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Pathology => Human Diseases => Rabies
Rabies
INTRODUCTION
Rabies, acute, contagious infection of the central nervous system, caused by a specific virus that enters the body through the bite of an animal. All warm-blooded animals are susceptible, but in North America the disease is most common in skunks, foxes, bats, raccoons, dogs, and cats. Most of the cases of rabies in humans are caused by the bite of one of these animals. The incubation period in humans varies from three weeks to 120 days, with an average of about four to six weeks. Rabies is virtually always fatal when vaccine is not administered.
COURSE IN HUMANS
At the end of the incubation period the site of the now healed wound becomes irritated and painful, and the local tissues may become numb. Depression and anxiety are common. This initial stage lasts for about two days. In the next stage, the period of excitation, the patient becomes irritable and hypersensitive; the general attitude is one of terror, intensified by the onset of difficult breathing and swallowing and a feeling of strangulation, caused by spasmodic contractions of the diaphragm and larynx. The patient is extremely thirsty but experiences spasms of the larynx when water is presented or even mentioned, whence the original name of the disease, hydrophobia (Greek hydor,"water"; phobos,"fear"). Vomiting, pallor, and fever of about 39° C (102° F) are common during this stage. A thick secretion of mucus collects in the mouth and throat, and the individual expectorates frequently or attempts to cough. This stage lasts three to five days and usually terminates in death from a convulsive seizure or from cardiac or respiratory failure.
COURSE IN ANIMALS
In animals rabies takes two forms, furious or irritable rabies and a dumb or paralytic rabies. The stages of furious rabies are similar to those through which an infected human passes; during the stage of excitement the animal usually runs amuck, biting and snapping at any living thing in its path. In dumb rabies, which is not as common as furious rabies, the stage of excitement is of very short duration or is absent, and the paralytic stage sets in early in the disease, first attacking the muscles of the jaws and larynx. Domestic animals such as dogs and cats are generally immunized against rabies; in many areas this is required by law. The spread of rabies among wild animals such as raccoons has prompted efforts to develop methods of vaccinating animals who may come into contact with pets or with human beings.
HISTORY, PREVENTION, AND TREATMENT
Rabies is described in medical writings dating from 300 BC, but the method of transmission or contagion was not recognized until 1804. In 1884 the French bacteriologist Louis Pasteur developed a preventive vaccine against rabies, and modifications of Pasteur's methods are still used in rabies therapy today. The Pasteur program, or variations of it, has greatly reduced the fatalities in humans from rabies. Modern treatment, following a bite by a rabid or presumed rabid animal, consists of immediate and thorough cleansing of the bite wound and injection into the wound and elsewhere of hyperimmune antirabies serum. A 14- to 30-day course of daily injections of rabies vaccine is then given; booster doses are given 10 days after this course and again 20 days later.
The traditional vaccine contains inactivated rabies virus grown in duck eggs. A newer vaccine, which contains virus prepared from human cells grown in the laboratory, is safer and requires a shorter course of injections.
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