Equine rabies can be prevented by vaccination

By Josie Traub-Dargatz, DVM, MS
Colorado State University

Rabies is caused by a virus contained in the saliva of a rabid animal. Any warm-blooded vertebrate animals, including horses, are susceptible to infection.

Because horses are curious, and many types of wildlife with rabies lose their fear of humans and other domestic animals, the likelihood of exposure is heightened.

"In eastern Colorado we are seeing the skunk strain of rabies circulating farther west than at anytime in the last 30 years," said John Pape of the zoonosis unit of the Colorado Department of Public Health and Environment. "Skunks are highly efficient at transmitting rabies to other animals like pets."

Domestic animals account for less than 10 percent of all animal rabies cases in the United States. The number of laboratory-confirmed equine rabies cases reported in the United States in the recent past is generally around 50 cases per year across the continental states. The largest number of equine rabies cases is generally reported in Texas. The majority of rabies cases occur in animals with no rabies vaccination history.

Terrestrial rabies provides more risk of exposure to pets as well as livestock than if rabies is occurring only in bat populations. For more information go to the CDPHE web site www.cdphe.state.co.us/dc/zoonosis/rabies/index.html or call 303-692-2700 and ask to speak to someone in the Colorado Department of Public Health Disease Control Division.

The reported signs of rabies in horses have ranged from poor racing performance to bizarre behavior. Some animals develop an apparent lameness, colic-like signs and genitourinary signs. The classic description is of the brain form, with evidence of progressive depression, called dumb rabies, or aggression with self-mutilation and biting, called furious rabies. Equine rabies patients also may have an inability to swallow, as well as excessive salivation.

One of the most consistent signs of rabies in horses in a case series from Canada was irritability when touched, called hyperesthesia. Veterinarians who have seen multiple equine rabies cases have said the classic signs may not be initially apparent or never develop. Once signs develop, the course of the disease is hours to days, but the time from exposure to onset of signs can be quite variable and may be long. The disease is fatal.

There is no laboratory test that can be done on the live animal to make a definitive diagnosis of rabies in horses. A rabies-infected horse can expose owners, caretakers, veterinary personnel and many other people to rabies.

Once the animal dies or is euthanized, a veterinarian should be involved in collection of appropriate samples to make a diagnosis. This includes the collection of the brain to be submitted for specific laboratory testing to detect the rabies virus in this tissue. It is important that those involved in the necropsy take appropriate precautions to avoid exposure to the virus during the collection of tissues and that all samples collected from suspect animals be labeled appropriately so those performing testing can take precautions.

There is no known effective treatment of horses with clinical rabies. Rabies is a disease that is better prevented. The mainstay of prevention of rabies is through vaccination. Equine owners should have their veterinarian involved in the development of a vaccination plan for their horses, including the use of rabies vaccine.

Rabies vaccine is now considered a core vaccine by the American Association of Equine Practitioners. Vaccination guidelines are available at the AAEP web site www.aaep.org/vaccination_guidelines.htm.

Rabies vaccine meets the criteria as a core vaccine based on the fact that rabies is recognized in wildlife in all geographic areas of the continental United States, the vaccine has been demonstrated to be safe and effective, and there is a public health risk from exposure if a horse develops the disease.