Encephalitis, an inflammation of parts of the brain, spinal cord and meninges, causes
headache, stiff neck, fever and altered mental status. It can result from infection with
a number of different agents including viral, parasitic, fungal, rickettsial,
bacterial and chemical. Public health surveillance is limited to cases of suspected
or confirmed viral etiology, which includes primary and post-infectious
encephalitisóbut excludes individuals with underlying Human Immunodeficiency
Virus (HIV) infection. Of special concern is arboviral (mosquitoborne) encephalitis,
which can be prevented by personal protection and mosquito control (See WNV section).
Arthropod-borne viruses, i.e., arboviruses, are viruses that are maintained in
nature through biological transmission between susceptible vertebrate hosts by
blood feeding arthropods (mosquitoes, ticks, and certain mites and gnats). All arboviral encephalitides are zoonotic, being maintained in complex life cycles
involving a nonhuman vertebrate primary host and a primary arthropod vector.
Arboviral encephalitides have a global distribution. There are five main viral
agents of encephalitis in the United States: West Nile virus (WNV), eastern
equine encephalitis (EEE), western equine encephalitis (WEE), St. Louis
encephalitis (SLE) and La Crosse (LAC) encephalitis, all of which are transmitted