Influence of Climatic Factors on Dengue Transmission and Larval indices: A Comparative Analysis between Colombo and Nuwara Eliya districts, Sri Lanka

Abstract

Dengue fever remains a major public health threat in Sri Lanka, with significant geographic and seasonal variability in incidence rates. This study investigated the impact of climatic variables - temperature, rainfall, and humidity- on dengue transmission dynamics in two ecologically contrasting districts: Colombo, alowland urban tropical zone, and Nuwara Eliya, a high-altitude, cooler region. Using a mixed-methods approach, the study analysed quantitative data from 2017 to 2023 sourced from the Dengue Control Unit and the Department of Meteorology, including monthly dengue cases, precipitation, temperature, relative humidity, and vector indices such as the House Index (HI) and Breteau Index (BI). Qualitative insights were gathered through expert interviews. Findings revealed consistently higher dengue incidence in Colombo, with peak outbreaks aligning with the Yala monsoon season (May–August). In contrast, Nuwara Eliya exhibited lower overall transmission, with occasional peaks during the Maha season (September– December). Elevated HI and BI values in Colombo (HI = 16.6; BI = 25.3 in May 2022) reflect more favourable conditions for Ae. aegypti breeding, while cooler temperatures in Nuwara Eliya generally suppressed vector development, though a notable rise in indices in late 2023 suggested emerging risks due to climaticanomalies. A statistical analysis between dengue incidence and climatic variables, particularly temperature and rainfall were conducted. The study underscores the importance of integrating climate-sensitive entomological surveillance into public health strategies. Tailored vector control efforts, especially in highrisk urban zones like Colombo, and continuous monitoring in emerging-risk areas such as Nuwara Eliya,are essential for early warning and prevention.