Most people’s connotation of rabies is a snarling mad dog, foaming at the mouth. But livestock are also susceptible, and the symptoms easily can be mistaken for some other problem. Unfortunately, the result is often human exposure when the owner or veterinarian tries to examine or treat the animal.
Rabies can occur in all warm-blooded animals and is always fatal. Caused by a virus that affects the nervous system, it’s transmitted by saliva of an infected animal – usually via a bite, by saliva coming in contact with mucous membranes (eyes, nose or mouth) or an opening in the skin.
Rabies is uncommon in cattle but there are always a few livestock cases when wildlife cases increase, as there are more opportunities for exposure.
This year in Texas, for instance, reports of rabid animals rose dramatically as the summer became hot and dry, and wildlife migrated closer to human habitation to find food and water. James Alexander, Regional Zoonosis Control Veterinarian, Texas Department of State Health Services, Canyon, TX, says cases in livestock and horses are much higher than usual this year.
Missy Looney, a vet technician with Central Plains Vet Clinic in Plainview, TX, says she saw six cases in the first three months of 2011, and almost 40 by July.
“Most of these were in skunks, but now we’re seeing spillover into other species. A rabid cow 60 miles east of us exposed at least six people, and a horse was brought to our clinic with neurological signs,” she says.
Alexander stresses that livestock owners need to pay attention to animal behavior. An animal acting out of character is a clue, as rabies symptoms in cattle and horses are unpredictable. For instance, a normally gentle or tame animal may suddenly become skittish or aggressive. Or, a typically wild animal may be unafraid.
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A big clue is an animal having trouble eating or drinking because it can’t swallow, a condition often mistaken for an obstruction in the mouth or throat.
“We’ve heard of many veterinarians or feedlot cowboys who think a certain animal is choking and try to get their hands down the throat to resolve it. We’ve also heard about a calf that wouldn’t take a bottle, and some friends/neighbors tried to help the family get the calf to suck. Both cases turned out to be rabies and all those people had to be treated,” Alexander says.
Looney says one vet in her clinic, while in vet school, worked with a show steer exhibiting neurological signs and not swallowing properly. Numerous students and veterinarians were exposed because they thought there was something caught in the mouth or throat. The animal wasn’t eating and when it was put down a week later, it tested positive for rabies. She reminds livestock owners that if an animal is put down, don’t shoot it in the head. The brain must be intact to send for testing.
Vaccinate For Rabies
In Texas, most cases of rabies are spread by skunks, but occasionally by coyotes, foxes or bats. Alexander has also seen cattle come from Mexico that developed vampire bat rabies.
“Incubation time in large animals can be weeks or months, depending on the bite location. The virus works its way along the nerves to the brain. If a horse or cow is curious about a skunk and gets bitten on the nose, this would result in a shorter incubation time than if bitten on the hind leg,” he explains.
Most pets are vaccinated for rabies, to protect both the animals and their owners. The American Association of Equine Practitioners now recommends all horses be vaccinated for rabies, listing it as a “core” vaccine in every vaccination program.
Cattle, however, are rarely vaccinated. But, in regions where rabies cases occur, valuable animals should be vaccinated, along with any cattle handled by people. Alexander recommends vaccination for 4-H, FFA and other show animals.
Alexander points out that in a herd of cattle, generally only one animal becomes infected. It’s rare to have multiple cases.
“The worst situation I know of was a herd of registered Shorthorns west of San Angelo during a surge of fox rabies a few years ago. One rancher lost seven head. A fox or bobcat probably went berserk and bit numerous animals in that herd,” he says. Or, since cattle will sometimes attack a predator to protect calves, the cows might have grouped around it attempting to chase it off.
Rabies has many genetically different strains, each of which is adapted to a particular species of animal. This adaptation makes that species a reservoir for that variant, as the host species isn’t killed as quickly as a species into which that variant spills over.
“This enables the variant to survive and propagate in nature,” says James Alexander, regional zoonosis control veterinarian, Texas Department of State Health Services. “There are several rabies variants in skunks, including the North Central Skunk, South Central Skunk, and Spotted Skunk, and even more variants in bats.”
The variants were named for the species (and sometimes the region) in which first detected. Many distinct rabies virus variants have been identified in different bat species – there are as many as 40 bat species that may each have their own rabies variant.
Rabies variants in the U.S. include raccoon, skunk, fox and mongoose (Puerto Rico). “Fox variants include the Texas Gray Fox, Arizona Fox, Arctic Fox, Red Fox, etc., while different canine variants are the predominant form of rabies in other countries,” Alexander says.
A new rabies virus variant associated with Mexican free-tail bats was identified in the U.S. in 2008 after the death of a Mexican immigrant who was exposed to bats prior to her arrival in the U.S.
CDC On Rabies In Livestock
The Centers for Disease Control and Prevention (CDC) offers this guidance to veterinarians dealing with rabies-infected livestock:
• For client animals with up-to-date rabies vaccinations
Livestock exposed to a rabid animal and currently vaccinated with a USDA-approved vaccine for that species should be revaccinated immediately and observed for 45 days.
If an exposed animal is to be slaughtered for consumption, it should be done immediately after exposure. Barrier precautions should be used by persons handling the animal, and all tissues should be cooked thoroughly.
Historically, federal guidelines for meat inspectors have required that any animal known to have been exposed to rabies within eight months be rejected for slaughter. USDA Food and Inspection Service meat inspectors should be notified if such exposures occur in food animals before slaughter.
Multiple rabid animals in a herd or herbivore-to-herbivore transmission is uncommon. Therefore, restricting the rest of the herd if a single animal has been exposed to rabies usually isn’t necessary.
• For client animals without up-to-date rabies vaccinations
Unvaccinated livestock should be euthanized immediately. If the animal is not euthanized, the animal should be closely observed for six months. Any illness while under observation should be reported immediately to the local health department.
If signs suggestive of rabies develop, euthanize the animal and ship the head for testing. Multiple cases in a herd or herbivore-to-herbivore transmission is uncommon. Therefore, restricting the rest of the herd if a single animal has been exposed to or infected by rabies usually isn’t necessary.
Treatment for humans
Until the 1980s, treatment for rabies in humans consisted of a long series of very painful injections, generally in the abdomen, says James Alexander, regional zoonosis control veterinarian, Texas Department of State Health Services. That particular area was chosen for administration because it could swell and not be as uncomfortable or noticeable as other parts of the body.
“There was a lot of tissue reaction, however. Now, we use different products and there’s a lot less reaction, and it’s not as painful,” he adds.
In addition, fewer injections are needed today.
“Up until two years ago, the series consisted of five vaccinations (the last one on week four). But, now, it’s just four shots, which can all be given within a two-week period,” Alexander says.
The first shots are a dose of vaccine (in the upper arm) and a dose of human rabies immunoglobulin. A second vaccination is given on day three, and the third injection a week after that. Number four is given two weeks after the first treatment.
Heather Smith Thomas is a Salmon, ID-based rancher and freelancer.
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