According to a new study by an international team of researchers, increases in three climate factors – temperature, rainfall and ocean warming – predict an increase in Sri Lanka’s mosquito population over the next one to six months. Findings published in The Lancet Planetary Health, can provide information on the design and timing of programs to limit the spread of mosquito-borne diseases such as dengue.
Almost half of the world’s population lives in areas at risk of dengue, which has become a major public health problem in Sri Lanka. Because the development of a safe and effective dengue vaccine has proven difficult, controlling the mosquito population is considered the most effective strategy to prevent the spread of the virus.
Dengue transmission patterns in Sri Lanka closely follow the country’s monsoon rains, with transmission peaking in July after the southwest monsoon, followed by a smaller peak in December-January following the northeast monsoon. Research shows a relationship between some climatic variables and the number, feeding pattern and life span Aedes mosquitoes that transmit dengue, but the relationship between Aedes mosquito activity and climate are still poorly understood.
“Dengue transmission is expected to increase with climate change. If we can use climate and weather data to predict seasonal patterns of mosquitoes, this timely information will enable public health authorities to proactively manage mosquito control operations,” the author said. study Yesim Tozan, assistant professor in the Department of Global Health at New York University’s School of Global Public Health.
Researchers sought to quantify the impact of climate on Aedes mosquitoes in Kalutara, an area in south-western Sri Lanka with a persistently high dengue prevalence. They measured three monthly weather variables – precipitation, temperature and the oceanic Niño index – from 2010 to 2018. The Oceanic Niño Index measures whether water in the tropical Pacific Ocean is warmer or cooler than average, including the El Niño and La Niña phases of weather change. Three El Niño events, or unusually high ocean temperatures, occurred between 2010 and 2018.
The researchers then compared the climate variables with systematically collected mosquito observation data in Kalutara, including measurements of Aedes mosquitoes and larvae found in houses and open water containers.
All three climate variables predicted mosquito activity, but with different time lags. Higher rainfall, which often caused open containers to fill with water, creating breeding grounds for mosquitoes, predicted higher mosquito prevalence in the same month. Warmer temperatures were associated with increased mosquito numbers one to two months later. Rising ocean temperatures from El Niño events predicted increased mosquito populations with a five- to six-month lag.
“These climatic factors can serve as predictors of mosquito activity at different times and may allow us to quantify risk and implement effective mosquito control measures before a dengue epidemic occurs,” said lead study author Prasad Liyanage of the Sri Lankan Ministry of . of Public Health and Umeå University in Sweden, who will join NYU’s School of Global Public Health as a postdoctoral fellow this fall.
“Tracking El Niño events has the added advantage of predicting seasonal prevalence Aedes of mosquitoes with a lead time of six months, which could enable early warnings of mosquito prevalence throughout the dengue season,” Tozan added.
Additional study authors include Hans Overgaard of the Norwegian University of Life Sciences and Khon Kaen University in Thailand, Hasith Aravind Tissera of the Sri Lankan Ministry of Health, and Joachim Rocklew of Umeå University and Heidelberg University in Germany.