Immunization of cattle with Anaplasma marginale derived from tick cell culture

Anaplasmosis is a hemolytic disease of cattle caused by the ehrlichial tick -borne pathogen Anaplasma marginale. Killed vaccines used for control of an aplasmosis in the US used antigen harvested from infected bovine erythrocyt es which was often contaminated with bovine cells and other pathogens. In t his study, we performed an initial cattle trial to test A. marginale harves ted from tick cell culture as an immunogen for cattle. Eleven yearling Hols tein cattle were immunized with the cell culture-derived A. marginale and I I cattle were non-immunized contact controls. Each vaccine dose contained approximately 2 x 10(10) A. marginale in an oil-based adjuvant. Two immuniz ations were administered subcutaneously 4 weeks apart and the cattle were c hallenge-exposed 10 weeks after the second immunization with A. marginale i nfected blood. Maximum antibody levels as determined by an A. marginale spe cific competitive ELISA were observed 2 weeks after the last immunization. Antibody responses against major surface proteins (MSPs) 1a and 1 beta1 wer e also characterized and immunized cattle demonstrated a preferential recog nition for MSP1 beta1. Cattle immunized with the cell culture-derived A. ma rginale had a significantly lower percent reduction in the packed cell volu me (P < 0.05) after challenge exposure as compared with the controls and di d not display clinical anaplasmosis. The cell culture-derived A. marginale shows promise for use as antigen in development of a new killed vaccine for anaplasmosis. (C) 2001 Elsevier Science B.V. All rights reserved.