Five separate human populations in the Brazilian Amazon were examined serologically for antibody to hepatitis B virus, Plasmodium falciparum, Toxoplasma gondii and Treponema pallidum by the reverse passive hemagglutination, indirect immunofluorescence, indirect hemagglutination, and flocculation (VDRL) tests, respectively. Each population was classified according to social and economic status, and degree of contact with other civilizations. Hepatitis, falciparum malaria, syphilis and toxoplasmosis had prevalences of 38.1, 27.3, 21.9 and 73.9%, respectively, in the Manaus population; the Barcelos population had corresponding values of 40.7, 33.8, 22.1 and 63.8%; the Mundurucu Indian tribe 20.2, 17.3, 15.4 and 70.8%; the Mayongong Indian tribe 1.3, 80.1, 4.5 and 66%; and the Sanoma Indian tribe 0.9, 77.7, 1.8 and 56.2%. Malaria and toxoplasmosis were the most prevalent infections in all five populations. Hepatitis B virus and syphilis were less prevalent among those populations with little contact with other civilizations, especially the relatively isolated Indian tribes. Antibody titers to all four diseases dropped significantly with age in all five populations.
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