There are many factors that can influence mosquito activity, including temperature, humidity, and rainfall. Warmer temperatures and higher humidity levels can lead to increased mosquito activity, as these conditions are favorable for mosquito breeding and survival. Similarly, heavy rainfall can create standing water, which is a prime breeding ground for mosquitoes. Conversely, dry conditions can reduce mosquito populations, as these conditions are not favorable for mosquito development. Climate change is also expected to alter the distribution and abundance of mosquitoes, with some species potentially expanding their ranges into new areas.
According to a new study by an international team of researchers, increases in three climate factors – temperature, rainfall, and ocean warming – predicted mosquito population growth in Sri Lanka over the next one to six months. The findings, published in The Lancet Planetary Health, can help to shape the design and timing of programs to combat mosquito-borne diseases like dengue fever.
Dengue, which has become a major public health problem in Sri Lanka, affects nearly half of the world’s population. Controlling mosquito populations is thought to be the most effective strategy for preventing the virus’s spread because developing a safe and effective vaccine against dengue has proven difficult.
Dengue transmission is expected to intensify due to climate change. If we can use climate and weather data to predict seasonal patterns of mosquitos, this timely information would allow public health authorities to proactively manage mosquito control operations.Yesim Tozan
Dengue transmission patterns in Sri Lanka closely follow the country’s monsoonal rainfalls, with peak transmission occurring in July following the southwest monsoon and a smaller peak occurring in December to January following the northeast monsoon. Although research has found a link between some climate variables and the quantity, feeding patterns, and lifespan of Aedes mosquitos, which transmit dengue fever, the relationship between Aedes mosquito activity and climate remains unknown.
“Dengue transmission is expected to intensify due to climate change. If we can use climate and weather data to predict seasonal patterns of mosquitos, this timely information would allow public health authorities to proactively manage mosquito control operations,” said study author Yesim Tozan, assistant professor of global health at NYU School of Global Public Health.
The researchers aimed to quantify the effect of climate on Aedes mosquitoes in Kalutara, a district in southwestern Sri Lanka with a persistent, high presence of dengue. They measured three monthly weather variables — rainfall, temperature, and Oceanic Niño Index – from 2010 to 2018. The Oceanic Niño Index measures whether waters in the tropical Pacific Ocean are warmer or cooler than average, with El Niño and La Niña phases triggering changes in weather. Three El Niño events, or unusually warm ocean temperatures, occurred from 2010 to 2018.
The researchers then compared the climate variables with systematically collected surveillance data of mosquitoes in Kalutara, including measurements of Aedes mosquitoes and larvae found in homes and outdoor water containers.
All three climate variables predicted mosquito activity, but with different time lags. More rainfall – which often led to outdoor containers filling with water, creating mosquito breeding sites – predicted a greater prevalence of mosquitoes within the same month. Hotter temperatures were associated with increases in mosquitoes one to two months later. The warmer ocean temperatures of El Niño events predicted increases in mosquitoes with a five to six months delay.
“These climate factors have the potential to serve as predictors of mosquito activity at different times and may enable us to quantify the risk and implement effective mosquito control interventions before a dengue epidemic emerges,” said the study’s lead author Prasad Liyanage of the Sri Lanka Ministry of Health and Umeå University in Sweden, who will join NYU School of Global Public Health this fall as a postdoctoral associate.
“Tracking El Niño events has the added advantage of predicting the seasonal prevalence of Aedes mosquitoes with a lead time of six months, which could provide opportunities to issue early warnings on mosquito prevalence for the entire dengue season,” added Tozan.