Rabies is a viral disease that is spread most often from the bite of a rabid animal to another animal or to a human.
The rabies virus affects the central nervous system including the brain and spinal cord of humans and animals. During the incubation period, which is the time between exposure to the virus and the appearance of symptoms, the virus travels along nerves towards the brain. This process takes at least 10 days, but may (uncommonly) take as long as 1 year. The infection causes inflammation of the brain and spinal cord that can lead to encephalopathy and, later, death. Encephalopathy is any type of disease that changes the brain's function or structure.