Trial cuts dengue 77% by infecting mozzies with ‘miraculous’ bacteria

The mosquito-borne disease dengue fever has been a scourge of tropical countries for decades.

Now a research team has found a way to cut infections by 77% in a ground-breaking trial in Indonesia, that manipulates the mosquitoes that spread it.

World Mosquito Programme (WMP) scientists are now taking the method to other regions in the hope of eventually eradicating the virus.

In 1970, only nine countries had faced severe dengue outbreaks but it is now common in more than 100 countries around the world. 40% of the world’s population, about three billion people, live in areas where being infected is a daily risk. It causes severe pain in muscles and bones, and sometimes hallucinations. Outbreaks can overwhelm hospitals.

In the trial, which took place in Yogyakarta, WMP researchers infected mosquitoes with Wolbachia bacteria.

Wolbachia doesn’t harm the mosquito, but it takes over parts of the insect’s body that the dengue virus needs to get into, making it much harder for the dengue virus to replicate, so the mosquito is less likely to cause an infection when it bites.

The trial used five million mosquito eggs infected with Wolbachia. Some of the eggs were placed in buckets of water in the city every two weeks to build up a population of infected mosquitoes, which took nine months.

Yogyakarta was split into 24 zones and the mosquitoes were released in just half of them.

The results, published in the New England Journal of Medicine, showed a 77% reduction in cases and an 86% reduction in people needing hospital care after the infected insects were released.

The technique has been so successful the mosquitoes have since been released across the whole city and the project is moving to surrounding areas with the aim of eradicating dengue in the region.

The WMP director of impact assessment, Dr Katie Anders, told the BBC, “It’s very exciting. We think it can have an even greater impact when it is deployed at scale around the world in large cities where dengue is a huge public health problem.”

Wolbachia are spectacularly manipulative and can alter the fertility of their hosts to ensure they are passed on to the next generation of mosquitoes. This means once Wolbachia has been established, it will continue to protect against dengue infection.

This is in sharp contrast to other control methods – such as insecticides or releasing large numbers of sterile male mosquitoes – that need to be regularly employed.

Dr Yudiria Amelia, the head of disease prevention in Yogyakarta said, “We are delighted with the outcome of this trial. We hope this method can be implemented in all areas of Yogyakarta and further expanded in all cities in Indonesia.”

David Hamer, a professor of global health and medicine at Boston University, said the method has “exciting potential” for other diseases such as Zika, yellow fever and chikungunya, which are also spread by mosquito bites.