The impact of mosquito salivary factors on Chikungunya virus transmission

Abstract

Vector-borne diseases affect an estimated 3.9 billion people in over 128 countries annually (WHO, 2017b). Mosquito-borne viruses, such as Chikungunya virus (CHIKV), are transmitted to human hosts through the saliva of female blood-feeding mosquitoes. During blood-feeding, salivary molecules enhance blood-feeding efficiency, dampen specific inflammatory signals, and enhance virus infection and dissemination. Skin is the interface where mosquito salivary molecules and viruses interact with the human immune system. Our long-term goal is to understand the impact of mosquito saliva on the skin and the role of salivary molecules in potentiating virus infection. This thesis aims to model the human skin bite site, identify mosquito salivary molecules present during virus infection, and investigate their impact on virus replication. We developed a human skin arbovirus infection model that was viable for four days ex vivo (Esterly et al., 2022a). Arbovirus infection in human skin ex vivo allowed flavivirus and alphavirus replication and dissemination. Using this model, we will investigate mosquito salivary factors and their impact on virus transmission. Next, we identified mosquito salivary factors highly expressed in Ae. aegypti salivary glands during CHIKV infection. We hypothesize that salivary proteins that contain secretion signals and are found to be highly expressed during CHIKV infection are delivered to the bite site during mosquito feeding. Through a combination of RNA-seq and miRNA-seq analysis, we identified several salivary factors, protein and small non-coding RNAs, which warrant further investigation. Lastly, we assessed the impact of identified and recombinantly expressed proteins or specific small RNA inhibitors on CHIKV replication in vitro relative to Ae. aegypti salivary gland extract (SGE). We found that both protein and small RNAs can influence CHIKV replication in a significant manner; however, the effect observed by mosquito saliva is a combination of multiple factors and will require more investigation to characterize fully. In summary, mosquito salivary factors work in concert to enhance virus replication and dissemination. Although individual factors may not recapitulate the total effect of SGE, the discovery and isolation of these factors further our understanding of arbovirus transmission. These studies highlight the complexity of mosquito salivary secretion and further our knowledge of mosquito-borne virus transmission. The following thesis will describe our most recent findings and contribution to understanding mosquito saliva's role during arbovirus transmission.