A female Aedes aegypti mosquito in the process of acquiring a blood meal from a human host. (James Gathany/Centers for Disease Control and Prevention via AP, File)

In the global rush to find a way to stop the spread of the Zika virus, a new player has emerged — a genetically modified mosquito whose developers claim it could be a game-changer. But while initial reports of the mosquito’s effectiveness at halting the disease seem promising, the GM bug is still quite a new item in the global arsenal of anti-mosquito weapons — and there are a number of factors that could determine whether it will really succeed.

The mosquito, a product of the British biotechnology company Oxitec, is designed to reduce populations of Aedes aegypti mosquitoes — the species best known for carrying dengue fever, chikungunya, yellow fever and now Zika virus — using a relatively simple concept. Oxitec has introduced a “self destruct” gene into its mosquitoes that causes new generations of the bugs to die before they reach adulthood. Releasing batches of the modified insects and allowing them to mate with wild Aedes aegypti can knock out new generations and reduce mosquito populations.

The Oxitec mosquito has made it to field trials in several countries already, but the biggest ongoing project has taken place in Brazil, the epicenter of the current Zika crisis. Brazil is the first country in which the GM mosquito has made it out of field trials and been permitted for limited use as a control method. It’s currently deployed in the city of Piracicaba in what’s called the “Friendly Aedes aegypti” project, and is awaiting government safety approval for use throughout the country, according to Oxitec CEO Hadyn Parry.

The Oxitec mosquito has been the subject of numerous headlines in recent weeks — first, for its novelty as a disease control agent, but more recently as the subject of a conspiracy theory suggesting that the release of the GM bug in Brazil somehow helped cause the current Zika crisis. Experts have largely dismissed that theory, however, and focused on the GM insect’s potential to help stop the spread of the disease instead.

Reports from Oxitec on the success of its field trials have been glowing so far — the company claims that the GM bug has reduced Aedes aegypti populations by upwards of 90 percent in its trials. And according to Parry, models have suggested that these reductions lower mosquito populations below the threshold required for effective disease transmission (although he cautions that this information is based on models alone and not field studies).

“Certainly people seem to be very happy with the results so far,” he told The Washington Post.

So, for all appearances, the GM bug could be a major new contender in the fight against Zika and other mosquito-borne diseases. However, there are a few other points to consider that may affect the ways and locations in which the bug is used in the future.

The consequences of knocking out Aedes aegypti

One notable concern is whether there are any negative side effects associated with eliminating Aedes aegypti populations in the wild. Some experts believe that such an outcome would leave an ecological hole, so to speak, that another species would eventually move in and fill.

“If you really suppress Aedes aegypti, an ecological equivalent is going to fill that background — most likely Aedes albopictus,” said Phil Lounibos, a University of Florida entomologist and mosquito expert.

Aedes albopictus, more commonly known as the Asian tiger mosquito, is another species of mosquito found in many of the same locations as Aedes aegypti. This species possesses the ability to transmit some of the same diseases commonly carried by Aedes aegypti, including dengue fever, although it’s not considered the primary vector in most cases and it’s still unclear how effectively it can transmit Zika virus, if at all.

So while more research is needed on the effectiveness of Aedes albopictus at transmitting certain diseases, there is the hypothetical possibility that it could rise up and take Aedes aegypti’s place as a vector. In that case, “the alternative could be that [Oxitec] will need to have a GM Aedes albopictus to suppress that,” Lounibos said.

In fact, Oxitec is already working on a genetically modified Aedes albopictus — however, it’s still in the early stages of testing and far behind the GM Aedes aegypti in terms of when it might emerge as a commercially viable product. In any case, Parry emphasized that Aedes aegypti is still considered the primary vector in the spread of the most troublesome diseases, including dengue fever and Zika virus.

So in the very worst case, where you find that you eliminated Aedes aegypti in an area and the Aedes albopictus went up, then you would actually be replacing a very dangerous vector with a far less effective one,” Parry said.

