November 28, 2023

Releasing millions of GM mosquitoes – into the unknown. No risk assessments published in Cayman Islands

by Helen Wallace

Millions of GM mosquitoes are being released into countries including Brazil in an attempt to tackle dengue fever, but one campaigner questions whether the experiments are driven by public health concerns or profit

British biotech company Oxitec has released genetically modified mosquitoes in large numbers in the Cayman Islands – three million and Brazil – 10 million – as well as a smaller number in Malaysia – 6,000. These actions are part of experiments to reduce the incidence of the tropical disease dengue fever. They are the first open experiments involving GM insects anywhere in the world. How well have the risks been assessed?

Risk assessments were not published prior to the release of GM mosquitoes in Cayman or Brazil and only Malaysia had any kind of consultation process. Failure to publish risk assessments can lead to poor quality assessments and people cannot give informed consent to trials, if they are not given complete information. The company has repeatedly referred to its GM mosquitoes as sterile, when this so-called sterility is partial and conditional – it is dependent on the absence of the antibiotic tetracycline, which is used to breed the GM insects in the lab. The male GM mosquitoes breed with wild female mosquitoes and most of the offspring die as larvae: the extent to which some offspring survive to adulthood is one of many factors which influences the efficacy and safety of the firm’s approach.

We at GeneWatch UK have recently published an investigation based on an analysis of the risk assessments, obtained using Freedom of Information requests in the United Kingdom. Our new briefing highlights numerous errors and omissions in the risk assessment process for GM mosquitoes. The process did not correctly follow the regulatory procedure for notifying shipments of its GM mosquito eggs overseas. The practical consequence of this is that risk assessments were not made publicly available prior to open release trials and might not meet the necessary standards. This means that most potential adverse impacts have effectively been excluded from public debate, the risk assessment process and the process of seeking consent from local populations.

Numerous important issues were not properly considered before millions of GM mosquitoes were released into the environment in the Cayman Islands and Brazil. Smaller experiments in Malaysia did include a consultation process. However there were some deficiencies with the process, which need to be addressed. Issues include: the possibility that another invasive mosquito species which carries dengue becomes established at release sites; the potential for large numbers of GM mosquitoes to survive and breed in sites contaminated with the antibiotic tetracycline; and loss of human immunity and cross-immunity, if the releases are only temporarily or partially effective in dengue-endemic areas.

The results of the experiments have been press released, but not published in scientific journals. Although information in the public domain suggests that the GM mosquitoes may not be particularly effective at suppressing wild mosquito populations. The effects on human immunity mean that ineffective measures can increase severe cases of the disease in dengue-endemic countries such as Brazil, putting people’s health at unnecessary risk.

Further documents obtained through FoI requests show that the British and Brazilian governments agreed in 2007 to test and commercialise GM mosquitoes in Brazil – based on claims made by the company that its technology would be effective. A new production facility has now been built in Brazil to increase GM mosquito releases to 2.5 million per week. The decision to scale-up these experiments appears to be driven by this political agreement to commercialise the technology, rather than by a thorough assessment of the likely risks and benefits. The rush to marketise GM mosquitoes in Brazil means there has been no attempt to consider human immunity effects or to monitor the impacts on immune response, or the incidence of dengue.

Dr Helen Wallace is director of the GeneWatch UK campaign group
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