Millions of disease carrying mosquitoes are to be freed in a well-meaning bid to decimate natural populations of the malaria-spreading insects.
The lab-grown versions are infected with a disease which prevents natural mosquito populations from breeding.
But some activists fear the disease could transfer to humans ultimately making all human males sterile.
Despite claims it is safe for humans, there are also some concerns, it could affect other arthropods, such as spiders which pray on mosquitoes, therefore increasing populations in the long run, or even people, rendering humans unable to breed.
In a decision that has not been formally announced, the US Environmental Protection Agency (EPA) will allow the release of the killer insects in 20 states and Washington DC.
They have been bred by the company MosquitoMate in a bid to drastically reduce the population of the disease-carrying Asian tiger mosquito (A aegypti), which is responsible for infecting humans with viruses such as dengue, yellow fever and Zika, which has caused birth defects in babies.
The firm creates mosquitoes infected with the bacterium Wolbachia pipientis which prevents natural mosquitoes from breeding.
These risks of humans or other arthropods being affected are said to be extremely low, but the full impact will not been known until mass releases happen, according to scientists.
Canadian blogger Rose Webster is behind a campaign to stop the releases.
She has spent months speaking to scientists and fears that it may be possible for Wolbachia to infect humans, and prevent individuals from breeding.
She is also convinced that Wolbachia releases have actually helped the spread of the Zika virus.
She said: “Wolbachia is responsible for the most widespread pandemics in the animal kingdom.
“Safety tests were never carried out on vertebrate species prior to Wolbachia-infected mosquito releases carried out in Brazil, Columbia, India, Indonesia, Vietnam, China, Australia, California, and Florida.
“It’s akin to putting genetic dynamite in a species.
“Wolbachia can survive about a week in a dead host. Lateral transfers to other species have happened.
“This could be the reason that Zika is spreading out of control.
“Wolbachia doesn’t just magically disappear when these mosquitoes die off naturally or are consumed.
“Here is what I am sure of:
“The CDC and WHO (and Health Canada) have ignored critical scientific facts and solid evidence from ethical scientists.
“Why? I don’t know. Perhaps because some regions of the world are so overpopulated that even certain governments are willing to fund something that is likely cause men to become sterile (Wolbachia) and is the unspoken co-factor amplifying Zika.”
An article about the risk on “truth finding” website Courtofrecord.com said: “Years ago, a laboratory experiment to infect mice with Wolbachia failed.
“Scott O’Neill of Yale Medical School points out that the bacteria are intolerant of the basal body temperature of mammals.
“However, Werren points out that it is too early to dismiss the possibility of Wolbachia infecting vertebrates.
“At least some scientists believe the notion of Wolbachia in humans is not entirely preposterous.”
A February 2015 a scientific study of a patient with non-Hodgkin’s lymphoma who was found to have wolbachia genes was published on clinicalmicrobiologyandinfection.com.
It concluded there was the potential for the bacteria to infect humans.
The report said: “Wolbachia spp should be further evaluated as causes of human infection, especially as Wolbachia infection of mosquitoes is increasingly considered to be a tool for interfering with mosquito-borne transmission of human pathogens.
“The findings suggest the potential for Wolbachia bacteria to infect humans.”
Yet many scientists believe it is perfectly safe.
David O’Brochta, an entomologist at the University of Maryland in Rockville, said: “It’s a non-chemical way of dealing with mosquitoes, so from that perspective, you’d think it would have a lot of appeal.
“I’m glad to see it pushed forward, as I think it could be potentially really important.”
MosquitoMate rears the infected insects in laboratories.
Males, which do not bite, are released into a high mosquito population area.
They mate with wild females, and the infection of Wolbachia into the latter means the fertilised eggs do not hatch, because paternal chromosomes do not form properly.
The plan is that over time the natural population will dwindle.
Stephen Dobson, an entomologist at the University of Kentucky in Lexington and founder of MosquitoMate, said other insect populations, including mosquito predators, are not affected by the lab-grown disease.
