Anaplasma marginale: effect of the treatment of cattle with an interferon gamma-neutralizing monoclonal antibody or the nitric oxide synthetase inhibitor aminoguanidine on the course of infection.

Cattle undergoing initial infection with the rickettsia Anaplasma marginale were treated with either a monoclonal antibody (MoAb) with neutralizing activity for bovine interferon gamma (IFN-gamma) or aminoguanidine (AG), a specific inhibitor of the inducible form of nitric oxide synthetase (iNOS). Plasma levels of MoAb and AG were measured over the time of administration. The course of A. marginale infection was not altered in the MoAb-treated cattle relative to untreated controls. In cattle treated with AG however, A. marginale infection was significantly ameliorated, as judged by lower parasite levels and decreased anaemia in these cattle relative to the controls. The implications of these findings in relation to the basis for immunity against this economically important haemoparasite are discussed.