Dengue fever, a viral infection spread by mosquitos, has hit Malaysia particularly hard. As of the end of November 2019 there were 119,198 infections recorded for the year and 162 deaths. The virus tends to congregate in certain areas, creating dengue hotspots throughout the country. Now however, the culmination of a series of trials to tackle the disease offers some hope.
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The trials, conducted by an international team of scientists from the Universities of Melbourne and Glasgow and the Institute for Medical Research in Malaysia, involve a strain of bacterium called Wolbachia. This bacterium has the ability to inhibit Dengue-carrying mosquitoes (known as Aedes aegypti) from transmitting viruses to humans. By inserting Wolbachia into mosquitos in the lab and then releasing them across the six test sites, the researchers were able to ensure that it spread throughout the wild population. By the end of the trials, incidences of dengue in humans dropped by 40 per cent.
‘Dengue is a really focal disease and particular sites see high levels of transmission,’ says Steven Sinkins, a professor at the MRC-University of Glasgow Centre for Virus Research. ‘By focusing on those sites we can start to have a really significant impact. Eventually it will be a case of tackling wider areas and filling in gaps, but at the moment, we’re concentrating on those really problematic sites where you have high levels of dengue year after year.’
Trials have been carried out before but without the same success. Previously-used strains of Wolbachia proved less effective in the very hot conditions of Malaysia and it was not passed on to wild mosquitos in sufficient quantities. The new strain used in these trials (wAlbB) has proved to be more stable and effective, even in daily peak temperatures of 36°C and higher.
The scheme is now being rolled out to wider areas in Malaysia. The initial tests covered around 40,000 people and are being expanded to cover land home to a further 100,000 individuals. The researchers are confident that it will prove a cost-efficient and sustainable way to tackle the disease, in particular limiting the need for harmful and unpleasant insecticide fogging. ‘The next step is to deploy this strain in larger sites,’ says Sinkins, ‘but we are confident that this will become an effective way to control dengue on a large scale.’
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