THE REALITY OF RABIES

With fewer than 100 cases of rabies reported in horses, donkeys and burros every year, it’s easy to disregard the disease. But while the incidence of rabies in the United States is low, the fatality rate is high – 100 percent. That’s why the American Association of Equine Practitioners (AAEP) has made rabies a core vaccine, meaning rabies vaccination is recommended for every horse, every year, regardless of geography or lifestyle. Over the past 20 years, the number of rabies cases in both wildlife and domestic animals has increased. Typically, more than 9,000 total cases of rabies are reported in the United States every year. The rise of rabies is due, in large part, to the increased urbanization of areas where the disease is endemic in wildlife populations.

TRANSMISSION

Just because your horse doesn’t live in the woods doesn’t mean he’s out of the woods. Horses in barns are just as likely to be exposed to rabid animals as pastured horses are. Rabid animals can easily find their way into closed barns, climb up rafters and even enter stalls.

Horses contract rabies through the bite of an infected (rabid) animal, such as a raccoon, fox, skunk or bat. These bites typically occur on the horse’s face and muzzle or lower limbs. It’s easy to mistake a rabies bite as simply a scratch, or not notice it at all. In one retrospective study of 21 horses with rabies, bite wounds weren’t found on any of the horses.

Once bitten, the horse’s peripheral nerves transmit the virus to the brain where it initiates rapidly progressive, invariably fatal encephalitis. The incubation period — the time between the virus’ entry into the body and the onset of clinical signs — averages two to nine weeks, but may be as long as fifteen months.

CLINICAL SIGNS

Don’t expect a rabid horse to look like Cujo. Equine rabies can take on many different clinical signs — signs that can be nonspecific and confusing. For this reason, the disease is frequently misdiagnosed at first. Veterinarians often state that rabies “can look like anything.”

The most commonly reported clinical signs include colic, lameness, ataxia (incoordination), paralysis, urinary incontinence, muscle tremors, fever, depression, aggressiveness, hyperesthesia (increased sensitivity to touch or other stimulation) and convulsions. Because of the extreme variability in clinical signs, it’s difficult to make generalizations. However, most rabid horses exhibit some degree of hyperesthesia, fever and neurological signs (ataxia and/or paralysis) at some point during the course of the disease.

While some horses exhibit intermittent or continuous signs of aggression, most infected horses are depressed or stuporous. Some may become anorectic and refuse to drink, while others will continue to eat and drink until shortly before death. Occasionally, horses exhibit signs of bruxism (grinding of the teeth). Obscure lameness and posterior ataxia (incoordination) are relatively common early signs.

In most horses, the progression of the disease is rapid with death in three to five days following the onset of clinical signs. Prior to death, most horses will become recumbent with convulsions and/or a comatose state and violent thrashing. Rabies infection in the unvaccinated horse is always fatal.