The epidemiology of hepatitis B antigen and antibody among Panamanian Cuna Indians.

Previous studies of hepatitis B antigen (HBsAg) and antibody to it (anti-HBs) showed widely differing exposures between Panamanian Indian tribes. Cuna Indians living on islands appeared infrequently exposed to HBsAg; we found no one antigenemic and low age specific anti-HBs rates. In contrast, mainland dwelling Guaymi and Chocó Indians had a high prevalence of anti-HBs. We have now measured HBsAg by counterelectrophoresis and anti-HBs by radioimmunoassay in two Cuna Indian groups who live in the Darien forest. The prevalence of HBsAg among Darien Cuna was low, 3 positive of 239 tested, but 106 (44%) had anti-HBs. Darien Cuna thus evidenced greater exposure to HBsAg than island Cuna (8% had anti-HBs) and had an anti-HBs prevalence similar to the neighboring Chocó Indians (42%). The Guaymi Indians of western Panama had a lower frequency of anti-HBs (29%) than either Chocó or mainland Cuna but their frequency of chronic antigenemia was significantly greater. These data suggest that while exposure may be a function of village habitat, chronic antigenemia may reflect differences in host responses.