RABIES

DEFINITION

Rabies is a rare but serious disease caused by a virus. The virus that causes rabies is carried in saliva. It is transmitted when an infected animal bites another animal. Rabies affects humans and other mammals.

Another name for rabies is hydrophobia (pronounced HI-dro-fo-bee-uh). Hydrophobia means "fear of water." About half the people infected with rabies develop this symptom. Other symptoms include fever; depression; confusion; painful muscle spasms; sensitivity to touch, loud noise, and light; extreme thirst; painful swallowing; excessive salivation; and loss of muscle quality. Rabies can be prevented and treated by immunization (a protective treatment that causes the body's immune system to build up resistance to a particular disease; usually given as a shot). Without treatment, however, a person who is infected with rabies will almost certainly die.

DESCRIPTION

Worldwide, approximately fifteen thousand cases of human rabies occur each year. Remarkably, although more than one million persons in the United States are bitten each year by animals, only one or two die of rabies each year. Nonetheless, rabies is likely to remain a public-health problem in the future. Humans are continually moving into lands occupied by wild animals. As they do, they run the risk of being bitten by an animal with rabies.

Both domestic and wild animals can transmit rabies. At one time, domestic animals, such as cats and dogs, were the main source of rabies bites in the United States. In 1955, 47 percent of all reported rabies cases were caused by dog bites.

That situation has changed. Most cities, towns, and counties now require that dogs be vaccinated for rabies. The number of dogs infected with the virus has dropped dramatically. In 1994, fewer than 2 percent of all dogs tested positive for the rabies virus. Today, the vast majority of rabies cases in humans are caused by bites from wild animals, such as bats, raccoons, skunks, foxes, wolves, and coyotes.

Anyone who has been bitten by an animal can contract rabies. Age and sex make no difference in people's chances of getting the disease. However, people who work in certain occupations are at higher risk for rabies than the general public. These populations include farm and ranch workers, animal trainers and caretakers, forest rangers, animal exterminators, and veterinarians. People in these occupations often handle wild animals or domestic animals that may not have been vaccinated.

CAUSES

Rabies is caused by a virus that belongs to the family Rhabdoviridae. The virus is usually transmitted by way of an animal bite. The virus is present in the saliva of an infected animal. When an infected animal bites another animal, the virus in its saliva may flow into the second animal's bloodstream. The second animal becomes infected with the virus.

On rare occasions, the rabies virus can be transmitted in other ways. It can enter an animal's body through moist tissues around the eyes or lips or through a scratch in the skin. Some scientists believe the virus can even be inhaled. For example, the air in a cave occupied by bats may contain high levels of the rabies virus. A person who walks through the cave may breathe in some of the virus.

Once it enters the body, the rabies virus travels to the nerves branching from the spinal cord and brain. It also travels to the salivary glands. The virus may lie dormant for several weeks or months. In its dormant stage, the virus is still alive, but it does not attack the body or produce any symptoms. It may continue to reproduce and spread through the body in its dormant stage. The only sign of a rabies infection at first may be a burning or painful sensation around the bite wound.

SYMPTOMS

Eventually, early symptoms of rabies begin to appear. These symptoms include a sore throat, low-grade fever (above normal, but in the lower ranges), headache, loss of appetite, nausea and vomiting, and diarrhea. Painful spasms (contractions) may develop in the muscles that control breathing and swallowing. The infected person may begin to drool thick saliva. Other symptoms include dilated (enlarged) pupils, increased flow of tears and perspiration, and low blood pressure.

As the disease progresses the patient may begin to feel excited, confused, and sensitive to bright lights, loud noises, and touch. He or she becomes very thirsty but is unable to drink because swallowing is so painful. Just looking at water can cause painful spasms. It is this reaction that accounts for the name hydrophobia. Other severe symptoms include excessive salivation, dehydration, and loss of muscle tone (quality). Death usually occurs three to twenty days after symptoms first appear. Once a person or animal has developed rabies, recovery is very rare.

DIAGNOSIS

A doctor who sees these symptoms will order tests to confirm the diagnosis. One test is called a lumbar puncture or spinal tap. A lumbar puncture is a procedure in which a long, thin needle is inserted between the vertebrae in a person's spinal cord. A sample of the fluid surrounding the vertebrae is removed. This fluid is called cerebrospinal fluid (CSF). A lumbar puncture is important because it rules out other possible causes of the patient's symptoms.

Tests can also be performed to detect the virus or antibodies produced by the body against the virus. Antibodies are chemicals produced by the immune system. They are manufactured when some kind of foreign substance enters the body. A different kind of antibody is produced for each different foreign substance. If the rabies virus is present, the immune system will have produced a very specific kind of antibody.

