Abstract
The intracellular, symbiotic bacterium Wolbachia pipientis has garnered attention for the ability to modulate the reproductive biology of the host insect, and block pathogen replication and transmission. It has been proven effective at both reducing disease occurrence and crashing vector populations in laboratory and field-settings. Arthropod-borne viruses are increasing in prevalence across Europe; they pose an increasing risk to the United Kingdom. Existing control methods are lacking and these approaches, such as insecticides and larval source management are difficult to coordinate and hampered by insecticide resistance. Novel controls, such as Wolbachia-based strategies could be vital to controlling emerging and invasive vector species and pathogens. In this thesis, I aimed to first investigate the native Wolbachia infections in UK mosquito species of medical importance, including optimizing techniques for removal of Wolbachia. Second, I used both in-vivo and in-vitro systems to investigate how Wolbachia and Usutu virus (USUV) interact and any implications for future vector control methods.Native UK mosquito species were assessed for their USUV and West Nile virus (WNV) vector potential through a review of the literature. Through this review I identified 15 species, which were then screened for endogenous Wolbachia infections. Detected Wolbachia were characterised further by multi-locus sequence typing (MLST). Wolbachia was detected in five of the 15 screened species, including a new detection in Aedes sticticus.
Different antibiotic treatment methods for the clearance of native Wolbachia infections from Culex pipiens f. molestus mosquito larvae were assessed over three generations. Tetracycline was found to be the most effective at clearing Wolbachia infections. It was also proven that AWZ1066S, a novel compound for arthropod-Wolbachia clearance, was able to remove Wolbachia from mosquitoes and doxycycline is toxic to mosquito larvae.
The effect of native Wolbachia strain wPip on USUV infection in Cx. pipiens f. molestus was assessed through an infection using a Wolbachia-uninfected line. USUV titres, viral growth rates, mosquito survival, infection frequency, or dissemination percentage, were not associated with the presence of Wolbachia strain wPip.
Wolbachia strain wAlbB and USUV interactions were studied in an Ae. albopictus cell line (C6/36). Each of the three isolates of USUV used in this study displayed different growth dynamics in the presence of Wolbachia. These varying viral growth patterns were somewhat reduced when the cells were supplemented with cholesterol, and they also induced varying gene expression in the Toll immune pathway.
Collectively, this thesis provides important information for those considering implementation of Wolbachia-biocontrols in the UK/Europe. Wolbachia strain wAlbB induces differential blocking phenotypes across USUV variants. These varied Wolbachia-blocking provide a potential system for exploring the underlying mechanisms of Wolbachia-induced blocking. Native Wolbachia infections are present in some British mosquito species, and this information could become increasingly important as the arbovirus risk to the UK increases and Wolbachia-based controls are explored further.
| Date of Award | 11 Nov 2025 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Grant Hughes (Supervisor), Matthew Baylis (Supervisor) & Jolyon Medlock (Supervisor) |