Differential perpetuation of malaria species among Amazonian Yanomami Amerindians

To determine whether malaria perpetuates within isolated Amerindian village s in the Venezuelan Amazon, we surveyed malaria infection and disease among 1,311 Yanomami in three communities during a 16-month period. Plasmodium v ivax was generally present in each of these small, isolated villages; asymp tomatic infection was frequent, and clinical disease was most evident among children less than five years of age (odds ratio [OR] = 6.3, 95% confidenc e interval [CI] = 1.4-29.2) and among persons experiencing parasitemias gre ater than or equal to 1,000 parasites/mm(3) of blood (OR = 45.0, 95% CI = 5 .5-370.7). Plasmodium falciparum, in contrast, was less prevalent, except d uring an abrupt outbreak in which 72 infections resulted in symptoms in all age groups and at all levels of parasitemia, and occasionally were life-th reatening. The observed endemic pattern of P. vivax infection may derive fr om the capacity of this pathogen to relapse, while the epidemic pattern of P. falciparum infection may reflect occasional introductions of strains car ried by immigrants or residents of distant villages and the subsequent disa ppearance of this non-relapsing pathogen.