Walsh & Hoyt: Ehrlichiosis

Ehrlichiae, once classified as rickettsiae but now placed in a separate family, are obligate intracellular organisms similar to rickettsiae but that have a tropism for PMNs. A specific species of Ehrlichia, E. canis, orginally was described in Algeria as the causative agent of canine ehrlichiosis (tropical canine pancytopenia), a tick-borne disease of dogs, in 1935. E. canis subsequently was identified in the United States in 1962 and now is known to be present throughout the world. The acute phase of canine ehrlichiosis is characterized by mild constitutional manifestations, including fever, dyspnea, anorexia, lymphadenopathy, and weight loss, whereas the chronic phase is characterized by hemorrhages, epistaxis, peripheraledema, emaciation, and hypotensive shock leading to death. Wild and domestic dogs and other members of the Canidae family (e.g., wolves, coyotes, foxes) are the natural reservoirs of E. canis and are the only animals susceptible to infection with this species.