Hydrophobia ("fear of water") is the historic name for rabies. It refers to a set of symptoms in the later stages of an infection in which the person has difficulty swallowing, shows panic when presented with liquids to drink, and cannot quench his or her thirst. Any mammal infected with the virus may demonstrate hydrophobia.
Saliva production is greatly increased, and attempts to drink, or even the intention or suggestion of drinking, may cause excruciatingly painful spasms of the muscles in the throat and larynx. This can be attributed to the fact that the virus multiplies and assimilates in the salivary glands of the infected animal for the purpose of further transmission through biting. The infected animal's ability to transmit the virus would reduce significantly if it could swallow saliva and water.
Hydrophobia is commonly associated with furious rabies, which affects 80% of the infected people. The remaining 20% may experience a paralytic form of rabies that is marked by muscle weakness, loss of sensation, and paralysis; this form of rabies does not usually cause fear of water.