The United States has taken another step toward clearing the way for a trial of genetically modified mosquitoes in Florida as a way of reducing populations of mosquitoes that carry Zika.
The US Food and Drug Administration said on Friday that a field trial testing Intrexon Corp's genetically engineered mosquitoes would not have a significant impact on the environment.
The announcement comes as Florida officials ramp up aerial pesticide spraying of a neighbourhood in Miami, Florida - the first state to report local transmission of the virus.
Florida Health authorities have identified 16 Zika cases spread by local mosquitoes and expect there may be more.
Zika, a virus spread by Aedes aegypti mosquitoes, poses the most serious risk to pregnant women.
The virus has been linked to birth defects including microcephaly, which results in small head size and can lead to severe developmental problems in babies.
The Zika outbreak was first detected last year in Brazil, where it has been linked to more than 1700 cases of microcephaly.
Intrexon's Oxitec unit has been working for years to kick off a trial of the mosquitoes in the Florida Keys to assess the effectiveness of its mosquitoes to reduce levels of mosquitoes that carry diseases, including Zika, dengue, Yellow Fever and chikungunya.
The FDA has been reviewing Oxitec's application for use of its technology as an investigational new animal drug.
Its environmental assessment helps clear the way for the company to begin a clinical trial in Key Haven, Florida, which would assess whether the genetically modified mosquitoes will mate with local, wild mosquitoes and suppress their population over time.
Results of that trial would be used to support approval of the company's drug, a process that could take more than a year.
Oxitec's mosquitoes are genetically altered so their offspring die before they can reproduce.
Trials in Brazil, Panama and the Cayman Islands have shown that the Oxitec mosquitoes can reduce localised Aedes aegypti populations by more than 90 per cent.
To begin the trial in Key Haven, however, the company must first await the results of a vote in November seeking community approval for the trial.
Use of the genetically altered mosquitoes has raised concerns among community members about its safety.
Oxitec Chief Executive Hadyn Parry said in a conference call that the vote is non-binding, and the decision about whether to proceed is up to the Florida Keys Mosquito Control District.
As his company awaits the vote, Mr Parry said he intends to ask the FDA for an emergency use authorisation that would make the product available for use to help battle Zika in the United States.
FDA has already approved several diagnostic products under this designation.
That is not likely to be granted under current statutes.
FDA spokeswoman Theresa Eisenman said in an email that there is no "fast-track" designation for new animal drugs, and emergency use provisions in the Federal Food, Drug, and Cosmetic Act do not apply to animal drugs.
The World Health Organization has declared Zika a global health emergency, and has suggested that alternative approaches to fighting mosquitoes that carry the virus might be an important way to suppress mosquito populations.
The virus has spread rapidly through the Americas and Caribbean and its arrival in the continental United States, where Aedes aegypti mosquitoes thrive in the warmer southern states, had been widely anticipated.