Stacking up against other mosquito controls  

Of course, ecological concerns also arise with more conventional forms of mosquito control, such as pesticides, which are also designed to reduce insect populations as much as possible. And pesticide use can have spotty success as a control method, Lounibos noted, because it’s so difficult to effectively target adult mosquitoes and their larvae with pesticide sprays.

So that’s a point earned for the GM mosquito, which requires fewer tactical considerations in comparison. But there are other contenders, too.

An Australian research project known as the Eliminate Dengue program has turned to a different kind of altered mosquito with great success, Lounibos said. The project’s researchers have infected their Aedes aegypti mosquitoes with a bacterium called Wolbachia, which is naturally found in other insects, although typically not in mosquitoes. The bacterium — which can then be passed down to new generations in the insect’s eggs — is known to reduce mosquitoes’ ability to become infected with dengue fever, which then prevents them from transmitting the virus to humans. Theoretically, it could have a similar effect on Zika.

The benefit of this tactic is that it doesn’t actually kill off mosquito populations — it just renders them less effective at spreading disease. So the ecological concerns associated with removing an entire species from an ecosystem become irrelevant, Lounibos said. 

The first tests of the Wolbachia-carrying mosquitoes began in Australia in 2011, but the Eliminate Dengue program has begun limited field trials in Vietnam, Indonesia, Colombia and Brazil.

Winning approval — both public and bureaucratic

Between the two modified bugs, the Oxitec mosquito is still ahead in Brazil in terms of how far it’s gotten in the approval process and how much press it’s received. It’s also still unclear how effective the Wolbachia mosquitoes will be at reducing Zika transmission, although they’ve shown success when it comes to dengue. One additional hurdle that the Oxitec mosquito may face when scoping out new locations for field trials in the future, however, is its status as a genetically modified organism.

One of the benefits of the Aussie technique to eliminate dengue is that the Wolbachia is a naturally occurring bacterium that is not regarded as GM,” Lounibos said.

In most places where field trials have been conducted so far, the insect’s GM status hasn’t seemed to be much of a problem for public opinion. However, it has received some pushback in the U.S. — notably, in the Florida Keys, where Oxitec has proposed a field trial.

Many of these fears have centered on whether the insect’s genetic modifications make it safe for the environment and safe for any humans that may potentially be bitten by a modified bug. However, Lounibos — who is based in Florida — said, “I don’t think most of the fear about the GM mosquito has a good scientific or logical basis.”

Such fears may also be a luxury that U.S. communities unlike those living in other, tropical countries — can afford, given that dengue outbreaks are sporadic and Zika reports so far have been few, isolated and travel-related.

What we’ve found is that where you have the disease present — and I mean dengue or chikungunya or Zika — where you’ve got the disease, then people very rapidly take to our solution, because they don’t like the disease, they don’t like mosquitoes,” Parry said. “They’re very keen that someone’s working on a way of getting rid of the mosquito and reducing disease.”

And while he acknowledged that anti-GMO camps are not likely to change their minds easily, he also said that such groups tend to represent small percentages of their communities.

A bigger hurdle to the GM mosquito’s success as a global tool might be simply the bureaucratic hoops it’s required to jump through to receive regulatory approval. In any country where the GM mosquito might be useful, government approval is required — first for field testing, and then later for regular use.

That said, Parry pointed out that once approval is gained in one or two countries, other governments might be willing to fast-track the mosquito’s approval in their countries using existing data. In any case, how these situations play out will proceed on a country-by-country basis and a concrete timeline can’t necessarily be predicted.

For now, if its success as a disease control agent grows in Brazil, Lounibos predicts that the GM mosquito will continue to gain global popularity and status. In the meantime, conversations about the pros and cons of different control methods will almost certainly grow more pressing as the Zika virus continues to spread in the Americas.

Which control method wins out remains to be seen — but Parry is optimistic about the future of the Oxitec mosquito. The company has made recent plans to expand its project in Brazil, and he expects to see its success continue.

“There’s not a single country, there’s not a single team, that has actually managed to [fully] control this mosquito today in terms of an open environment,” Parry said. “And I think what we offer is a way of doing that.”