Mad dogs oftentimes had rabies and a bite or scratch from one would mean almost certain death. The Rabies virus attacks the nerve cells in the spinal cord and brain. Depending on where the person is bitten it can take from 20-60 days for symptoms to occur. The virus destroys the nerves in the spinal cord causing paralysis and mental delusions. A person with rabies is eventually unable to swallow properly and as a result develops a fear of water.
Hydrophobia is another name for rabies.
Eventually, the virus destroys the part of the brain that controls breathing and the person dies. Only 3 people have ever survived rabies once symptoms of the viral infection begin. Many people have been sucessfully treated to prevent the virus from destroying the person's nervous system. Therefore, in this disease prevention is key to avoiding rabies infections and disease. Rabies can infect almost all mammals.