Scientific Uncertainties and Regulatory Gaps Related to GM Mosquitoes


Dear friends and colleagues

Re: Scientific uncertainties and regulatory gaps related to GM mosquitoes

We are pleased to highlight below two articles on GM mosquitoes that have been recently published in the Council for Responsible Genetics’ magazine, GeneWatch (Volume 25, Issue 3, April-May 2012).

The articles focus on the biosafety issues – the scientific uncertainties and the regulatory gaps – that are raised by Oxitec’s RIDL GM mosquitoes, which have been released in the Cayman Islands, Malaysia and Brazil. Given this, a thorough analysis of the appropriateness of this strategy is warranted.

We thank GeneWatch for permission to reproduce the articles. They are available at:

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Item 1


By Camilo Rodríguez-Beltrán

In 2010 I read for the first time about the initial field experiments of genetically engineered mosquitoes that had taken place a year earlier in the Cayman Islands. This news came as a surprise to me, as I considered myself part of the independent scientific community continuously monitoring modern biotechnology advances and applications. Although British biotech company Oxitec’s venture in developing GE mosquitoes was known, the astonishment came from the sudden jump to field release. I soon realized that I was not the only one missing a year of surveillance on this exercise: the release remained a de facto confidential test for a year.

It was difficult to understand the silence, intentional or not, on the experimental release of these mosquitoes, in particular because there were not hidden military or obscure purposes underlying the technology. In fact, the intended use was described as a tool to tackle dengue fever, one of the major public health issues in many developing countries. With over 50 million infections every year, the fight against this disease is one of the most important priorities for societies not only in the developing world but also in some regions of the developed world. Strategies range from vector management to early and accurate diagnosis, and while the research on vaccines and viral drugs is under development, no commercial vaccine is available for the moment.

Aedes aegypti is the principal, but not only, species of mosquito capable of transmitting the virus through bites from the female to humans. For this specific case, the technological strategy revolves around the release of mainly male engineered A. aegypti mosquitoes. This technology is called RIDL—Release with a Dominant Lethal—where the insects carry a specific genetic switch that under certain conditions causes death at the larval stage of their offspring. This application aims to reduce the incidence of dengue fever by suppressing the mosquito population.

At the molecular level, these GE mosquitoes have been designed with two transgenes. The first one (DsRed2) produces a red fluorescency in the organism under white light. This is a useful marker for selection and also for monitoring. But the most interesting, and also complex, piece of the system comes from the second transgene, the RIDL regulation system.

Imagine your office door slightly open on a windy day: little by little the door opens more and more as the wind pushes through. You can stand up to try to close it but the wind is so strong that it will reopen it again, and at one stage the door will be so wide open that the wind will be strong enough to create a chaos (flying pages, knocking over the coffee cup etc.). But suddenly you find the key to that door, and by closing the door you have reduced the flow necessary to create the chaos. Well, that is the RIDL system, a positive genetic feedback loop that produces a protein (tTAV) that is able to guide more production of itself (by acting positively on its own genetic promoter). This results in an over expression of tTAV, at a concentration that becomes lethal to mosquitoes’ larvae. However there is one antidote, a chemical called tetracycline, which if present will bind the tTAV protein, reducing its presence in a free form to activate its promoter. tTAV will still be produced, but at a lower concentration with no toxic effect for the larvae. Just like the absence of a key allowed wind to knock over the coffee cup inside the office, absence of tetracycline will produce a lethal effect at the larval stage of the mosquitoes.

From a biosafety standpoint, risks related to these organisms follow some general issues:

(1) On modified mosquitoes: What will be the consequences in the ecological network of mosquitoes? What will be the effect on preys and predators? What will be the influence in other species of disease carrying mosquitoes? Could they benefit from a reduction in competition? Can the virus adapt better to other vectors because of this selection pressure?

(2) On GE organisms: What is the effect of the exposure to the DSRed2 and the tTAV proteins? What is the likelihood of instability of the genetically added trait? Could it evolve resistance to the lethal mechanism?

There are other specific issues related to the ability of flying and the difficulty of monitoring the distribution of the mosquitoes (in particular during transboundary movements), as well as issues related to the associated technology (for example, the need to act under absence of tetracycline).

