Genetically Modified Mosquitoes And Zika: Is There A Case To Answer?


Aedes aegypti

Much has been said about zika virus and the release of genetically modified mosquitoes, but most reports state their cases in black and white. In reality diseases and their spread often inhabit a murky grey area somewhere between the two extremes.

Zika virus was first discovered in Uganda in 1947. It spread to many African countries but not a single case of microcephaly was noted. Not one. It moved out of Africa, still causing the mild flu like symptoms we associate with it today but again there were no recorded cases of microcephaly associated with it. You can see a complete timeline for Zika here.

So what changed? Did anything change? Is it just a case of less medical reporting in Africa? Or maybe immunity to zika having been exposed to it, in the case of women, before reaching childbearing age.

Scientists are saying that something in the mosquitoes has changed as they traversed the globe. The World Health Organisation has not mentioned the release of genetically modified mosquitoes in the area most affected by cases of microcephaly and therefore seems to feel it has no bearing on the steep rise in microcephaly cases.

If you clicked on the timeline for zika you will see that for almost 70 years Zika has done its thing, causing itchy rashes and a mild flu-like illness, then, all of a sudden babies in Brazil are being born with little brain matter and this has now been scientifically linked  to the virus.

In 2015, Oxitec, a British company announced that they had completed a field trial of a genetically modified mosquito:

Releases of the genetically engineered Oxitec mosquito, commonly known as ‘Friendly Aedes aegypti’, reduced the dengue mosquito population in an area of Juazeiro, Brazil by 95%, well below the modelled threshold for epidemic disease transmission.

Juazeiro is the exact same area where microcephalic babies started to be born later that year. Coincidence? Maybe, but it should be taken into account that the company had released GM mosquitoes in Brazil before, three years before in 2012  according to The Guardian. Could this second release of adulterated mosquitoes be having an effect on the microcephaly rates in the area?



The problem with genetic modification is the possible unanticipated side effects. The use of ‘Judas‘ animals is not unheard of. Sterile goats fitted with radio transmitters were introduced into the Galapagos island to stop the spread of wild goats wiping out flora found nowhere else on the planet. More recently Sweden has introduced Judas racoon dogs to halt the spread of the animal that they feel threatens local wildlife. Both of these cases involved getting rid of something that was introduced and was/is affecting indigenous flora and fauna. They are animals that were captured, sterilised and released back into the wild no longer able to reproduce but capable of leading hunters to others of the same species in order to eradicate them.

Mosquitoes are rather different, it would be impossible to trap and individually sterilise the males to prevent impregnation of the females, so a different approach was adopted.

OX513A was the name given to the modified male mosquitoes that were released in Brazil. They were bred in a lab in the UK and modified to require tetracycline, an antibiotic, to stay alive and destined to die if they didn’t get a regular supply of it.

All well and good so far.

Except they didn’t all die without the Tetracycline. The Department of Biosafety, Ministery of Natural Resources and Environment of Malaysia (sic) reports that 3-4% of the GM mosquitoes don’t actually die, they go on breeding and reproducing at their usual alarming rate. 

In theory at least a mosquito that bit a person or animal that had tetracycline in their bloodstream would survive and possible thrive, but more importantly why did 3-4% of the released mosquitos survive? What ongoing and unexpected effects could that have on mosquitoes and the humans they bite?

Eleonore Pauwels, a member of the Science and Technology Innovation Program at the Woodrow Wilson International Center for Scholars in Washington, D.C. speaking at an event in Washington in February said:

“We now have the power to hijack evolution.Many people think it’ll be efficient and predictable. But that’s not the case here. We need to know how to talk about to the public, so they understand the risks.” (source)

At the same event, called by President Obama to call for funds to fight the zika virus, Kevin Esvelt, a genetic researcher at MIT’s Media Lab is quoted as saying:

“It is not something that we should do lightly — to deliberately alter the traits of a wild population. Even with something like a mosquito, which most of us are probably not very fond of, there might be unexpected ecological side affects.”

One also has to ask the question as to why Colombia, a neighbour of Brazil has recorded more than 20,000 cases of zika but has only reported a small increase of microcephaly related to zika. (up to April 16th 2016)

Mosquitoes are food for a wide variety of animals and birds and the knock on effect on those animals is unknown, as is the effect of those mosquitoes getting into the human food chain by the same mechanism.

In 2012, after the first release by Oxitec published a report into ongoing concerns and risk assessments of Oxitec’s ‘experiments’.

