Rabies is a serious — almost always fatal — viral infection of the central nervous system. The virus is present in the saliva of infected mammals, and is most often spread via a bite wound. Raccoons, skunks, bats, foxes, and coyotes are the most common carriers of rabies in the United States, though any mammal, including domestic dogs and cats, can become infected and transmit the disease. The U.S. Centers for Disease Control and Prevention keeps statistics on rabies incidence in the U.S., and notes that cases are quite rare. Only one or two individuals a year become infected with the rabies virus, and prophylaxis (vaccination post-exposure, but prior to the development of symptoms) is almost always effective.