Revisiting the Impact of Temperature on Survival of Anopheles stephensi and Aedes aegypti and Implications on Extrinsic Incubation Period

Abstract

Background: Vector-borne diseases are climate-sensitive as vectors are poikilothermic. Among climatic factors, temperature is of prime importance as it affects vectors' development and pathogen transmission as well. Therefore, the present study was undertaken to understand the impact of constant variable temperatures, and indoor versus outdoor temperatures on the survival of An. stephensi and Ae. aegypti and its implication on the transmission of malaria and dengue respectively. Method: Two to three days old laboratory-bred An. stephensi and Ae. Aaegypti female mosquitoes were kept individually in environmental chambers at different temperatures ranging from 32-42 °C and relative humidity i.e. 65-75 ± 5%. Control experiment was set up at 26 °C and 65-75% RH. Kaplan-Meier method was employed for estimation of survival probabilities and log-rank (Mantel-Cox test) for comparison, and Chi-square was determined. The daily recorded temperature was used to calculate extrinsic incubation periods of malaria parasites and dengue virus using Indirect Moshkovsky's and Oganov-Rayevsky methods, respectively. Results: The Kaplan Meier plots of adult survival revealed that the overall survival of exposed groups significantly decreased with increasing temperature in both the vectors. The median days of survival were found higher in Ae. aegypti than An. stephensi. EIP was shorter in dengue as compared to malaria parasites. Indoor temperature was found to be more conducive for both the pathogens' transmission. Ae. aegypti appears more sturdy in terms of thermal tolerance. Conclusion: The potential increase in the faster rate of development of dengue at a higher temperature indicates that with a projected rise in temperatures due to climate change, the transmission of dengue would expand temporally. Further prospective studies are needed in real-time monitoring of temperature and RH in field conditions, vis-a-vis survival of vectors for refinement of the projected scenario of vectors' survival and/or disease transmission.