Mosquitoes are helping to fight one of the world’s fastest spreading viruses - this is how

Mosquitoes are helping scientists tackle a lethal virus for which there is no effective vaccine or treatment.

Dengue fever causes up to 400 million infections a year and can lead to serious illness and death. It’s now the fastest spreading mosquito-borne disease in the world.

Now a trial in Indonesia has seen a 77% drop in dengue fever cases after mosquitoes were infected with a bacteria commonly found in insects. It’s called Wolbachia and it reduces a mosquito’s ability to spread dengue, by making it harder for the virus to replicate.

There are around 8 million dengue cases a year in Indonesia. The trial took place in Yogyakarta, a city on the island of Java. Mosquitoes hatched from five million eggs infected with Wolbachia were released across half of a 26km2 urban area housing about 300,000 people.

The World Mosquito Program, which is working in 11 countries to help reduce the impact of mosquito-borne diseases, said the results of the trial, published in The New England Journal of Medicine, have “significant implications” for the 40% of the world’s population at risk of dengue.

“This is the result we’ve been waiting for,” said Professor Scott O’Neill, director of the World Mosquito Program. “We have evidence our Wolbachia method is safe, sustainable and dramatically reduces incidence of dengue.”

As the chart below shows, the success of the trial in Indonesia has been replicated in a number of countries where similar studies have taken place.

Rapid growth

According to the World Health Organisation (WHO), reported dengue cases have grown eight-fold in 20 years. Before 1970, only nine countries had experienced severe dengue epidemics.

The disease is now regularly found in more than 100 countries throughout the tropics, where it is a threat to nearly half the world’s population, the WHO says. Affected countries in 2021 include Brazil, Colombia, Fiji, Kenya, Paraguay and Peru.

What dengue fever does

At its mildest, symptoms include fever, headache and nausea. More severe symptoms can include severe abdominal pain and persistent vomiting. Life-threatening complications can include severe organ dysfunction.

Severe dengue is a leading cause of serious illness in some tropical countries and needs intensive care by experienced medical professionals.

With COVID-19 putting health systems under huge risk, the WHO has stressed the importance of continuing to tackle diseases like dengue, especially as case numbers surge.

“The combined impact of COVID-19 and dengue epidemics can potentially result in devastating consequences on the populations at risk,” WHO says.

The virus is transmitted to humans through the bites of infected female mosquitoes, primarily the Aedes aegypti mosquito, which also spreads viruses including yellow fever, chikungunya and the Zika virus.