Reviewing Rabies In Horses

By Sarah Gee
©Voice, October 2006

Considering the recent announcement of a case of rabies at the Tennessee Walking Horse National Celebration, we think the time is ripe for an overview of rabies in horses. Rabies in the horse is a relatively uncommon disease. The number of rabies cases in the horse industry peaked at 88 in 1981 and has leveled off since then to about 40 cases per year over the past few years. While the incidence of rabies in horses in low, the potential for human exposure makes it a topic worth covering.

Rabies is a sporadic viral disease caused by a neurotropic rhabdovirus (a virus that affects the nervous system). Horses get rabies from the saliva of an infected animal, either through a bite or by the saliva contaminating an open wound. Rabid skunks are responsible for the majority of rabies cases in horses. However, foxes, raccoons, bats, and unimmunized dogs and cats have also been known to transmit the disease to horses. Horses are very curious, especially foals and yearlings, and will investigate wildlife roaming the pasture. This makes them likely to get bitten, especially on the nostrils or lips.

The incubation period for rabies is usually two to six weeks, although sometimes it may take up to three months before symptoms appear. Diagnosing rabies is difficult because of the wide range of clinical signs. The most common sign of rabies is behavioral changes. A low-grade fever usually is present along with convulsions, increased sensitivity at the site of injury, lameness, gnawing at the affected area, and refusal to eat. Symptoms usually progress quickly over five to seven days ultimately resulting in death. In many cases, rabies is not diagnosed upon the initial onset of symptoms, as the horse is still calm, alert, and eating. The most important thing a horse owner should remember is to think rabies first when dealing with unexplainable clinical signs. Also, remember that, once symptoms appear, rabies progresses rapidly. If the clinical signs you are seeing have not worsened after a period of five days, it probably isn’t rabies.

Since rabies is relatively rare in horses, a veterinarian should attempt to rule out other diseases before diagnosing rabies. Other diseases which present clinical symptoms similar to rabies are tetanus, equine herpesvirus, botulism, lead poisoning, moldy corn poisoning, protozoal myelitis, the various causes of encephalomyelitis, and trauma to the brain or spinal cord.

Presently, there is no drug that will treat rabies. Immediate cleansing of the affected wound area may prevent infection, but post-vaccination of the animal really is not useful. The best thing a horse owner can do to protect their horses is to vaccinate. Vaccination should begin at three to four months of age with a booster shot given annually.

For horses that contract rabies the outlook is grim. If the horse has been previously immunized, an immediate booster shot should be given. Strict quarantine and observation for six months are mandatory in all cases. If clinical symptoms develop, the horse should be humanely destroyed and the intact head should be submitted to a designated public health laboratory for diagnosis.

References:
Rabies in Horses, Cooperative Extension Service,
University of Kentucky College of Agriculture, #ASC-125.

Rabies in Horses, College of Veterinary Medicine,
Michigan State University.