Rabies is a viral disease that can affect all warm-blooded mammals, including cats, dogs, wildlife and humans. The virus infects cells of the nervous system, producing incoordination and behavioral abnormalities, such as unusual aggression or withdrawal. Once the signs of rabies appear, the disease is always fatal. Rabies is usually transmitted by bite wounds, often from infected wildlife, which represent the largest reservoir of the disease in the U.S. Vaccines are very effective in preventing rabies. Most states in the U.S. require rabies vaccination of dogs at 1 to 3-year intervals. Many states also require rabies vaccination of cats.