Rabies is an acute viral disease of the central nervous system that affects humans and other mammals. It is almost exclusively transmitted through saliva from the bite of an infected animal. Another name for the disease is hydrophobia, which literally means fear of water a symptom shared by half of all people infected with rabies. Other symptoms include fever, depression, confusion, painful muscle spasms, sensitivity to touch, loud noise, and light, extreme thirst, painful swallowing, excessive salivation, and loss of muscle tone. If rabies is not prevented by immunization, it is essentially always fatal.