Five years ago when Key West, FL, had its dengue outbreak, the regional mosquito-control agency stepped up truck and aerial spraying using larvicide and handheld adulticide foggers and ovitraps, even going door-to-door to find mosquito breeding sites.
Now, the Florida Keys Mosquito Control District hopes a preventive measure can stave off a future outbreak of dengue or another mosquito-borne viral disease, chikungunya. The district wants to deploy mosquitoes genetically modified by Oxitec to combat mosquito-borne diseases, saying the approach is not only safer and cheaper, but more effective.
Oxitec is seeking FDA approval for a field trial of the company’s GM mosquito. The field trial would take place in Key Haven, FL, some four miles north of Key West, where the City Commission in 2012 passed a resolution opposing the test.
Key West officials have sided with residents in and around the resort community, joined by several environmental groups. They argue the GM mosquito plan is unnecessary and poses potential environmental and safety risks that outweigh its benefits and should be examined before any decision.
The district and Oxitec say the need for genetically modified mosquitoes has increased in the eight months since the first locally-acquired case of chikungunya was reported in Florida. The outbreak began on the French side of the Caribbean island of St. Martin in December 2013, and has grown to more than 1.2 million cases (1,217,093 suspected cases, 27,529 confirmed locally acquired cases, and 3,471 imported cases) as of February 20, according to the Pan American Health Organization. Cases have been reported in the U.S. and some 50 Caribbean nations and territories.
“The issue here is that Florida is at risk,” Oxitec CEO Hadyn Parry told GEN. “They [the district] are worried because they know they have the mosquito, and they know they can’t control it. The game plan is, let’s give ourselves another tool, because if we do run into a problem, and we do run into a disease issue, then we’ve got another tool with which we can combat this.”
Oxitec’s assurances have been met skeptically by local residents and environmental groups. As of February 26, 150,354 people signed a petition posted on Change.org by the owner of a Key West real estate firm, Mila de Mier, opposing the field trial.
“Nearly all experiments with genetically modified crops have eventually resulted in unintended consequences: superweeds more resistant to herbicides, mutated and resistant insects, also collateral damage to ecosystems,” the petition reads. “Why would we not expect GM (genetically modified) insects, especially those that bite humans, to have similar unintended negative consequences?”
While no cases of dengue have been reported in Key West since October 2010, according to the district, mosquito suppression offers the best option for protecting public health, especially if types 2-4 should occur (a type 1 strain was associated with the 2009-10 outbreak and its associated 88 cases). Oxitec has also cited the chikungunya outbreak, which includes 11 confirmed cases in Florida.
Walter J. Tabachnick, Ph.D., director of the Florida Medical Entomology Laboratory at the University of Florida, Institute of Food and Agricultural Sciences, told GEN the chikungunya outbreak’s small number of cases in Florida poses a conundrum for the community: There’s no epidemic, yet Oxitec’s trial won’t work should one occur. While conventional spraying has been effective against common outdoor mosquitoes that breed in marshes and swamps, he said it won’t be effective on urban mosquitoes like aegypti, which breed in and around houses, in areas that collect water: “That’s the compelling idea of having the male mosquitoes go out and do the work for you.”
Oxitec says “it’s very unlikely” its mosquito would have any major effects on local ecosystems, saying they would benefit from removal of aegypti since it is an invasive species. The company acknowledges dengue can mutate, but says reducing the number of mosquitoes can prevent new outbreaks.
A Tale of Two Species
Critics have raised concerns that controlling Aedes aegypti may result in another mosquito species, Aedes albopictus, spreading disease. Both are vectors of chikungunya and dengue viruses.
Dr. Tabachnick believes that is unlikely in the Florida Keys, where albopictus has not been able to establish long-term populations. But in a study published in January, two Smithsonian Tropical Research Institute researchers cited two earlier studies suggesting that aegypti may be less effective at reducing chikungunya and dengue outbreaks without efforts to lower the albopictus population.
Writing in PLOS Neglected Tropical Diseases, Matthew J. Miller, Ph.D., and Jose R. Loaiza, Ph.D., who is also at Panama’s INDICASAT AIP, said supplanting aegypti with albopictus “could have both favorable and unfavorable consequences that are difficult to predict a priori.”
The researchers also raised the possibility that Oxitec’s success against aegypti in Panama—the company said January 27 its Panama trial reduced that population by “over 90%”—could be reversed without continuous release of modified mosquitos.
Dr. Tabachnick agreed repeated mosquito releases will likely be needed: “This is not a one-bullet type of strategy. This is a strategy that is going to require continual application.”
Parry said results of Oxitec’s initial release will determine whether and how it carries out subsequent releases.
“What Oxitec hasn’t answered is, what kind of effect will multiple releases have on the ecosystem?” Jeremy Gruber, J.D., president and executive director of the Council for Responsible Genetics, told GEN. “That’s not to say that we know that these mosquitoes will absolutely harm the environment, or they will absolutely harm humans. But that potential is there, and that potential needs to be fully and thoroughly investigated through peer-reviewed study.”
Especially, Gruber added, since past field trials have occurred in less-developed areas where residents lack representation and means to ensure their views are heard: “They (Oxitec) have done that intentionally, to ensure that they can move through these field trials without limitation.”
Parry counters that Oxitec carries out trials where directed by local authorities, and dismisses as “pretty good nonsense” the argument that it seeks to exploit poorer areas.
FDA spokeswoman Theresa Eisenman told GEN the agency is reviewing information on Oxitec’s field-trial plan and mosquito, “in consultation with government experts.” The agency won’t discuss details of its review, citing confidentiality concerns.
“FDA will not support a field release until it has thoroughly reviewed all the necessary information and assessed potential environmental impacts. We cannot offer a timeline for when FDA will complete its review,” Eisenman said.