Rabies in Horses
Dr. Philip Johnson
Rabies is a word derived from the Latin expression "rabere," which means "to be mad." It is a disease of the central nervous system that can afflict all domestic animals, as well as humans and various wildlife species.
Rabies is caused by a virus that gains access to the horse through a bite wound inflicted by another rabid animal. Although horses are not commonly afflicted with rabies, it is recommended that owners vaccinate their equines against this serious threat. Vaccination is especially important in areas of the United States where the disease is endemic.
Although there has never been a reported transmission of rabies from horse to human in the United States, that may be the result of vaccination of both horses, and more recently, the recommended vaccination of animal caregivers (veterinarians, technicians, etc.).
Recently, some have suggested that vaccination might suppress the symptoms of rabies, making early signs of the disease unrecognizable and potentially increasing the risk of human infection. This may be true. Cases of rabies in large animals are seen almost exclusively in unvaccinated animals, but in some cases, fully vaccinated animals contracted the disease. This has shed light on the possibility that the vaccine is not consistently effective. It is more likely that the rabies vaccine, like any vaccine, is not perfect, and there are cases that break through the protective barrier of the vaccine.
Protect Yourself from Rabies
The people at the greatest risk are the handlers of the horses: owners, trainers, grooms, and transporters. This is because the early signs are not recognized as rabies. As veterinarians are familiar with the disease and put on gloves for examination of most neurologic animals, their exposure rate may be lower. To avoid exposure, you need to know what the early signs are, and put on latex or similar protective gloves the minute you think it's a possibility, no matter how remote.
How Horses Get Rabies
An animal, usually a dog or fox, contracts rabies then wanders into the barn or onto the property of the horse. The rabid animal bites the horse, which may have approached the animal out of curiosity, or because the animal is aggressive. Certainly, if you see a wild fox around that doesn't look right, keep your horses in until the animal clears the area. With the increase in coyotes and foxes in some rural areas, due to the uprooting of their habitat, this is getting to be a more frequent scenario.
Symptoms of Rabies
In some cases, you can see a bite wound. But there is a long delay from the bite to the onset of symptoms (the incubation time is 3 weeks to 6 months), which makes it unlikely you'll see the wound. You might remember having seen one, however.
The rabies virus attacks the central nervous system and causes any form of neurologic malfunction. The famous veterinarian Dr. Francis Fox (Cornell University) once said that "rabies can look like anything," and others have said that the only thing that is typical about rabies is that it's never typical. This is important to keep in mind before being dogmatic about whether a horse has rabies or not. One thing is for sure, horses with rabies get worse and die, so it is important to call your veterinarian when a little weird behavior gets worse. This is generally a good thumb-rule, because other diseases that look like rabies in this respect (Eastern Encephalitis, West Nile fever) need immediate attention.
Early symptoms may include an intense scratching, licking, biting and even tearing of tissue around the bite wound. If the wound is long gone, these signs will not be recognized. Bizarre "hypersensitivity" to touch (hyperesthesia ) is an early sign. Lameness due to sudden weakness or paralysis of a limb has been seen in many cases. This can appear as a front leg knuckling or dragging, but there is no tenderness or lack of mobility as you would expect in lameness.
As the disease progresses, signs of locomotion are further affected. Poor coordination, knuckling, tripping, outright stumbling or falling, or inability to rise, swaying, or sinking in the back or front end are typical signs. Horses are not hydrophobic (afraid of water), rather they develop swallowing problems and slobbering, making it look like they're afraid of water -- the water goes part way in, but then falls out due to inability to swallow. Horses can show other bizarre signs, such as spasmodic movements of the corners of the lips, mini-convulsions involving the face or whole body, a lingering gaze, somnolence interrupted by intense activity or recklessness, or destructive behavior.
The aggressive behavior of horses with rabies is quite remarkable and dangerous. It appears as an "intentional" rather than accidental form of aggression, that latter which can be seen in any horse in distress or severe pain as in colic. Horses attack mangers, buckets, and bars on the stall, and will certainly bite you! Later, there can be further paralysis of any area of the body, severe depression, a "flat out unresponsive" appearance, or seizures, coma, and sudden death. Presumably, the horse is scared and stressed, and this explains the high heart rate and respiratory rate seen. In other cases, when the horse is flat out, the heart and respiratory rate can be oddly slow and even.
It is essential that the diagnosis is confirmed, but this can only be done at autopsy. Your veterinarian is skilled at removing the brain carefully, for proper submission to the state public health laboratory. All tissues are considered a human health hazard, so stay away.