The Influence of Climate and Public Health Interventions on Aedes Vectors and Dengue in Sri Lanka

Abstract: Introduction: Dengue, a viral infection transmitted by Aedes mosquitos, flourishes in urban tropical environments by a complex process. Interactions among susceptible humans, dengue viruses, and Aedes mosquitoes determine dengue transmission patterns, and these interactions are modified by driving factors related to weather, the environment, and human behaviour, including mobility. Understanding the drivers of dengue and evaluating the effectiveness and costeffectiveness of existing vector control policies are vital to developing evidence-based and timely interventions.Methods: The exposure-lag-response associations between weather variables, Aedes vector indices and dengue at each sub-district Medical Officer of Health (MOH) divisions in Kalutara district, Sri Lanka, were estimated using distributed lag non-linear models. These estimates were meta-analyzed to obtain the average estimates for the district, while exploring the heterogeneities among MOH divisions. Non-linear extension to the interrupted time series analysis was used to evaluate the impact of nation wide mobility restrictions implemented during COVID-19 pandemic on dengue risk at each district, at different age groups in the western province and at the climate zones in Sir Lanka. The effects of the vector control interventions implemented through the civil military cooporation (CIMIC) on dengue were estimated at Panadura MOH division of Kalutara district using interrupted time series analysis while adjusting for potential confounders. The costeffectiveness of the CIMIC intervention was evaluated using a decision analytical modelling framework.Results: We found that El Niño, rainfall, temperature and Aedes larval indices were associated with each other, and dengue, at lag intervals expanding from one to six months. The nation wide mobility restriction was associated with a statistically significant reduction in dengue risk in all climate zones in Sri Lanka. The highest impact was observed among the children age less than 19 years. We found that the CIMIC intervention reduced dengue risk by 50% and was cost-effectivein a defined area.Conclusion: The manifestation of dengue is preceded by the biologically plausible latencies of increasing Aedes larvae and the onset of weather events in Kalutara district. When augmented with location-specific information of vector activities, one to six months lead time from the onset of weather events enables public health authorities to set up short, intermediate, and long-term goals for vector control interventions. The observed significant reduction in dengue risk following the national lockdown in Sri Lanka further highlighted the importance of vector control at public places and schools. The findings of these studies suggest that communities affected by dengue can benefit from investments in vector control if interventions are implemented rigorously and coordinated well across sectors. The methodological framework we developed in this doctoral thesis will contribute to the understanding of the local determinants of dengue and the developmentof early warning systems blended with effective and cost-effective vector control interventions in Sri Lanka and beyond.