2d • Vet Cases⚕️
🐑 Case Study: Why Are the Healthy Sheep Dying Overnight?
Meet a flock of 85 Rambouillet ewes on a farm in east Texas. The pasture has low-lying boggy ground near a drainage pond and the producer has not vaccinated for clostridial diseases in three years. It is late September.
Over the past three weeks twelve ewes have been found dead in the morning. Every single one appeared completely normal the evening before.
You arrive to perform a postmortem on a ewe that died within the last two hours. When you open the abdominal cavity the liver stops you immediately. It is massively enlarged, dark red, and so friable it tears when you handle it. Hemorrhagic tracts run through the parenchyma in every direction. When you cut across those tracts and squeeze the tissue, dozens of tiny white organisms 3 to 5 millimeters long wriggle out onto the cut surface.
Juvenile Fasciola hepatica. Hundreds of them. Physically tunneling through the liver.
This is acute fasciolosis, and these flukes have been migrating through the liver parenchyma for the past several weeks, destroying hepatocytes as they go and filling the peritoneal cavity with blood-tinged fluid. The ewes on this property spent summer grazing wet boggy ground where lymnaeid snails thrived and shed metacercariae onto the grass. When the ewes ingested massive numbers of those metacercariae, the juvenile flukes excysted in the intestine, penetrated the liver capsule, and began their devastating migration.
You collect a rectal fecal sample from a live depressed flockmate and submit it for sedimentation. The result comes back negative.
The producer calls confused. No eggs means no flukes, right?
Wrong. This is the most important diagnostic concept in liver fluke disease. The prepatent period for Fasciola hepatica is 8 to 12 weeks. These flukes are still in the liver parenchyma and have not yet reached the bile ducts where egg production occurs. A negative fecal sedimentation during acute fasciolosis is not reassuring. It is expected. The diagnosis here rests on the postmortem pathology, the seasonal risk, and the wet pasture history.
You explain to the producer that the live animals need treatment immediately. The only flukicide that kills one to three week old juvenile flukes is triclabendazole. Albendazole and clorsulon, the US-approved options, have minimal activity against these early-stage migrants and would leave the flukes killing liver tissue unimpeded.
There is a second urgent problem. The unvaccinated flock is at high risk for black disease. As juvenile flukes tear through the liver they create anaerobic necrotic tissue, and that microenvironment is exactly what Clostridium novyi spores need to germinate. Those spores have been sitting dormant in the liver macrophages of these sheep for months, ingested from the soil without causing harm. The fluke damage is now the trigger. You vaccinate the entire remaining flock with a multivalent clostridial product covering C. novyi type B the same day.
The producer fences off the boggy pasture area by the pond the following week.
💡 The takeaway: Sudden death in sheep on wet pasture in autumn with a negative fecal sedimentation is acute fasciolosis until proven otherwise. The absence of eggs is not reassurance. It is the disease telling you the flukes are still in the liver.
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🐑 Case Study: Why Are the Healthy Sheep Dying Overnight?
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