Another week, another ridiculous conspiracy theory. While perhaps not quite as outlandish as the idea that Earth is flat, which has somehow resurfaced much to the dismay of scientists, it has now been claimed that genetically modified organisms (GMOs) are responsible for the outbreak of Zika virus.
According to media reports, “critics” have identified a suspicious trend that could implicate the release of GM mosquitoes, designed to reduce the burden of insect-borne diseases, as a possible cause of South America’s current epidemic. Namely, that where these insects were released in trial zones in Brazil coincides with the outbreak’s epicenter.
Now, this is repeated a lot in science, because situations such as this call for it: correlation does not imply causation. If it did, then we could say that a reduction in the number of pirates caused global warming. Regardless, this claim is actually not true: Trial sites of these insects were in fact more than 400 kilometers (250 miles) from the centers of disease outbreak, British Biotech firm Oxitec said in a response. In addition, this species of mosquito only flies a couple of hundred meters in its entire lifetime.
— The D.C. Clothesline (@DCClothesline) January 29, 2016
Zika is not a new thing – we’ve known about this virus for more than half a century, while outdoor trials for Oxitec's GM mosquitoes only began in 2009. First identified in a monkey in Africa back in 1947, Zika subsequently spread to Asia but gained little attention, presumably because symptoms are generally so mild that few cases were identified or reported. Things then stayed quiet until 2007 when it surfaced in the South Pacific and caused several large outbreaks.
While we don’t know how Zika subsequently ended up in South America, it’s been speculated that it was brought over to Brazil during the 2014 World Cup by travelers coming from an affected area. The Aedes aegypti mosquitoes that spread Zika, alongside dengue and other serious viral fevers, are abundant in Brazil and throughout Latin America, so an infected traveler seems a likely route of entry.
But the idea is that somehow, GM mosquitoes exacerbated the situation. These insects have a gene that causes offspring to die before they’re mature enough to reproduce, so by releasing them in sufficient numbers, they successfully compete with males in the wild for females and ultimately end up significantly reducing populations.
To be able to raise these insects to sufficient numbers for release, scientists engineered a system whereby the lethal gene is switched off in the presence of an antibiotic called tetracycline. Sometimes used in agriculture to boost livestock growth, this drug gets excreted by animals and is known to be present in the environment in small amounts. There has therefore been concern that this could allow the modified mosquitoes to persist in the environment, but studies have shown that the amount the insects would be exposed to isn’t enough to reduce the effectiveness of the system.
"Brazil actually banned the use of tetracycline in agriculture food additives in 2009," Andy McKemey from Oxitec told IFLScience. "But even if it was present in the environment where mosquitoes lay eggs, it wouldn't result in more mosquitoes than you would have otherwise. The offspring would still contain the gene, so the next generation would die. The efficacy of the gene is not lost."
The modified mosquitoes also have fluorescent genes so that they can be monitored in the environment. Oxitec
Moreover, trials have consistently shown that releases result in local population suppression rates of greater than 90 percent. This is compared to traditional methods, such as insecticide spraying, which only drop numbers by around 50 percent at best and also have negative impacts on the environment. And this is beginning to have demonstrable effects on disease transmission. Following a trial in the Brazilian city of Piracicaba, dengue cases dropped from 133 in 2014/2015 to just one in 2015/2016. To unjustifiably smear an approach that has real potential to safely make a difference and save lives is therefore extremely irresponsible.
There have also been genetic comments regarding genetic modification, stating that we don't know all of the possible effects of the inserted genes. But McKemey points out that the system is highly controlled and well-understood, unlike previous sterile insect methods which involved blasting insects with radiation and causing random mutations. "The gene represents a tiny fraction of the total genetic makeup of the insect," he adds.
With no proof to substantiate the claim that GM mosquitoes caused the Zika outbreak, it’s best to treat the idea as it is: a conspiracy theory. In addition, any websites that compare verified genetic techniques to "Jurassic Park" are probably best ignored.