Rabies is a viral infection of the brain that is transmitted by animals and that causes inflammation of the brain and spinal cord. Once the virus reaches the spinal cord and brain, rabies is fatal.

• The virus can be transmitted when people are bitten by an infected animal, usually a wild animal.
• Rabies can cause restlessness and confusion or paralysis.
• A skin biopsy can detect the virus.
• Infection can be prevented by immediately cleaning the wound and by injecting rabies vaccine and immune globulin.

From the point of entry (usually a bite), the rabies virus travels along nerves to the spinal cord and then to the brain, where it multiplies. From there, it travels along other nerves to the salivary glands and into the saliva. Once the rabies virus reaches the spinal cord and brain, rabies is fatal. However, the virus takes at least 10 days—usually 30 to 50 days—to reach the brain (how long depends on the bite's location). During that interval, measures can be taken to stop the virus and help prevent death.

Rabies causes an estimated 55,000 deaths worldwide each year. Most deaths occur in rural areas of Asia and Africa. In the United States, only a few people die each year.

Causes

The rabies virus is present in many species of wild and domestic animals throughout most of the world. Animals with rabies may be sick for several weeks before they die. During that time, they often spread the disease.

The rabies virus, which is present in the saliva of a rabid animal, is transmitted when the animal bites or, very rarely, licks another animal or a person. The virus cannot pass through intact skin. It can enter the body only through a puncture or another break in the skin or through the nose or mouth when many airborne droplets containing the virus are inhaled (as can occur in a cave that contains infected bats).

Many different mammals—such as dogs, cats, bats, raccoons, skunks, and foxes—can transmit rabies to people. Rabies rarely affects rodents (such as hamsters, guinea pigs, gerbils, squirrels, chipmunks, rats, and mice), rabbits, or hares. In the United States, these animals have not been known to cause rabies among people. Rabies does not affect birds and reptiles.

In the United States, vaccination has largely eliminated rabies in dogs, and the source of rabies is almost always wild animals, usually bats. In many cases, the bat bites are unnoticed. Most deaths due to rabies result from being bitten by an infected bat.

Worldwide, during the last 30 years, most people who have contracted rabies were bitten by rabid wild animals. In most countries of Latin America, Africa, Asia, and the Middle East (where vaccination of dogs is not widespread), rabies in dogs is fairly common, and dogs are responsible for most deaths due to rabies.

Symptoms

The wound from the bite may be painful or numb. Bat bites typically cause no symptoms.

Symptoms appear when the rabies virus reaches the brain or spinal cord, usually 30 to 50 days after a person is bitten. However, this interval can vary from 10 days to more than a year. The closer the bite to the brain (for example, on the face), the more quickly symptoms appear.

Rabies may begin with a fever, headache, and a general feeling of illness (malaise). Most people become restless, confused, and uncontrollably excited. Their behavior may be bizarre. They may hallucinate and have insomnia. Saliva production greatly increases. Spasms of the muscles in the throat and larynx occur because rabies affects the area in the brain that controls swallowing, speaking, and breathing. The spasms can be excruciatingly painful. A slight breeze or an attempt to drink water can trigger the spasms. Thus, people with rabies cannot drink. For this reason, the disease is sometimes called hydrophobia (fear of water).

As the disease spreads through the brain, people become more confused and agitated. Eventually, coma and death result. The cause of death can be blockage of airways, seizures, exhaustion, or widespread paralysis.

In 20% of people, rabies begins with paralysis of the limb that was bitten. The paralysis then moves through the body. In these people, thinking is typically unaffected, and most of the other symptoms of rabies do not develop.

Did You Know... In the United States, people who are bitten by rabbits and most small rodents—such as hamsters, gerbils, squirrels, rats, and mice—almost never need a rabies vaccination. Bats are responsible for most deaths due to rabies in the United States.

Diagnosis

Doctors suspect rabies when people have a headache, confusion, and other symptoms of the disease, especially if people have been bitten by an animal or exposed to bats (for example, if they were exploring a cave). However, many people with rabies are unaware of having been bitten by an animal or exposed to bats. A sample of skin is taken (usually from the neck) and examined under a microscope (skin biopsy) to determine whether the virus is present. Samples of saliva and urine are also examined to check for the virus. A spinal tap (lumbar puncture) is done to obtain a sample of cerebrospinal fluid, which is also examined. A variation of the polymerase chain reaction (PCR) technique, which produces many copies of a gene, is often used to identify the bacteria's unique DNA sequence. Several samples of these fluids, taken at different times, are tested to increase the chances of detecting the virus.

