Page 77 - January 2016 Speedhorse

Rabies Symptoms In Horses
Signs of rabies can include attitude change, depression, weakness and inco- ordination, mild lameness, mild muscle contractions in the upper neck and face, inability to swallow, drooling, and often a tendency toward aggression and irritabil- ity. Death usually occurs 2-4 days after the horse starts showing signs, but some horses may linger for as long as two weeks. The horse may go into a coma at the end or may have convulsions and thrash violently.
Since the neurological signs are similar to symptoms of West Nile, EPM, and encephalomyelitis, it is very impor- tant to have an accurate diagnosis. If the horse dies or is euthanized, a sample of brain tissue should be sent to a diagnostic laboratory for testing.
multiple neighbors, had all been tending the sick horse and were all exposed. The horse was only here for a couple of days. We were suspicious at that point that it was rabies and euthanized the horse to confirm it.”
In the interim, between when the horse
was at the farm and before it came to the New Bolton Center, one of the exposed people had gone overseas to Africa for a summer program. “It then became an international search to locate her. She had to be air-lifted to a different country in Africa for treatment because the country where she was staying did not have access to the post-exposure series for rabies,” says Johnson.
As of 2010, rabies vaccination is now con- sidered by the AAEP to be one of the core vac- cines that should be required for all horses. Yet, this vaccine is sometimes forgotten by horse owners. “It’s not one that everyone has access to. You may have to get it from, or have it given by, your veterinarian,” she says. If there haven’t been any reported cases in your area, you may not think about it.
“In our area, the strain that’s endemic is raccoon rabies, which is the most common
one in the eastern part of the country,” says Johnson. In other areas there are different vari- ants, including skunk, fox and bat rabies. There are several different strains of rabies, just as there are multiple strains of flu virus.
“Pennsylvania is one of the states with the highest incidence of rabies. We see it
Horses infected with rabies may initially present with colic or lameness, but will increasingly have more abnormal behavior and become disoriented and uncoordinated.
in all species, including cows and horses, but especially in cats and dogs. There were also some whitetail deer that had rabies in the last few years. Human risk is generally considered to be fairly low when handling horses or cattle with rabies, just because these animals don’t usually bite and punc- ture the skin,” she says.
“There is always a risk when coming into contact with saliva, however. If you get the animal’s saliva in your eyes, mucous mem- branes or cuts, you could get rabies. A few years ago, a report was published discuss-
ing the first known case of a veterinarian contracting rabies after handling rabid cattle and goats in South America. This was scary because it was the first documented case of transmission from a large animal (non-carniv- orous),” says Johnson. There is always some risk when handling the mouth of any animal that might have rabies.
The rabies virus multiplies at the site of infection: the bite wound or wherever saliva comes into contact with open tissue. The salivary glands and central nervous system of the rabid animal are infected by the time the animal begins to show clinical signs of the disease.
Signs of rabies are varied and not always clear, and people may try to treat the animal for something else. Horses with rabies may look like they have colic or may just appear lame. People are often exposed because, at first, they didn’t realize the horse had rabies. Often the inability to swallow is mistaken for chok-
ing, and the horse owner or veterinarian may become exposed when examining the mouth and throat. A veterinarian may try to pass a stomach tube and it goes right down. So he/ she uses an endoscope to check things further, and there’s no blockage and the trachea is fine, and then realizes this is rabies and hopes he/she wore gloves.
There hasn’t been much published on rabies in horses. “The largest retrospective series had only 21 cases, and 10% of those horses showed colic as an initial sign. Another 24% showed lameness. This might lead a vet- erinarian off the track, but then the animals always progress to show other signs,” she says. The infected animal becomes increasingly abnormal in its behavior and may become uncoordinated or disoriented.
“They almost always become recum- bent—unable to get up—at the end. Once they start showing signs, it may take up to 4 or 5 days or even longer until they progress to the point where they are euthanized or die. The actual length of time may vary from case to case.” Incubation time between exposure and the start of symptoms is also quite variable, depending on the location
of the bite. An animal bitten on the nose or face, for instance, will usually start showing severe signs of illness much sooner than an animal bitten low on the hind leg. In the latter situation, it might be several months between the time of the bite and the onset of illness. The virus has to travel farther along the nerves before it gets to the brain. By that time, the bite wound that allowed entrance to the body may have healed and be impossible to locate.
Some horse owners feel it’s not healthy to over-vaccinate their horses and may not vac- cinate their animals adequately. “Some think they can just check titers to see if the horse has immunity rather than re-vaccinate for various diseases. This is unwise, especially with rabies. There isn’t any data available to indicate that a certain level of antibody (titer) is truly protective. It’s not safe to just check the horse’s titer and think it doesn’t need to be revaccinated. We know there are cases where horses have been previously vaccinated in earlier years and still get rabies from being bitten. So, we don’t recommend just check- ing titers,” she says. It’s better to keep up the annual vaccination program.
“We can only diagnose rabies definitively after the horse is dead. If you have a horse that dies or is euthanized after a short course of unexplained progressive neurologic disease, that horse should be tested for rabies. If you don’t test, you wouldn’t know, and humans may have been exposed. To play it safe, if the horse has been showing signs for 3 weeks, you should probably have it tested. This is routinely done at our hospital,” says Johnson.
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equine health