Controlling Rabies : Part 2

by Food and Drug Administration (FDA)

(Page 2 of 3)

No matter where the wound, however, authorities emphasize that the first and most valuable preventive measure is thorough cleaning of the site with soap and water and immediate medical attention. If rabies vaccine treatment is called for, it should be started as soon as possible after exposure. Counting the first day of vaccine treatment as day 0, injections are administered on days 0, 3, 7, 14, and 28.

Two rabies vaccines are currently licensed for use in the United States, and both are markedly different from the crude, rabbit brain material Pasteur used more than 100 years ago. The Michigan Department of Public Health produces a vaccine in rhesus monkey cells that is used primarily in Michigan. The more widely used product, human diploid cell vaccine (HDCV), Imovax, is produced in cultures of human cells. Both vaccines are dramatically safer and more effective than Pasteur's material, but the principle at work is the same — make the patient's immune system produce antibodies to neutralize the virus before it causes disease.

In addition to vaccine, patients who have not previously been vaccinated for rabies also receive an injection of rabies immune globulin (RIG) on the day they first get the vaccine (day 0). RIG is prepared from the blood of persons who have been immunized against rabies and contains antibodies to the rabies virus. This "passive" immunity helps protect patients during the period before rabies vaccine causes their own immune systems to produce antibodies to counter the virus — so-called "active" immunity.

Certain people have a comparatively high risk of exposure to rabies. These include: veterinarians, animal handlers, cave explorers, laboratory workers who come in contact with tissue from rabid animals, and anyone who spends extended periods in areas where rabies is prevalent, such as parts of Africa, India, and Latin America. Such persons are encouraged to have preexposure immunization consisting of three vaccine injections over three to four weeks. Two years ago, FDA approved a low-dose version of HDCV for preexposure use. Booster injections are given when previously immunized persons are known to have been exposed to rabies.

Controlling Rabies in Animals

Medical and public health authorities agree that rabies prevention depends on controlling the disease in animals. That strategy became a realistic one in the 1920s with the development of a successful rabies vaccine for dogs. Vaccines for other domestic animals followed, and there are now rabies vaccines for dogs, cats, sheep, cattle, and horses. The most recent addition to this list, a vaccine for ferrets, was approved earlier this year by the U.S. Department of Agriculture, which regulates animal vaccines. Experimental vaccines for other wild animal species are under investigation.

Control of rabies in domestic animals in recent years has been remarkably successful, thanks to large-scale vaccination of pets and vigorous control of stray animals. Some 2,700 cases of rabies in dogs were reported to CDC in 1955. By 1988, the number had fallen to 128. In that year, cats, with 192 reported cases, became the major victims of rabies among domestic animals. As a result, public health authorities are concentrating efforts to make sure pet cats are properly vaccinated.

Wild animals account for nearly 9 out of 10 cases of animal rabies. While skunks are the most commonly reported rabid animal, the disease is increasing among raccoons, especially in Delaware, Maryland, Pennsylvania, Virginia, West Virginia, and the District of Columbia. Nationwide, 1,465 cases of rabies in raccoons were reported in 1988, all but 1 percent of them from the Mid- and South-Atlantic regions.

Because there is as yet no practical way to eliminate rabies in susceptible wild animal populations, public health agencies advise people to stay clear of wild animals, especially those acting in a bizarre or unusual manner. Signs that could mean rabies include: extreme aggressiveness; apparent loss of the fear of people; daytime activity in animals normally active only at night, such as bats and skunks; and lethargy in an animal that would otherwise move quickly away from other animals or people.

When such animals are sighted, they should be reported to local health authorities. Anyone who comes in direct contact with a possibly rabid animal needs immediate medical attention. Details about the potential exposure, together with information from health authorities who monitor animal rabies, allow a physician to decide whether rabies treatment is necessary.

The risk of exposure to rabies from the bite or scratch of a rabid animal — or from the contaminated air of a cave occupied by rabid bats — is difficult to quantify. But experts recognize that the risk is far from 100 percent. Yet, given the nature of rabies, few people would choose to forgo treatment and take their chances. On the other hand, no one should undergo rabies immunization needlessly. Here are the chief criteria doctors use to decide whether to begin rabies immunization:

1. Was the patient's skin broken or mucous membranes contaminated? If not, no exposure occurred.

2. If the bite was by a dog or cat, is domestic animal rabies found in the area? In many cities, even stray animals are extremely unlikely to be rabid. 3. Has the dog or cat been vaccinated against rabies?

4. Is the biting animal a healthy dog or cat and available for confinement and observation? In that case, vaccination can begin, but then be stopped if the animal shows no sign of rabies after 10 days. If the animal can be killed and its tissue examined, a highly accurate fluorescent antibody test can detect rabies in only about four hours.

5. If the bite was inflicted by a wild animal that can't be tested because it got away, is it a species likely to be rabid?

6. Was the bite provoked or unprovoked? Rabid animals are more likely to attack without provocation.

Human rabies is extremely rare in the United States, and rabies in domestic animals is far less common than it was a few decades ago. In wild animals, however, rabies is still a serious concern because it poses a threat to humans and unvaccinated domestic animals. Until science devises an effective way to eliminate the disease in wild animal populations, the price of rabies control will continue to be eternal vigilance.

About the Author

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