Sensitive detection of Ehrlichia chaffeensis in cell culture, blood, and tick specimens by reverse transcription-PCR.

Ehrlichia chaffeensis is an obligatory intracellular bacterium of monocytes and macrophages and the etiologic agent of human monocytic ehrlichiosis, an emerging zoonosis. The Lone Star tick (Amblyomma americanum) has been implicated as the primary vector of E. chaffeensis. The present study examined the sensitivity of the nested reverse transcription (RT)-PCR based on the 16S rRNA gene relative to that of the nested PCR for detection of E. chaffeensis in infected DH82 cells, experimentally infected dog peripheral blood mononuclear cells, or experimentally infected A. americanum tick samples. The RT-PCR was found to be approximately 100 times more sensitive than the PCR for detection of E. chaffeensis regardless of the nature of the specimens. Thus, this RT-PCR is useful for detection of E. chaffeensis when a high sensitivity is required. Positive results by RT-PCR also imply the presence of viable pathogens. This is the first demonstration of RNA of E. chaffeensis in infected blood and acquisition-fed male, nymphal, and larval A. americanum ticks.