Abstract: Wolbachia bacteria naturally infect many insect species but until recently have not been detected in the Anopheles mosquito genera which exclusively transmit malaria Plasmodium parasites. Despite promising evidence from lab experiments that transinfected strains can inhibit Plasmodium, whether Wolbachia exist in symbiotic associations in wild Anopheles populations is less certain. Numerous studies focusing on the Anopheles gambiae complex (the major vectors in Sub-Saharan Africa) provided PCR-based evidence for both the presence of Wolbachia strains and an inhibitory effect on Plasmodium parasites. However, the vast majority of studies report Wolbachia DNA sequence detection at low density and infection frequencies using only highly sensitive nested PCR. This is problematic given the possibility of environmental contamination or integration into the host genome. Stronger evidence using multiple detection methods is required to determine whether Wolbachia strains are established as natural endosymbionts in Anopheles species. We have identified higher density Wolbachia strains in two species: Anopheles moucheti (wAnM strain) and Anopheles demeilloni (wAnD strain). In this talk, I will provide robust evidence for high-density natural Wolbachia strains in diverse geographical mosquito populations. In contrast to previously detected strains, wAnD and wAnM can be visualized in the ovaries, are maternally inherited, dominate the mosquito microbiome and can infect somatic tissue. We have also assembled Wolbachia genomes and provide evidence that these strains are likely CI inducing from the presence of CI factor (cif) gene homologs. Given these strains exist in wild Anopheles populations they appear ideal candidates for transinfection to major malaria vector species.

Biography: Tom is a medical entomologist who joined SLS in September 2022 and his research group studies novel methods of control for insect-borne diseases such as malaria. The main focus of his research is on the endosymbiotic bacterium Wolbachia and his group explores ways in which this bacterium can be used to reduce human pathogen transmission. The Walker group undertakes both field and lab research and have worked on collaborative projects in numerous malaria-endemic countries including Cameroon, Guinea, Madagascar, Kenya and the DRC. Tom’s main interest is now leading the development of Wolbachia-based biological control methods for Anopheles mosquitoes that transmit malaria following the success of his previous work as part of the World Mosquito Program (based in Australia) and a Wellcome Trust/Royal Society Sir Henry Dale Fellowship (2014-2022) at LSHTM. The Wolbachia-infected Aedes aegypti mosquito lines he created were released into wild populations and have recently been shown to reduce the incidence of symptomatic dengue and hospitalisations by ~77% in a randomised control trial in Indonesia. These lines Tom created have now been released into more than 12 dengue endemic countries and are having significant effects on dengue transmission.

Tom’s research interests in malaria have expanded to include collaborations on molecular insecticide resistance and the wider mosquito microbiome. Tom has also been involved in mosquito surveillance projects in Greece & Albania (West Nile virus), Ghana (malaria), Ethiopia (yellow fever virus), Brazil (Zika virus), Tanzania (lymphatic filariasis), St Lucia (arboviruses) and Madagascar (rift valley fever virus). Tom is particularly interested in novel methods for vector and pathogen surveillance. In the lab the Walker group undertake molecular analysis of wild caught insect samples (mosquitoes, sandflies, ticks) and develop insect embryo injection protocols including projects supporting genetic modification of sandflies (vectors of leishmaniasis) and Triatomine bugs (vectors of Chagas disease). Tom’s research has been funded by the Wellcome Trust, Bill and Melinda Gates Foundation, Royal Society, MRC, BBSRC, USAid, RSHTM and the Sir Halley Stewart Trust.