infections of the brain caused by arthropod-borne viruses primarily from the families togaviridae, flaviviridae, bunyaviridae, reoviridae and rhabdoviridae; life cycles of these viruses are characterized by zoonoses, with birds and lower mammals serving as intermediate hosts; the virus is transmitted to humans by the bite of mosquitoes or ticks; clinical manifestations include fever, headache, alterations of mentation, focal neurologic deficits, and coma.
The symptoms of encephalitis lethargica can be variable, but the illness usually starts with a high fever, headache and sore throat. Double vision, disturbance of eye movements, weakness of the upper body, tremors and strange movements, neck stiffness, intense muscle pains, a slowing of physical and mental response, drowsiness and lethargy soon follow.
Many people believe a virus or other type of infection may be to blame for encephalitis lethargica, but there's currently no good evidence to suggest any particular organism. Some researchers have suggested it might be an autoimmune disease, where the body's immune system is triggered by a throat infection (perhaps with a Streptococcus-like bacteria) to attack the nervous system. Research shows that areas of the brain called the mid-brain and basal ganglia become inflamed during the illness. But while antibrain antibodies can be detected, no viruses have been found.
There's no cure for encephalitis lethargica, but treatment is targeted at supporting the person through their illness and dealing with the symptoms as they occur. In the early stages, treatment in an intensive care unit may be necessary to keep the person breathing, fed and protected from other infections, especially if they're in a coma. Steroid drugs may help to reduce inflammation in the brain.