ABSTRACT
African green monkeys (AGMs) are naturally infected with SIV at high prevalence levels and do not progress to AIDS. Sexual transmission is the main transmission route in AGM, while maternal-to-infant transmission (MTIT) is negligible. We investigated SIV transmission in wild AGMs, to assess whether or not high SIV prevalence is due to differences in mucosal permissivity to SIV (i.e., whether the genetic bottleneck of viral transmission reported in humans and macaques is also observed in AGMs in the wild). We tested 121 sabaeus AGMs (Chlorocebus sabaeus) from Gambia and found that 53 were SIV-infected (44%). By combining serology and viral load quantitation we identified 4 acutely infected AGMs in which we assessed the diversity of the quasispecies by single genome amplification (SGA) and documented a single strain transmission. We thus show that natural SIV transmission in the wild is associated with a similar genetic bottleneck to that described for mucosal HIV transmission in humans. Flow cytometry assessment of the immune cell populations did not identify major differences between infected and uninfected AGM. The expression of the SIV coreceptor CCR5 on CD4+ T cells dramatically increased in adults, being higher in infected vs. uninfected infant and juvenile AGMs. Thus, the limited SIV MTIT in natural hosts appears to be due to low target cell availability in newborns and infants, which supports HIV MTIT prevention strategies aimed at limiting the target cells at mucosal sites. Combined, the (i) extremely high prevalence in sexually active AGMs, (ii) very efficient SIV transmission in the wild, and (iii) existence of a fraction of multiparous females that remain uninfected in spite of massive exposure to SIV, identifies wild AGMs as an acceptable model of exposed, uninfected individuals.
Importance We report an extensive analysis of the natural history of SIVagm infection in its sabaeus monkey host, the African green monkey species endemic to West Africa. Virtually no study has investigated the natural history of SIV infection in the wild. The novelty of our approach is that we report for the first time that SIV infection has no discernible impact on the major immune cell populations in natural hosts, thus confirming the nonpathogenic nature of SIV infection in the wild. We also focused on the correlates of SIV transmission and we report, also for the first time, that SIV transmission in the wild is characterized by a major genetic bottleneck, similar to that described for HIV-1 transmission in humans. Finally, we report here that the restriction of target cell availability is a major correlate of the lack of SIV transmission to the offspring in natural hosts of SIVs.
FOOTNOTES
- Address correspondence and reprint requests to: Dr. Cristian Apetrei, Center for Vaccine Research of the University of Pittsburgh, 9044 Biomedical Science Tower 3, 3501 Fifth Avenue, Pittsburgh, Pennsylvania 15261. E-mail address: apetreic{at}pitt.edu
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