in Animals
- Infectious necrotic hepatitis is an acute toxemia primarily of sheep caused by Clostridium novyi type B. Death is sudden, often without clinical signs, and seems to be limited to animals infected with liver flukes. The most characteristic gross lesions are grayish yellow, necrotic foci in hepatic tissue, caused by young, migrating flukes. Control is by disrupting the life cycle of the liver fluke (by reducing populations of the intermediate snail host) and by active immunization with C novyi toxoid.
- The etiologic agent of infectious necrotic hepatitis, Clostridium novyi type B, is soilborne and part of the intestinal microbiota. It is also present in the liver of herbivores; it may be present on skin surfaces and dormant in muscles and is a potential source of wound infections. Fecal contamination of pasture by carrier animals is the most important source of infection. The organism multiplies in areas of liver necrosis caused by migration of liver flukes and produces a powerful necrotizing toxin (alpha toxin). The disease is worldwide, wherever sheep and liver flukes are both found, and is increasing in cattle where liver flukes are accidentally introduced.
- Typically, death is sudden, without clear clinical signs. Affected animals often are 2–4 years old, tend to lag behind the flock, assume sternal recumbency, and die within a few hours.
- Differentiation from acute fascioliasis may be difficult, but peracute deaths of animals with typical lesions found on a necropsy examination should arouse suspicion of infectious necrotic hepatitis.