Rabies: Discussion, Causes, Treatment, Prevention

Invariably fatal, rabies is found across the entire US.
By Jon Geller, D.V.M.
June/July 1999
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Distribution of major carriers of rabies across the US.
MAP ILLUSTRATION:KENNETH LIN


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The rancher, who we will call Bill Williams could see no signs of a broken leg or any other injuries. He called his veterinarian, Dr. Larson, who instructed Williams to attempt to trailer the horse to the veterinary hospital. Williams finally got his horse up with the help of his family and a few neighbors.

Rabies is primarily a disease of wildlife. That is why we (and our sundry critters) who live as far from pavement as possible are at greatest risk. Raccoons, skunks, bats and foxes are the animals most affected in the United States.

The paint gelding was completely uncoordinated in his back legs and swayed unsteadily as he was loaded into the trailer. By the time the rancher arrived at the clinic, the horse was back down and needed to be coaxed up and out of the trailer.

Dr. Larson's examination showed no evidence of trauma, except where the gelding had banged its head on the trailer when it went down. In his case report, Larson described profound neurological signs, most likely involving the spinal cord. The horse would kick out and jerk reflexively when touched on a back leg. Unable to stand, it would stagger and finally go down in its stall.

Results of X rays of the horse's neck area proved normal. The animal was sedated and treated with intravenous fluids and anti-inflammatories. Dr. Larson told Williams that the horse probably had either injured, or had an infection in, its spinal cord or else had ingested a toxin causing neurological damage. In any event, response to treatment within 24 hours would likely indicate the severity of the problem and the possibility of recovery.

Rabies is an invariably fatal disease of the nervous system. Transmitted by saliva, it is passed from one victim to the next through either a bite wound or contact with an open cut. The rabies virus slowly but inexorably travels up nerve cells to the salivary glands and the brain, where it wreaks its deadly havoc. It can take days or months for the virus to reach the brain, depending on the size of the animal and location of the bite.

There are typically only one or two cases a year of equine rabies in Wyoming, but Dr. Larson was alert enough to keep it on his list of possibilities. Both he and Williams spent the rest of that long night wondering how the horse would be the next day.

The following morning, the paint was much worse. Unable to stand, it lay helplessly in its stall. The time had come to euthanize the horse. Afterward, Larson faced the grisly task of severing the paint's head, extracting the brain and submitting it for rabies testing. Strangely, in these times of sophisticated biotechnology, this is still the only method to confirm rabies in animals.

Amy Boerger-Fields is a technician with the Wyoming Department of Public Health. She routinely analyzes samples of tissue and blood for signs of infectious disease, especially ones that are highly contagious in livestock or can spread to humans. To diagnose rabies, she must look at a sample of brain tissue that has been sectioned into paper-thin slices and treated with a fluorescent antibody stain. If rabies is present, the antibodies will bind to the virus multiplying in the brain tissue and glow when viewed under a microscope.

Boerger-Fields received the gelding's brain the next day, protected in a Styrofoam cooler. After donning gloves and a face shield, she prepared the slide and slipped it onto her scope. She tweaked the fine focus knob, and her eyes widened as the distinct glow of fluorescing antibodies confirmed the diagnosis of rabies.

Phone lines zipped with the news Within 24 hours, Williams, Dr. Larson and six other people who had contact with the horse received a series of rabies vaccinations and antibody injections. Larson only needed a booster, as he had previously been vaccinated for rabies, as had Amy Boerger-Fields.

The tale of the paint gelding should serve as warning to all of us who live in the country: rabies is out there. Thankfully, so is the vaccine; so rest easy and read on.

A Little Background

Rabies has been around forever hut since the development of the vaccine by Louis Pasteur a little over a century ago, incidences have been greatly reduced. Extensive vaccination programs have largely eliminated rabies in domesticated animals. Still, the dreaded disease continues to simmer and occasionally boil over in wild and domestic populations in much of the U.S. and other parts of the world.

Although most common in wild animals, the spillover into domestic animals can be alarming. Cats, dogs, horses (and mules and donkeys), cattle and sheep are all susceptible to rabies. If you live in or travel to Mexico, don't pet the dogs. Last year alone, 20 people died there as a result of rabid dog bites.

If you want to live without rabies, go to an island-Australia, Hawaii and Great Britain are all rabies-free.

Prevention is Easy

Prevention of rabies is straightforward: vaccinate. While a large majority of all dogs and many cats are vaccinated, livestock is often unprotected. If you live in an area where rabies is present, vaccinate all of your valuable livestock annually. Only one vaccine, Imrab 3 by Merial, is approved for use in dogs, cats, sheep, cattle, horses and ferrets.

Vaccinate all barn cats. Their inquisitiveness and cohabitation with uninvited foxes, raccoons, skunks and bats has put them on top of the list of domestic animals affected by rabies, with 300 laboratory confirmed cases last year in the United States. (The number of actual cases is probably much higher.)

