Last year, a horse that had been stabled at the 2006 Tennessee Walking Horse National Convention in Shelbyville, Tennessee, was diagnosed with rabies, and a frantic search was launched to identify people who may have had close contact with the rabid horse. Suddenly, the topic of rabies in horses was thrown into the national spotlight.
But just how many horses do get rabies? What are the risks of your horse getting it, and how much risk does a rabid horse pose to the people working with him?
No Need to Panic
Fortunately, rabies in horses is relatively rare. Less than 100 cases per year are recorded out of the estimated 7.5 million horses in this country. In 2004, there were only 10 cases in horses and mules. However, given the seriousness of this disease, and the risk to owners if their horses do become rabid, vaccination is often recommended-particularly if a horse spends a considerable amount of time outside and you live in an area with high rabies activity.
Handle Potential Cases with Care
- If you're in an area of high rabies activity, vaccinate against the disease annually.
- Treat any neurological disorder in your horse as a possible rabies case.
- Leave the exam up to your veterinarian.
- Use gloves when looking in your horse's mouth, especially if he has neurological symptoms.
- Inspect your horse daily for evidence of bite wounds, especially if he lives outdoors.
- If your horse dies of an unknown neurological disorder, turn his brain over to the state veterinary laboratory for testing.
The lower case numbers in horses probably reflects their quickness and wariness of close contact with other animals. Typically, there are many more cases in cattle, which are slower than horses, while the bulk of cases in domestic animals involve dogs and cats, which are actually attracted to any wild animal that is acting strangely.
Wouldn't You See a Wound?
If the horse has an obvious bite wound, or had one in the two to three weeks before showing symptoms, obviously the index of suspicion for rabies should jump if that horse develops neurological signs. However, the incubation period (time from infection to symptoms) can be as long as three months. Horses may also be bitten around the ankle/fetlock, and the longer hair there can easily hide puncture marks from a bite.
It's just plain good management to inspect horses kept outside at least once daily. This should include picking out the feet and checking for wounds, bearing in mind you are also looking for punctures.
Different than Dogs & Cats
Rabies in horses is different from the way the disease is expressed in dogs and cats. Horses typically develop the "dumb" form of rabies, which means they are significantly depressed rather than agitated or violent. In fact, depression is usually the first symptom, often with a low-grade fever. The horse may also begin to chew on the area where the bite originally occurred. Eating and drinking are greatly reduced.
As the disease progresses, the horse may show more signs of irritability, disorientation or panic. This will progress quickly to obvious neurological signs, usually including seizures. The horse eventually goes down and is unable to rise. Death typically occurs in a week or less.
It is important to realize that the symptoms of rabies are not specific; they're easily confused with other conditions. In the very early stages, the horse may be thought to be coming down with a respiratory virus. The neurological involvement also mimics other causes of encephalitis or may be confused with botulism, moldy corn poisoning or other toxicities.
Rabies cannot be diagnosed while the horse is alive. Any horse that develops a rapidly progressive neurological disease with behavioral changes needs to be considered a rabies suspect. Index of suspicion is lower for horses that do not show behavioral changes and continue to eat and drink well. A horse that survives for longer than seven days, or whose symptoms stabilize, also probably does not have rabies.
There is no cure or treatment for rabies. Because of the human health risk, any unvaccinated horse that dies after a short and rapidly progressive neurological disease should be tested for rabies. This is done by submitting the horse's brain to your state veterinary laboratory for testing.
From Horse to Human
A horse with rabies is not likely to attack and bite you, but because one of the early symptoms is difficulty with eating and drinking, a problem in the mouth might be suspected, resulting in an oral examination. Virus in the horse's saliva can enter your body through even tiny surface cuts or scrapes on your skin. Never put your hand in the mouth of a horse that might have rabies.
If your vet thinks an oral exam is necessary, he or she can do it using protective gloves. The virus can also be present in any of the horse's secretions, including urine and possibly the blood. There are human cases on record where people developed rabies after receiving an organ transplant from someone who had the disease.
The Imrab 3 vaccine from Merial is the only product approved for use in horses. Because studies in horses are limited, it is currently recommended that all horses be vaccinated annually. However, some vets and owners choose to let their decision about vaccination be guided by testing rabies antibody titers. The Rabies Laboratory at Kansas Status University does this testing. The website is:
www.vet.ksu.edu/depts/dmp/service/rabies/index.htm. For information, call 785-532-4483.
A minimum titer of 0.5 I.U./ml is the standard set by most rabies-free countries for horses being imported, but the KSU Rabies Lab points out that studies to determine what is truly a protective titer (level that guarantees against infection) have not been done.