Rabies virus as seen through a microscope. (Reproduced by permission of

Custom Medical Stock Photo

)

Some tests can detect the virus itself. For example, a small amount of liquid material in the cornea of the eye can be collected on a slide. The liquid can then be examined under a microscope. If the rabies virus is present in the body, it can be seen under a microscope.

TREATMENT

Any animal bite should be treated first with standard cleansing procedures. The wound should be washed thoroughly with medical soap and water. Antibiotics and tetanus injections (see tetanus entry) are usually given as well. These injections protect against bacterial infections.

The most important aspect of treatment is deciding whether a rabies immunization should be given. In some cases, the bite may have come from a domestic animal, such as a dog or a cat. If the animal is caught, it is placed in seclusion and observed. If the animal shows no signs of rabies in four to seven days, it is probably not rabid (not infected with rabies). The person who was bitten does not need a rabies immunization. If there is doubt as to whether the animal is rabid, it is killed. Its brain can then be examined to see if the rabies virus is present.

Sometimes the animal is not caught. In that case, a doctor has to decide whether to give the person who was bitten an immunization. That decision is usually based on how common rabies is in the area. If the disease is very rare, an immunization may not be necessary. If rabies is fairly common, an immunization will probably be given.

A rabies immunization usually consists of two parts. One part consists of injecting the patient with rabies antibodies taken from a person who has already been immunized. These antibodies will be of some help in destroying the rabies virus in the infected person's body. This part of the immunization process is given once, at the beginning of the treatment.

The second part of the immunization consists of injecting the patient with dead rabies viruses. These viruses will cause the patient's body to start manufacturing antibodies of its own without causing infection because they are dead. This part of the rabies immunization is given in a series of five injections, usually given one, three, seven, fourteen, and twenty-eight days after the animal bite. If successful, the antibodies from these two different sources will fight off the rabies infection.

Until the 1970s the rabies vaccination was a painful and frightening procedure that consisted of between fourteen and twenty-one shots that had to be given in the abdomen. Today the vaccine is given in the arm muscle, like a flu or tetanus shot.

Sometimes it may be too late to start immunizations. In that case, the main goal of treatment is to relieve the symptoms of the disease. For example, pain relievers can be given for painful muscle spasms. Other forms of medication can prevent seizures and relieve a person's anxiety. In the late stages of the disease, a patient may need mechanical devices to aid with breathing and heart function. Survival in such cases is rare but not unheard of.

PROGNOSIS

The key to successful treatment of rabies is timing. An infected person must begin a series of immunizations as soon as possible after being bitten. If immunizations begin within two days of the bite, chances of survival are very good. Even if the immunizations do not begin until later, there is a chance that the patient can survive. The longer the delay in starting immunizations, however, the less hopeful the prognosis for recovery is. Without immunizations, a patient will almost certainly die of the disease.

PREVENTION

Rabies can be prevented to a large extent by following some simple rules. These rules govern the way people interact with domestic and wild animals. They include:

• Domesticated animals, including household pets, should be vaccinated against rabies on a regular basis.
• Wild animals should not be touched or petted. Even if they seem friendly, they should be avoided. Special care should be taken with animals that behave strangely. For example, an animal may seem to have no fear of humans. Or animals that are normally out only at night may show up during the day. Such behaviors may be symptoms of rabies.
• Do not interfere in fights between animals.
• Use extra caution in handling a pet that has come into contact with a wild animal. Wear rubber gloves with the pet until you are sure that it has not been infected with rabies.
• Windows and doors should be covered with screens. Animals sometimes enter a building through unprotected openings. People have been bitten by rabid animals that got into their houses by this route.
• Citizens can become informed about the frequency of rabies in an area by calling the local health department.
• People who work with domestic or wild animals should be vaccinated against rabies.
• Bites from mice, rats, and squirrels rarely transmit rabies. Small animals like these that are bitten by a larger rabid animal usually die. Therefore, they are not likely to carry the disease.
• Ask about the prevalence of rabies in new areas to which you might be traveling.

FOR MORE INFORMATION

Books

Cockrum, E. Lendell. Rabies, Lyme Disease, Hanta Virus, and Other Animal-Borne Human Diseases in the United States and Canada. Tucson, AZ: Fisher Books, 1997.

Finley, Don. Mad Dogs: The New Rabies Plague. Texas Station: Texas A&M University Press, 1998.

Silverstein, Alvin, Virginia Silverstein, and Robert Silverstein. Rabies. Hillside, NJ: Enslow Publishers, Inc., 1994.

Web sites

Rabies.com. [Online] http://www.rabies.com (accessed on October 31, 1999).

"Rabies—What You Need To Know." [Online] http://www.cfainc.org/articles/rabies.html (accessed on October 31, 1999).

"Rabies." Who Information Fact Sheets. [Online] http://www.who.int/inffs/en/fact099.html (accessed on October 31, 1999).