Abstract
The endosymbiont Wolbachia wAlbB induces refractoriness to Plasmodium falciparum in Anopheles stephensi, the primary mosquito vector of human malaria in the Middle East and South Asia. However, it remains unknown whether such refractoriness can be extended to other malaria species. In particular, it was reported that under very specific conditions, wAlbB can enhance Plasmodium infection in some hosts. Here, we measured the impact of wAlbB on the rodent malaria parasite Plasmodium berghei in A. stephensi by comparing the load of oocysts and sporozoites in midguts and salivary glands, respectively, between wAlbB-infected and -uninfected mosquitoes. To investigate whether wAlbB modulated mosquito immune defense against parasites, we compared the expression of the immune genes, which were previously reported to involve in antimalarial response, in both midguts and the remaining carcass tissues of mosquitoes. The stable association of wAlbB with A. stephensi resulted in reduction of parasites by more than half at the oocyst stage, and up to 91.8% at the sporzoite stage. The anti-plasmodium immune genes, including TEP1, LRIM1, Toll pathway gene Rel1 and the effector Defensin 1, were induced by wAlbB in different mosquito body tissues. These findings suggest that immune priming is a potential cause of wAlbB-mediated antimalarial response in A. stephensi. More importantly, no evidence was found for any enhancement of Plasmodium infection in A. stephensi stably infected with wAlbB. We discuss these findings with possible implementations of Wolbachia for malaria control in disease endemic areas.
Highlights
Transmitted by Anopheles mosquitoes, malaria is one of the world’s deadliest diseases caused by protozoan parasites of the genus Plasmodium
Given the lack of a highly effective vaccine and the Wolbachia-Mediated Plasmodium Interference development of drug resistance in parasites and insecticide resistance in mosquito vectors, there is an urgent need for novel control strategies to target the vectors that are difficult to control by the existing methods (The malERA Consultative Group on Vector Control, 2011)
We previously showed that a stable wAlbB infection reduced P. falciparum oocyst loads in midguts of A. stephensi (Bian et al, 2013)
Summary
Transmitted by Anopheles mosquitoes, malaria is one of the world’s deadliest diseases caused by protozoan parasites of the genus Plasmodium. One of the potential approaches is to suppress or modify mosquito population using either genetically modified techniques or the endosymbiotic bacterium Wolbachia (Ito et al, 2002; The malERA Consultative Group on Vector Control, 2011), which was recently tested for proof-ofconcept through field release to control mosquito-borne diseases (Hoffmann et al, 2011; Carvalho et al, 2015; Mains et al, 2016). Wolbachia-infected male mosquitoes are proposed to be released to induce incompatible (or sterile) mating and reduce vector density below a threshold required for disease transmission (Laven, 1967; Brelsfoard et al, 2008). The feasibility of the above two strategies in disease control is currently being tested to combat Zika and dengue through field trials in many countries, including Australia, USA, China and Brazil, using Aedes mosquitoes carrying different type of Wolbachia (Hoffmann et al, 2011; Bourtzis et al, 2014; Xi and Joshi, 2015; Dutra et al, 2016; Mains et al, 2016)
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