Whereas monocytic ehrlichiosis in dogs is most commonly due to infection with E. canis, human monocytic ehrlichiosis (HME) is most commonly due to infection with E. chaffeensis. Human infections with E. chaffeensis occur seasonally (most commonly from May through July), and most commonly among people in the southeastern and south central U.S. (Missouri). Symptoms include:

• fever and malaise, chills
• headache, myalgia, arthralgia
• anorexia and nausea
• leukopenia, thrombocytopenia, and elevated levels of liver enzymes

Does Ehrlichia canis infect humans?:

Confirmed infections of people with E. canis are very limited and E. canis is not thought to pose a substantial zoonotic risk.

Human monocytic ehrlichiosis and the role of dogs:

Ehrlichia chaffeensis is transmitted by the Lone Star tick (Amblyomma americanum) and Dermacentor variabilis. Dogs can be persistently infected experimentally with E. chaffeensis, and E. chaffeensis has been recovered from naturally infected dogs with severe clinical disease indistinguishable from E. canis infection. However, the importance of dogs as a possible reservoir of this organism (white-tailed deer are the important reservoir) and as an epidemiologically significant factor for humans remains to be determined. E. chaffeensis and E. canis are antigenically related.

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