Rabies is an acute viral disease that can be transmitted from wild animals to unvaccinated pets and livestock, as well as to humans. It is caused by the rabies virus, which is present in the saliva of infected animals, and is transmitted through infected secretions (usually through the bite of a rabid animal). Once infection occurs, the virus spreads to the central nervous system and causes inflammation in the brain (acute encephalitis). Rabies is almost always fatal.

Effective pet vaccinations, postexposure treatment for humans, and effective animal control have nearly eliminated rabies in dogs in the United States. In parts of the world where vaccinations and postexposure treatment are not available, rabies remains a serious health threat for animals and for humans. Rabies kills more than 35,000 people every year, mostly in Asia, Africa, and Latin America.

Incidence

Rabies occurs worldwide, affecting pets and wildlife. Overall prevalence is low in most places, but in some areas, the virus poses a serious threat to animals and humans. In the Northeastern United States, rabies has been epidemic among raccoons since the late 1970s.

More than 50% of all rabies cases in the United States involve raccoons. Skunks (22.5%), foxes (6.5%), and insectivorous bats (10%) are other common carriers. Rabies is rarely found in smaller mammals such as rabbits, squirrels, rats, and opossums. Domestic animals account for less than 10% of all cases in the United States.

Rabies remains a serious problem among domestic animals in certain parts of Latin America, Africa, and Asia. Mongooses and vampire bats are common carriers in these areas.

There are rabies-free countries, where the disease has either never been recorded or has been eradicated through strict quarantines and prevention programs. These areas include the British Isles, Australia, New Zealand, Hawaii, Japan, and parts of Scandinavia. Dogs and cats entering rabies-free countries are usually required to be quarantined for about 6 months, allowing time to observe the animal for behavioral signs of rabies.

In the United States, rabies is rare, but probably under diagnosed in humans. There were 32 laboratory-confirmed cases of rabies in humans between 1980 and 1996. It is believed that most of these cases occurred as a result of bat bites and dog bites that occurred in foreign countries. Human rabies is most prevalent in Asia, particularly India.

Cause

Rabies virus is in the Rhabdoviridae family. The virus cannot live outside its host's body for more than a couple of seconds, but live virus has been found in animals that have been dead as long as 48 hours.

Transmission

Rabies usually is transmitted through infected saliva as a result of a bite from an infected animal. Rarely, it is transmitted by viral contamination of a fresh wound, through a scratch, or through contamination of a mucous membrane (i.e., eyes, nose, mouth). There have been reports of rabies being transmitted through the air in bat-infested caves.

Testing

Though the behavioral symptoms of rabies are classic, a diagnosis based solely on the symptoms can be difficult because they are similar to other diseases, conditions, and complications. The inability to swallow, for example, could be caused by an object lodged in the throat. Many factors can trigger aggressive, strange behavior and many animals are easily provoked when injured.

The only way to be 100% sure that an animal is rabid is to perform a direct fluorescent antibody test (dFA) on the brain tissue, which requires that the animal be euthanized. This is the most rapid and reliable test for rabies and it has been used for more than 40 years.

The dFA test is based on the principle that infected animals have rabies virus antigen (a protein) in brain tissue that reacts to antirabies antibodies (proteins produced by the immune system to fight disease and infection). The test involves inserting fluorescently labeled antirabies antibody molecules into the brain tissue, which bind to the rabies virus antigens and give off a bright glow when viewed through a special fluorescent microscope. A dFA test can also detect the presence of rabies antigens in the skin.

Tests that do not require euthanasia can be used to examine serum, spinal fluid, and saliva, but none of them can rule out rabies with 100% certainty. These tests are used only in humans and animals that cannot be euthanized.

Pets suspected of having rabies must be diagnosed as early as possible, especially if people have been exposed to the animal. Rabies is a fatal disease. Humans who have been exposed can be treated with safe postexposure prophylaxis, but only if it is administered before the person begins showing symptoms.

Treatment

If a rabid animal bites an unvaccinated cat or dog, the cat or dog must be quarantined immediately. Local health officers determine the length of time and conditions of the quarantine.

If a rabid animal bites a vaccinated cat or dog, the cat or dog should be immediately revaccinated and observed for up to 60 days, depending on local regulations.

If a vaccinated cat or dog bites a person, the animal should be quarantined for 10 days, to be observed for signs of rabies. If it shows signs of rabies within 10 days, it should be euthanized and submitted for rabies testing. If the animal remains healthy for 10 days, it may not have been infected when it bit the person. If the animal shows behavioral symptoms of rabies within those 10 days, the virus was present in the saliva when the animal bit the person.

If a stray or unvaccinated cat, dog, or other animal bites a person, the animal should be immediately euthanized and submitted for rabies testing. Unvaccinated people should receive postexposure treatment within 48 hours. Each year in the United States, 40,000 people receive postexposure treatment, which involves immediate cleansing of the wound and injection of human rabies immune globulin into the wound site and one other site (e.g., the buttocks). At the same time, a series of five injections of vaccine are administered. The local public health official should also be notified.

Prevention

The most effective way to prevent rabies in pets is through vaccination. Safe, effective vaccines are available for dogs, cats, horses, cattle, and sheep. All dogs and cats should be vaccinated after 12 weeks of age, one year later, and then every 2 years. Vaccinated cats and dogs should wear rabies tags, and their owners should keep their rabies certificates. Rabies shots should be administered by a licensed veterinarian.

Pet owners in the Northeastern United States, where rabies is epidemic among raccoons, should be especially diligent in vaccinating all cats and dogs. Any unvaccinated pet that comes into contact with a rabid animal is at risk for rabies.

Rabies poses a serious health threat to humans. People who have frequent contact with animals (e.g., pet groomers, zookeepers) should get a pre-exposure rabies vaccination. Do not keep skunks, foxes, raccoons, or bats as pets; they cannot be vaccinated and are susceptible to rabies. Avoid animals that seem to be behaving abnormally, especially wild animals that seem too friendly.

More information about rabies?

Learn more about rabies at CDC's Rabies site, and Rabies Kids Rabies Home Page which includes questions and answers, prevention and control information, and more.