Rabies is a viral zoonotic disease that causes acute encephalitis in animals. In non-vaccinated humans, rabies is almost invariably fatal after neurological symptoms have developed, but prompt post-exposure vaccination may prevent the virus from progressing. Cats, dogs, ferrets, raccoons, skunks, foxes, wolves, coyotes, bears, bats, and horses can become rabid. Squirrels, chipmunks, other rodents (except beavers), and rabbits are very seldom infected. The virus is usually present in the saliva of a symptomatic rabid animal; the route of infection is nearly always by a bite, and in many cases in animals, causes the victim to be exceptionally aggressive, attack without provocation, and exhibit otherwise uncharacteristic behavior. Rabies may also be present in a so-called "paralytic" form, rendering the victim abnormally quiet and withdrawn.