Scientists develop early warning system to predict dengue outbreak

Dengue is spread by the Aedes aegypti mosquito in the Caribbean
Dengue is spread by the Aedes aegypti mosquito in the Caribbean Credit: Pilar Olivares/Reuters

Scientists have developed an early warning system to alert countries when an outbreak of dengue fever is most likely to strike.

Dengue is a debilitating flu-like illness, spread by mosquitoes, which has become more widespread over recent years. According to figures from the World Health Organization there were around three million cases of the disease in 2015, compared to around two million in 2010 – although these figures are though to be a vast underestimate. 

Now, a global consortium of researchers has developed an early warning system to alert authorities on the Caribbean island of Barbados when a dengue outbreak is likely to strike.

The study, published in the journal PLOS Medicine, has shown that a period of drought, followed by intense rainfall four or five months later provide the optimum conditions for an outbreak of the disease.

Barbados, which is one of the 10 countries in the world where water is most scarce, has experienced three large outbreaks of dengue in the last five years and there have been more than 7,000 cases over that time.

Chikungunya and Zika – diseases which are also transmitted by mosquitoes – have also emerged in the region.

Researchers compared meteorological data – rainfall and temperature – with data on past dengue outbreaks to predict when there might be a spike in the number of cases.

They found that there is most likely to be an epidemic five months after a drought. However, if there is intense rainfall after the drought an outbreak is even more likely.

During periods of drought people tend to store water in containers, providing an ideal breeding ground for mosquitoes, which lay their eggs in pools of standing water.

The researchers believe that after a drought people are more likely to leave water containers out. So, next time there is a period of intense rainfall there are more places for water to collect and therefore more breeding grounds for mosquitoes.

The researchers warn that water storage containers become a greater hazard for dengue when they are not used and maintained regularly and instead serve as a back-up water source.

Barbados has experienced three droughts since 2002 and the government introduced new building regulations requiring the construction of water storage containers alongside any new building.

After this led to an increase in the number of mosquito breeding sites the government said that all storage containers should be covered in mesh.

Rachel Lowe, assistant professor at the London School of Hygiene and Tropical Medicine and lead author, said that predicting when an outbreak was likely to occur would enable authorities to plan better.

“If public health decision makers have an advance warning of when an epidemic might occur they can focus control ahead of these high-risk periods. They can control the mosquitoes and make sure a public education campaign is in place,” she said.

She added that the warning system – a version of which has already been developed for Ecuador and which showed that the dengue season occurred three months earlier than expected – could also be used elsewhere.

“Our next job is to test it and use it for another island. There are similarities in terms of climate and social factors but we need to test it first,” she said.

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