Contributor: Gordon K. Klintworth
Rabies (hydrophobia, lyssa)(Greek: lyssa  = madness) is an extremely serious lethal acute encephalomyelitis caused by the rabies virus. This viral infection affects animals and humans and continues to be a significant public health problem, particularly in some parts of the world. The virus is usually spread by the saliva from a bite of an rabid animal (especially dogs and bats). Animal rabies is prominent in certain wild animals such as the raccoon, bat and skunk in the USA and the red-fox in Europe. The virus is excreted in the saliva and the bite of an infected animal is an important mode of transmission. Cases of rabies have been spread in recipients of corneal grafts from donors that died of rabies.
After a prolonged incubation period (usually 30-90 days, but sometimes >1 year) the central nervous system becomes infected. A distinct fear of drinking is conspicuous and often dominant manifestation of the acute phase of the disease. It results from the choking, gagging and laryngeal spasms that can be triggered by drinking liquids. Following the central nervous infection the virus spreads centifugally along autonomic and sensory nerves to extraneural organs, including the salivary glands, gastrointestinal tract, heart, tongue, adrenal gland and larynx.  Rabies can be diagnosed in paraffin embedded tissue with the immunoperoxidase stain using a mouse monoclonal antirabies antibody. Death usually comes <7 days after the onset of neurological manifestations. A diagnostic feature of the encephalitis is the Negri body within certain neurons, such as the Purkinje cells of the cerebellum and the large pyramidal neurons of  Ammon's horn.