Rabid animals were reported from every state except Hawaii in 1997, according to the Centers for Disease Control and Prevention (CDC), Atlanta, GA. Rabies was confirmed in 47 horses, donkeys, and mules in 21 states and Puerto Rico in comparison to 46 equid cases in 1996. These figures represent only laboratory-confirmed cases since not every neurological horse which dies is submitted for necropsy and rabies testing.

A variety of clinical signs occur in rabid horses, such as behavior changes ranging from aggression to depression, ataxia, paresis, hyperesthesia(hypersensitivty to stimuli), fever, colic, lameness and recumbency. With such a variety of clinical presentations, diagnosis in the live animal is difficult. The disease usually progresses to death in four to five days, although survival to 15 days is possible. Rabies is 100% fatal in horses and most other domestic species. Diagnosis is made on laboratory testing of tissues taken at necropsy.

There are several reservoirs of the rabies virus in the United States: raccoon, skunk, fox, bat and coyote. Wild animals were the source of 7,899 (93%) of all rabies cases in 1997, with raccoons being the most frequently detected (4,300), followed by skunks (2,040), bats (958) and foxes (448). Most of the rabid raccoons were found in 19 states along the eastern seaboard, east of the Appalachian Mountains in the South, where there is currently an epizootic of raccoon rabies.

In general horses are assumed to be infected with the predominant variant of rabies found in their home area, raccoons in the east, skunks in the central United States. However, in 1994 one Kentucky horse was confirmed to have been infected with bat rabies. Specialized testing of brain tissue to determine the source of rabies is routinely done in humans, but is not commonly performed on animals