Treatment

After symptoms develop, no treatment can help. The infection is virtually always fatal. Treatment involves relieving symptoms and making people as comfortable as possible.

Prevention

Before an Animal Bite: Avoiding being bitten by animals, especially wild animals, is best. Pets that are not known and wild animals should not be approached. Signs of rabies in wild animals may be subtle, but their behavior is typically abnormal, as in the following:

• Wild animals may not appear vicious, shy, or afraid when people approach them.
• Nocturnal animals (such as bats, skunks, raccoons, and foxes) are out during the day.
• Bats make unusual noises or have difficulty flying.
• Animals bite without being provoked.
• Animals are weak or agitated and vicious.

An animal that may be rabid should not be picked up to try to help it. A sick animal often bites. If an animal appears sick, people should call local health authorities, who can help remove it.

People who are likely to be exposed to the rabies virus should be given an injection of the rabies vaccine before exposure. Such people include veterinarians, laboratory workers who handle animals that may be rabid, people who live or stay more than 30 days in developing countries where rabies in dogs is widespread, and people who explore bat caves. Vaccination protects most people to some degree for the rest of their life. However, protection decreases with time, and if exposure is likely to continue, people should get a booster dose of vaccine every 2 years.

After an Animal Bite: Immediately after being bitten, people should clean the wound thoroughly with soap and water. Deep puncture wounds are flushed out with running water. Then people should see a doctor. Doctors clean the wound further with an antiseptic called benzalkonium chloride. They may trim ragged edges of the wound.

Who Should Receive the Rabies Vaccine?
In the United States, the decision to give the rabies vaccine to a person who has been bitten by an animal depends on the type and status of the animal. For people bitten by a pet dog, cat, or ferret: If the animal appears healthy and can be observed for 10 days, the vaccine is not given unless the animal develops symptoms of rabies. If the animal develops any symptom suggesting rabies, people are given vaccine immediately. Animals that develop symptoms of rabies are put to sleep (euthanized), and their brain is examined for the rabies virus. If the animal is still healthy after 10 days, it did not have rabies at the time of the bite, and vaccine is not needed. If an animal has or appears to have rabies, the vaccine is given immediately. If the status of an animal cannot be determined—for example, because it escaped—public health officials are consulted to determine how likely rabies is and whether the vaccine should be given. For people bitten by skunks, raccoons, foxes, most other carnivores, or bats: Such an animal is considered rabid unless it can be tested and the results are negative. Usually, the vaccine is given immediately. Waiting to observe wild animals for 10 days is not recommended. Because people may not notice a bat bite, they are given the vaccine if a bite seems possible. For example, if someone awakens and a bat is in the room, the vaccine is given. For people bitten by livestock, small rodents, large rodents (such as woodchucks and beavers), rabbits, or hares: Each biting incident is considered individually, and public health officials are consulted. People who are bitten by hamsters, guinea pigs, gerbils, squirrels, chipmunks, rats, mice, other small rodents, rabbits, or hares almost never require rabies vaccination.

Doctors also try to determine the likelihood that rabies was transmitted. Early determination is essential because rabies can usually be prevented if appropriate measures are taken promptly.

No test can determine whether the rabies virus has been transmitted immediately after an animal bite. Thus, people who have been bitten may be given immune globulin and vaccine by injection to prevent rabies. Rabies immune globulin, which consists of antibodies to the virus, provides protection immediately but only for a short time. The rabies vaccine stimulates the body to produce antibodies to the virus. The vaccine provides protection that begins more gradually but that lasts for a much longer time.

Whether vaccine and immune globulin are needed depends on whether people have been previously immunized with rabies vaccine and what the type and status of animal are. For example, doctors determine the following:

• Whether the animal was a dog, a raccoon, or something else
• Whether it appeared sick
• Whether the attack was provoked
• Whether the animal is available for observation

If people need preventive treatment and have not been immunized previously, they are given rabies immune globulin and rabies vaccine right away (on day 0). Immune globulin is injected around the wound if possible. They are given four more injections of the vaccine on days 3, 7, 14, and 28. The injection site may be painful and swollen but usually only slightly. Serious allergic reactions are rare.

If people have already been vaccinated, the risk of developing rabies is reduced. However, the wound must be cleaned promptly, and an injection of rabies vaccine is given immediately and on day 3.

Last full review/revision May 2008 by Michael Jacewicz, MD