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Background  Measurement of malaria endemicity is typically based on vector or parasite measures. A complementary approach is the detection of parasite specific IgG antibodies. We determined the antibody levels and seroconversion rates to both  P. vivax  and  P. falciparum  merozoite antigens in individuals living in areas of varying  P. vivax  endemicity in Pará state, Brazilian Amazon region.    Methodology/Principal Findings  The prevalence of antibodies to recombinant antigens from  P. vivax  and  P. falciparum  was determined in 1,330 individuals. Cross sectional surveys were conducted in the north of Brazil in Anajás, Belém, Goianésia do Pará, Jacareacanga, Itaituba, Trairão, all in the Pará state, and Sucuriju, a free-malaria site in the neighboring state Amapá. Seroprevalence to any  P. vivax  antigens (MSP1 or AMA-1) was 52.5%, whereas 24.7% of the individuals were seropositive to any  P. falciparum  antigens (MSP1 or AMA-1). For  P. vivax  antigens, the seroconversion rates (SCR) ranged from 0.005 (Sucuriju) to 0.201 (Goianésia do Pará), and are strongly correlated to the corresponding Annual Parasite Index (API). We detected two sites with distinct characteristics: Goianésia do Pará where seroprevalence curve does not change with age, and Sucuriju where seroprevalence curve is better described by a model with two SCRs compatible with a decrease in force of infection occurred 14 years ago (from 0.069 to 0.005). For  P. falciparum  antigens, current SCR estimates varied from 0.002 (Belém) to 0.018 (Goianésia do Pará). We also detected a putative decrease in disease transmission occurred ∼29 years ago in Anajás, Goianésia do Pará, Itaituba, Jacareacanga, and Trairão.    Conclusions  We observed heterogeneity of serological indices across study sites with different endemicity levels and temporal changes in the force of infection in some of the sites. Our study provides further evidence that serology can be used to measure and monitor transmission of both major species of malaria parasite.

Serologically Defined Variations in Malaria Endemicity in Pará State, Brazil