<P> Certain types are preventable with vaccines . Treatment may include, antiviral medication (such as acyclovir), anticonvulsants, and corticosteroids . Treatment generally takes place in hospital . Some people require artificial respiration . Once the immediate problem is under control, rehabilitation may be required . In 2015, encephalitis was estimated to have affected 4.3 million people and resulted in 150,000 deaths worldwide . </P> <P> Adult patients with encephalitis present with acute onset of fever, headache, confusion, and sometimes seizures . Younger children or infants may present irritability, poor appetite and fever . Neurological examinations usually reveal a drowsy or confused patient . Stiff neck, due to the irritation of the meninges covering the brain, indicates that the patient has either meningitis or meningoencephalitis . </P> <P> Viral encephalitis can occur either as a direct effect of an acute infection, or as one of the sequelae of a latent infection . The majority of viral cases of encephalitis have an unknown cause, however the most common identifiable cause of viral encephalitis is from herpes simplex infection . Other causes of acute viral encephalitis are rabies virus, poliovirus, and measles virus . </P> <P> Additional possible viral causes are arbovirus (St. Louis encephalitis, West Nile encephalitis virus), bunyavirus (La Crosse strain), arenavirus (lymphocytic choriomeningitis virus) and reovirus (Colorado tick virus). The Powassan virus is a rare cause of encephalitis . </P>

Which is the most common cause of acute encephalitis in the united states