Rabies is a viral infection of the central nervous system that occurs in wild and domestic mammals, particularly carnivores (flesh-eating animals). The rabies virus is contained in saliva and is transmitted to humans mainly by the bites of infected animals. Rabies is almost always fatal if the preventive vaccine is not given promptly.
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Central nervous system
The word "rabies" is Latin for madness or rage, referring to the extreme agitation that is a symptom of the disease. Rabies has also been called hydrophobia, which means "fear of water," because of another of its symptoms: despite extreme thirst, even the sight of water produces painful spasms of the throat in people or animals with rabies.
What Is the Incidence of Rabies in Animals and Humans?
No one can reliably estimate how many animals are infected with rabies at any given time. The incidence varies greatly from country to country and from one year to the next. Among humans, however, it has been estimated that there are about 15,000 new cases of rabies each year worldwide.
In the United States and other developed countries, human rabies is very rare owing to programs to vaccinate pets and to control stray dogs. More than half of the few cases that do occur are among immigrants and returning travelers who were exposed to dogs in other countries.
Common wild animal vectors * in North America include skunks, rac-coons, foxes, and bats. Major carriers in other parts of the world include foxes in Europe, wolves in western Asia, jackals and mongooses in Africa, and bats in South America. Wild or stray dogs are major transmitters of the disease in Africa and in many countries of Asia and Latin America.
* vectors are animals or insects that carry diseases and transfer them from one host to another.
How Do Rabies Infections Occur?
Rabies in humans occurs when infected animals bite people. The rabies virus is carried in the animal's saliva and may also be transmitted to humans if the saliva enters through a break in the skin, as from a lick, or onto a mucous membrane, which is the moist lining of body openings such as the mouth or nose. In rare cases, transmission of rabies can occur by exposure to air in caves occupied by swarms of rabid bats.
After the rabies virus has entered the body, it causes the disease by traveling along nerve pathways to the brain. There it produces inflammation that brings on delirium * and the other severe symptoms of the disease.
It is almost impossible for one human being to catch rabies from another. The only time this has ever happened was when one person received a transplanted cornea (a part of the eye) from someone who had rabies.
What Are the Signs and Symptoms of Rabies?
The incubation period of rabies (the time between an animal bite or other exposure and the beginning of symptoms) averages about one to two months, although symptoms may occur as soon as 10 days after a bite or as late as one year after. Bites closer to the brain, such as to the face, tend to produce symptoms sooner than bites farther away, such as arm or leg bites.
Symptoms in humans usually begin with restlessness, loss of appetite, depression, and a mild fever. These early symptoms are soon followed by uncontrollable excitement, salivation, throat spasms, delirium, and convulsions. Coma and death from paralysis and exhaustion take place in a few days to three weeks after the onset of symptoms.
* delirium (dee-LEER-ee-um) is a condition in which a person becomes confused, is unable to think clearly, and has a reduced level of consciousness.
a Dread Disease Known to the Ancients
Rabies has been known since ancient times as one of the most dreaded of all diseases. The Greek philosopher Democritus (ca. 460—370 B.C.) was the first to describe the disease, believing it to be an inflammation of the nervous system. Aristotle (384-322 B.C.) described rabies in animals. The renowned Greek physician Galen (A.D. 129-ca. 199) knew that it "follows the bite of a mad dog and is accompanied by an aversion to drinking liquids."
In modern times, the French chemist and bacteriologist Louis Pasteur (1822-1895) made medical history when, in 1885, he developed a preventive vaccine for rabies. He successfully tested his vaccine on a peasant boy, Joseph Meister, who had been bitten by a rabid dog. Although some historians have wondered whether Meister really did have rabies, this achievement made Pasteur famous and helped establish the Pasteur Institute in Paris, which conducts medical teaching and research. Joseph Meister worked at the Pasteur Institute for many years.
In animals such as dogs, the incubation period is shorter. Signs include excitability, ferocity and biting, a hoarse bark followed by low howls, or complete loss of voice. Wild animals that normally avoid humans may be fearless toward them and appear agitated. Normally night-active animals may be active in daylight.
How Do Doctors Diagnose Rabies?
A doctor should be contacted immediately following an animal bite, and the wound should be washed out with soap and water. Because rabies is a fatal disease if left untreated, immediate medical attention is required. Doctors can diagnose rabies by observing its most severe symptoms and signs, but there is not yet a laboratory test available to detect rabies before it reaches the central nervous system.
Diagnosis is of special importance in animals. If an animal that has bitten someone can be captured and appears rabid, it is killed and its brain tissue is examined for evidence of rabies infection. If rabies is found, the person who has been bitten must receive protective rabies vaccine.
How Do Doctors Treat and Prevent Rabies?
Preventive therapeutic measures before symptoms appear are the only reliable form of treatment. After symptoms begin, there is almost no treatment that can lead to a cure. Sedative * and painkilling drugs may be given, but only a very small number of people who were given aggressive intensive care to maintain vital functions have survived rabies infection.
Preventive treatment is called "post-exposure immunization." People who are immunized shortly after being bitten can be sure that they will be protected against rabies. Immunization consists of a series of vaccinations administered over several weeks, but it may or may not be given to a person who has been bitten by an animal. It is given if doctors and local public health authorities determine that there is a risk of rabies. For example, if a wild animal such as a fox or raccoon has bitten someone and it is found or believed to have rabies, then treatment is given. On the other hand, if the biting animal is a neighbor's dog known to be healthy and wearing a tag showing up-dated rabies vaccinations, then no treatment is needed.
Preexposure immunization is given to people, such as veterinarians and forest rangers, whose work puts them at increased risk of animal bites. It is also available for campers and spelunkers (cave enthusiasts) and for people traveling in countries where rabies is a threat.
In the United States and other developed countries where there are wild animals with rabies, domestic dogs and cats are vaccinated. Control measures involving wild animals, and quarantine * of imported animals, are also important measures in rabies prevention.
* sedatives are medications that calm people and reduce excitement and irritability.
* quarantine is the confining of a person or animal possibly carrying a contagious disease until it is clear that there is no infection.
Public education efforts stress the importance of vaccinating domestic animals and avoiding contact with wild animals. Young children, in particular, need to be told not to approach or pet wild animals.
Finley, Don. Mad Dogs: The New Rabies Plague. College Station: Texas A&M University Press, 1998. Describes in nontechnical language the present-day outbreaks of rabies and methods being used to combat them.
Silverstein, Alvin, Virginia B. Silverstein, and Robert A. Silverstein. Rabies (Diseases and People). Hillside, NJ: Enslow Publishers, 1994. Provides general information for young adults, supplemented with many case studies.
The U.S. National Institute of Allergy and Infectious Diseases posts a
fact sheet about rabies at its website.
Travel Health Online posts traveler information about rabies preexposure
at its website.