Epidemiologists are usually cautious, but they have made “astonishing” and “landmark” assessments of the results of a new biotechnology aimed at stopping mosquito-borne diseases. Tests in Yogyalyak, Indonesia, have shown that the release of modified Wolbachia-carrying mosquitoes can prevent the insect from spreading certain viruses, leading to a sharp drop in dengue cases there. The researchers say the results provide the strongest evidence that Wolbachia, developed in the 1990s, could free the world from some deadly mosquito-borne diseases.
Author: Wen Lele.
Some mosquitoes carry Wolbachia. Picture: WMP.
Starting in 2016, mosquitoes carrying Wolbachia were released within six months in randomly designated areas of Yogyast.
The incidence of dengue fever in these areas decreased by 77 per cent in the years after release compared to areas where mosquitoes were not released.
“It’s important to look closely at all the data, but the 77 per cent drop is really extraordinary, which means a lot of hope.” Philip McCall, a biologist at the Liverpool School of Tropical Medicine, said.
The trial, coordinated by the non-profit World Mosquito Program (WMP), hopes to deploy the mosquito to dengue-endemic areas around the world.
Scientists say the results support the technology’s worldwide spread.
The method used in the Yogyast trial was pioneered by a team led by Scott O’Neill, a microbiologist and WMP director at Monash University in Australia.
About 60 percent of insects carry Wolbachia, but the bacteria do not naturally infect the Aedes aegypti mosquito, which transmits dengue, Zika and many other viruses.
Since the 1990s, O’Neill’s team has bred laboratory populations of Aedes aegypti-infected Aedes aegypti and found that these Aedes aegypti mosquitoes do not transmit the virus, including dengue virus.
The team first began releasing the mosquitoes in parts of north-eastern Australia, where periodic outbreaks of dengue fever affect nearly 400 million people worldwide each year, killing 25,000 people, mainly in low- and middle-income countries in Asia, the Pacific and Latin America.
The bacteria tend to spread quickly to local mosquito populations, and a 2018 study in Townsville, Australia, found that dengue fever rates plummeted after 4 million mosquitoes were released in different neighbourhoods.
But the study did not include control areas that did not release mosquitoes.
At the same time, dengue outbreaks in Australia are less severe and less frequent than in South-East Asia and Latin America, where the virus is endemic.
WMP launched the Yogyayaly test to fill these gaps.
Adi Utarini, a public health researcher at the University of Ghazamada in Yogyayalyka, and colleagues divided nearly 400,000 people in the city into 24 clusters, randomly selecting 12 clusters in mosquito-releasing areas and 12 clusters in control areas.
Researchers worked with clinics across Yogyalyo to find 400 confirmed cases of dengue fever out of thousands of cases of acute fever.
They then compared dengue patients, most of them children, over the past two weeks to determine if they were in areas where mosquitoes had been released.
Due to the increasing number of coronavirus cases in Indonesia, the trial in June was several months ahead of schedule. In areas where bacteria are released, dengue cases have decreased by 77 per cent, reducing the risk of developing the disease by three-quarters.
“I’ve never been involved in such a successful study.”
Nicholas Jewell, a biostatists at the London School of Hygiene and Tropical Medicine (LSHTM) and the University of California, Berkeley, says he has been studying infectious disease interventions since the AIDS epidemic of the 1980s.
Jewell believes their estimates of a decrease in dengue cases are conservative because many people may move between areas where bacteria are distributed.
McCall said many questions remain unanswered because the underlying data have not yet been released, such as how protection levels vary from region to region and its association with the prevalence of Wolbachia among local residents.
“The decline in dengue incidence provides strong evidence to support the use of Wolbachia,” said Neal Alexander, an LSHTM epidemiologist. “
Studying how mobility between treatment areas and untreated areas affects conservation outcomes should help determine the availability of released bacteria-carrying mosquitoes elsewhere.
O’Neill’s next step is to scale up.
WMP hopes to release Wolbachia-carrying mosquitoes in areas that cover 75 million people at risk of dengue fever within the next five years and reach 500 million people within 10 years.