So what's to worry about?
The idea of the Oxitec mosquitoes is simple enough: the males produce non-viable offspring which all die. So the GM mosqitoes are 'self-extinguishing' and the altered genes cannot survive in the wild population. All very clever, and nothing to worry about!
But in fact, it's not so simple. In 2010 geneticist Ricarda Steinbrecher wrote to the biosafety regulator in Malaysia - also considering a release of the Oxitec mosquitoes - with a number of safety concerns, pointing out the 2007 finding by Phuc et al that 3-4% of the first generation mosquitos actually survive.
The genetic engineering method employed by Oxitec allows the popular antibiotic tetracycline to be used to repress the lethality during breeding. But as a side-effect, the lethality is also reduced by the presence of tetracycline in the environment; and as Bernish points out, Brazil is among the world's biggest users of anti-microbials including tetracycline in its commercial farming sector:
"As a study by the American Society of Agronomy, et. al., explained, 'It is estimated that approximately 75% of antibiotics are not absorbed by animals and are excreted in waste.' One of the antibiotics (or antimicrobials) specifically named in that report for its environmental persistence is tetracycline.
In fact, as a confidential internal Oxitec document divulged in 2012, that survival rate could be as high as 15% - even with low levels of tetracycline present. 'Even small amounts of tetracycline can repress' the engineered lethality. Indeed, that 15% survival rate was described by Oxitec."
She then quotes the leaked Oxitec paper: "After a lot of testing and comparing experimental design, it was found that [researchers] had used a cat food to feed the [OX513A] larvae and this cat food contained chicken. It is known that tetracycline is routinely used to prevent infections in chickens, especially in the cheap, mass produced, chicken used for animal food. The chicken is heat-treated before being used, but this does not remove all the tetracycline. This meant that a small amount of tetracycline was being added from the food to the larvae and repressing the [designed] lethal system."
So in other words, there is every possibility for Oxitec's modified genes to persist in wild populations of Aedes aegypti mosquitos, especially in the environmental presence of tetracycline which is widely present in sewage, septic tanks, contaminated water sources and farm runoff.
'Promiscuous' jumping genes
On the face of it, there is no obvious way in which the spread of Oxitec's GM mosquitos into the wild could have anything to do with Brazil's wave of microcephaly. Is there?
Actually, yes. The problem may arise from the use of the 'transposon' ('jumping' sequence of DNA used in the genetic engineering process to introduce the new genes into the target organism). There are several such DNA sequences in use, and one of the most popular is known as known as piggyBac.
As a 2001 review article by Dr Mae Wan Ho shows, piggyBac is notoriously active, inserting itself into genes way beyond its intended target: "These 'promiscuous' transposons have found special favour with genetic engineers, whose goal is to create 'universal' systems for transferring genes into any and every species on earth. Almost none of the geneticists has considered the hazards involved ...
"It would seem obvious that integrated transposon vectors may easily jump out again, to another site in the same genome, or to the genome of unrelated species. There are already signs of that in the transposon, piggyBac, used in the GM bollworms to be released by the USDA this summer.
The piggyBac transposon was discovered in cell cultures of the moth Trichopulsia, the cabbage looper, where it caused high rates of mutations in the baculovirus infecting the cells by jumping into its genes ... This transposon was later found to be active in a wide range of species, including the fruitfly Drosophila, the mosquito transmitting yellow fever, Aedes aegypti, the medfly, Ceratitis capitata, and the original host, the cabbage looper.
"The piggyBac vector gave high frequencies of transpositions, 37 times higher than mariner and nearly four times higher than Hirmar."
In a later 2014 report Dr Mae Wan Ho returned to the theme with additional detail and fresh scientific evidence (please refer to her original article for references): "The piggyBac transposon was discovered in cell cultures of the moth Trichopulsia, the cabbage looper, where it caused high rates of mutations in the baculovirus infecting the cells by jumping into its genes ...
"There is also evidence that the disabled piggyBac vector carrying the transgene, even when stripped down to the bare minimum of the border repeats, was nevertheless able to replicate and spread, because the transposase enzyme enabling the piggyBac inserts to move can be provided by transposons present in all genomes.
"The main reason initially for using transposons as vectors in insect control was precisely because they can spread the transgenes rapidly by 'non-Mendelian' means within a population, i.e., by replicating copies and jumping into genomes, thereby 'driving' the trait through the insect population. However, the scientists involved neglected the fact that the transposons could also jump into the genomes of the mammalian hosts including human beings ...
"In spite of instability and resulting genotoxicity, the piggyBac transposon has been used extensively also in human gene therapy. Several human cell lines have been transformed, even primary human T cells using piggyBac. These findings leave us little doubt that the transposon-borne transgenes in the transgenic mosquito can transfer horizontally to human cells. The piggyBac transposon was found to induce genome wide insertionmutations disrupting many gene functions."
Has the GM nightmare finally come true?
So down to the key question: was the Oxitec's GM Aedes aegypti male-sterile mosquito released in Juazeiro engineered with the piggyBac transposon? Yes, it was. And that creates a highly significant possibility: that Oxitec's release of its GM mosquitos led directly to the development of Brazil's microcephaly epidemic through the following mechanism:
1. Many of the millions of Oxitec GM mosquitos released in Juazeiro in 2011/2012 survive, assisted, but not dependent on, the presence of tetracycline in the environment.
2. These mosquitos interbreed with with the wild population and their novel genes become widespread.
3. The promiscuous piggyBac transposon now present in the local Aedes aegyptipopulation takes the opportunity to jump into the Zika virus, probably on numerous occasions.
4. In the process certain mutated strains of Zika acquire a selective advantage, making them more virulent and giving them an enhanced ability to enter and disrupt human DNA.
5. One way in which this manifests is by disrupting a key stage in the development of human embryos in the womb, causing microcephaly and the other reported deformations. Note that as Melo Oliveira et al warn, there are almost certainly other manifestations that have not yet been detected.
6. It may be that the piggyBac transposon has itself entered the DNA of babies exposed in utero to the modified Zika virus. Indeed, this may form part of the mechanism by which embryonic development is disrupted.
In the latter case, one implication is that the action of the gene could be blocked by giving pregnant women tetracycline in order to block its activity. The chances of success are probably low, but it has to be worth trying.
No further releases of GM insects!
While I am certainly not claiming that this is what actually took place, it is at least a credible hypothesis, and moreover a highly testable one. Nothing would be easier for genetic engineers than to test amniotic fluids, babies' blood, wild Aedes mosquitos and the Zika virus itself for the presence of the piggyBac transposon, using well established and highly sensitive PCR (polymerase chain reaction) techniques.
[See Author's notes 1 & 2, below. Recent Zika genome snapshots examined as a result of this article are, in fact, free of the piggyBac transposon.]
If this proves to be the case, those urging caution on the release of GMOs generally, and transgenic insects bearing promiscuous transposons in particular, will have been proved right on all counts.
But most important, such experiments, and any deployment of similar GM insects, must be immediately halted until the possibilities outlined above can be safely ruled out. There are plans, for example, to release similarly modified Anopheles mosquitos as an anti-malarial measure.
There are also calls for even more of the Oxitec Aedes aegypti mosquitos to be released in order to halt the transmission of the Zika virus. If that were to take place, it could give rise to numerous new mutations of the virus with the potential to cause even more damage to the human genome, that we can, at this stage, only guess at.
