Prevalence of antibodies to SIV in baboons in their native habitat.

We have documented rare infection of baboons in their native habitat with simian immunodeficiency virus (SIV). Of 124 sera collected from yellow baboons in central Tanzania, two gave high readings by SIVagm ELISA (greater than 1.0) and moderate by SIVmac ELISA (0.5-1.0). These two sera gave strong reactions to the major SIVagm proteins, including gp130, by western blot analysis; their reactivity to SIVmac protein was considerably weaker. Similar testing of 155 sera from olive baboons of Ethiopia revealed no clearly positive sera. Thus, 2 of 279 baboon sera or 0.7% were positive for antibodies to SIV. The strong reactivity of the two positive yellow baboon sera with SIVagm proteins raises questions about whether these animals may have been infected by green monkeys in their native habitat; baboons occasionally prey upon and eat green monkeys. In addition to these two clearly positive samples, one olive baboon serum and one yellow baboon serum reacted only with major gag protein (p24-p26). Continued study of prevalence and diversity of SIV in primates will be important for understanding the history and evolution of primate lentiviruses and, it is hoped, the origins of viruses that cause AIDS in humans.