<prompt> The most common cause of sporadic viral encephalitis is:Japanese B encephalitisHerpes simplex encephalitisHW encephalitisRubeola encephalitis  <response>: Ans. is b i.e., Herpes simplex encephalitis Ref: David Greenwood, 18the, p. 424 Encephalitis caused by HSV - 1 is a rare condition, but it is the most common cause of sporadic fatal encephalitis in developed countries 1 - 2 cases per million population annually. The disease carries a high mortality rate, and those who survive often have residual neurologic defects. About half of patients with HSV encephalitis appear to have primary infections, and the rest appear to have recurrent infection. 