High prevalence of simian foamy virus infection of South American Indians.

Simian foamy viruses (SFV) are retroviruses that widely infect nonhuman primates of New and Old-World origin and exhibit long-standing co-evolution with their hosts. Humans can acquire SFV from zoonotic exposures but are not known to be endemically infected and typically exhibit dead-end infections. South American Indian populations (Amerindians) historically have frequent contact with New World monkeys (NWM) and are endemically infected with the retrovirus human T-cell lymphotropic virus type 2 (HTLV-2) originally acquired before populating the Americas. We tested archived serum samples collected from numerous South American Indian persons (n = 1,998) in 1966-1997 from 18 tribes by validated ELISA and Western blot assays containing NWM SFV antigens. We also screened samples for HTLV-2 to compare SFV and HTLV-2 infection. We combined demographic and familial relationship data with the serologic results to evaluate transmission dynamics. We found a high SFV seroprevalence of 9.5% in 15 tribes compared to an HTLV-2 prevalence of 6.1% in 11 tribes. Testing of seropositive samples with Old World SFV antigen showed no reactivity confirming a NWM SFV origin. We found the odds of SFV and HTLV positivity increased with age and documented familial clustering of SFV among spouses and children. Serotyping showed co-circulation of SFV from different NWM species. Our results show that NWM SFV established longstanding prevalence among Amerindians post population of America. The high SFV prevalence will enable studies of disease association and human transmissibility to better understand the public health significance of SFV infections in humans.