics PCR-based assays, including conventional PCR, real-time PCR, and high-throughput sequencing, enable species-specific identification of parasites [1]. These methods are particularly valuable for detecting mixed infections and for confirming anthelmintic resistance [1]. ### Postmortem Examination Necropsy with worm counts from the gastrointestinal tract and other organs provides definitive diagnosis and quantification of parasite burdens [1, 23]. ## Treatment Anthelmintic therapy is the primary means of controlling parasitic infections [10, 24, 25]. Drug classes include: - **Benzimidazoles** (e.g., albendazole, fenbendazole): Inhibit microtubule polymerization [1, 26]. - **Macrocyclic lactones** (e.g., ivermectin): Potentiate glutamate-gated chloride channels [1, 10]. - **Imidazothiazoles** (e.g., levamisole): Nicotinic acetylcholine receptor agonists [1, 25]. - **Salicylanilides** (e.g., closantel): Uncouple oxidative phosphorylation, effective against blood-feeding parasites [1]. - **Amino-acetonitrile derivatives** (e.g., monepantel): Novel mode of action targeting acetylcholine receptors [1]. - **Spiroindoles** (e.g., derquantel): Nicotinic antagonist [1]. Anthelmintic resistance is a global threat to sheep production [1, 7]. Resistance has been reported to all major drug classes [1, 7]. The [fecal egg count reduction test](/knowledge/diagnostics/parasitology/fecal-egg-count-reduction-test-for-anthelmintic-resistance) (FECRT) is the standard method for detecting resistance [21]. Guidelines for conducting FECRT have been updated to improve accuracy [21]. ## Control and Management Integrated parasite management (IPM) combines strategic anthelmintic use, grazing management, genetic selection, and monitoring [6, 7, 14]. ### Grazing Management Pasture rotation, mixed-species grazing, and the use of clean or rested pastures reduce larval contamination [7, 15]. Co-grazing with cattle can lower sheep parasite burdens because most sheep nematodes are host-specific [15]. ### Targeted Selective Treatment The FAMACHA system allows for targeted treatment of only anemic sheep, reducing selection pressure for resistance [1]. Targeted selective treatment (TST) strategies treat only animals with high FEC or clinical signs [1]. ### Genetic Selection Breeding for parasite resistance is a long-term strategy [1]. Some sheep breeds, such as the Red Maasai and certain wool breeds, exhibit genetic resistance to **H. contortus** [1]. ### Nutritional Management Adequate protein and trace element nutrition supports immune function and resilience to parasitism [17, 18, 19]. ### Biosecurity Quarantine drenching of introduced animals with a combination of anthelmintics from different classes is recommended to prevent introduction of resistant parasites [1, 6]. ## Diagnostic and Management Decision Flowchart ```mermaid flowchart TD A["Clinical Signs: Anemia, Diarrhea, Weight Loss, Cough"] --> B["Fecal Sample Collection"] B --> C{"Quantitative FEC"} C -->|"High EPG"| D["Identify Genus via Larval Culture or PCR"] C -->|"Low EPG"| E["Consider Baermann for Lungworms or Sedimentation for Flukes"] D --> F{"Anthelmintic Resistance Suspect?"} F -->|"Yes"| G["Conduct FECRT"] F -->|"No"| H["Select Anthelmintic Based on Genus"] G --> I["Change Drug Class or Use Combination Therapy"] H --> J["Administer Treatment"] J --> K["Post-Treatment FEC at 10-14 Days"] K --> L{"Reduction < 95%?"} L -->|"Yes"| M["Confirm Resistance, Adjust Strategy"] L -->|"No"| N["Monitor and Implement IPM"] E --> O["Specific Diagnosis: Lungworm or Fluke"] O --> P["Targeted Treatment"] P --> N M --> N N --> Q["Grazing Management, FAMACHA, Genetic Selection"] Q --> R["Re-evaluate at Next Season"] ``` ## Conclusion [Internal parasites of sheep](/knowledge/parasites/livestock-parasites/internal-parasites-sheep-gastrointestinal-nematodes), particularly gastrointestinal nematodes, remain a significant challenge to global sheep production [1, 2, 4]. Effective management requires a comprehensive understanding of parasite biology, epidemiology, and the mechanisms of anthelmintic resistance [1, 7]. Diagnostic tools, including FEC, FAMACHA, and molecular assays, are essential for informed decision-making [20, 21]. Integrated parasite management, combining strategic anthelmintic use with grazing management, genetic selection, and nutritional support, is critical for sustainable control [6, 7, 14]. Continued research into parasite biology, resistance mechanisms, and novel control strategies is necessary to mitigate the impact of these pathogens [1, 7]. ## References [1] Starkey L, Pugh D. [Internal parasites of sheep](/knowledge/parasites/livestock-parasites/internal-parasites-sheep-gastrointestinal-nematodes), goats, and cervids. Journal. 