|Rabies in Raccoons
Raccoons act as a reservoir for rabies in the United States.
In fact, the majority of rabies cases in the U.S. are in wildlife,
with raccoon cases predominating. In the U.S., 90% of all
rabies cases occur in wildlife. During 2000, raccoon rabies
made up 41% of wildlife cases diagnosed with skunks, bats
and foxes making up the balance. To limit the exposure of
humans and domestic animals to rabies, it is important for
veterinarians to know the current geographic distribution
of rabies, the procedure if a human or animal is bitten by
a wild animal, and be familiar with rabies diagnostic testing.
Geographic distribution: Raccoon rabies was much
less prevalent in the U.S. prior to 1950. From 1950-1970,
the incidence of raccoon rabies began to rise, especially
in Florida and Georgia. In 1977, a variant of raccoon rabies
distinct from the southern variant was detected in Virginia
and West Virginia. This variant has since spread north along
the eastern seaboard to Ontario, Canada, and was reported
in northwest Ohio in 1996. Eventually this rabies variant
converged with the southern variant in North Carolina.
In most states with raccoon rabies, there has been an
increased number of cases; however, Ohio has reported fewer
cases. In 2000, 10 of 19 states which have reported raccoon
variant rabies reported an increase in the number of cases.
However, Ohio reported no cases in 2000. This was a decrease
from the 6 cases reported in 1999. This may be because Ohio
has used extensive wildlife rabies control programs, including
rabies vaccine baiting.
Human or Domestic Animal Exposure:
Veterinarians should discourage ownership of raccoons
or any wildlife. No parenteral vaccines are approved for
use in raccoons and prior vaccination does not contraindicate
euthanasia and testing. Captive raccoons in exhibits may
have been incubating rabies when caught and, therefore, should
be quarantined for a minimum of 180 days before exhibition.
If a human is bitten by a raccoon (or any wildlife) the
animal should be regarded as rabid. The raccoon should be
humanely euthanized and the brain tested for rabies. If
human exposure occurs, it should always be reported to the
local or state health department. Bites or scratches should
be thoroughly washed immediately. A bite to a human requires
the initiation of post-exposure prophylaxis.
Animals potentially exposed to rabies by a raccoon or
other wild animal not availablefor testing should be handled
as an exposure. Unvaccinated domestic animals which are exposed
should be euthanized immediately. If the owner is unwilling
to do this, the animal should be placed in strict isolation
for six months. The animal should be vaccinated one month
before release. Animals that are current on rabies vaccinations
should be revaccinated immediately and observed for 45 days.
It is important to remember that the guidelines for bites
from wildlife are different from those for bites to humans
from healthy domestic animals. If a dog, cat, or ferret bites
a human, the animal should be quarantined and observed for
ten days. The animal should not be given a rabies vaccination
during this time. At the first sign of illness, the animal
should be evaluated by a veterinarian and reported to the
local health department. If signs of rabies develop, the
animal should be euthanized, appropriate brain tissue removed
and shipped refrigerated to the State Board of Health. Any
unwanted animal that bites a human may be euthanized immediately
and submitted for testing.
Diagnostics: No antemortem tests are sensitive
enough to be considered reliable for diagnosis. Handling
live suspect animals should be done cautiously using safety
equipment such as rabies poles, cages, and heavy gloves.
The animal should be euthanized humanely in a way that does
not damage the animal’s brain. The head can be removed
and the whole animal or head should be chilled until examined.
The head should not be frozen as freezing causes tissue damage
and may delay diagnosis.
The standard diagnostic test for rabies is the direct
fluorescent antibody test (FAT). This test can be performed
quickly and has a sensitivity and specificity approaching
100%. In this test, microscope slides of brain from the affected
animal are fixed in acetone. The slides are then exposed
to rabies specific nucleocapsid fluorescent antibody. They
are evaluated on a microscope with an energy source which
allows visualization of fluorescent marker fixed to the antibodies.
It is not necessary that the animal be showing neurologic
signs at the time of examination. If there is virus in the
saliva, there will be detectable virus in the CNS by FAT.
Rabies can also be diagnosed histopathologically through
the identification of intracytoplasmic inclusions in large
neurons called Negri bodies. Negri bodies can be found in
the thalamus, hypothalamus, pons, cerebral cortex, and dorsal
horn of the spinal cord. In carnivores, they are most common
in the neurons of the hippocampus. In herbivores, they are
often found in the Purkinje cells. The bodies are best seen
with Seller’s or van Gieson’s stain; they stain
magenta. Negri bodies are not seen during all stages of infection
and this test is no longer used for routine diagnosis.
In Indiana, animals or brain tissue is sent directly
to the Board of Health as soon as possible for official examination
Indiana State Board of Health
P.O. Box 7203
635 N. Barnhill Dr.
Indianapolis, IN 46207
Conclusion: There have been no confirmed human
deaths associated with rabid raccoons; however, there has
been an increased number of rabies cases in domestic animals
in the northeast due to raccoon rabies. Therefore, rabid
raccoons could potentially lead to human exposure through
rabid domestic animals.
-by Paul Rennekamp, Class of 2003
-edited by Dr. Christine Hanika, ADDL Pathologist