Scrub typhus and chiggers in northern Thailand.

It was reconfirmed that L. deliense was the most dominant chigger during the rainy season in northern Thailand. Overall prevalence of IgG antibody against R. tsutsugamushi among the rural villagers in the northern most part of Thailand was nearly 60% at the level over 1 : 10 by an indirect immunofluorescent test. The level of IgG and IgM antibody titers was considerably high as greater than or equal to 1 : 2560 in some sera, but did not markedly vary by age groups or sexes. Based on detection of IgM antibody, the probability of new or reinfections were considered.