Rabies
March, 1996
Rabies is a frightening and deadly disease. Prevention is of
extreme importance beacuse once infection occurs, it is nearly
always fatal. In the 1990’s, the U.S. has experienced an
increase in the number of reported Rabies cases in wild and
domestic animals. In 1994, there were also six people to die of
Rabies in the U. S., and probably thousands worldwide.
The disease is caused by a virus which has an affinity for
nervous tissue. It is nearly always spread by the bite of an
infected animal, but transmission through the air is probably
important in highly suseptable species in high density
populations, such as colonies of cave dwelling bats. All
warm-blooded animals can become infected, but birds and primative
mamals are not very susepible. The virus needs the host’s
body in order to survive. Once the infected animal is dead, the
virus survives about 24 hours at 6570 degrees ferenheit. it may
survive longer at lower temperatures, but is very sensitive to
ultraviolet light and heat.
Following the bite of a contagious ani
mal, the virus spreads to the nerve endings and then multiplies
as it travels up nerve fibers to the spinal cord and then the
brain. Th incubation period, the time from exposure until signs
are seen, is variable and depends on such factors as the site of
the bite, the number of virus particals introduced, and the
species that is biten. In naturally occuring infections,
incubation periods have been reported to be 3 weeks to 6 months
in dogs and 3 weeks to 12 months in humans.
As previously mentioned, the virus like to live in the nervous
tissue of its host. It is not even detectable in the bloodstream
of rabid animals, but is found in saliva, as this is necessary
for the transmission via bite wounds and ensures the survival of
the virus. The virus’ presence in saliva always occurs after
the brain is infected, but may precede clinical signs of the
disease by up to 10 days. This is why most public health laws
require a 10 day quarantine or observation period following a
bite fron a suspected dog or cat.
All the major signs of Rabies infection are attributable to brain
disease and include: personality changes, pica (de-. prayed
appetite), excessive salivation due to inability to swallow,
viciousness, sei
zures and death. Definitive diagnosis is accomplished by analysis
of brain tissue.
The most common wild animal species affected are raccoons,
skunks, foxes and bats. The incidence of Rabies in rabbits and
hares is extremely low, possibly because they rarely survive the
bite od a babid animal. No cases of human Rabies have ever been
associated with a bite inflicted by a rabbit.
No single measure has helped reduce the incidence of human rabies
a effectively as the widespread vaccination of domestic dogs.
Currently available vaccines are given at a minimum of three
months of age and repeated one year later. Subsequent
vaccinations are given every one to three years, depending on the
product used and the local public health laws. Several states are
currently testing the effectivness of a vaccination program for
raccoons in the wild, by disseminating baits containing an oral
Rabies vaccine. Results of earlier trials have been favorable.