A novel pattern of treponemal antibody distribution in isolated South American Indian populations.

Serologic surveys for treponemal disease were carried out in 1970-1976 among three linguistically distinct and isolated population groups in the Brazilian Amazon Region and among the Mapuche Indians of southern Chile. Three patterns were found: 1) no evidence for treponemal infection in two very recently contacted groups; 2) sporadic positive individuals in groups with long periods of contact with non-Indian populations; and 3) a high prevalence of positive tests in one cultural group with limited exposure to non-Indians. The seroepidemiology and clinical manifestations of a possible treponemal infection in those villages with a high prevalence of positive tests were unlike those of the classically described human treponematoses.