Oxitec responds to article entitled 'Transgenic Aedes aegypti Mosquitoes Transfer Genes into a Natural Population'

The study’s data in Scientific Reports paper does not identify negative, deleterious or unanticipated effect on people or the environment from the release of Oxitec’s 1st Generation (OX513A) mosquitoes.

The paper’s authors made speculative statements and selectively ignored body of critical peer-reviewed evidence, including their own, describing safety and effectiveness of technology.

Oxitec’s OX513A self-limiting genes have been tested for a decade and have demonstrated to disappear from the environment; natural background genes also decline over time. Data in this paper and other scientific literature confirm that there is no hybrid vigor or selective mating observed.


Oxford, UK, and Campinas, Brazil (para ler em português, clique aqui)

In response to the recently published open access report titled “Transgenic Aedes aegypti Mosquitoes Transfer Genes into a Natural Population” (Evans et al. 2019 Scientific Reports, Vol 9, Article number: 13047), Oxitec has filed a complaint to Nature Research, publishers of the journal, to address the range of misleading and speculative statements made about Oxitec’s 1st Generation Aedes aegypti mosquito technology.

The paper explores the flow of genes between the local population of Aedes aegypti and the natural background strain of OX513A. The gene transfer referenced in the title does not refer to the persistence of Oxitec’s self-limiting and marker genes. This paper includes findings from previously described work carried out alongside field releases of OX513A in Jacobina, Brazil in 2013-2015. That project was a successful field pilot of the OX513A Aedes aegypti strain that suppressed wild populations of the invasive Aedes aegypti mosquito and demonstrated the disappearance of the OX513A self-limiting genes from the environment after the cessation of mosquito releases.

Unfortunately, the study’s authors used dramatized statements to create unfounded concern, ignoring scientific evidence within their own study that demonstrates the technology’s safety and efficacy and more than 100 peer-reviewed scientific publications relating to Oxitec’s technology.

Key Facts

The narrative of the paper selectively dismisses key facts, including:

  • There was no negative impact documented by this study or by any other study conducted on Oxitec technology;

  • The described project in the Brazilian city of Jacobina was successful, with sustained suppression of treated Aedes aegypti populations, even for some weeks after releases of Oxitec mosquitoes stopped at the end of the project;

  • The self-limiting gene carried by the Oxitec mosquito (OX513A) died out soon after releases stopped, as expected;

  • A small proportion (3-5%) of the OX513A mosquitoes can survive, a fact well-documented in regulatory filings and peer-reviewed publications over the past decade; if survivors mate with females and transfer the transgene to the next generation, it continues to be lethal to >95% of offspring, thus declining over time;

  • Natural genes carried by Oxitec mosquitoes do not confer increased capacity to transmit disease nor resistance to commonly used insecticides;

  • The natural genes passed on by the few surviving OX513A mosquitoes declined over time in treated areas after releases stopped;

  • As expected, local mosquito populations in Jacobina slowly rebounded after the releases of OX513A mosquitoes stopped at the project’s conclusion.

 Each of the key facts is supported by independent peer-reviewed studies, publications, and Oxitec’s regulatory findings.[1]


Response to Paper’s Speculative Statements

Several of the statements in the paper represent speculation and are not supported by scientific data – either in the paper itself or in the larger body of peer-reviewed literature on Oxitec’s technology. These include:

  • The paper’s hypothesis that introducing background genetics would lead to increased “hybrid vigor” in the mosquito. The data published in this paper and in the entire body of peer-reviewed literature do not support this hypothesis.

  • The paper’s hypothesis regarding introgression [passing on of genes other than the self-limiting gene from OX513A, into the wild mosquitoes], suggesting that this may introduce other relevant genes such as with insecticide resistance. To the contrary, Oxitec has demonstrated that OX513A is not resistant to commonly used insecticides.

  • The paper’s hypothesis regarding the potential impact of introgression on disease control and transmission. The data in the paper itself demonstrate that OX513A is not a more competent disease vector than the local wild mosquitoes.

  • The paper’s hypothesis regarding breakdown of effectiveness and selective mating. The suppression project described showed sustained suppression, even for some time after releases of OX513A males stopped, as the authors of this paper themselves describe in an earlier publication. Selective mating has never been observed in any releases of close to 1 billion Oxitec males worldwide. The authors provide no data to support this hypothesis.

Oxitec’s 2nd Generation Aedes aegypti Mosquito

Oxitec has applied to the EPA to pilot the 2nd Generation of this technology, OX5034, in the USA, under an Experimental Use Permit (EUP).

  • Oxitec’s new 2nd Generation self-limiting Aedes aegypti builds on the demonstrated effectiveness of OX513A but provides additional anticipated performance and operational benefits, including greater cost-effectiveness and potentially higher rates of pest control. In recent trials in Brazil, releases of these 2nd Generation male mosquitoes achieved up to 96% suppression of wild Aedes aegypti populations in the city of Indaiatuba.

  • The 2nd Generation mosquito, OX5034, is male-selecting, meaning that all female mosquitoes that carry the OX5034 genes die. There is, therefore, no potential for release of biting female mosquitoes.

  • Because male OX5034 mosquitoes are designed to survive through to adulthood, they are able to pass on the self-limiting gene for multiple but limited generations, with the potential for enhanced performance in suppressing wild mosquito populations.


About Oxitec
Oxitec is a pioneer in using genetic engineering to control insect pests that spread disease and damage crops, and was founded in 2002 as a spinout from the University of Oxford (UK). Oxitec is a subsidiary of Intrexon Corporation (NASDAQ: XON), which engineers biology to help solve some of the world’s biggest problems. Follow us on Twitter at @Oxitec.

About Intrexon Corporation
Intrexon Corporation (NASDAQ: XON) is Powering the Bioindustrial Revolution with Better DNA™ to create biologically-based products that improve the quality of life and the health of the planet through two operating units – Intrexon Health and Intrexon Bioengineering. Intrexon Health is focused on addressing unmet medical needs through a diverse spectrum of therapeutic modalities, including gene and cell therapies, microbial bioproduction, and regenerative medicine. Intrexon Bioengineering seeks to address global challenges across food, agriculture, environmental, and industrial fields by advancing biologically engineered solutions to improve sustainability and efficiency. Our integrated technology suite provides industrial-scale design and development of complex biological systems delivering unprecedented control, quality, function, and performance of living cells. We call our synthetic biology approach Better DNA®, and we invite you to discover more at www.dna.com or follow us on Twitter at @Intrexon, on Facebook, and LinkedIn.

Safe Harbor Statement
Some of the statements made in this press release are forward-looking statements. These forward-looking statements are based upon our current expectations and projections about future events and generally relate to our plans, objectives and expectations for the development of our business. Although management believes that the plans and objectives reflected in or suggested by these forward-looking statements are reasonable, all forward-looking statements involve risks and uncertainties and actual future results may be materially different from the plans, objectives and expectations expressed in this press release.


For more information, contact:

Oxitec Contact
Joshua Van Raalte
Communications Lead
U.S.: +1-781-519-9981
International: +44 20 7785 7383
Email: oxitec@agencybrazil.com

Intrexon Contact
Marie Rossi, PhD
Vice President, Communications
Tel: +1 (301) 556-9850


[1] https://www.oxitec.com/our-technology

Neil Morrison