Vaccinating horses against rabies virus provides best prevention from disease

With the increasing number of rabies outbreaks this year, horse owners should make sure to vaccinate their horses against this fatal disease. 

“Rabies is fatal in all mammals with clinical signs,” according to Amanda House, DVM at the University of Florida. “Death occurs within three to seven days once the clinical signs develop.”

Rabies prevalence

Rabies is an acute, zoonotic, fatal viral disease of domestic and wild animals worldwide, as well as humans. There are only a handful of countries on earth that have never had an outbreak of this disease. 

More than 55,000 people die of rabies each year, although 95 percent of the deaths are in Asia and Africa, House said. The U.S. has between one and three human deaths each year from the disease. 

House reported that in 2007, 7,258 cases of rabies in animals were reported in the U.S. and one human case. 

In this instance, 93 percent of those cases were in wildlife and seven percent in domestic animals. 

“Wildlife provide a natural reservoir for the virus,” she explained. 

In 2005-06, the number of cases of rabies in horses and mules increased 12.8 percent, but in 2007, they decreased 20 percent. House attributes the decline to more horses being vaccinated for rabies. 

Unlike humans, once a rabid animal bites a horse, there is no treatment. Horses that live in an endemic area, haven’t been vaccinated and live outside 24 hours a day are considered the most susceptible, she explained. The disease also occurs more in young horses because they are more curious and more likely to seek out a strange animal that has wandered into their pasture. 

Typically, only one horse will be infected, not every horse in the pasture, Young noted.

Clinical signs 

The development of clinical signs, once a horse is bitten, can vary based on where it is bitten. 

“If they are bitten on the head, the development of clinical signs will be quicker than if they are bitten on a distal leg,” she explained. 

Once a horse is bitten, the incubation period of the disease can be two to nine weeks, with death within three to five days once signs develop. 

The problem with rabies is the clinical signs mimic several other diseases and issues that may not be as serious or fatal, Young said. EEE, WEE, VEE, West Nile Virus, Equine Herpesvirus, Hepatic encephalopathy, space-occupying mass, EPM and even some colics can mimic symptoms of the disease. 

House said to remember that rabies symptoms can look like anything. The horse can experience behavior changes and blindness. It can suffer from ataxia and incoordination. It may also have a fever, hyperventilate, show paresis or paralysis, have difficulty swallowing or show signs of colic or obscure lameness. 

The horse can have bladder distension or incontinence and may have a tilted head or facial paralysis. 

In severe cases, the horse may even experience seizures.

Diagnosis

It is important to contact a veterinarian immediately if rabies is suspected. 

House said there is no definitive ante mortem test in animals, and blood tests aren’t specific. 

Even a cerebral spinal fluid analysis may be normal if the horse is infected. A veterinarian can have the horse perform a gait analysis, conduct a neurologic exam, radiograph the head and spinal cord and possibly conduct a spinal tap to analyze the cerebral spinal fluid. 

Vaccination for prevention

The best prevention of the disease is vaccination of all horses once a year, House says. 

“The vaccine is safe and effective. No vaccine can be guaranteed 100 percent effective, but I’m not aware of any horse that has contracted rabies after being vaccinated,” she said. 

Pregnant mares should receive a booster prior to breeding or foaling. 

“In foals of vaccinated mares, the foals should be vaccinated at six months with two doses, then re-dosed at one  year of age,” she explained. “Foals from unvaccinated mares can receive a vaccination as early as three months. Two doses are more likely to induce more durable immunity.”

If a horse has been bitten by a rabid animal, House recommends re-vaccinating the horse immediately and then observing it for 45 to 90 days. A list should also be kept of everyone who comes in contact with the horse. 

The Centers for Disease Control recommends euthanizing a horse that has been bitten and was not vaccinated. 

“The horse could be isolated and observed for six months. Then, if signs develop, euthanize it immediately and test it for rabies,” House said. 

If rabies is suspected, House cautioned owners to wear protective clothing and equipment when handling the horse. The horse should also be quarantined, and a veterinarian should be called immediately.

Gayle Smith is a correspondent for the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.