The federal government has given preliminary approval for a trial to deploy genetically altered mosquitoes in the US as a possible method of fighting the Zika virus. The Food and Drug Administration (FDA) said today that such a field trial would have no significant impact on animal or human health, or on the wider environment. However, the agency still needs to collect comments from the public on the trial — a process that could take months — before the tests can actually go ahead.

Offspring of the mosquitoes die before reaching adulthood

The trial would see genetically altered male mosquitoes released into the wild near Key West in Florida. These mosquitoes — of the species Aedes aegypti — contain a gene that kills the animal (referred to as a "lethality trait") as well as fluorescent markers used for lab identification. When the genetically altered males mate with the local female mosquito population they produce offspring that die while still young, minimizing the spread of diseases carried by the animals, including Zika and dengue.

The FDA says its decision was based partly on data produced by Oxitec, the British company that designs the mosquitoes. This includes a nearly 300-page document outlining the potential hazards involved with the tests. The FDA notes that because the genetically altered mosquitoes will nearly all be male, they can't bite other animals, and that there was "no convincing evidence" that the altered proteins carried by the females could cause allergic or toxic reactions. Most importantly, the mosquitoes will not be able to settle in the wild: any offspring is programmed to die while still young, and the male mosquitoes' lifespan is estimated to be just two days.

"Risk of establishment or spread has been determined to be negligible."

"The consequences of escape, survival, and establishment of [the mosquito] in the environment have been extensively studied: data and information from those studies indicate that there are unlikely to be any adverse effects on non-target species, including humans," concludes the FDA. "Risk of establishment or spread has been determined to be negligible. The investigational trial is short in duration and any unanticipated adverse effects are unlikely to be widespread or persistent in the environment."

Scientist have welcomed the FDA's tentative approval of the trials. Zachary Adelman, an associate professor at Virginia Tech's Department of Entomology, said he was "glad to see that cooler heads have prevailed." He added: "By allowing the trial, the FDA will be signaling that science and evidence-based practices should prevail over the hysteria and irrationality long associated with genetically-modified organisms."

Oxitec, which describes itself as "the only GM insect company in the world," has already carried out trials using its genetically altered mosquitoes in Piracicaba, a city in the Brazilian state of São Paulo. The company said in January that this reduced the local population of Aedes aegypti mosquitoes by 82 percent, and that it was building a new factory in the city to expand the project. Bringing these measures to the US may seem extreme, but it could be necessary as climate change and urbanization help spread mosquito-borne diseases to new regions.