GM mosquitoes: inside the lab breeding six-legged agents in the war on malaria

The Guardian

06-05-2025

I n an unassuming building on an industrial estate outside Oxford, Michal Bilski sits in a windowless room with electric fly swatters and sticky tape on the wall, peering down a microscope. On the slide before him is a line of mosquito eggs that he collected less than an hour previously and put into position with a brush.
Bilski manoeuvres a small needle filled with a DNA concoction and uses it to pierce each egg and inject a tiny amount.
'Each slide has between 50 and 100 eggs on it, and it takes from 15 minutes to half an hour to inject them all,' he says. 'Normally in a day we would inject between 500 to over 1,000 eggs.' Michal Bilski's lab can inject 1,000 eggs a day with modified DNA. Photograph: Tom Pilston/Guardian
Bilski, a research and development team leader for the biotechnology company Oxitec, is carrying out one of the early stages in the process of making genetically modified (GM) mosquitoes.
It is hoped the insects that hatch will prove instrumental in the fight against diseases such as malaria, dengue fever, Zika and chikungunya of which mosquitoes are vectors.
Last year, Oxitec released tens of thousands of GM mosquitoes in Djibouti, where there has been a resurgence of malaria caused by an invasive species. It was the first time such mosquitoes have been released in east Africa and the second time on the continent.
It follows multiple releases of modified mosquitoes in Florida and Brazil to combat dengue fever, a neglected tropical disease.
The impact of these mosquitoes on malaria transmission could be significant, believes Lottie Renwick, head of strategy for Malaria No More UK. 'They will play a really major role and be gamechanging,' she says, but adds that the intervention needs to work alongside other tools such as mosquito nets and injections. Workers in Djibouti release a batch of Oxitec's GM mosquitoes. Photograph: Courtesy of Oxitec
Malaria is transmitted by female mosquitoes and is one of the biggest killers of children under five. According to the World Health Organization, in 2023 there were an estimated 263m cases of malaria and 597,000 deaths in 83 countries.
Africa bears the greatest burden (94% of cases) and children under five accounted for more than three-quarters (76%) of all malaria deaths. Normally in a day, we would inject between 500 to over 1,000 eggs Michal Bilski, Oxitec
Djibouti, an east African country of a million people, had been close to eliminating the disease, but cases jumped from just 27 in 2012 to more than 73,000 in 2020. The cause was a species of mosquito that came from south Asia and the Arabian peninsula into Africa.
The Anopheles stephensi mosquito has since been detected in Ethiopia, Sudan, Somalia and Kenya, as well as Nigeria and Ghana in west Africa. According to one study, if this mosquito is left unchecked an additional 126 million people on the continent will be at risk of malaria. If the invasive Anopheles stephensi mosquito is left unchecked, one study estimates that 126 million more people in Africa will be at risk of malaria. Photograph: Tom Pilston/Guardian
It is a big threat because it thrives in urban environments, unlike other malaria-carrying mosquitoes in Africa that primarily breed in rural areas. Cities in Africa are growing rapidly, with more than half of Africans predicted to be urban dwellers by 2035.
Anopheles stephensi has also been found to be resistant to many of the insecticides used to control mosquito populations. They bite in the evening before most people's bedtime – not in the middle of the night like other mosquitoes – making bed nets less effective as protection.
The government of Djibouti – aware of the work to develop and deploy GM mosquitoes to fight invasive species that spread dengue fever in Brazil – has partnered with Oxitec to tackle the threat.
In the laboratory, once every egg has been injected with the DNA, they are taken to a warm and humid room in which the conditions are ripe for them to mature into adults. skip past newsletter promotion
Sign up to Global Dispatch
Get a different world view with a roundup of the best news, features and pictures, curated by our global development team Privacy Notice: Newsletters may contain info about charities, online ads, and content funded by outside parties. For more information see our Privacy Policy. We use Google reCaptcha to protect our website and the Google Privacy Policy and Terms of Service apply.
after newsletter promotion Michal Bilski inserts genes into mosquito eggs. Photograph: Tom Pilston/Guardian
White shelves line the walls; on one side of the room are trays of water with mosquito larvae in them, while on the adjacent wall are plastic boxes filled with fully grown insects. One box has a contraption containing blood on top for the female mosquitoes to feed on. Inside the box the mosquitoes' bottoms are pointing up, a sign that these insects carry the parasite that causes malaria.
It takes four or five days for the 5-30% of the eggs that usually survive the injection to hatch into larvae. In total, an egg typically takes about 14 days to develop into an adult mosquito.
In another room a few doors down, Anna Schoenauer, a team leader, is also glued to a microscope. When she shines blue light on the slide, a group of mosquitoes, magnified on a screen, can be seen wriggling around, glowing fluorescent green. This is as a result of a marker that they were injected with alongside the DNA, to signify whether they are carrying the altered gene. GM mosquitoes carry a gene that stops normal cellular functions. If they mate, female offspring die, while males, which do not bite, mate and spread the gene. Photograph: Tom Pilston/Guardian
The lab-produced mosquitoes carry a 'self-limiting' gene that blocks normal cellular processes, which means if they mate, any female offspring will die. The male progeny, which do not bite, will survive and go on to mate with other wild females. With sustained releases of these 'friendly mosquitoes', more females die off, greatly reducing the mosquito population and the spread of malaria.
Scientists at Oxitec and malaria and mosquito experts insist these mosquitoes are safe. After evaluating the risk, the US Food and Drug Administration in 2016 and the US Environmental Protection Agency in 2022 confirmed that the mosquitoes did not pose a threat to humans or the environment.
Climate crisis 'may put 8bn at risk of malaria and dengue'
There are no results published yet from the work going on in Djibouti, and Grey Frandsen, chief executive officer at Oxitec, acknowledges that much work remains to be done.
'We're working on the invasive species but there are multiple species that transmit malaria,' he says. 'There is no silver bullet in the malaria fight.'
Currently, most of the funding going into technologies such as this comes from international donors and philanthropists. With the Trump administration's shutdown of USAID, the landscape for international humanitarian work has changed, but Frandsen is undeterred.
'We recognise what's happening, and the impact it might be having on the international health community, but this is our time to shine,' he says.
'This is when disruptive tools are needed the most. This is where new technologies have to now play a more important role than ever.'