Detection of pathogenic Ehrlichia in ticks collected at acquisition sites of human ehrlichiosis in Missouri.

We collected 385 ticks from sites in Missouri associated with human monocytic ehrlichiosis. Using PCR, we detected E. chaffeensis or E. ewingii in 2 of 19 pools of adult Amblyomma americanum, 0 of 32 pools of Dermacentor variabilis, and 6 (18%) of 39 pools of unspeciated nymphal ticks from 3 of 6 sites associated with disease and one site not associated with disease. We also detected a variant of A. phagocytophila in one nymph pool.