My seven-year-old niece was bitten on the face by the family cat. The bite was very small, with a drop of blood noted. This cat was current on its rabies vaccinations, but since the bite was unprovoked, my sister had the cat tested, and it was positive for rabies. The series of rabies shots was started within 30 hours for my niece and five other children who had been around the cat but were not known to be bitten. My sister is a nervous wreck worrying that the children will get rabies in spite of the shots. Do we have reason to worry? How common is it for a twice-vaccinated animal to get rabies? Does my niece have an increased risk since the bite was on her face? Will the shots cause health problems now or later in life?

C.A.

Human rabies is among the most serious of all infections, in that virtually all cases are fatal without preventive treatment. There have been only three confirmed survivors of the disease. The World Health Organization estimates that about 35,000 people develop and die of rabies each year worldwide. Only a few get the disease in the United States.

Almost all humans with rabies were exposed to rabid animals, and in most cases they were bitten. Rabies is common in animals, even in the United States. In the past, dogs were most responsible for transmitting the disease to humans in the United States. (This is still the case in less-developed regions of the world.) Currently, bats, raccoons and skunks are the most common sources of rabies in the United States.

The incubation period for rabies (the time between exposure to the rabies virus and disease) varies greatly, but it is between 20 and 90 days. The virus enters the body through the bite wound. It can eventually enter a nerve, where it slowly travels to the central nervous system (spinal cord and brain). Once the virus enters the nerve, the disease cannot be prevented. The location of the wound affects the length of the incubation period. It takes longer for the virus to reach the central nervous system when the bite is on a hand or foot than when the bite is on the head.

Before any obvious signs of rabies develop, the person may have pain from the bite and nonspecific symptoms such as fever, cough, nausea, vomiting and abdominal pain. Later, the person develops acute nervous-system disease, described as "furious" rabies or "paralytic" rabies. In furious rabies, the patient is hyperactive, behaves bizarrely and has spasms of the muscles of the throat and diaphragm when attempting to drink, a symptom sometimes called hydrophobia or "fear of water." In addition, there may be excess saliva production -- causing the "foaming at the mouth" that rabid animals display. Invariably, the patient falls into a coma and dies. In paralytic rabies, which occurs in a minority of patients, the patient feels relatively calm throughout most of the illness, but paralysis, coma and then death invariably develop.

If there is one good thing about rabies, it is that the disease can be prevented if a person is treated soon after being exposed to the virus. Such treatment is almost always successful. There have been no well-documented cases of human rabies when all three recommended forms of prevention have been given. The first of the preventive measures is vigorously cleaning the wound with a soap solution. The second measure is receiving disease-fighting antibodies against the rabies virus, called human rabies immunoglobulin, or HRIG. The last preventive measure is vaccination. The most common vaccine given in the United States is HDCV (for human diploid cell vaccine). This rabies vaccine, as opposed to some of the earlier ones, is quite safe, with very few serious adverse reactions reported despite millions of inoculations. The vaccine is given in the muscle or skin a total of five times over four weeks. Again, if all three methods of prevention are given, it would be highly unlikely that rabies would develop.

As far as your question is concerned, I am quite confident that your niece will not develop rabies. Although a bite on the face has a shorter incubation period than one on the hand or foot, rabies is still easily prevented. You asked about serious consequences of the vaccine, but there should be no problem. I cannot explain why the cat developed rabies, however. The vaccine for animals is highly effective, which has made human rabies rare in the United States. Even the best vaccines are not perfect, however.