Keep in mind that without a vaccination certificate from a veterinarian, you won't be able to transport your animals across state lines. A certificate is also needed to board or license small animals. Have your veterinarian vaccinate them during the next visit.

It- you decide to vaccinate your animals yourself, follow the guidelines shown above. Don't worry-if you accidentally inject yourself, you won't get rabies, but you won't be protected, either.

A vaccine for humans is available but not generally necessary, except for those who spend time on a regular basis in close proximity to wild animals, especially raccoons, skunks, foxes or coyotes.

Vaccination Guidelines for Rabies

WHAT ANIMALS TO VACCINATE:  

All valuable livestock in areas of known rabies. All cats, dogs and ferrets.

WHEN TO VACCINATE:  

At four months of age, then annually. Three-year vaccine for dogs, and cats is approved for some regions of the United States with low incidence of rabies in wild populations.

WHAT TO VACCINATE WITH:
Imbrab 3, by Merial or other approved product.

Keep refrigerated, use before expiration.

HOW TO VACCINATE:  

Give 2 ml as an intramuscular injection to horses, cattle and sheep. Use an 18-gauge by 1 1/2" needle. Inject 1 ml under the skin in dogs, cats and ferrets. Use a 22- or 23-gauge by 3/4" needle, or smaller.

Human Exposure

Only four people in the United States died of rabies last year, which makes it a negligible health risk to humans. Though the family of one 32-year-old man of Warren County, New Jersey, might not agree. His old home was well ventilated, allowing an occasional bat to find its way into the living room. His wife recounts that in July 1997, he had captured several bats with his hand, protected only by a cloth. There was no recollection of a bite wound. On October 12, the man developed an aching sensation in his right shoulder and neck. He was hospitalized with symptoms including fever, agitation, insomnia and inability to swallow. His condition deteriorated despite heroic attempts to diagnose and treat him, and he died on October 23. Biopsies and blood tests confirmed rabies transmitted from the eastern pipistrelle bat.

If you enjoy attracting these flying insectivorous rodents to your property excellent. Just don't invite them in for dinner. Apply screening and mesh to all open eaves, cupolas, attic or soffit vents to keep them out. Almost all of the human deaths from rabies in the last ten years have occurred through unknown contact with bats, probably while the victims were sleeping. Don't forget to batproof your outbuildings, as well.

If Someone Does Get Bitten

If the bite is from a vaccinated pet, immediately and thoroughly clean out the wound .and keep an eye on the pet for ten days. If the bite is from an unvaccinated pet, the animal must be confined under close observation for ten days.

Any stray dog, cat or ferret that bites a person should be euthanized immediately, and the head must be submitted to the local health department for rabies examination.

Any wild animal that bites a person is considered rabid unless proved otherwise. Attempts should be made to trap and euthanize the animal for rabies testing. Anyone bitten by a wild animal should, after thoroughly cleansing the wound, visit a physician to determine the need for antirabies treatment. This consists of a series of intramuscular injections of both the rabies vaccine (to stimulate antibody production) arid a serum containing antibodies to rabies.

Wild Animals as Pets

Don't do it. Raccoons, skunks, coyotes, foxes and, of course, bats are significant rabies carriers. Oral vaccines for these species are being used widely by state

and federal agencies to control rabies in the wild, but these are not available for private use. Besides, it's illegal to keep wild animals as pets in most states.

By the way, those of you who enjoy keeping wolf hybrids as pees have no legal means to vaccinate them for rabies, as they fall into the same category as wild animals. Vaccinate them anyway, since the vaccine most likely is protective, even if it does not provide "official" protection. (If you do need a rabies certificate, you may want to list the breed as malamute/husky cross)

Signs of Rabies in Animals

A rabid dog may not always try to demolish your car, as did Stephen King's "Cujo." Still, behavior changes are the earliest signs of rabies. Dogs and cats may become aggressive, act frenzied and hyper-stimulated if they have the "furious" form of rabies, or may act strangely sedate, unable to swallow and drooling in the "dumb" form. In either form, death follows within five days of behavior changes, which provides the rationale for the seven- to ten-day quarantine when a dog or cat bites a person. Any animal alive ten days after biting someone could not have had the rabies virus in its saliva at the time of the bite.

Cattle, when infected, usually have been bitten by a rabid skunk or raccoon and will display strange bellowing, knuckling in the hind limbs, difficulty swallowing and excessive salivation. In South American cattle, rabid vampire bats cause paralysis. Horses may show the signs of uncoordination seen in the paint gelding or may chew at the original bite, occasionally acting aggressively.

If you're concerned about the possibility of rabies, get your vet out as soon as possible. Isolate the animal, wearing durable gloves during handling, and minimize contact, especially with the animal's mouth and saliva. Be proactive and get livestock, dogs and barn cats vaccinated, especially if you live in an area of known rabies. Bat-proof your house and outbuildings. Rural life makes for a fine existence, but it has its own set of worries. Make sure rabies is not one of them.


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