Microbiology

Rabies. Rabies is a viral disease of the brain that has a mortality rate approaching 100 percent. The agent is an RNA virus of the family Rhabdoviridae. Transmitted from warm‐blooded animals, the rabies virus affects the brain, causing neurological distress and paralysis in muscles. Paralysis of the swallowing muscles results in hydrophobia, the fear of water. Immunization with inactivated viruses may be rendered after the virus has been transmitted in a bite. Four or five inoculations in the shoulder muscle are sufficient to induce immunity and prevent the development of symptoms. Pre‐exposure vaccination is also possible.

Encephalitis. Encephalitis is an inflammation of the brain tissue, usually due to any of a variety of RNA‐containing viruses. Among the kinds of encephalitis are eastern equine encephalitis (EEE), western equine encephalitis (WEE), and Venezuelan eastern equine encephalitis (VEEE). All are transmitted from horses by arthropods such as mosquitoes. Other forms of encephalitis include St. Louis encephalitis, California encephalitis, and La Crosse encephalitis. Patients suffer fever and severe headache, and fatalities are common. Control consists of killing the arthropods that transmit the viruses.

Poliomyelitis. Poliomyelitis (or polio) is a nervous system disease caused by an RNA virus belonging to the Picornaviridae family. The virus is usually transmitted by contaminated food and water and causes intestinal distress. Viruses then reach the central nervous system and may cause meningitis or paralysis if they reach the spinal cord. Prevention is available with the inactivated virus vaccine (Salk) or the attenuated virus vaccine (Sabin). Both vaccines contain the three known strains of polio virus. Postpolio syndrome may occur in patients who experienced polio many years before. Weakened muscles and local paralysis characterize this condition.