THE BLOG

Why Zika Is Not Caused by Genetically Engineered Mosquitoes

07/03/2016 11:08 GMT | Updated 05/03/2017 10:12 GMT

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*Alexandra Mannerings [nee Kamins - 2009] did her PhD in Veterinary Science at the University of Cambridge and is now a healthcare research analyst for the Colorado Hospital Association in the United States. Picture credit: Wikipedia.

A recent internet-fuelled rumour suggested that genetically modified mosquitos released in Brazil by the company Oxitec caused the Zika virus to become more dangerous, leading to the current public health emergency.

A member of the same viral family as yellow fever and dengue, Zika itself is not new; it was discovered in Uganda in 1947. But there is now some evidence that the Zika virus may be linked to a rise in infants with unusually small heads and brain damage (microcephaly).

The link is not yet proven, but it is surely folly to think that genetically modified mosquitos could have caused any changes in the Zika virus.

What is clear is that there is a wide gulf between scientific understanding and public viewpoint when it comes to genetic engineering despite a number of breakthroughs, including the production of the human insulin now used to treat diabetes.

At its core, genetic engineering is simply a suite of techniques that can deliberately alter the genetic material (the chemical instruction manual) of an organism. Most people are comfortable with "natural" genetic engineering, the kind of genetic changes that arise from selective breeding and that humans have used for millennia that have resulted in our immense array of domesticated livestock and crops. The only difference between choosing which animals to breed and modifying genes in a lab is that, in the former, we are selecting based on the physical trait we see, while in the latter, we are selecting the specific gene or exact bit of genetic material we want.

We have a number of tools at our disposal to make these precise genetic changes. The most important tool is the enzymes, or proteins, that can cut DNA or RNA in specific places. These are like tiny molecular scissors that will only snip a particular genetic sequence. We can then use these enzymes to cut open DNA and insert or remove particular genes.

One method of getting these modified genetic sequences into organisms is to use a transposon. Transposons are special bits of DNA that have the ability to relocate themselves within a genome. Scientists can insert genes into the transposon, using the scissor-like enzymes.

While in many ways these techniques are just more precise versions of selective breeding, the possibility of creating combinations that couldn't occur naturally leads people to think that any organism that is genetically modified in a lab has the possibility of escaping our control, taking over the environment or - worst of all - somehow spreading its mutant genes to other organisms or us. The truth is that just because an organism is genetically modified doesn't automatically mean it has any ability to cause such harm any more than a new breed of dog or rose.

Explaining the science

In the case of genetically engineered mosquitoes, Oxitec [https://bch.cbd.int/database/record.shtml?documentid=105831] used a transposon called piggyBac to modify the Aedes aegypti mosquito. Oxitec added two genes to this transposon, one of which caused the mosquito to die.

Now, the idea that these "jumping genes" have been released into the environment might sound a bit concerning at first. But we are exposed to foreign DNA all the time with no ill effects. Despite the 80% of surveyed - and sadly misinformed - people who support labelling all food containing DNA, the DNA still poses no threat and will never wiggle its way into your cells. DNA is the instruction book for every cell in your body. It is so essential that every living thing on earth has evolved incredibly advanced ways of protecting its integrity and that includes keeping out random bits of foreign DNA.

The only way that Oxitec scientists can create genetically modified mosquitos is with the help of very specific molecular tools, precise chemicals, absurdly tiny needles, microscopes, heat shocks and more - and even then, the success rate is incredibly small. Even if, against all odds, a bit of DNA got into a human cell AND it didn't cause a fatal mistake that caused the cell to simply self-destruct as would normally happen, that would last exactly as long at the cell was around. For most cells, that's a few days to a few months at most. And that would be it; the cell would die, and the foreign DNA would be chopped up along with the cell by the body's clean-up crew. A mosquito simply would not be able to somehow modify another organism with its own genes. It would be even more impossible for the Zika virus to absorb the transposon because the transposon is nearly as big as all the genetic material of the original Zika virus. And if that was not enough, Zika viruses use RNA, not DNA.

Even without evidence showing there are no genetic sequences from a mosquito or modified genes in the genetic material of the viruses causing the latest Zika outbreak, we know scientifically that it's not possible for genetically engineered mosquitoes to be behind this epidemic.

The reason that it is so important for all of us to understand the basics of genetic engineering is because it may be the best and safest recourse we have in response to outbreaks like this. As tragic as it is for the several thousand babies and families that have been infected, on the scale of possible and past pandemics Zika is small. The CDC, for instance, estimates that 60,000 people die each year from dengue and yellow fever, the deadlier cousins of Zika. Stopping these pathogens requires controlling the mosquitoes that carry them. So far, the only other ways that currently stop them is to spread millions of gallons of insecticides and drain out every swamp in which they live - which, incidentally, are the reasons that yellow fever, malaria and dengue are no longer endemic to the US. But does anyone remember Silent Spring? This book led the charge to remove DDT from common use because of its destructive impact on the environment, particularly birds, and DDT was the safest insecticide we've yet found. Genetically modifying mosquitoes provides an environmentally sound, effective and relatively inexpensive way to save lives.

There is a vital need for informed, engaged discussion about what we should do with these rapidly developing tools. Headline-grabbing CRISPR, for example, opens up the ability to edit genomes with unprecedented accuracy and has already been used on human embryos in China. Its potential to prevent disease is immense, but it also opens up huge ethical questions for science, for instance, about so-called designer babies. Of course, we need to make sure we're critically assessing the outcomes of our experiments, but Franken-squitoes and rampant mutant jumping genes taking over the world are not the parts of genetic engineering we need to worry about. What we as humans choose to do with our newfound power should concern us much more.