Climate factors predict future mosquito activity

(ORDO NEWS) — 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, according to a new study by an international team of scientists.

The results, published in The Lancet Planetary Health, could influence the design and timing of programs to limit the spread of mosquito-borne diseases such as dengue.

Nearly half of the world’s population lives in areas at risk for dengue fever, which has become a major public health problem in Sri Lanka. Since it has proven difficult to develop a safe and effective vaccine against the disease, control of mosquito populations is considered the most effective strategy to prevent the spread of the virus.

The pattern of dengue fever in Sri Lanka is closely related to the country’s monsoon rains, with a peak in July after the southwest monsoon and then a smaller peak in December-January after the northeast monsoon.

Research shows a relationship between several climate variables and the number, feeding habits, and longevity of Aedes mosquitoes that carry dengue fever, but the relationship between Aedes mosquito activity and climate is still poorly understood.

“The spread of dengue fever is expected to increase due to climate change.

If we can use climate and weather data to predict the seasonal distribution of mosquitoes, this timely information will enable public health authorities to proactively manage mosquito control operations,” said study author Yesim Tozan, associate professor of global health at New York University School of Global Public Health.

The researchers sought to quantify the impact of climate on Aedes mosquitoes in Kalutara, an area in southwest Sri Lanka with a persistently high incidence of dengue fever. They measured three monthly weather variables rainfall, temperature, and the oceanic niño index from 2010 to 2018.

The Oceanic Niño Index measures whether the waters in the tropical Pacific are warmer or colder than average, with El Niño and La Niña phases causing weather changes. Between 2010 and 2018, there were three El Niño events, or unusually warm ocean temperatures.

The researchers then compared climate variables with systematically collected mosquito surveillance data at Kalutara, including measurements of mosquito populations and Aedes larvae found in homes and open waters.

All three climatic variables predicted mosquito activity, but with different time delays. Increased rainfall, which often causes open containers to fill with water, creating breeding grounds for mosquitoes, predicted higher mosquito prevalence in the same month.

Higher temperatures were associated with an increase in mosquito numbers after one or two months. Higher ocean temperatures during El Niño predicted an increase in mosquito numbers with a delay of five to six months.

“These climatic factors have the potential to predict mosquito activity at different times and may allow us to quantify risk and take effective mosquito control measures before a dengue epidemic occurs,” the scientists say.

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