Rabies: Discussion, Causes, Treatment, Prevention

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MAP ILLUSTRATION:KENNETH LIN
Distribution of major carriers of rabies across the US.

On a frosty December evening in 1997, a
Wyoming rancher went out to feed his horses and noticed
that his three-year-old paint gelding was down in tile
pasture, struggling to get up.

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.