Equine Serum Hepatitis

Also known as:

Theiller's disease

Description

Equins Serum Hepatitis (ESH) leading to acute liver failure is most commonly associated with administration of an equine biologic product. This is usually tetanus antitoxin, but encephalitis vaccines and equine serum have also been implicated. Other possible hypotheses include alkaloid toxicity and mycotoxins. Several cases have been reported in which no biologic product had been administered, leading to the possibility that an infectious agent may be involved.

Signalment

ESH occurs predominantly in older horses. Cases (both individual cases and outbreaks) occur relatively frequently during the autumn months in north western USA. Some parts of the world have no reported cases.

Clinical Signs

The history may include administration of an equine-derived biologic product, often four to six weeks prior to the onset of clinical signs. These may range from mild lethargy or inappetance to signs of acute or chronic hepatic failure. They are generally sudden in onset and rapidly progressive. The course of the disease is usually around five days, with death ususally occuring within ten days.

Signs may be non-specific such as depression or anorexia. Affected horses are often severely icteric and may pass dark urine due to the presence of bilirubin. Signs relating to hepatic encephalopathy may be present, such as head pressing, excitement, yawning or aimless wandering.

Mild forms of the disease have also been reported, characterised by a mild malaise and increased serum hepatic enzyme concentrations.

Pathology

Post mortem examination often shows the liver to be enlarged and pale with rounded edges. Generalised icterus is often present. Histologically there may be centrilobular necrosis with mononuclear cell accumulation within the portal triads. Contusions, lacerations or fractures may be present if the disease has had a violent clinical course.

Prognosis

The prognosis is extremely poor with a mortality rate approaching 100%. Morbidity, however is often low.

References

• Edward Robinson, N and Sprayberry, K. A. (2009) Current Therapy In Equine Medicine Sixth edition Saunders Elsevier

• Knottenbelt, D.C. A Handbook of Equine Medicine for Final Year Students University of Liverpool

• Lavoie, J. P., Hinchcliff, K. W. (2009) Blackwell's Five-Minute Veterinary Consult: Equine Wiley-Blackwell

• Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial

• Smith, H. L., Chalmers, G. A., Wedel, R. (1991) Acute hepatic failure (Theiler's disease) in a horse Canadian Veterinary Journal 32, 362-364.