Amber Gigi Hoi, Benjamin Gilbert, and Nicole Mideo (Sep 2020)
Mosquitoes are not flying syringes—researchers at UofT dissects how mosquito diversity amplify malaria risk
“Deconstructing the impact of malaria vector diversity on disease risk”
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Mosquitoes are bad, but diverse mosquitoes are worse
A growing body of research explores how the structure of diverse host communities mediates the spread of infectious diseases; however, much less is known about the influence of vector communities despite their being major targets for disease control. In a new paper published in The American Naturalist, researchers at the University of Toronto, Amber Gigi Hoi, Benjamin Gilbert, and Nicole Mideo, present the first empirical evidence of mosquito diversity amplifying malaria prevalence. The parasites that cause malaria, one of the world’s deadliest vector-borne diseases, can be transmitted by more than 70 species of mosquitoes. Comparing mosquito communities around the globe, the precise number of species, and their relative abundances, vary considerably. These mosquito species also encompass substantial diversity in seasonal activity, habitat, and feeding preferences. Mosquitoes are not simply flying syringes (although it is sometimes convenient to think of them this way), and so nuances of their ecology and the structure of vector communities will influence disease risk.
Amber and coauthors use publicly available mosquito and malaria survey data to tease apart the direct and indirect influences of total mosquito abundance, the number of species present, and the relative abundance of those species on malaria risk. They find that increasing the number of mosquito species directly increases malaria prevalence, though this effect is weakened slightly by more diverse mosquito communities harboring a lower relative abundance of the most ‘competent’ vector species. Total mosquito abundance is only indirectly associated with malaria prevalence through its relationship with these other measures of diversity. The researchers speculate that this is a consequence of species being active at different times of the year, prolonging the period over which disease transmission occurs. These results are consistent with previous theoretical work that predicts diverse vector communities will promote disease spread, and the study emphasizes the importance of understanding vector community ecology for designing sound vector management strategies.
Abstract
Recent years have seen significant progress in understanding the impact of host community assemblage on disease risk, yet diversity in disease vectors has rarely been investigated. Using published malaria and mosquito surveys from Kenya, we analyzed the relationship between malaria prevalence and multiple axes of mosquito diversity: abundance, species richness, and composition. We found a net amplification of malaria prevalence by vector species richness, a result of a strong direct positive association between richness and prevalence alongside a weak indirect negative association between the two, mediated through mosquito community composition. One plausible explanation of these patterns is species niche complementarity, whereby less competent vector species contribute to disease transmission by filling spatial or temporal gaps in transmission left by dominant vectors. A greater understanding of vector community assemblage and function, as well as any interactions between host and vector biodiversity, could offer insights to both fundamental and applied ecology.