Microbiology and Immunology

Rabies WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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Rabies is caused by a number of different virusesthat

vary depending on geographic area and species. While the

viruses are different, the disease they cause is singular in its

course. The bullet-shaped virus is spread when it breaks

through skin or has contact with a mucous membrane. The

virus begins to reproduce itself initially in muscle cells near

the place of first contact. At this point, within the first five

days or so, treatment by vaccinationhas a high rate of success.

Once the rabies virus passes to the nervous system,

immunizationis no longer effective. The virus passes to the

central nervous system, where it replicates itself in the system

and moves to other tissues such as the heart, the lung, the liver,

and the salivary glands. Symptoms appear when the virus

reaches the spinal cord.

A bite from a rabid animal does not guarantee that one

will get rabies; only about 50% of people who are bitten and do

not receive treatment ever develop the disease. If one is bitten

by or has had any exposure to an animal that may have rabies,

medical intervention should be sought immediately. Treatment

virtually ensures that one will not come down with the disease.

Any delay could diminish the treatment’s effectiveness.

In humans and in animals, rabies may be manifest in

one of two forms: the furious (agitated) type or the paralytic

(dumb) type. Furious rabies in animals, especially in the dog,

is characterized by altered behavior such as restlessness, hid-

ing, depraved appetite, excitement, unprovoked biting, aim-

less wandering, excessive salivation, altered voice, pharyngeal

paralysis, staggering, general paralysis, and finally death.

Death usually occurs within three to four days after the onset

of symptoms. The paralytic form of rabies is frequently

observed in animals inoculated with fixed virus, and is occa-

sionally observed in other animals with street virus contracted

under natural conditions. Animals showing this type usually

show a short period of excitement followed by uncoordina-

tion, ataxia, paralysis, dehydration, loss of weight, followed

by death.

The raccoon is a common transmitter of the rabies virus to humans.

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