NEWS
Rabies in horses
Posted: Saturday, July 23, 1994
What to do if one of your horses becomes infectedNumer one on the list of diseases you do not want your horse(s) to get is rabies. It is a one-way street, and human involvement is a serious consideration.
Rabies differs from most diseases in that it is not species-specific. Any warm-blooded animal can contract it, although the most commonly infected are skunks, foxes, and bats among wild animals. Among domestic species, cattle once had the highest incidence, but that is no longer the case. The latest statistics seem to indicate that cats are now number one among domestic animals, and this has significant implications for a horse operation.
The cause of rabies is a virus, and entry into an animal is via salivary contamination of an open wound. A bite from an infected animal is the usual source. Other reported routes of infection are inhalation, oral, and transplacental.
The rabies virus proliferates at the site of entry, then travels on the axons of peripheral nerves (it is not blood-borne) until it reaches the brain stem or spinal cord. How quickly this occurs depends on the site of entry: if the virus enters on the face or muzzle, signs may develop within two or three weeks, but if entry occurs on a hind ankle, it could be many weeks or even months before clinical signs begin.
Once the virus reaches the brain, it is disseminated throughout the central nervous system. The cranial nerves carry it to the salivary glands before clinical signs occur, and herein lies the danger to handlers. The simple placing of a bit in an infected horses mouth or washing off a hand in a water bucket of an infected horse could result in the virus entering through a hangnail or open blister.
The disease is impossible to diagnose in the live animal, but should be considered in any horse which shows any peripheral or central nervous system problems. A differential diagnosis would include any of several poisonings: tetanus, encephalitis, brain trauma, any of the several encephalomyelitides, etc.
Signs that may be associated with early rabies, but which I must stress are not specific, include depression, lameness or ataxia, colic, vocal alteration, paralysis, and/or mania, characterized by hyperexcitability. It progresses rapidly from this point and within five days the horse will die. In the terminal stages, there may be urine and fecal retention, knuckling or inability to stand, inability to swallow, and/or the classical rabid form of the disease, where the horse may not be able to be restrained and will charge people or other animals, biting itself or others. Violent thrashing occurs shortly before death.
How to treat
There is no treatment for the disease, although if a known bite occurs, debride and thoroughly cleanse the site (wearing rubber gloves) and disinfect the bite using iodine or 7% alcohol. Do not suture the lesion. If the horse had been previously vaccinated, it is probably a good idea to revaccinate immediately, but if there is no history of previous vaccination, a vaccination at this point is not indicated as it is likely to slow the progress of the disease. If the biting animal can be captured, it should be submitted for observation or examination. If the biter is killed, do not shoot it in the head; the brain is needed for diagnosis. Likewise, if a horse dies which is a suspected rabies case, the brain must be examined to verify diagnosis.
Also, if there is a suspected rabid horse, all people who have handled it should be treated. If rabies has occurred in the area, it is not a bad idea for those who work with the animals to be vaccinated themselves. This is both unpleasant and expensive, but is preferable to death and less costly than a funeral, the two outcomes of a rabies infection.
Fortunately, a bite, even from a rabid animal, may not result in rabies. If a horse is bitten and the biter is identified as rabid, the horse must be quarantined for six months. It is a good idea to quarantine a horse which was known to be bitten by a wild animal, even if the animal was not captured. Public health officials will outline how the quarantine is to be accomplished and will go over precautions necessary for the animals handlers. If at any time in the six-month period the horse shows presumptive signs of rabies, both the quarantine and the animal should be terminated.
Vaccination of horses, of course, is recommended. It is a cheap precaution and may well avert a potential disaster. Foals may be vaccinated initially after 90 days of age and boosted annually. Older horses can be started at any time and then boosted on a yearly basis, also. The vaccine should be given by a veterinarian, because not all rabies vaccines are intended for use in horses and the site of injection is important.
All horses should receive the vaccination. Horses at pasturemares, foals, etc.are at the greatest risk simply because they are more apt to have contact with wild species. Unfortunately, there is the thought that horses in a closed situationracetracks or show barnsare not in danger of contracting rabies, but this is not true. Cats are a necessary adjunct to any horse operation and the feral cat population around the country is uncountable; these facts, coupled with the documented increase in feline rabies, mean that it is equally important to vaccinate indoor horses as well. Vaccination of barn cats is also essential.
Remember: as with all infectious diseases, prevention is the key to controlling and combating rabies.
Brent Kelley, DVM, is a practicing veterinarian living in Paris, Kentucky.
