FIG. 2.

Molecular epidemiology of SIVsm lineages in different primate centers in the United States. The lineage prevalence in each SM colony was estimated based on the present results. Not all of the animals at YNPRC and CNPRC were tested. Therefore, additional SIVsm lineages may be present and the relative prevalence of SIVsm lineages may be different from that established based on limited sampling. Due to the close relationship in gag between lineage 4 strains and SIVmac (lineage 8), it is possible that lineage 4 or its ancestors circulated at CNPRC. However, based on the current data, there is no proof of its presence at CNPRC. Therefore, the alternative hypothesis that lineage 4 was imported directly from Africa to the NIRC cannot be ruled out. Transfers of SIV-infected animals from CNPRC to other primate centers are shown.