Rabies is a serious disease. It is caused by a virus Rabies is mainly a disease of animals. Humans get rabies when they are bitten by infected animals. At first, there might not be any symptoms. But weeks, or even months after a bite, rabies can cause pain, fatigue, headaches, fever, and irritability. These are followed by seizures, hallucinations, and paralysis. Human rabies is almost always fatal.