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 and are frequently present in the intestines of plant-eating animals (herbivores). They may be present on skin surfaces and are a potential source of wound infections. 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. The disease is worldwide in distribution. Affected animals tend to become lethargic, lie down, and die within a few hours. Abdominal pain and inflammation may occur. Most cases occur in the summer and early fall when liver fluke infection is at its peak. Usually, there is extensive rupture of the blood capillaries in the tissue under the skin, which causes the adjacent 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 of infectious necrotic hepatitis. However, these procedures are not always practical. There is currently no vaccine available for use in horses.

Last full review/revision July 2011 by Otto M. Radostits, CM, DVM, MSc, DACVIM (Deceased); Delores E. Hill, PhD; Barton W. Rohrbach, VMD, MPH, DACVPM; Charles J. Issel, DVM, PhD; Max J. Appel, DMV, PhD; David A. Ashford, DVM, MPH, DS; Daniela Bedenice, DrVetMed, DACVIM, DACVECC; Farouk M. Hamdy, DVM, MSc, PhD, MPA (Deceased); Kenneth R. Harkin, DVM, DACVIM; Johnny D. Hoskins, DVM, PhD; Eugene D. Janzen, DVM, MVS; Jodie Low Choy, BVMS; John E. Madigan, DVM, MS; Dale A. Moore, MS, DVM, MPVM, PhD; J. Glenn Songer, PhD; Joseph Taboada, DVM, DACVIM; Charles O. Thoen, DVM, PhD; John F. Timoney, MVB, PhD, Dsc, MRCVS; Ian Tizard, BVMS, PhD, DACVM; Brian J. McCluskey, DVM, MS, PhD, DACVPM; Bert E. Stromberg, PhD; Peter J. Timoney, MVB, MS, PhD, FRCVS