A nested polymerase chain reaction specific for Ehrlichia chaffeensis
was used to attempt to amplify DNA from extracts of 100 individual tic
ks collected from 13 counties in central Missouri. Seventeen of 59 Amb
lyomma americanum and six of 41 Dermacentor variabilis ticks exhibited
the characteristic 389-basepair product. This supports the hypothesis
that these tick species may be vectors of human monocytic ehrlichiosi
s.