(Odocoileus virginianus) is known to be the main competent reservoir for E. chaffeensis and the lone star tick (Amblyomma americanum) is the principal vector for human transmission. Some evidence shows that other organisms may serve as reservoirs for the bacteria such as domestic goats, domestic dogs, raccoons, and coyotes.

E. chaffeensis can be transmitted to uninfected tick larvae when feeding on the blood from an infected host. The infection is then maintained and can be transmitted to a reservoir organism or humans at the nymphal