Rabies in humans can be difficult to diagnose. After symptoms start, tests that can be done include:

• Direct fluorescent antibody (DFA) test. This common, rapid test detects the rabies virus protein. DFA testing is done by taking a sample of tissue from the potentially affected area.
• Polymerase chain reaction (PCR) assay. This test detects the genetic material (DNA) of the rabies virus proteins. PCR testing is very accurate and can be done on saliva, cerebrospinal fluid, or tissue.

To find out if a person was exposed to the rabies virus, the animal must be tested. Diagnosis in animals also is difficult. A lab exam of the animal's brain tissue is needed. Animals that show signs of abnormal behavior but can't be tested often are assumed to be rabid. (For more information, see the Symptoms section of this topic.) The risk that an animal is infected with the rabies virus is based on:

• The type of animal. Some animals are more likely to carry rabies than others. Bats, skunks, raccoons, foxes, and coyotes are common carriers of the rabies virus.
• The behavior of the animal, such as excessive drooling or aggression.
• Risk for rabies in a specific geographic area. Your local health department will have information about the risk of rabies in your area.
• The date of the animal's last rabies vaccination.

If you have been bitten by or exposed to a potentially rabid animal, you may be given a series of shots while you are waiting for test results. These shots are given to help prevent you from getting rabies before tests confirm whether or not you have been exposed to it.

Bites from or exposure to a low-risk animal

If you are bitten by or exposed to an animal at a low risk for having rabies, such as a domestic dog, cat, or ferret, the animal should be captured by authorities specifically trained to capture rabid animals, quarantined, and observed for 10 days.

• If the animal does not show signs of rabies in that time span, the animal is assumed to be free of rabies at the time of the bite, and you will not need treatment.
• If the animal starts having signs of rabies or dies in that time span, you will begin preventive treatment for the disease. An animal with signs of rabies will be killed (euthanized), and its brain tissue will be tested to confirm whether it had rabies. It takes only a few hours to test the brain tissue after it is received by the appropriate lab. If the test results show that the animal does not have rabies, you can stop preventive treatment.

Bites from or exposure to a high-risk animal

If you are bitten by or exposed to an animal that you think may have rabies, contact your local health department immediately. Trained personnel will attempt to safely capture the animal. The animal may be observed or killed (euthanized), depending on your local health department policy. If the animal is euthanized because of its high risk for having rabies, its brain tissue will be examined. You probably will undergo preventive treatment until testing on the animal can be completed.

• If the animal does not have rabies, you can stop preventive treatment.
• If the animal has rabies, you need to complete treatment.