Bunyamwera Virus Infection of Wolbachia-Carrying Aedes aegypti Mosquitoes Reduces Wolbachia Density

<i>Wolbachia</i> symbionts introduced into <i>Aedes</i> mosquitoes provide a highly effective dengue virus transmission control strategy, increasingly utilised in many countries in an attempt to reduce disease burden. Whilst highly effective against dengue and other positive-sense RNA viruses, it remains unclear how effective <i>Wolbachia</i> is against negative-sense RNA viruses. Therefore, the effect of <i>Wolbachia</i> on Bunyamwera virus (BUNV) infection in <i>Aedes aegypti</i> was investigated using <i>w</i>Mel and <i>w</i>AlbB, two strains currently used in <i>Wolbachia</i> releases for dengue control, as well as <i>w</i>Au, a strain that typically persists at a high density and is an extremely efficient blocker of positive-sense viruses. <i>Wolbachia</i> was found to reduce BUNV infection in vitro but not in vivo. Instead, BUNV caused significant impacts on density of all three <i>Wolbachia</i> strains following infection of <i>Ae. aegypti</i> mosquitoes. The ability of <i>Wolbachia</i> to successfully persist within the mosquito and block virus transmission is partially dependent on its intracellular density. However, reduction in <i>Wolbachia</i> density was not observed in offspring of infected mothers. This could be due in part to a lack of transovarial transmission of BUNV observed. The results highlight the importance of understanding the complex interactions between multiple arboviruses, mosquitoes and <i>Wolbachia</i> in natural environments, the impact this can have on maintaining protection against diseases, and the necessity for monitoring <i>Wolbachia</i> prevalence at release sites.