SCOTS scientists are part of an international team who have reported an effective and environmentally sustainable way of blocking the transmission of mosquito-borne dengue fever.

Researchers from the universities of Glasgow and Melbourne, and the Institute for Medical Research in Malaysia, carried were able to reduce cases of dengue at sites in Kuala Lumpur, using a strain of the bacteria Wolbachia, which inhibit mosquitoes from transmitting viruses to

humans. Their data, published yesterday in Current Biology, showed that mosquitoes carrying the wAlbB strain of Wolbachia, when released into the wild, had the effect of reducing the incidence of dengue cases by 40%.

Previously, scientists has carried out successful mosquito releases using a different strain of the bacteria, but while this was effective in some conditions, it did not appear to be suitable for use in the very hot conditions experienced in equatorial countries such as Malaysia. Now, the international team of researchers has shown the wAlbB strain is stable and effective, even in daily peak temperatures of 36 degrees and higher, as commonly experienced in parts of Malaysia where dengue is prevalent.

There are around 90 million symptomatic cases of dengue every year, with severe disease in around 1%, including life-threatening haemorrhage or shock syndrome.

In Malaysia alone, more than 100,000 dengue cases were reported in 2016, with an annual cost estimated at $175m (£135m). Researchers released batches of Aedes aegypti – the yellow fever mosquito – carrying the wAlbB strain into the wild, in six sites in greater Kuala Lumpur with high levels of dengue transmission. The mosquitoes – male and female – then went on to mate with the wild mosquito population, resulting in the spread and establishment of the virus-inhibiting bacteria. In some sites, Wolbachia-carrying mosquitoes were measured at over 90% frequency more than a year after the mosquito releases ended.

The success of lowering dengue cases at these sites has led to a cessation of insecticide fogging in them, highlighting the environmental and economic benefits of this method.

Professor Steven Sinkins, from the MRC-University of Glasgow Centre for Virus Research, said: “We are excited by these findings, which show that we have a strain of Wolbachia that can be used to effectively reduce the number of dengue cases in very hot climates.

“The next step is to deploy this strain in more and larger sites, but we are now confident that this will become an effective way to control dengue on a large scale.”

Michael Chew, a portfolio manager at Wellcome, said: “These findings mark important progress in the future of dengue fever control.”

Professor Ary Hoffmann, from Melbourne’s Bio21 Institute, added: “The intervention succeeded despite ongoing pesticide applications and other challenges that can make it hard for the Wolbachia to become established, and the approach holds promise not only in Malaysia but also in other countries.”