Rabies in Horses: Preventable but Still Invariably Fatal

Rabies in Horses: Preventable but Still Invariably Fatal

The risk of rabies exposure for horses is higher in geographic localities where the disease is endemic in raccoons, skunks, foxes, or other terrestrial reservoirs.

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Rabies is endemic in several insectivorous bat species throughout the Americas. The disease also is endemic in raccoons from southeastern Canada to the Gulf of Mexico and from the East Coast to Ohio and the Appalachian Mountains. Four rabies variants are found in striped skunks throughout the midwestern United States; the Flagstaff, Ariz., area; and in mid-to-southern California. Rabies in foxes is endemic in Alaska and the southwestern United States and in mongooses in Puerto Rico. In each of these mammals, unique rabies viral variants are exquisitely adapted to and efficiently perpetuated animal-to-animal. These variants cause rabies in other mammals, but the probability of sustained transmission is lower than in the reservoir mammals. (Hawaii is the only rabies-free U.S. state or territory.)

An important consideration in evaluating risk based on recorded cases is the level of surveillance. If the index of suspicion and infrastructure support for animal management and testing is low, such that few or no domestic and wildlife species are tested, endemic cases might be present in a locality but not be reflected in numbers of positive cases. The definitive test for rabies requires postmortem testing of the brain.

The risk of rabies exposure for horses is higher in geographic localities where the disease is endemic in raccoons, skunks, foxes, or other terrestrial reservoirs. Rabies transmission can also occur from a rabid bat to a horse or secondarily from terrestrial carnivores infected with bat rabies. Fortunately, only about 50 horses are diagnosed with rabies every year in the United States. However, even a single case can have significant public health ramifications. These cases then trigger extensive investigations to identify potentially exposed humans and other animals.

In a retrospective analysis of horse cases, signs of furious rabies, including aggression, were present in 40%, general neurologic signs and ataxia in approximately 30%, and excessive salivation and prostration in approximately 25%. In contrast to other livestock, rabid horses were more likely to expose humans by biting them.

All mammals are susceptible to rabies, and once an animal is affected, the disease is invariably fatal. However, rabies prevention is easy: Vaccinate horses with a licensed product; reduce exposure of horses to skunks, raccoons, and bats in barns; and promptly clean and treat any wounds found on horses.

No matter what the vaccination status of a horse, if it is bitten by a wild animal, call a veterinarian immediately. The recommendation for an unvaccinated horse exposed to a rabid animal is euthanasia or a six-month quarantine. The majority of cases occur several weeks to months after an exposure. Longer incubation periods have occurred, however (hence the six-month quarantine), after which it is highly unlikely the animal will develop rabies from the exposure.

If a rabies-vaccinated horse is exposed to the disease, the site of exposure (i.e., wound) should be cleansed thoroughly, he should be administered a booster vaccination, and observed for 45 days as a precaution. Rabies in vaccinated animals is rare.

By Cathleen A Hanlon, VMD, PhD, Dipl ACVPM, director of the Kansas State University Rabies Laboratory, Manhattan, Kansas

This is an excerpt from Equine Disease Quarterly, funded by underwriters at Lloyd's, London, brokers, and their Kentucky agents.

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Equine Disease Quarterly

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