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Rabies

A viral disease that is fatal in humans if not treated immediately. It typically spreads to humans from animals through a scratch or a bite and causes inflammation of the brain.

Although the vaccine first used in 1885 is widely used today, fatalities from rabies still occur. Most fatalities take place in Africa and Asia, but some also happen in the United States. Prevention of rabies in the United States can cost as high as $ 1 billion per year.

From animal to human

While many animal diseases cannot be passed from animal to humans, rabies can, and since ancient times it has been known as an easy traveler from one species to the next. The very name rabies, Latin for "rage" or "madness," suggests the fear early men and women must have had for the disease. For centuries no treatment existed, and the disease was left to run a rapid course leading to death.

This changed in 1885, when French scientist Louis Pasteur saved the life of a nine-year-old boy who had been attacked by a rabid dog. Pasteur used a live virus vaccine made from spinal cords of infected rabbits. To be effective, the vaccine needed to be administered 14 to 21 times.

The vaccine has since been refined and improved many times. Currently, two rabies vaccines are used in the United States. Yet rabies continues to plague most underdeveloped parts of the world, particularly regions without access to health care.

Rabies is caused by a number of different viruses that vary depending on the 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 comes in contact with broken skin or a mucous membrane. Initially, the virus begins to reproduce itself in muscle cells near the place of first contact. At this point, within the first five days or so, treatment by vaccination has a high rate of success.

Once the rabies virus passes to the central nervous system, immunization is no longer effective. When it moves into the brain, it replicates itself there before finally moving to other tissues such as the heart, lungs, liver, and salivary glands. Symptoms appear when the virus reaches the spinal cord.

Since rabies symptoms for humans and animals mirror each other, sick animals are an excellent guide to understanding the disease. The common symptoms are muscle spasms, confusion, sensitivity to bright light, and fever. In addition, a fear of water and so-called foaming of the mouth, a symptom that occurs due to difficulty in swallowing and abnormally active salivation, are present. The incubation period from the time one is exposed to rabies to the time the disease develops is usually one to two months, but it can take as long as seven years for symptoms to make their appearance.

Dogs, cats, and bats

The likelihood that certain animals will contract rabies varies from one location to the next. Dogs are one example. In areas where public health efforts to control rabies have been aggressive, dogs make up less than 5% of rabies cases in animals. These areas include the United States, most European countries, and Canada. However, dogs are the most common source of rabies in many countries. They make up at least 90% of reported cases of rabies in the developing countries of Africa, Asia, and many parts of Latin America. In these countries, public health efforts to control rabies have not been as aggressive. Other key carriers of rabies include the fox in Europe and Canada, the jackal in Africa, and the vampire bat in Latin America.

In the United States, raccoons comprised 60% of all reported rabies cases. A total number of 4,311 rabid raccoons was reported in 1992. The high number of these cases suggests an animal epidemic, or epizootic. The epizootic began when diseased raccoons were carried further south from Virginia and West Virginia. Since then, rabies in raccoons has spread up the eastern seaboard of the United States. Concentrations of animals with rabies include coyotes in southern Texas, skunks in California and in south and north central states, and gray foxes in southeastern Arizona. Bats throughout the United States also develop rabies. When rabies first enters a species, large numbers of animals die. When it has been exposed for a long period of time, the species adapts, and smaller numbers of animals die.

Rabies in humans

Few deaths from rabies have occurred in the United States in recent years. Between 1980 and the middle of 1994, a total of 19 people in the United States died of rabies, which, by comparison, is far fewer than the 200 Americans killed by lightning during the same period. Eight of these cases were acquired outside the United States, and of the 11 cases contracted in the United States, eight stemmed from bat-transmitted strains of rabies. Internationally, the statistics are much higher. According to the World Health Association, more than 33,000 people die each year from rabies. A majority of these cases stem from dog bites.

Different countries employ different strategies in the fight against rabies. The United States depends primarily on vaccination of domestic animals and on immunization following exposure to possibly rabid animals. In Great Britain, where rabies has never been established, a strict quarantine for all domestic animals entering the country is utilized.

Continental Europe, which has a long history of rabies, developed an aggressive program in the 1990s of airdropping a new vaccine for wild animals. The laboratory-engineered, live vaccine is mixed with pellets of food for red foxes, the primary carrier there. Public health officials have announced that fox rabies may be eliminated from western Europe by the end of the decade. The World Health Organization now intends to use the vaccine in parts of Africa. Trials of the new vaccine have also been conducted in the United States. However, concern over the cost of distributing the vaccine across large areas of the United States has prohibited extensive use of the substance. Such concerns also reflect the limited loss of human life due to rabies in the United States.

Although the United States has been largely successful in controlling rabies in humans, the disease remains present in the animal population. This is a constant reminder of the serious threat rabies could become without effective, on-going prevention.

For Further Study

Books

Kaplan, Colin, G.S. Turner, D. A. Warrell. Rabies: The Facts. (2d ed.) New York: Oxford University Press, 1986.

Rabies: A Warm Weather Hazard. Washington, DC: Department of Health and Human Services, 1987.

Smith, Jane S. Patenting the Sun. New York: William Morrow and Company, Inc., 1990.

Periodicals

Browne, Malcolm W. "Rabies, Rampant in U. S., Yields to Vaccine in Europe." The New York Times, July 5, 1994, p. Cl.

Cantor, Scott B., Richard D. Clover, and Robert F. Thompson. "A Decision-Analytic Approach to Postexposure Rabies Prophylaxis." American Journal of Public Health 84, no. 7. July 1994, pp 1144-48.

Clark, Ross. "Mad Dogs and Englishmen." The Spectator, August 20, 1994, pp. 16-17.

Corey, Lawrence. "Rabies, Rhabdoviruses, and Marburg-Like Agents." In Harrison's Principles of Internal Medicine 1. Edited by Kurt J. Isselbacher, et al. 13th ed. New York: McGraw-Hill Inc., 1994.

Fishbein, Daniel B., and Laura E. Robinson. "Rabies." The New England Journal of Medicine 329, no. 22, November 25, 1993, pp. l632-38.

—Karen L. Rice, M.A.