Some of these uncertainties regarding the implications on ecosystems and health have apparently been accepted by some risk assessors, who have given approvals for the field release of the GM mosquitoes not only in the Cayman Islands but also in Malaysia and Brazil, with further approvals pending in the United States. Some have highly criticized the scientific approach used on these regulatory processes, and another article in this issue of GeneWatch addresses the regulatory gaps in these experiences.

I believe that the issues related to the associated technology are of particular interest. It has been acknowledged by Oxitec that in the absence of tetracycline, the survival rate of the GM mosquito larvae is about 3% under laboratory conditions (the specific reasons for this percentage of survival are unknown). It is interesting that some of the strongest discussions with the promoter of these technologies are about the numbers of surviving mosquitoes: Does it matter? Is it significant? Is it negligible? Debates are currently ongoing and will continue, but the fact is that the potential of having survivors is a reality, and some of these will be females—and female mosquitoes, genetically engineered or not, bite humans.

Another interesting factor is that the survival rate of GE mosquitoes can be underestimated in real conditions—not only because of the possibility of building a genetic resistance, but in particular because the antidote, tetracycline, is one of the major antibiotics used both for human health and agricultural practices. The major concentration of tetracycline in urban areas is likely to be in sewage systems, and recent literature has shown that A. aegypti does breed in dirty water; therefore the scenario of breeding and development in potentially tetracycline-contaminated aquatic environments, with the risk of suppressing the lethal system, should now be considered. One could argue that the concentrations in these environments will not be enough to trigger survival, but in order to know this a meticulous surveillance system of tetracycline concentration over time will be needed in the regions intended for release. For the moment I am not aware of any such initiatives, and I believe these will be very expensive and hard to put in place.

Aside from these questions, what has not been covered is a thorough analysis of the appropriateness of this strategy. It seems that the context is not ready for the technology. The RIDL system was not developed to tackle dengue; before mosquitoes, the technology was designed for cotton bollworms, and it seems that other agricultural pests will be targeted in the future. In other words, rather than developing a technology for the purpose of reducing the incidence of dengue fever, Oxitec developed the technology first and then looked for situations where it could be put into use. In this particular case, the use of tetracycline as an antidote makes things out in the environment a little bit more complicated. If the technological solution had started from the real challenge or opportunity then it seems very unlikely that it would rely on an antidote that is currently available exactly where you don’t want it: in the waters where mosquito larvae grow.

I advocate for challenging solutions that rely solely on technology and forget to start from a context-centered approach. I put the weight on the challenge not really to the private companies, but on the governments and public research initiatives that should be deciding the best for all. Before asking “Does it work?” we need to ask: “Is it appropriate?”

Camilo Rodríguez-Beltrán, MSc, is co-founder of the Taleo Initiative and was awarded the TEDGlobal2010 Fellowship.

Item 2


By Lim Li Ching

In December 2010, 6,000 genetically modified mosquitoes were released in my country, Malaysia. This followed releases of large numbers of mosquitoes engineered with the same modification—a dominant lethal gene—in the Cayman Islands, where over 3.3 million GM mosquitoes were released in 2009 and 2010. Since February 2011, more than 3 million of these mosquitoes were released in the city of Juaziero in northeastern Brazil. The release of these same mosquitoes is currently being considered in the Florida Keys in the United States. Many other countries are reportedly evaluating the GM mosquitoes for laboratory research and possible future field releases.

The genetic modification in question targets Aedes aegypti, commonly known as the yellow fever mosquito, which is a vector of dengue fever and other diseases. The so-called RIDL technology involves a genetic regulation that, in the absence of the antibiotic tetracycline, causes death at the larval stage of the offspring. The release of mainly male GM mosquitoes carrying this lethal gene is intended to result in mosquito population suppression, with the consequent aim of reducing the incidence of dengue fever.

The GM mosquitoes were developed and the associated technology patented by the UK-based company Oxitec, which appears to be approaching many countries and offering the mosquitoes as a potential solution to the dengue problem. Dengue fever is a serious problem in many countries, and authorities are increasingly looking for alternatives, as tools such as pesticides are rendered ineffective due to resistance development.

However, the release of these GM mosquitoes into the environment raises many scientific, social, ethical and regulatory concerns. Even while these issues are still being debated, it seems that there is a headlong rush to release the GM mosquitoes.
The situation is compounded by the fact that the international regulatory and risk assessment frameworks governing GM insects in general, and GM mosquitoes in particular, are still immature. So much so that in the US, discussion is on-going as to which agency should regulate the proposed release of GM mosquitoes in Florida, since this is a completely new area which the regulatory world is unfamiliar with.

