Horizontal Transmission of the Symbiont Microsporidia MB in Anopheles arabiensis.

Fidel G Otieno,Edward E Makhulu,Enock Mararo,Juan Paredes,Joel L Bargul,Evan Teal,Thomas O Onchuru,Jeremy K Herren,Lilian Mbaisi,Tracy Maina,Everline A Onyango,Tullu Bukhari,Steven P Sinkins,David M Mburu,Gabriel Magoma,Godfrey Nattoh

doi:10.3389/fmicb.2021.647183

Abstract

The recently discovered Anopheles symbiont, Microsporidia MB, has a strong malaria transmission-blocking phenotype in Anopheles arabiensis, the predominant Anopheles gambiae species complex member in many active transmission areas in eastern Africa. The ability of Microsporidia MB to block Plasmodium transmission together with vertical transmission and avirulence makes it a candidate for the development of a symbiont-based malaria transmission blocking strategy. We investigate the characteristics and efficiencies of Microsporidia MB transmission between An. arabiensis mosquitoes. We show that Microsporidia MB is not transmitted between larvae but is effectively transmitted horizontally between adult mosquitoes. Notably, Microsporidia MB was only found to be transmitted between male and female An. arabiensis, suggesting sexual horizontal transmission. In addition, Microsporidia MB cells were observed infecting the An. arabiensis ejaculatory duct. Female An. arabiensis that acquire Microsporidia MB horizontally are able to transmit the symbiont vertically to their offspring. We also investigate the possibility that Microsporidia MB can infect alternate hosts that live in the same habitats as their An. arabiensis hosts, but find no other non-anopheline hosts. Notably, Microsporidia MB infections were found in another primary malaria African vector, Anopheles funestus s.s. The finding that Microsporidia MB can be transmitted horizontally is relevant for the development of dissemination strategies to control malaria that are based on the targeted release of Microsporidia MB infected Anopheles mosquitoes.

Highlights

Malaria continues to be a major health threat across subSaharan Africa, with this region accounting for 93% of the global malaria deaths (World Health Organization, 2020)
The addition of homogenized infected larvae to the rearing water of uninfected larvae and to sugar sources given to uninfected adult An. arabiensis did not result in horizontal transmission of Microsporidia MB (Table 2)
The results clearly demonstrate that Microsporidia MB is transmitted horizontally between adult An. arabiensis

Summary

Introduction

Malaria continues to be a major health threat across subSaharan Africa, with this region accounting for 93% of the global malaria deaths (World Health Organization, 2020). One of the most promising new management strategies involves the use of vertically (mother to offspring) transmitted symbiotic microbes that prevent the establishment of disease-causing viruses in mosquito vectors. This strategy is currently used as a control mechanism against the arboviral disease, Dengue, through the bacterial symbiont, Wolbachia (Moreira et al, 2009; Bian et al, 2010; Hoffmann et al, 2011; Walker et al, 2011; Frentiu et al, 2014; Ant et al, 2018; Nazni et al, 2019)

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Results

Conclusion