Serological measures to assess the efficacy of malaria control programme on Ambae Island, Vanuatu

Seroepidemiology can provide evidence for temporal changes in malaria transmission and is animportant tool to evaluate the effectiveness of control interventions. During the early 2000s, Vanuatu experiencedan acute increase in malaria incidence due to a lapse in funding for vector control. After the distribution ofsubsidised insecticide-treated nets (ITNs) resumed in 2003, malaria incidence decreased in the subsequent years.This study was conducted to find the serological evidence supporting the impact of ITN on exposure toAnophelesvector bites and parasite prevalence.Methods:On Ambae Island, blood samples were collected from 231 and 282 individuals in 2003 and 2007,respectively. Parasite prevalence was determined by microscopy. Antibodies to threePlasmodium falciparum(PfSE,PfMSP-119, and PfAMA-1) and threePlasmodium vivax(PvSE, PvMSP-119, and PvAMA-1) antigens, as well as theAnopheles-specific salivary antigen gSG6, were detected by ELISA. Age-specific seroprevalence was analysed using areverse catalytic modelling approach to estimate seroconversion rates (SCRs).Results:Parasite rate decreased significantly (P< 0.001) from 19.0% in 2003 to 3.2% in 2007, with a shift fromP.falciparumpredominance toP. falciparum-P. vivaxco-dominance. Significant (P< 0.001) decreases were observed inseroprevalence to all threeP. falciparumantigens but only two of threeP. vivaxantigens (except PvAMA-1;P=0.153), consistent with the more pronounced decrease inP. falciparumprevalence. Seroprevalence to gSG6 alsodecreased significantly (P< 0.001), suggesting that reduced exposure to vector bites was important to the decreasein parasite prevalence between 2003 and 2007. Analyses of age-specific seroprevalence showed a three-folddecrease inP. falciparumtransmission, but the evidence for the decrease inP. vivaxtransmission was less clear.Conclusions:Serological markers pointed to the effectiveness of ITNs in reducing malaria prevalence on AmbaeIsland between 2003 and 2007. The recombinant gSG6 antigen originally developed to indicate exposure to theAfrotropical vectorAn. gambiaemay be used in the Pacific to complement the traditional measure ofentomological inoculation rate (EIR).