No risk assessment was published for public scrutiny or consultation prior to releases of GM mosquitoes in the Cayman Islands or Brazil. In Malaysia only a summary was published. GeneWatch has obtained copies of the risk assessments in the UK because they must be provided by Oxitec when exporting GM mosquito eggs for open release for the first time to a given country. In no case did the company correctly follow this notification procedure, with the result that there was no independent scrutiny of whether these risk assessments met the required European standards.

Oxitec has repeatedly referred to its GM mosquitoes as sterile, when this so-called sterility is partial and conditional. The GM mosquitoes do breed and most die at the larval stage: the extent to which their offspring survive to adulthood is one of many factors which influences the efficacy and safety of this approach. (my emphasis)

The debate over genetically modified insects, animals and foodstuffs will continue to rage, with the scientific community split over whether the advantages outweigh the problems, both the known and the unknown.

It seems slightly out of whack that a small group of elite scientists get to decide on matters that could potentially affect all of us. The problem with releasing genetically modified insects back into the wild is that unlike goats and racoon dogs they can’t be tracked, trapped, recalled or eliminated in numbers large enough to eradicate any unforeseen problems their release has created, and this in itself is a major problem of releasing genetically modified insects of any kind.

Take Care


18 thoughts on “Genetically Modified Mosquitoes And Zika: Is There A Case To Answer?”

  1. Liz, I had not heard of this correlation before. Quite interesting. I wonder if the GM mosquitos will be outbred by the native mosquitos or whether, like African honey bees, they outcompete and spread beyond their original release area. Do you have any information on whether the GM mosquito population is expanding? The few cases in Colombia says that they might be spreading but perhaps slowly.

    1. Hiya Steve,

      I don’t have anything more at this point…I have dug around for a couple of weeks trying to find out about some of the things you mention but no joy so far sadly. I called Oxitec…sadly nobody there wanted to talk to me lol. I would think, using logic, that the native mosquitoes should outbreed the GM ones, especially as the GM mosquitoes do not seem to breed as well as the unadulterated bugs. Having said that nature throws up many surprises.As you point out, Africanised bees managed it and if my memory serves me correctly in comparison to the population of ‘regular’ bees a miniscule number of African bees were released. I am watching for an increase in casein Colombia but as you say it could be a slow burn thing. Mosquitoes typically fly slow and low and don’t tend to move more than a few miles from the area they matured in, estimates vary but all come in at just a few miles, further with a bit of wind but not the distance to Colombia. Travellers can spread them, they get into luggage etc.

      What I would like to know is when they bred the ‘several generations’ of mosquitoes in the lab did they check to see the results if two GM mosquitoes get it together? In theory this shouldn’t happen as only males are fed tetracycline and released but, and it’s a big but the mosquitoes are ‘manually sorted’ and scientists outside Oxitec say that it’s impossible that the odd female doesn’t get through and gets released with the males. Of those that survive, which depending on how many were released could be a sizeable number, what happens when they get into the food chain? This really concerns me on every level. There are so far too many unanswered questions in my opinion and I think the companies doing this type of modification should be forced to be more transparent. Like I said, it’s not like doing these sorts of experiments with a goat that you can tag and trap if things go wrong. These bugs are out there and will continue passing on their altered genetics down the generations and considering a female can lay 500 eggs over the course of several days from just one sexual encounter I worry that the Africanised bees scenario you mentioned could become reality and super-mozzies could emerge from this.

      Thanks so much for commenting, plenty of food for thought on this one I think.

      Take Care



      I was surprised that this was the second release of the GM mosquitos in Brazil, not much was said about the 2012 release. Also there are many things I would like to know, for example,

      1. Thanks, Liz. I just shake my head at the way these companies automatically assume everything will work out, that their processes will work 100%. The company that worked on salmon that would grow all year said none would ever be released from their pens – uh huh. This mosquito firm knows their selection process is less than perfect, but that’s OK, we’ll release them anyway. GMO plants won’t spread from their test fields – uh, huh. It’s either greed, or arrogance, or a complete inability to think past their noses. Could it be that people who decide to work on this kind of stuff self-select into groups of believers who cannot imagine that their fantastic work could have a flaw or fail?

        1. Hiya Steve

          I couldn’t agree more. With mosquitoes spreading so many killer diseases I really believe we should n to be altering them unless the results of such alterations are certain and scientifically tested by people with no money or kudos invested in the company concerned. There is no idea of the reactions of humans to the bites of GM mosquitoes, because as you rightly say they didn’t accept that some of their bugs would live on.

          Thanks for commenting


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