GeneWatch UK Press Release: GM mosquito risks still not properly assessed (10th August 2012)

In a new briefing published today, GeneWatch UK highlights numerous errors and omissions in the risk assessment process for genetically modified (GM) mosquitoes.  UK company Oxitec has released GM mosquitoes in large numbers in the Cayman Islands (3 million mosquitoes) and Brazil (10 million) and a smaller number in Malaysia (6,000), as part of experiments to reduce the incidence of the tropical disease dengue fever. Risk assessments were not published prior to the releases in Cayman or Brazil and only Malaysia had any kind of consultation process.

The new briefing is based on an analysis of Oxitec's risk assessments obtained using Freedom of Information requests in the UK. It identifies many issues that have not been properly considered, including: 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. 

"Failure to publish risk assessments before trials of GM mosquitoes in Cayman and Brazil, and the omission of known adverse effects, is irresponsible", said Dr Helen Wallace, Director of GeneWatch UK "People cannot give informed consent to trials if they are not given complete information".

The results of Oxitec's experiments have been press released but not published in scientific journals and the briefing questions whether the releases are an effective way to reduce mosquito populations. It highlights how 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. The briefing also cites documents obtained through Freedom of Information requests which show that the UK and Brazilian governments agreed in 2007 to test and commercialise the technology in Brazil, based on claims made by the company that it 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 rush to commercialise Oxitec's GM mosquitoes in Brazil could be putting people's health at unnecessary risk", said Dr. Wallace, "There has been no attempt to consider human immunity effects or to monitor the impacts on immune response or the incidence of dengue".

Issues highlighted in the briefing include:

  • The results of Oxitec's population suppression experiments in Cayman and Brazil have not been published in scientific journals, but information in the public domain suggests that the GM mosquitoes may not be particularly effective at suppressing wild mosquito populations.
  • Ineffectiveness is a matter of particular concern in dengue endemic areas because in some situations partial or temporary suppression of mosquito populations could make the dengue situation worse.
  • Oxitec did not correctly follow the procedure for transboundary notification of shipments of GM mosquito eggs overseas: the practical consequence of this is that risk assessments were not made publicly available prior to open release trials and did not meet the necessary standards.
  • Numerous important issues were therefore not properly considered before millions of GM mosquitoes were released in to 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.
  • In its publicity about the trials, Oxitec has oversimplified the complex relationship between Aedes aegypti mosquitoes, other mosquito species, the humans that are bitten, and the four serotypes of dengue virus. 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.
  • 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.
  • The decision to scale-up experiments in Brazil appears to be driven by a political agreement to commercialise Oxitec's technology there, rather than by a thorough assessment of the likely risks and benefits.

For further information contact:

Dr Helen Wallace: 01298-24300 (office); 07903-311584 (mobile).

Notes for Editors:

(1)    Oxitec's Genetically Modified Mosquitoes: Ongoing Concerns. GeneWatch UK Briefing. Available on:

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