Differential perpetuation of malaria species among Amazonian Yanomami Amerindians.

Abstract

Abstract. To determine whether malaria perpetuates within isolated Amerindian villages in the Venezuelan Amazon, we surveyed malaria infection and disease among 1,311 Yanomami in three communities during a 16-month period. Plasmodium vivax was generally present in each of these small, isolated villages; asymptomatic infection was frequent, and clinical disease was most evident among children less than five years of age (odds ratio [OR] ϭ 6.3, 95% confidence interval [CI] ϭ 1.4-29.2) and among persons experiencing parasitemias Ն 1,000 parasites/mm 3 of blood (ORϭ 45.0, 95% CI ϭ 5.5-370.7). Plasmodium falciparum, in contrast, was less prevalent, except during an abrupt outbreak in which 72 infections resulted in symptoms in all age groups and at all levels of parasitemia, and occasionally were life-threatening. The observed endemic pattern of P. vivax infection may derive from the capacity of this pathogen to relapse, while the epidemic pattern of P. falciparum infection may reflect occasional introductions of strains carried by immigrants or residents of distant villages and the subsequent disappearance of this non-relapsing pathogen.

High prevalence of asymptomatic Plasmodium vivax and Plasmodium falciparum infections in native Amazonian populations.

“…32,33 However, absence of symptoms in a sectional study is not tantamount to asymptomatic malaria, which can only be ascertained through follow-up protocols. Studies carried out in Papua New Guinea and Thailand have clearly shown the existence of asymptomatic Plasmodium infections out of Africa.…”

Cross-sectional study defines difference in malaria morbidity in two Yanomami communities on Amazonian boundary between Brazil and Venezuela

“…Antimalarial immunity can suppress gametocytemia (Baird et al 1991), and therefore reduce malaria transmission, and control parasitemia (Bull & Marsh 2002), leading to a reduction in malaria morbidity. It can be assumed that the relative isolation of Yanomami villagers (Laserson et al 1999) restricted the variety of circulating isolates of malaria parasites (Maitland et al 2000) and contributed to the efficacy of immunity.…”

A new challenge for malaria control in Brazil: asymptomatic Plasmodium infection - a review

“…Other studies carried out in Brazil (Jones & Neto 1971Prata et al 1988, Andrade 2001a,b, Pithan et al 2002, Scopel et al 2005 and in other Latin American countries (Gonzalez 1997, Pérez 1998, Laserson et al 1999, Suárez-Mutis et al 2000a,b, Roper et al 2000, Roshnavaran et al 2003, Branch et al 2005 were important for the global comprehension of the problem.…”

“…P. vivax was found in 74.7% of the infections, P. falciparum in 26.6%, including mixed infection in 1.6%, and P. malariae in 0.3%. IgG antibodies for P. vivax and P. falciparum were detected by indirect immunofluorescence in 83.2 and 71.7%, respectively, but the geometrical means of the assays were low (72.5 and 54.6), thus characterizing unstable transmission.Other studies carried out in Brazil (Jones & Neto 1971Prata et al 1988, Andrade 2001a,b, Pithan et al 2002, Scopel et al 2005 and in other Latin American countries (Gonzalez 1997, Pérez 1998, Laserson et al 1999, Suárez-Mutis et al 2000a,b, Roper et al 2000, Roshnavaran et al 2003, Branch et al 2005 were important for the global comprehension of the problem. …”