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Climate variables can predict future mosquito activity

Almost half of the world’s population lives in areas at risk for dengue fever – a mosquito-borne infectious disease caused by the dengue virus. Currently, dengue is considered a major public health problem in Sri Lanka. Since it is difficult to develop safe and effective vaccines against this virus, controlling mosquito populations is considered the most effective strategy for preventing the spread of the disease.

An international team of scientists has now found that increases in three climate factors – rainfall, temperatures, and ocean warming – can reliably predict mosquito population growth in Sri Lanka, and thus provide opportunities to issue early warnings on the prevalence of the insects for the entire dengue season.

In Sri Lanka, dengue transmission patterns closely follow the country’s monsoonal rainfalls, with a peak in July following the southwest monsoon, and another one in December-January, after the northeast monsoon. While scientists have long known that there is a relationship between climate variables and the abundance, feeding patterns, and lifespan of Aedes mosquitoes – the primary vector that transmits the disease – the precise relation between the climate and insect activity is still poorly understood.

“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 co-author Yesim Tozan, an assistant professor of Global Health at New York University (NYU).

In order to quantify the effects of climate on Aedes mosquitoes in Kalutara, a district in Sri Lanka with a high prevalence of dengue, the scientists measured three monthly weather variables – rainfall, temperatures, and Oceanic Niño Index (which shows the degree of ocean warming) – from 2010 to 2018, and compared them with surveillance data of mosquito prevalence in Kalutara. They found that all three climate variables predicted mosquito activity, but with different time lags.

While an increase in rainfall – which frequently leads to outdoor containers filling with water and creating breeding sites – predicted a greater prevalence of mosquitoes within the same month, warmer temperatures were associated with increases in populations of these insects one or two months later. In addition, higher ocean temperatures caused by El Niño predicted increases in mosquito abundance 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 study lead author Prasad Liyanage, who conducted the research during his doctoral studies in Epidemiology and Global Health at Umeå University.

“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,” concluded Professor Tozan.

The study is published in the journal The Lancet Planetary Health

By Andrei Ionescu, Staff Writer  

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