Genetic sex change for mosquitoes could stop the spread of Zika

Two US scientists have proposed a new answer to the Zika epidemic: a sex-change operation for the mosquito that spreads the virus and other diseases. This genetic modification would turn deadly, blood-drinking females into harmless, nectar-sipping males.

The solution could potentially be used to limit not just Zika but malaria, dengue, yellow fever and other mosquito-borne infections such as chikungunya. However, the researchers accept there is a long way to go before the technique could be used in the field.

Since the spread of the Zika infection carried by the Aedes aegypti mosquito from Africaacross the Pacific to Brazil, Colombia and other Latin American nations, the British House of Lords has recommended new investment in GM weaponry, and the World Health Organisation in Geneva this week called for both “old and new approaches” to mosquito control.

In the fight against dengue fever, public health officials and scientists have already trialled the release of sterile mosquitoes that engender larvae that do not survive: in theory this could reduce an infectious mosquito population by 90%

A second team has proposed “gene drive” technology that would make a new generation of malarial mosquitos that could no longer be host to the plasmodium parasite that in Africa kills a child every minute.

But now Zach Adelman of Virginia Tech and his co-author Zhijan Tu, report in the journal Trends in Parasitology that a new discovery offers the promise of reducing or eliminating infection rates in all mosquito-borne infections

The duo last year reported the identification of the first male-determining factor in mosquitoes. If this gene was turned on in female embryos, they developed male genitalia.

The discovery raises the possibility that a new and efficient gene-editing technique called Crispr-Cas9 could be used to genetically alter a mosquito and introduce a new approach to infestation.

“We are at a turning point in our understanding of how mosquitoes determine whether to become a male (a good choice for us) or a female (trouble for us) as well as our ability to permanently modify wild populations using gene drive techniques,” said Dr Adelman, the entomologist in the partnership.

And his biochemist colleague Prof Tu said: “This discovery sets the stage for future efforts to leverage the Crispr-Cas9 system to drive maleness genes such as Nix into mosquito populations, thereby converting females into males or simply killing females. Either outcome would help reduce mosquito populations.”

For the moment, the female Anopheles mosquito remains not just the more deadly of the species but one of the planet’s great killers. In 2015, according to the World Health Organisation, there were 214 million malaria cases, which killed 438,000 people, most of them in sub-Saharan Africa, and most of those were children under five. Zika is a relatively mild disease, but infections in pregnant women have been linked to a rise in babies with microcephaly and with greater numbers of cases of an illness called Guillain-Barré syndrome.

Gene drive technology is an idea that has yet to be tested. The Crispr-Cas9 technology is still in its infancy and still the subject of controversy. And researchers have yet to work out just how the Nix gene controls sex determination in mosquitoes. A massive shift in any mosquito population is a long way in the future.

And, the scientists say, such a solution can only work with a proper regulatory structure and with public support. “Partnerships with supporting governments, local collaborators and a willing public will be crucial to establishing field-testing in areas that are most impacted by mosquito-borne diseases.”