Rabies is an acute viral infection of the nervous system that mainly affects carnivores and bats, although it can affect any mammal. It is caused by the rabies virus. Once signs appear, it is fatal. Rabies is found throughout the world, although a few countries are declared rabies-free due to successful elimination or prevention standards. Islands that have a strict quarantine program in effect are also often rabies-free. In North America and Europe, rabies has been mostly eliminated in domestic animals, although it still affects wildlife.
Transmission is almost always by the bite of an infected animal, when the saliva containing the rabies virus is introduced into the body. In horses, the virus can be in the body for days to months before signs develop.
The signs of rabies can vary and are not exclusive to this disease. In the first few days, signs are vague and nonspecific but then usually progress rapidly, leading to paralysis and death.
There are two major forms of the disease. The furious form of rabies is the classic “mad-dog” syndrome but may be seen in all species. Horses and mules often show evidence of distress and extreme agitation. When these signs are combined with rolling, they can be confused with a colic episode. Horses may bite or strike and become unmanageable in a few hours. They may also have self-inflicted wounds.
The paralytic form of rabies usually involves paralysis of the throat and jaw muscles, often with excess salivation and inability to swallow. Drooping of the lower jaw is common. People can be infected by this form when examining the horse’s mouth or giving it medication with bare hands. Paralysis progresses throughout the body and death occurs within a few hours.
Diagnosis is difficult, especially in areas where rabies is not common. Early stages of rabies can be easily confused with other diseases (such as colic) or with normal aggressive tendencies. A rabies diagnosis must be verified with laboratory tests. The animal must be euthanized and the remains sent for laboratory analysis. There is no effective treatment.
Guidelines for the control of rabies are routinely updated. In general, any animal that has bitten a person and has signs of rabies should be euthanized. An unvaccinated horse that has been bitten by or exposed to a rabid animal must be either euthanized or quarantined for 6 months and vaccinated for rabies 1 month before release. A vaccinated horse that is bitten by or exposed to a rabid animal should be given a rabies booster immediately and observed for 45 days for any signs of rabies.
Several rabies vaccines are available for horses; these appear to be both safe and effective in preventing rabies. Annual revaccination of adult horses is generally recommended. Your veterinarian can recommend aspecific vaccine and booster schedule based on current guidelines and status of horses to be vaccinated. There are several approaches to vaccination of breeding mares and their foals.
When a person is exposed to an animal suspected of rabies, the risk of rabies transmission should be evaluated carefully. Wild carnivores and bats present a considerable risk where the disease is commonly found, regardless of whether or not abnormal behavior has been seen.
Any healthy domestic animal, whether vaccinated or not, that bites a person or otherwise deposits saliva into a fresh wound, should be confined for 10 days for observation. If the animal develops signs within those 10 days, it should be promptly euthanized and submitted for testing.
Pre-exposure vaccination is strongly recommended for all people in high-risk groups, such as veterinary staff, animal control officers, rabies and diagnostic laboratory workers, and travelers working in countries where rabies is prevalent.