Strongyloidosis in Sheep
- Strongyloidosis in sheep is caused by the intestinal threadworm Strongyloides papillosus, a parasite that lives in the small intestine.
- Most infections are mild, but young lambs can develop diarrhea, poor weight gain, dehydration, rough haircoat, and weakness.
- Heavy infections can become serious, especially in housed or crowded lambs and in warm, humid bedding conditions.
- Diagnosis usually involves a fecal exam to look for the parasite's distinctive larvated eggs, plus a flock history and physical exam.
- Treatment options vary from targeted deworming and supportive care to more intensive veterinary care for weak or dehydrated lambs.
What Is Strongyloidosis in Sheep?
Strongyloidosis is an intestinal parasite infection caused by Strongyloides papillosus, also called the intestinal threadworm. In sheep, the adult worms live in the small intestine. On fecal testing, this parasite is recognized by its small, thin-shelled, larvated eggs, which already contain a larva when passed.
Many sheep carry low parasite burdens without obvious illness. Even so, lambs are more vulnerable than healthy adults. When parasite numbers rise, affected lambs may become unthrifty, develop soft stool or diarrhea, and fall behind in growth.
This parasite is often considered lower-pathogenicity than some other sheep worms, but that does not mean it is harmless. Cornell has reported that S. papillosus should be considered in outbreaks involving young ruminants, including weaned lambs, especially when losses are unexplained or conditions are warm and humid.
Symptoms of Strongyloidosis in Sheep
- Soft stool or diarrhea
- Poor growth or failure to thrive
- Weight loss or poor body condition
- Rough fleece or poor coat quality
- Weakness or lethargy
- Dehydration
- Sudden collapse or sudden death
See your vet immediately if a lamb is weak, dehydrated, unable to nurse or eat, or if you find sudden deaths in a group of young sheep. Mild diarrhea and poor growth can have many causes, including coccidiosis and other gastrointestinal worms, so it is important not to assume one parasite is responsible. A fecal exam and flock-level review help your vet decide what fits best.
What Causes Strongyloidosis in Sheep?
Strongyloides papillosus has a direct life cycle, so sheep become infected from contaminated bedding, soil, feed, water, or pasture. Infective larvae can enter through the skin or be swallowed. In sheep, transmammary spread has also been documented, which means lambs may become infected while nursing from infected ewes.
Warm, damp environments help larvae survive and build up. That is one reason housed lambs, crowded pens, and bedding that stays humid can increase risk. Cornell specifically notes concern in confinement settings and recommends attention to hygiene during periods of high temperature and humidity.
Heavy parasite exposure is more likely when manure accumulates, stocking density is high, and parasite control is based on routine deworming without testing. Young lambs are at the highest risk for clinical disease because their immune systems are still developing and they have less reserve if diarrhea or dehydration starts.
How Is Strongyloidosis in Sheep Diagnosed?
Diagnosis starts with a physical exam, age group affected, housing history, and a review of recent parasite control. Your vet will usually recommend fecal testing. In sheep, Strongyloides papillosus is identified by its characteristic larvated egg on fecal flotation. Merck also notes that centrifugal flotation improves sensitivity compared with simple flotation for parasite detection in general.
Because parasite shedding can vary, one sample does not always tell the whole story. Merck advises that, when trying to rule out parasitism, testing multiple fecal samples collected over consecutive days or across 7 to 10 days can improve confidence. In flock situations, your vet may also suggest testing several lambs, not only the sickest one.
If lambs are very ill, your vet may add packed cell volume, total protein, hydration assessment, or necropsy of animals that died. That matters because diarrhea and poor thrift in lambs can also be caused by coccidia, nutritional problems, bacterial disease, or other gastrointestinal nematodes. Accurate diagnosis helps your vet choose the most appropriate treatment option and avoid unnecessary dewormer use.
Treatment Options for Strongyloidosis in Sheep
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Farm or clinic exam if the sheep is stable
- Basic fecal flotation or fecal egg count
- Targeted oral deworming selected by your vet
- Fresh water, improved bedding hygiene, and reduced stocking density
- Close monitoring of appetite, manure, and hydration
Recommended Standard Treatment
- Veterinary exam and flock history review
- Fecal flotation or fecal egg count, with additional samples if needed
- Vet-directed deworming plan using an approved or legally prescribed product for sheep
- Oral or subcutaneous fluids as needed for mild-to-moderate dehydration
- Supportive care, nursing management, and follow-up fecal testing or response check
Advanced / Critical Care
- Urgent veterinary assessment for weak, collapsed, or severely dehydrated lambs
- More intensive fluid therapy and temperature monitoring
- Expanded diagnostics such as bloodwork, repeated fecal testing, or necropsy of deceased flockmates
- Individualized treatment plan for mixed parasite burdens or severe enteric disease
- Detailed flock prevention plan addressing housing, bedding moisture, and strategic parasite monitoring
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Strongyloidosis in Sheep
Bring these questions to your vet appointment to get the most out of your visit.
- Does this lamb's fecal exam fit Strongyloides, or should we also test for coccidia and other worms?
- Which sheep in the group should be tested so we get the most useful flock-level information?
- Is this a case where targeted deworming makes sense, or do you recommend treating a larger group?
- What drug, dose, and meat or milk withdrawal times apply for my flock?
- How dehydrated is this lamb, and can we manage fluids on-farm or is more intensive care needed?
- Could humid bedding, confinement, or nursing from infected ewes be contributing to this problem?
- When should we repeat fecal testing to confirm the treatment plan is working?
- What prevention steps would give us the biggest benefit for our setup and budget?
How to Prevent Strongyloidosis in Sheep
Prevention focuses on lowering environmental exposure and avoiding unnecessary deworming. Keep lambing and nursery areas as clean and dry as possible. Remove wet bedding promptly, improve drainage and ventilation, and avoid overcrowding. Cornell specifically recommends increased hygiene and frequent bedding replacement during warm, humid periods, when larval development is favored.
Work with your vet on a parasite-monitoring plan instead of relying on calendar-based deworming alone. Fecal egg counts can help identify when parasite pressure is rising and whether treatment is likely to help. This approach also supports better long-term parasite control by reducing overuse of dewormers.
Good prevention is flock-specific. Your vet may suggest separating age groups, paying close attention to ewes and nursing lambs, rotating heavily contaminated areas, and reviewing nutrition so lambs have the best chance to resist disease. If you have repeated diarrhea, poor growth, or unexplained losses in young lambs, ask your vet to reassess the whole management picture rather than focusing on one parasite alone.