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Kay, Grant Alistair (2023) Investigating the impact of insecticide exposure and resistance on the vector competence of Anopheles gambiae and Aedes aegypti for arboviruses, Thesis (Doctoral), Liverpool School of Tropical Medicine.
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G Kay Thesis Submission corrections 13.09.23.pdf - Accepted Version Download (4MB) | Preview |
Abstract
Arboviruses spread by mosquitoes pose a major threat to global health. Despite their importance, there are limited options available for their control. There are no specific medical treatments and few safe and effective vaccines. Therefore, control focuses on the use of insecticides to target the mosquito vectors. Extensive insecticide use has resulted in widespread insecticide resistance in Aedes and Anopheles mosquito vectors of arboviruses. Insecticide resistance and exposure can have marked effects on the physiology of vectors, and there are concerns that it may be capable of altering the innate permissiveness of vectors to acquire and transmit arboviruses, known as vector competence. This thesis aimed firstly to investigate how insecticide selection pressure can alter the transcriptome of mosquitoes, including the expression of genes relating to metabolic insecticide resistance and innate immunity. Secondly, it investigated how insecticide resistance and exposure can interact with the vector competence of mosquitoes for arboviruses.
Chapter 2 investigated how a target site resistance mechanism, the L1014F knockdown resistance allele, may affect the vector competence of Anopheles gambiae for O’nyong nyong virus (ONNV) using a CRISPR/Cas9 gene-edited mosquito line. Data from oral infections and intrathoracic injections show that L1014F homozygosity is not associated with changes in the infection susceptibility for ONNV.
Chapter 3 investigated how different insecticide rotation scenarios influence the transcriptome of Aedes aegypti. Switching insecticides was associated with widespread transcriptomic changes across multiple biological domains, including the expression of genes relating to metabolic insecticide resistance and innate immunity pathways. Removal of temephos selection pressure was associated with a widespread downregulation of genes encoding antimicrobial peptides, and potential activators of the Toll immune pathway.
Chapter 4 investigated the effects of altering insecticide selection pressures on the vector competence of Ae. aegypti for Zika virus (ZIKV). Temephos selection was associated with slower dissemination and lower body viral titres following oral infection compared to an insecticide unselected strain. Data from intrathoracic injections potentially showed the presence of salivary barriers associated with temephos selection.
Chapter 5 investigated the effects of sublethal larval exposure to temephos on the vector competence of Ae. aegypti for ZIKV. Larval exposure to temephos was associated with higher salivary titres of ZIKV in a temephos susceptible mosquito strain. No other differences in vector competence were observed relating to temephos exposure.
The available evidence suggests that insecticide resistance and exposure can have impacts on the vector competence of mosquitoes for arboviruses, however, there is not a clear consensus on the direction of the effect. Changes to vector competence due to insecticide resistance and exposure have the potential to alter the vectorial capacity of mosquito populations, especially in areas where the probability of daily survival is high. As insecticide resistance permits vectors to survive contact with insecticides, small changes to vector competence could become increasingly important for arbovirus transmission.
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