A SEROPREVALENCE AND DESCRIPTIVE EPIDEMIOLOGIC-STUDY OF MALARIA AMONGINDIAN TRIBES OF THE AMAZON BASIN OF BRAZIL

Data on the seroprevalences of Plasmodium falciparum, P. vivax, and P. malariae in four isolated Indian tribes of the Amazon basin in Brazil , as determined by IFAT, were re-analysed. Age-, sex- and tribe-specif ic geometric mean antibody titres and externally standardized prevalen ce ratios were calculated for each parasite species. Correlation coeff icients and prevalence odds ratios were also calculated for multiple i nfections with different combinations of the three Plasmodium species. Titres of all but one of the antibodies studied were similar in males and females; titres of antibodies to the blood stages of P. malariae were slightly higher in females than in males. Titres of antibodies to all three Plasmodium species increased with subject age, and this age effect was not confounded by sex or tribal differences. There were st riking differences between tribes, with the Parakana tribe having rela tively low titres of antibodies against P. falciparum and P. malariae; these tribal effects were not confounded by sex or age differences be tween tribes. The results indicate that conditions conducive to the tr ansmission of P. malariae exist in this region of the Amazon. The pote ntial for zoonotic transmission of P. brasilianum, a parasite of monke ys which is morphologically similar to P. malarie, and the generally h igh rates of seropositivity to all three species of Plasmodium indicat e that control measures which are adequate and applicable to the regio n studied need to be developed.