Tick-borne encephalitis in a 3-month-old child.

Tick-borne encephalitis has not been reported in infants younger than 12 months of age. We report a 3.5-month-old child with a serologically proven tick-borne encephalitis. The infant had a history of a tick bite 3.5 weeks before the first symptoms of encephalitis appeared. The family lives in an endemic area of the disease. There were no prodromal signs and the course of the disease was monophasic. In an endemic area, prophylactic treatment with hyperimmunoglobulin after a tick bite should be considered even in very young infants, but in most children active immunization is probably not necessary because of infrequent exposure. Active immunization is still recommended after the 1st year of life.