While rabies is relatively uncommon in equids, it is always fatal and is of particular concern to human health. The disease is caused by a rhabdovirus that devastates the central nervous system. It is spread through direct contact with bodily fluids (saliva) of infected animals. Most animals die quickly once showing signs of rabies, and thus are unlikely to spread the disease. Skunks, raccoons, foxes and coyotes are the primary reservoir hosts for rabies in the United States. Most of the reservoir hosts are nocturnal, and a curious horse that investigates a rabid animal wandering in the daytime may get a bite on the muzzle – the most common mode of rabies transmission. Other potential “carriers” of rabies include bats. Wolves, dogs, and cats are possible routes of exposure to a horse.
Once a horse is exposed to rabies through a bite wound, the virus has a typical incubation period of two to six weeks, and as long as six months, while it travels to the central nervous system and brain via nerve branches. The length of time between exposure and the onset of disease is one reason that rabies is difficult to diagnose in horses; another reason is the vagueness and variability of symptoms once the virus begins to replicate and cause illness.
Symptoms are neurological in origin, but that is often difficult to realize in the earliest stages of the disease. Horses will usually be depressed and anorexic (refusing food) and will have a low grade fever. What is common to all horses with rabies is the fact that symptoms and severity will progress rapidly in a very short period of time. Within a week, almost all will exhibit some degree of convulsions or neurological manifestation. Death is imminent usually within 10 days of clinical signs of rabies.
There is no test available to confirm rabies in a live animal, and there is no approved treatment for rabies in horses, or in any animal, for that matter. When people are exposed, they may be vaccinated several times within ten days to build immunity to the virus during its incubation period and before it reaches the central nervous system. When administered swiftly, this protocol will protect most people from developing and dying from the disease. Unfortunately, previously unvaccinated horses will most likely die from rabies before they can build immunity to a vaccine. It may be possible to cleanse the bite wound (immediately after it occurs) using a virucidal soap like betadine or chlorhexadine and prevent rabies infection, but extreme precaution should be taken against accidental human exposure to body fluids. This includes not only blood contamination into cuts or scratches on the hands and arms, but also fluids splashed into the eyes, nose, and mouth.
Pre-exposure rabies vaccination is very effective at preventing this fatal disease in horses. All horses should be vaccinated as foals and annually throughout their lifetime, or at the veterinarian’s recommendation. Vaccinated horses that have been exposed to a rabid animal should receive a booster vaccine as soon as possible to help raise antibodies levels as much as possible.
Ultimately, horses suspected of rabies should be humanely euthanized to avoid needless suffering and possible exposure to other animals and people. After death, the veterinarian will submit the horse’s brain tissue to a laboratory for testing and confirmation of the disease.
Horse owner can help reduce rabies exposure by keeping ranches clear of brush piles and excessive debris that may be ideal breeding grounds for rabies carriers.