Ehrlichia chaffeensis

Ehrlichia chaffeensis is an obligate intracellular, Gram-negative species of Rickettsiales bacteria. It is a zoonotic pathogen transmitted to humans by the lone star tick (Amblyomma americanum). It is the causative agent of human monocytic ehrlichiosis.

Human monocytic ehrlichiosis caused by E. chaffeensis is known to spread through tick infection primarily in the Southern, South-central and Mid-Atlantic regions of the United States. In recent years, the lone star tick has expanded its range along the East Coast to New England, putting more humans at risk for tick-borne infections.

It is named for Fort Chaffee, where the bacterium was first discovered in blood samples of infected patients.