Validation of mosquito salivary gland antigens as serological markers of human exposure to plasmodium falciparum infected anopheles gambiae mosquitoes in Kilifi county Kenya

Abstract

Malaria is a life-threatening disease responsible for more than 400,000 deaths annually worldwide, with sub-Saharan Africa being the most affected. Measurement of malaria transmission risk has been done using entomological tools which have the setback of inapplicability in low transmission settings. Due to heterogeneity in malaria exposure, serological tools which measure antibody responses to vector salivary gland antigens have been applied to measure exposure to vector bites. However, the aptitude of serological tools in distinguishing between infectious and non-infectious bites is limited. This study sought to validate biomarkers that measure exposure to infectious Anopheline mosquito bites. Nine mosquito salivary antigens, Hyp 10, Hyp 15, Hyp 37.7-2, D7rl , D7r2, D7r3, D7r4, D712 and SG6, were cloned into pEXP-5-CT/TOPO TA plasmid vector and in vitro expressed in competent BL21 (DE3) E. coli strain cells. Enzyme-linked immunosorbent assay (ELISA) was used to test antibody responses to the recombinant antigens using antibodies from archived plasma samples. The archived plasma samples that were used (n=684) reflect temporal variation in transmission intensity and were collected during a longitudinal study carried out in 2008 and 2014 in Junju ward, Kilifi County. All the data was analyzed using R (Version 3.5.1). After carrying out normality tests, Wilcoxon-Rank Sum Test Was used to compare two groups while Kruskal-Wallis Test was used to compare multiple groups. Antibody responses to SG6, Hyp 10, Hyp 15, Hyp 37.7-2, D7rl, D7r2, D7r3, D7r4 and D712 reflected a temporal variation in malaria transmission intensity. Antibody responses to SG6, D7r2 and D712 reflected parasitaemia and malaria infection outcome. In addition, antibody responses to D712 were lower in individuals who used bed-net as vector control strategy. In all the analyses, statistical significance was at P < 0.05. The findings of this study will contribute significantly towards evaluating the effectiveness of a vector control strategy and estimating the risk of malaria transmission at both the population and individual level in areas of varying transmission intensities. Additionally, the outcomes of this study will aid studies involving naturally acquired immunity to malaria.