2021. [2] Osman A, Hassan R, Sabri S, et al. Prevalence of Internal parasites of sheep In Khartoum State in summer. Journal. 2018. [3] Gordon G, O'Callaghan M, Tallis G. A deterministic model for the life cycle of a class of internal parasites of sheep. Journal. 1970. [4] Brunsdon RV. Internal parasites of sheep and their effects on production. Journal. 1966. [5] Elder C, Rodabaugh D. Internal parasites of sheep. Journal. 1949. [6] Peregrine A, Shakya K, Avula J, et al. Handbook for the Control of Internal Parasites of Sheep Developed With Support. Journal. 2010. [7] Dobson R, Knox M. A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP SCIPS, page 2 I. Journal. 2001. [8] Cameron T. The internal parasites of sheep: a survey. Journal. 1932. [9] Bevan L, Lawrence DA. A Note on the Internal Parasites of Sheep in S. Rhodesia. Journal. 1930. [10] Swan G, Schröder J, Carmichael I, et al. Efficacy of ivermectin against internal parasites of sheep. Journal of the South African Veterinary Association. 1984. [11] Solimán K. Observations on some internal parasites of sheep. Journal. 1961. [12] Mitton R. Internal parasites of sheep: the liver fluke. Journal. 1944. [13] Muller GL. The seasonal incidence survey of internal parasites of sheep-Part I. Journal. 1962. [14] Strum GE, Eveleth DF. Control Worms and Other Internal Parasites of Sheep year around program. Journal. 1955. [15] Moss R, Burton RN, Scales GH, et al. Effect of cattle grazing strategies and pasture species on internal parasites of sheep. Journal. 1998. [16] Khan K, Atiq-Ur-Rehman, Munir M, et al. Incidence of internal parasites of sheep in upland districts of Baluchistan. MART/AZR project: high elevation research in Pakistan: research report no. 18. Journal. 1988. [17] Threlkeld WL, Price NO, Linkous WN. An observation on the relationship of cobalt deficiency to internal parasites of sheep. American Journal of Veterinary Research. 1956. [18] El-Sebaie Ah, Fatah AA, Mm M. The Impact of Some Trace Elements Deficiency and Internal Parasites Inter-Relationship as Predisposing Factors for Foreign Bodies Formation in the Rumen of Sheep and Goats. Journal. 2017. [19] El-Ela M, Osman F. TRACE ELEMENTS VARIATION IN BLOOD SERUM OF SHEEP SUFFERING FROM INTERNAL PARASITES IN RECENTLY RECLAIMED AREAS (DARB AL-ARBAIYN) IN THE WESTERN EGYPTIAN DESERT. Journal. 2016. [20] Chaney A. Identification of Internal Parasites of Sheep and Goats. Journal. 2012. [21] Vatta A. Practical application of fecal testing for internal parasites. American Association of Bovine Practitioners Conference Proceedings. 2025. [22] Goldsby AI, Eveleth DF. Diagnosis of internal parasites of sheep. Veterinary medicine. 1946. [23] Tetley J. Research on the internal parasites of sheep. Journal. 1947. [24] Eveleth DF, Goldsby AI. Using chemicals in combating internal parasites of sheep. Journal. 1945. [25] Anderson GC, Heishman J, Welch J, et al. A comparison of several anthelmintics for the control of internal parasites of sheep. Journal. 1966. [26] Stanger N. Thiabenzadole Used Clinically for the Control of Internal Parasites of Sheep. The Canadian veterinary journal = La revue veterinaire canadienne. 1963. ## Related Clinical & Scientific Guides * [Tick-Borne Diseases in Dogs: Pathogens, Clinical Signs, Diagnosis, and Prevention](/knowledge/parasites/general/tick-borne-diseases-dogs) * [Toxoplasmosis in Cats and the Risk of Brain Infection in Humans](/knowledge/parasites/general/toxoplasmosis-cats-brain-infection-humans) * [Dog Heartworm and Tick-Borne Disease Prevention](/knowledge/parasites/general/dog-heartworm-and-tick-borne-disease-prevention)