Serologically Defined Variations in Malaria Endemicity in Pará State, Brazil

Abstract

BackgroundMeasurement 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 FindingsThe 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.ConclusionsWe 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.

Allele-specific antibodies to Plasmodium vivax merozoite surface protein-1: prevalence and inverse relationship to haemoglobin levels during infection

“…The results showed poor antigenicity of allelic variant antigens representing both block 2 and block 10 of PvMSP-1 in opposition to the high antigenicity of the conserved C-terminal, PvMSP-1 19 . The high magnitude of IgG response to the conserved C-terminal domain of the PvMSP-1 protein that is the only fragment that remains attached to the merozoite surface during erythrocyte invasion [18, 19] is an expected result and confirms previous data from several serological studies conducted in different epidemiological settings in the Brazilian endemic area [20–26]. …”

Sample size determination for estimating antibody seroconversion rate under stable malaria transmission intensity

“…Seroprevalence (SP) is then the percentage of seropositive individuals in the sample and embodies information over currently infected and recently exposed individuals. As expected, SP estimates are typically higher than those for PR measured in the same sample [ 1 , 7 ]. Although overcoming some of the shortcomings of PR and EIR, SP does not reflect the dynamics of malaria transmission directly.…”

“…Several studies have shown the utility of SCR as a malaria epidemiological tool with some demonstrating good agreement between this measure and EIR [ 1 ] and others detecting historical changes in transmission that otherwise would not have been possible with other measures of transmission [ 4 , 7 - 9 ]. Whilst the evidence for using serology as an adjunct epidemiological marker for malaria transmission is growing, there has been no formal examination of samples size considerations for SP and SCR as primary endpoints.…”

Anti–MSP-10 IgG indicates recent exposure to Plasmodium vivax infection in the Peruvian Amazon

“…Several cross-sectional sero-epidemiological studies in Amazonian countries have reported the association of antibody responses with previous malaria infections by P. vivax and P. falciparum (3,18,25,26). However, because these previous studies relied on individual recall of past malarial infection, they could not reliably date or confirm past infections.…”