Evidence for persistence of infectious agents in isolated human populations

Abstract

More than 900 members of three Carib and four Kayapo Indian tribes, living on the periphery of the Amazon basin, have been studied for immunity to various viral, bacterial and protozoal agents. These tribes are isolated from the main Brazilian culture, and severaI had remained hostile and dependent on stone tools until less than 10 years prior to the study. The prevalence of antibodies to herpesvirus types 1 and 2, Epstein-Barr virus, cytomegalovirus, varicella and hepatitis B antigen was very high in every tribe studied. The age of acquisition of immunity was lower than in previously studied cosmopolitan communities. These agents seem to maintain a very stable relation with their host populations. Antibodies to measles, mumps, rubella, influenza Ao, A2 and B, parainfluenza 1, 2 and 3 and poliovirus 1 were nearly or totally absent from one or more tribes. When these antibodies were found in anyone who had not been outside the tribial area, they were usually found in nearly everyone over a specific age. These agents seem to maintain an unstable relation with their hosts, appearing only when introduced from the outside and then disappearing again. There was no evidence of smallpox in any tribe. Antibodies to the arboviruses (yellow fever viruses, Ilhéus, and Mayaro) were found with high frequency in certain areas. Prevalence of antibody to these viruses increased gradually with age, suggesting endemicitv of a different arder from that of the herpes group viruses. Antibody to Toxoplasma was absent from children but was frequently present in older adults. Antibody to treponema had a very high prevalence in the Kayapo tribes without evidence of pathology, suggesting that the parasite present in these communities was well adapted to its host. Malaria and tuberculosis, on the other hand, caused extensive and severe morbidity and threatened destruction of their host populations. Tetanus antibodies were virtually absent.