Anaplasmosis, a tick-borne
cattle disease caused by the rickettsia Anaplasma marginale, is endemic in tropical and subtropical areas of the world. The disease causes considerable economic loss to both the dairy and beef industries worldwide. Analyses of
16S rRNA, groESL, and
surface proteins have resulted in the recent reclassification of the order Rickettsiales. The genus Anaplasma, of which A. marginale is the type species, now also includes A. bovis, A. platys, and A. phagocytophilum, which were previously known as Ehrlichia bovis, E. platys, and the E. phagocytophila group (which causes human granulocytic
ehrlichiosis), respectively. Live and
killed vaccines have been used for control of
anaplasmosis, and both types of
vaccines have advantages and disadvantages. These
vaccines have been effective in preventing clinical
anaplasmosis in cattle but have not blocked A. marginale
infection. Thus, persistently infected cattle serve as a reservoir of infective blood for both mechanical transmission and
infection of ticks. Advances in biochemical, immunologic, and molecular technologies during the last decade have been applied to research of A. marginale and related organisms. The recent development of a cell culture system for A. marginale provides a potential source of
antigen for the development of improved killed and live
vaccines, and the availability of cell culture-derived
antigen would eliminate the use of cattle in
vaccine production. Increased knowledge of A. marginale
antigen repertoires and an improved understanding of bovine cellular and humoral immune responses to A. marginale, combined with the new technologies, should contribute to the development of more effective
vaccines for control and prevention of
anaplasmosis.