Antigens and Alternatives for Control ofAnaplasma marginaleInfection in Cattle

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Abstract
SUMMARY: Anaplasmosis, a tick-borne cattle disease caused by the rickettsiaAnaplasma 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 genusAnaplasma, of whichA. marginaleis the type species, now also includesA. bovis,A. platys, andA. phagocytophilum, which were previously known asEhrlichia bovis,E. platys, and theE. phagocytophilagroup (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 blockedA. marginaleinfection. 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 ofA. marginaleand related organisms. The recent development of a cell culture system forA. marginaleprovides 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 ofA. marginaleantigen repertoires and an improved understanding of bovine cellular and humoral immune responses toA. marginale, combined with the new technologies, should contribute to the development of more effective vaccines for control and prevention of anaplasmosis.