Eastern equine encephalitis occurs in eastern and southeastern United States; western equine and California encephalitis occur throughout the West; and St. Louis encephalitis occurs throughout the country.
Because of the rarity of Reye's syndrome, it is often misdiagnosed as encephalitis, meningitis, diabetes, or poisoning, and the true incidence may be higher than the number of reported cases indicates.
An increase in WBCs may occur in many conditions, including infection (viral, bacterial, fungal, and parasitic), allergy, leukemia, hemorrhage, traumatic tap, encephalitis, and Guillain-Barré syndrome.
Although only one in 1,000 patients with measles will develop encephalitis, 10 to 15 percent of those who do will die, and about another 25 percent will be left with permanent brain damage.
An infection of the membrane covering the brain (meningitis) or an inflammation of the brain itself (encephalitis) cause swelling that in turn may cause brain damage and mental retardation.