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Pet Owner Version

Infectious Necrotic Hepatitis (Black Disease) in Horses


Henry R. Stämpfli

, DMV, Dr Med Vet, DACVIM-LAIM, Department of Clinical Studies, Ontario Veterinary College, University of Guelph

Reviewed/Revised May 2019 | Modified Oct 2022

Infectious necrotic hepatitis is an infectious disease of sheep and cattle that is rarely seen in horses. The bacteria that cause the disease, Clostridium novyi type B, are found in the soil worldwide and are frequently present in the intestines of plant-eating animals (herbivores). Contamination of pasture by the feces of carrier animals is the most important source of infection for horses.

The organism multiplies in areas of dead cells in the liver caused by migration of liver flukes and produces a powerful cell-killing toxin. Affected animals die within a few hours. Most cases occur in the summer and early fall when liver fluke infection is at its peak. Extensive rupture of the blood capillaries causes the skin to turn black (hence the common name, black disease). There is no effective treatment.

Reducing the numbers of snails (usually Lymnaea species) that act as intermediate hosts for liver flukes or otherwise reducing the number of liver flukes may reduce the occurrence. However, these procedures are not always practical. There is currently no vaccine available for use in horses.

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