The Horse

APR 2019

The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.

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22 April 2019 The Horse | through skin wounds or via mucous membranes such as the eyes, mouth, or nose. The rabies virus, Rhabdoviridae lys- savirus, then travels through the periph- eral nervous system to the brain, where it attacks the central nervous system. Signs of Rabies Although rabies isn't widely found among horses in the United States, veteri- narians diagnose about 40 cases per year. And, says Greene, the potential risk of human exposure from even one infected horse is significant. "The nonspecific early signs of infection can delay correct diagnosis and poten- tially expose handlers, caretakers, owners, veterinarians, veterinary technicians, and anyone else who handles the animal," she says. "Even though the chance of your horse contracting rabies is small, the im- plications of a rabies infection that occurs in your barn are significant." Greene says infected animals show signs anywhere from two to nine weeks following exposure and, once signs ap- pear, the animal invariably dies within three to 10 days. In more aggressive cases death can come within hours. "Early signs in horses can be easy to mistake for mild colic or (unexplained) lameness," Greene says. "Even the ad- vanced signs in horses can be similar to more common diseases such as Eastern or Western equine encephalitis, West Nile virus, or equine protozoal myeloen- cephalitis. If other neurologic diseases have been ruled out and the horse has an unknown vaccination status and/or sus- pected exposure to a rabid animal, rabies should be considered as a possibility." Other early signs include: ■ Decreased appetite; ■ Depression; and ■ Ataxia (incoordination). Advanced signs consist of: ■ Drooling and excessive salivation; ■ Extremely aggressive behavior in a normally docile animal; ■ Facial paralysis; ■ Hypersensitivity to touch; ■ Inability to swallow; ■ Jaw clenching; ■ Lack of awareness of limb location; ■ Limb weakness; ■ Localized itchiness; ■ Overreaching movements (hypermetria and dysmetria); ■ Repetitive twitching; ■ Self-mutilation; and ■ Superlibido in stallions. Because rabies signs are similar to those of other diseases and because veterinarians can only confirm a diagno- sis post-mortem, Greene says a surpris- ing number of people can be exposed before the disease is confirmed or even considered. This was the case with the students in the opening example. "Any human suspected of exposure should be seen immediately by a physician for post- exposure treatment protocol," she adds. Furious vs. Paralytic Rabies The word rabies commonly invokes mental images of a snarling, vicious animal, as in the movie "Old Yeller." Yet two forms of rabies exist: furious and paralytic. Greene says animals with furious rabies display the more aggressive signs, becoming agitated and irritable. Wild animals might lose their fear of humans, and normally nocturnal animals might venture out during the day. Normally gen- tle animals might charge or attack their human handlers, which is especially dan- gerous if they are horses or cattle, whose size alone can cause injury or death. And rabid animals might injure themselves further, especially at the bite site. Paralytic (also known as dumb or stuporous) rabies, she says, involves progressive paralysis. "The animal may become depressed, but there are few other behavioral changes," says Greene. "Ataxia, inability to swallow, and excessive drool- ing may be noted initially, followed by pa- ralysis, which leads to coma and death." How to Prevent Infection Because most horses spend at least part of their time outdoors, they innately come in contact with wildlife. But taking a few simple precautions can reduce their risk of rabies infection: The Scary Thing About Rabies COURTESY MARY DELTON Adult horses should be vaccinated against rabies annually. DUSTY PERIN A rabid skunk bit one of Mary Delton's horses (shown) in New York, but because he'd been vaccinated seven months prior, he received a booster and never developed clini- cal signs of rabies.

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