Moreover, under the Cartagena Protocol on Biosafety—the only international law dealing exclusively with genetic engineering and genetically modified organisms—a technical expert group revised its guidance last year for GM mosquito risk assessment. This guidance, part of a larger package of guidance on risk assessment, will be forwarded to the Parties of the Cartagena Protocol for consideration in October 2012. To my knowledge, a corresponding group which convened under the World Health Organization to develop guidance principles for GM mosquito evaluation has yet to finish this task.

At the national level, the first release of GM mosquitoes in the world, which occurred in the Cayman Islands, was conducted in the absence of a biosafety law. While the release was approved by the authorities concerned, the Cayman Islands only had a draft biosafety bill at the time. Moreover, the provisions of the Cartagena Protocol did not apply to the Cayman Islands, even though the UK, under which the Caymans are a British Overseas Territory, is a Party to the Protocol. This meant that specific biosafety questions may not have been fully considered nor evaluated, because of the absence of a detailed and comprehensive biosafety regulatory framework.

Indeed, the risk assessment that was used to support the approval of the releases in the Cayman Islands has been roundly criticized. Scientists at the Max Planck Institute for Evolutionary Biology in Germany conducted a thorough examination of the regulatory procedures and documents. They concluded that the risk assessment was incomplete, with no provision of experimental data on the releases; that there was poor referencing (unlikely to meet peer review standards); and worst of all, that there was a marked absence of discussion of the potential health or environmental hazards specific to the GM mosquito in question.

This trend of substandard regulatory oversight is regrettably not a one-off. The Max Planck scientists assessed the regulatory process in the first three countries (US, Cayman Islands, Malaysia) permitting releases of GM insects (including GM mosquitoes in the latter two countries) in terms of pre-release transparency and scientific quality, and found the process wanting. They suggest deficits in the scientific quality of the regulatory documents and a general absence of accurate experimental descriptions available to the public prior to the releases.

Worryingly, they judged the world’s first environmental impact statement on GM insects, produced by US authorities in 2008, to be scientifically deficient. This assertion is made on the basis that (1) by and large, the consideration of environmental risk was too generic to be scientifically meaningful; (2) it relied on unpublished data to establish central scientific points; and (3) despite the approximately 170 scientific publications cited, the endorsement of the majority of novel transgenic approaches was based on just two laboratory studies of only one of the four species covered by the document. However, the environmental impact statement appears to be used as the basis for regulatory approvals around the world, including that of the GM mosquitoes.

One of the most obvious questions to ask is whether humans can be bitten by the GM mosquitoes. In public information available on the Cayman Islands and Malaysian trials, however, this question is either conspicuously ignored or it is implied that there is no biting risk, ‘as only male mosquitoes are released and they cannot bite.’
However, as detailed by the Max Planck scientists, it is probable that transgenic daughters of the released males will bite humans. This is because the males are only partially sterile as the technology is not 100 percent effective. Furthermore, if the mosquitoes encounter tetracycline contamination in the wild, the numbers of survivors could increase. The likely presence of transgenic females in the environment requires the consideration of a more complex series of potential hazards, but this does not appear to have been done.

Public information, consultation and participation have been also lacking. In the case of the Cayman Islands, while Oxitec and the local Mosquito Research and Control Unit claim that adequate information was provided to the public prior to the release of the GM mosquitoes, the video information provided by MRCU for outreach does not once mention that the mosquitoes in question are genetically modified. Moreover, given the significance of the first release of GM mosquitoes in the world, it is puzzling as to why Oxitec only announced the fact of the release more than a year after they occurred, catching even scientists in the field of transgenic insects off guard.

It is clear that the regulatory processes that have governed the release of GM mosquitoes into the environment so far have been lacking. While international guidance may have recently been completed, the implementation at national level still suffers from a lack of adequate experience in dealing with this novel application of genetic engineering, a lack of rigorous risk assessment and robust investigation of unanswered questions and a lack of effective and meaningful public consultation and participation. In light of this, the push to release the GM mosquitoes in various countries is grossly premature.

Lim Li Ching, M.Phil., works in the biosafety program at Third World Network.


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