Ehrlichia , Anaplasma , and Related Intracellular Bacteria

Abstract The family Anaplasmataceae in the order Rickettsiales is composed of several genera of clinically significant bacteria encompassing both human and veterinary pathogens. Members of the genera Ehrlichia and Anaplasma are the best known, having been recognized as agents of veterinary importance for over a century and as human pathogens since 1987. This chapter focuses on the clinically relevant members of the Anaplasmataceae , with particular emphasis on Anaplasma phagocytophilum and Ehrlichia chaffeensis , the most common human pathogens in this family. The family Anaplasmataceae contains small, nonmotile, pleomorphic, obligately intracellular bacteria that reside and propagate within host membrane‐derived vacuoles in the host cell cytoplasm. Like other rickettsiae, members of the Anaplasmataceae have a reduced genome size and rely on host cell machinery for survival. As with anaplasmosis, the spectrum of clinical presentations of Ehrlichia chaffeensis ehrlichiosis ranges from subclinical infection to life‐threatening disease.