By Peter Galvin, MD
Rabies is a very rare but deadly disease caused by the rabies virus. Most rabies infections are due to exposure to infected saliva from an animal bite or scratch. Worldwide, dog bites are the most common source of rabies infections. Here in the U.S., however, because most dogs are vaccinated against rabies, rabies is spread to humans by bats, raccoons, skunks, and foxes. Rabies is more common in resource-poor countries, accounting for 59,000 deaths per year worldwide, but only three per year in the U.S. Initial symptoms may include fever, headache, weakness, and sometimes burning or itching at the wound site. The virus then travels to the brain and spinal cord (central nervous system or CNS) where it causes progressive CNS inflammation that results in neurological symptoms. The time frame (incubation period) between exposure and the development of neurological symptoms may be weeks to months, depending on both the specific type of rabies virus and the distance between the wound and the brain. Symptom onset also depends on whether or not the exposed individual has been vaccinated against rabies.
There are two forms of rabies: encephalitic, which accounts for 75% of U.S. cases, and paralytic. Encephalitic rabies presents with agitation, confusion, and a fear of water (since swallowing can cause intense throat spasms). Paralytic rabies presents with muscle weakness, paralysis, and coma. Death occurs in almost 100% of cases because there are no effective treatments once the virus infects the CNS. Rabies is diagnosed by a history of exposure to an infected animal along with detection of the virus in saliva, blood, skin, or cerebrospinal fluid. In the U.S., rabies testing is done only after consultation with the state or local health department. People in the U.S. should not feed or approach wild animals, and in other countries, they should also avoid stray dogs.
Preexposure prophylaxis with a series of rabies vaccinations can prevent rabies in people at high risk of infection, such as people who work directly in contact with the rabies virus or those at increased risk of exposure to wild animals (e.g., veterinarians and people who frequently explore caves [spelunkers]). Postexposure prophylaxis after a bite or scratch from a potentially rabid animal blocks the virus from entering the CNS, thus preventing the development of rabies. This is done with injections of human rabies immune globulin (rabies antibodies) and rabies vaccine. Both should be given as soon as possible after exposure, ideally on the same day as the exposure. Usually, three additional does of rabies vaccine is given within 14 days of the first vaccine. Animal bites or scratches should immediately be cleansed with soap and water. Individuals who may have been exposed to an animal with rabies should seek immediate medical attention. If possible, the responsible animal should be caught and tested. If the animal tests negative, then obviously postexposure prophylaxis unnecessary.
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