Dr. Thomas Walker

Supervisor Details

Contact Details

School of Life Sciences, University of Warwick

Scientific Background

Research Interests

My primary research interest is developing novel biocontrol strategies for mosquito-borne diseases and a significant focus of the lab research is on using the endosymbiotic bacterium Wolbachia to reduce the transmission of malaria transmitted by Anopheles mosquitoes.

My research interests in malaria have expanded to include collaborations on molecular insecticide resistance and the wider mosquito microbiome. I am also interested in novel methods for vector and pathogen surveillance and have been involved in surveillance projects in Greece & Albania (West Nile virus), Ghana (malaria parasites), Ethiopia (yellow fever virus), Brazil (Zika virus), Tanzania (lymphatic filariasis parasites), St Lucia (arboviruses) and Madagascar (rift valley fever virus). In the lab we 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) in addition to transinfection of mosquito species with Wolbachia bacteria

Research Groups

Microbiology and Infectious Disease

Environment and Ecology

Supervision Style

In three words or phrases: Outcome-oriented, supportive, organised.

Provision of Training

I prefer to take responsibility for your technical training at first, leading to more independence later with support from experienced post docs/PhD students.

Progression Monitoring and Management

I will set out my expectations of your progression on a weekly/monthly basis. If these progression criteria are not met we will always discuss a plan of action together.

Communication

The team will have a WhatsApp group chat with which we regularly communicate during the week and weekends. Whilst I expect you to keep up with my/ team communications I will expect you to manage your work/life balance.

PhD Students can expect scheduled meetings with me:

In a group meeting

At least once per week

In year 1 of PhD study

At least once per week

In year 2 of PhD study

At least once per fortnight

In year 3 of PhD study

At least once per fortnight

The meetings will be a mixture of face to face, via video chat or telephone and I am usually contactable for an instant response (if required) on every working day.

Working Pattern

The timing of work in my lab is completely flexible, and (other than attending pre-arranged meetings), I expect students to manage their own time.

Notice Period for Feedback

I need at least 2 week's notice to provide feedback on written work of up to 5000 words.

MIBTP Project Details

Current Projects (2025-26)

Primary supervisor for:

The effects of natural Wolbachia bacteria on their Anopheles mosquito hosts and implications for malaria biocontrol strategies

See the PhD Opportunities section to see if this project is currently open for applications via MIBTP.

Please Note: The main page lists projects via BBSRC Research Theme(s) quoted and then relevant Topic(s).

The effects of natural Wolbachia bacteria on their Anopheles mosquito hosts and implications for malaria biocontrol strategies

Secondary Supervisor(s): Dr Erin Gorsich

University of Registration: University of Warwick

BBSRC Research Themes: Understanding the Rules of Life (Immunology, Microbiology)

Project Outline

Wolbachia is an endosymbiotic bacterium being used for mosquito biocontrol strategies. Wolbachia transinfected Aedes aegypti mosquitoes which both replace wild populations and block transmission of major arboviruses, such as dengue virus (DENV), are now being applied for disease control. The wMel Aedes aegypti line (Walker et al. Nature 2011) has been released and established in >10 DENV-endemic countries and has significantly reduced incidence including by 77% in a randomised controlled trial in Indonesia. Globally, DENV causes ~10,000 deaths/year but this is significantly lower than ~409,000 deaths caused by malaria. Emergence of insecticide resistance has reduced the effectiveness of traditional malaria vector control so novel approaches are now critical. We have now confirmed Wolbachia strains in two species of Anopheles mosquitoes (malaria vectors) at significantly higher densities which can be visualised in ovaries by microscopy (Figure 1 – adapted from Walker et at. Current Biology 2021).Wolbachia induces a reproductive phenotype (cytoplasmic incompatibility) that allows this bacterium to invade insect populations (key to control strategies). Genome analysis has provided evidence for the presence of CI factor (cif) gene homologs and high prevalence rates consistent with CI induction. Our preliminary analysis also suggests the wAnD and wAnM strains dominate the host microbiome when present in both wild and early colony generations of Anopheles demeilloni and Anopheles moucheti respectively.

Figure 1. Stable high-density Wolbachia strains in wild Anopheles mosquito populations. (a). Mosquito collection sites and Wolbachia prevalence rates. (b). Molecular phylogenetic analyses using the Wolbachia surface protein (wsp) phylogenetic tree. (c). FISH Wolbachia visualization in the ovaries. (d). Wolbachia strain’s relative abundance in the mosquito microbiome.

In this PhD project proposal, the candidate would firstly further investigate the mosquito microbiome using targeted barcoded high-throughput amplicon sequencing of the bacterial 16S rRNA gene to determine if Wolbachia is the dominant bacterial species in different Anopheles life stages. This is important given Anopheles mosquitoes can acquire other bacteria from their environment – some of which (eg. Asaia) have shown to compete with Wolbachia in laboratory populations. Secondly, the project would look to investigate insecticide resistance in An. moucheti and An. demeilloni. Insecticide resistance has been shown to be a key reason why releases of Wolbachia-infected Ae. aegypti strains have failed to establish. Furthermore, there is growing evidence of an association between the Anopheles mosquito microbiota and insecticide resistance. This Phd project would look to measure phenotypic insecticide resistance in Wolbachia-infected and equivalent uninfected individuals. CDC resistance intensity bioassays for three pyrethroid insecticides will be conducted and RNA-seq will be carried out on naturally infected individuals to determine any interaction between Wolbachia strains and expression of key enzymes/pathways associated with insecticide resistance. RNA-seq reads will be screened for target site mutations associated with eg. DDT, pyrethroid resistance and known voltage-gated sodium channel mutations. qRT-PCR validation of RNA-seq data will be undertaken on differentially transcribed insecticide resistance genes. Finally, the effect of Wolbachia strains on mosquito immunity will be assessed through RNA-Seq to determine differential expression levels of mosquito immune genes such as cecropin D, defensin and transferrin. qRT-PCR validation of RNA-seq data will also be undertaken on differentially transcribed insect immune genes.

References

Walker, T. et al (2011). Nature,10.1038/nature10355.

Walker, T. et al (2021). Current Biology, 10.1016/j.cub.2021.03.056.