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An
Overview of Rabies
Rabies,
a serious disease caused by a rhabdovirus,
is one of the most feared infections of all time. References to the
illness go back thousands of years and, despite today’s modern
vaccination programs, the virus is still a threat to a significant number
of human and mammal lives every year. This disease is made particularly
dangerous by the fact that all warm-blooded mammals are susceptible.
Because the virus is classified as a major zoonosis
(disease which may be transmitted from animals to humans under natural
conditions), its spread has a considerable impact on public as well
as veterinary health. Vaccinations have helped to diminish the number
of cases annually, but rabies still exists even in developed countries
and runs rampant through Third World countries in Asia. The only nations
that remain untouched by the virus are Australia, New Zealand, the British
Isles, Hawaii, Scandinavia, Cyprus, and Japan.
Appearance
of disease symptoms after initial infection may take anywhere from a
few weeks to several months, but once they have appeared there is no
cure for the disease. Vaccination of your pets, including indoor cats,
is extremely important.
Why and how might my dog become infected?
Rabies
remains a threat due to its high prevalence among unvaccinated wild
animals. Species that are particularly likely to carry the virus are
known as “reservoir
species.” These reservoir species vary widely depending
upon geographic location, but in the United States they include raccoons,
skunks, bats, foxes, and coyotes. Highly susceptible animals in other
parts of the world include wolves, mongooses, and jackals.
The most
common way in which domesticated animals become infected with the rabies
virus is via a bite. Transmission has also occurred via ingestion of
infected tissue or by aerosol exposure, but bites remain by far the
most prevalent mode of infection. The amount of time that passes between
initial infection and onset of clinical symptoms is highly variable,
and what follows is a general overview of the average duration of each
stage of infection.
Once in
the body, viral particles undergo replication in muscular tissue at
or near the point of entry. The virus remains in the muscle for a few
days, then travels to local nerves and begins its journey to the brain.
It is here, in the peripheral
nerves, that the virus incubates. How long it takes to
reach the central
nervous system (CNS) and brain is somewhat dependent upon
the site of infection; the closer it is to the brain, the shorter the
incubation period
will be. Even with this guideline however, incubation times are highly
variable and impossible to predict.
Ultimately
of course the virus completes its journey to the spinal cord and brain.
Two days after its initial arrival in the CNS, viral particles are present
in all body secretions
and the victim is fully contagious. Clinical symptoms appear at or soon
after this point.
How
will my vet reach a diagnosis of rabies?
There is no definitive set of clinical symptoms that leads
to a diagnosis of rabies. Certain symptoms are however associated almost
exclusively with the disease. The progression of rabies infection has
traditionally been divided into three stages – prodromal, furious,
and paralytic (dumb). It should be noted that though these stages provide
a rough outline of disease progression, there is a remarkably high level
of variation associated with rabies, and every case is unique. Death
occurs within 10 days after onset of clinical signs.
Animals
experiencing the prodromal stage, which may persist for 2 to 5 days,
often exhibit vague, nonspecific symptoms. Signs include apprehension,
restlessness, loss of appetite, temperament changes and sometimes vomiting.
This initial phase is followed by either the paralytic or furious form
of the disease.
Approximately
25 to 30 percent of infected animals will progress from the prodromal
stage to the furious form, which is much more common in cats than in
dogs and generally lasts 2 to 4 days. This phase is characterized by
an increased level of restlessness, wandering, viciousness, howling,
panting, drooling, and occasionally convulsions. The classic “mad
dog” image of rabies is perpetrated by the furious form. Affected
animals will often attempt to attack objects that may or may not be
real.
The paralytic
form of rabies, which also lasts between 2 and 4 days, is most common
in dogs. Those animals not progressing to the furious form will develop
the paralytic form instead. Symptoms include ascending paralysis, beginning
near the bite site and gradually progressing up the body, paralysis
of the lower jaw, and facial paralysis. Biting is uncommon with this
form, but excessive drooling does occur. Victims have difficulty eating
and drinking. In dogs, a noticeable change in how the bark sounds occurs
as the larynx becomes paralyzed. Symptoms progress to coma and death
from respiratory paralysis.
Laboratory tests are the only certain way to diagnose rabies in animals,
and must be carried out postmortem. In the case of a suspicious death,
the head or entire body of the deceased animal is either donated to
the local animal control office or given to a veterinarian who can send
the specimen to the appropriate authority.
What are the treatment options for dogs with rabies?
Once clinical
symptoms have appeared, there is no treatment. Rabies is nearly 100
percent fatal at this point. Any animal that has been exposed to rabies
and is not properly immunized should be euthanized. If a vaccinated
animal is exposed to the virus he should be re-immunized and kept under
close observation for at least 3 months. Of course, if you ever suspect
that your pet has been exposed to rabies, contact your veterinarian
immediately.
How
do I vaccinate my pet against rabies?
Vaccines
are complicated substances and often raise many questions. For a brief
introduction to vaccines and how they work, please goto An
Introduction to the World of Vaccines.
Rabies
vaccines should be considered a requirement for any domestic dog or
cat. Vaccination is governed by law in most states. Rabies vaccines
are generally administered between 16 and 26 weeks of age and require
a booster shot that is given one year later. Beyond this point, recommendations
and laws vary widely from state to state. A specific vaccination schedule
should be discussed with your veterinarian.
How else can I help prevent the disease?
Contact
with all wild animals, not just suspicious looking ones, should be avoided.
Beyond that logical step, vaccination is the key!
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