Infrared thermal imaging to determine temperature parameters of dengue vector habitats across ecological regions of Nepal: a pilot feasibility study

Dengue is a major vector-borne disease in Nepal, driven by container-breeding Aedes mosquitoes that thrive in domestic, urban settings. Its risk is increasing from the lowland Terai to the Hill and Mountain regions due to urbanisation and global warming. Practical and innovative approaches are needed to better understand the impact on Aedes mosquito habitats that are the main targets for vector control. We conducted a pilot feasibility study to characterise Aedes aegypti and Aedes albopictus breeding sites, examine physicochemical parameters (total dissolved solids, pH, salinity, dissolved oxygen), and explore the utility of infrared thermal imaging as a novel tool for measuring temperature parameters of habitats across distinct ecological regions. We found that plastic containers, tin/metal items, and rubber tyres were common breeding sites. The dengue vectors Ae. aegypti and Ae. albopictus were identified in a variety of container types across most locations. Overall, there was reasonable agreement between the thermal camera and standard thermometer, although the camera recorded approximately 1 °C lower and showed divergence at higher temperatures. Most aquatic habitat temperatures were within an optimal mosquito breeding range (mid-20s to low 30s °C) and lower than non-breeding site temperatures. The breeding site water temperatures in the Terai region were ~ 4 °C higher than the Mid-Hill and Mountain regions. Aquatic habitat temperatures were also found to be significantly correlated with dissolved oxygen. Thermal imaging case studies provided key visual insights into varying temperatures in complex Aedes microclimates. Notably, inner rubber tyre temperatures remained relatively stable despite significant external temperature fluctuations and external tyre temperatures exceeding 50 °C. Thermal imaging shows promise for the field characterisation of mosquito breeding sites, but it is not interchangeable with standard thermometry without qualification, including calibration and uncertainty analysis.