There are concerns that female lab-grown insects, which do bite may be released.
Staff currently separate males from females by hand and mechanically based on size differences at pupal stage.
Zhiyong Xi, a medical entomologist and microbiologist at Michigan State University, who leads the project, said this is 99 percent successful, meaning up to one percent released could be female.
Mosquitoes released are then subject to radiation to sterilise females but not males.
The technique has been tested extensively in Brazil, following the 2015 zika outbreak, and populations of disease carriers have drastically dropped in test areas.
There were concerns from the public when another firm Oxitec wanted to test the mosquitoes in the Florida Keys area.
Objections from the public in late 2016 mean the tests were postponed.
Concerns ranged from any risk of the lab-grown insects being able to infect humans, the natural disease carriers becoming immune to them, or it decimating populations of other arthropods, including the spiders that feed on the natural mossies.
Oxitec said only 62 female mosquitoes per person in an area would be inadvertently released, but it was hard to predict how many would land on humans.
An EPA environmental impact document about the plan said: “Mosquitoes have been feeding on humans and other animals for millennia but there is no evidence of DNA transfer between mosquitoes and humans.
“There’s also ‘negligible’ risk that the GM mosquito saliva would have any toxic or allergenic effects on humans.”
Simon Warner, Oxitec’s chief scientific officer in Abingdon, Oxfordshire, in the UK, said there was “no reason to think their lab strain—descendants of mosquitoes collected in Cuba, crossed with a Mexican strain—would be any more dangerous than another strain of (Asian Tiger mosquito) A aegypti.
He said: “Vector competence is not a question that we’ve been asked by the regulators.
“We haven’t studied it, because we don’t think it’s a concern.”
Oxitec said in tests four percent of infected wild mosquitoes went onto to produce offspring, so some could be immune.
Entomologist Zach Adelman, of Texas A&M University in College Station, said: “That’s something that does have to be paid close attention to.
“When Oxitec stops its releases, mosquito numbers will rebound, and it is not clear whether or how the genes from the release strain would influence the recovered population, including how mosquitos seek out hosts, mate, or lay eggs.
“For example, of key concern is how good Oxitec’s strain is at transmitting viruses compared with wild mosquitoes—its so-called vector competence.
“So far, studies of such changes in a post-release population are missing.”
Insect geneticist Max Scott of North Carolina State University in Raleigh said it was a “theoretical possibility” that wild mosquitoes could become immune, but that should not stop the tests.
Express.co.uk found research carried out by the School of Biological Sciences, at The University of Queensland in Brisbane, Australia, in 2010, when they were looking to test a similar system.
The scientific study considered the risk to humans.
It said: “A major concern the community repeatedly expressed was whether Wolbachia could be transferred to humans through the bite of infected mosquitoes.”
However, it said: “Wolbachia have never been found in humans or other mammals, neither in birds, reptiles or fish.”
Despite the limited risks, tests were carried out on people, and no infections were found.
It said: “Both immunological investigations, Western blots and ELISA, show that humans repeatedly bitten by Wolbachia-infected Ae. aegypti develop antibodies against mosquitoes as already described for exposed humans, but do not develop IgG antibody against Wolbachia.
“All those results indicate that Wolbachia antigens are not injected into humans during the mosquito bloodmeal and therefore do not initiate an immune response in human host.”
However, in a section entitled “To implement or not to implement?”, it said the full effects would not be known until they were released on mass.
It said: “A number of experiments were conducted to verify that the Wolbachia-based strategy to control mosquito-borne disease is safe for people, other organisms and the environment.
“The results presented in this paper show that no experimental evidence of any negative impact of Wolbachia-infected mosquitoes was obtained.
“Assessing experimentally the potential consequences that could happen over a long-term period and large geographic scale could be a daunting task.
“Many questions related to long-term consequences can only be assessed once the release is done.
“Questions such as the evolution of the virus in response to the presence of Wolbachia, or the persistence of the virus blocking phenotype after generations in natural population are examples of key concerns for the scientific project and for the community but indeed require a priori the release to be answered.”