Genetically modified mosquitoes, like those released in Grand Cayman, successfully interbred with natural populations in Brazil, according to the authors of a new study in the Nature science journal.
Researchers from Yale University found evidence that mosquitoes released by British biotech firm Oxitec had impacted the genetics of the overall mosquito population following releases in Jacobina, Brazil.
The genetically modified OX513A mosquitoes – the same strain as those released in a similar project in Grand Cayman – were designed to be ‘self limiting’. When they were introduced in Cayman, officials said the GM mosquitoes were modified so that their offspring would die before reaching adulthood.
The aim was to release millions of them into the wild so that through weight of numbers they would out-compete the resident males for mates and cause the overall mosquito population to collapse. The goal was to help eradicate diseases like Zika, dengue fever and chikungunya which are spread by the Aedes aegypti mosquitoes. The project was abandoned in Cayman earlier this year amid doubts over its effectiveness.
The Yale research team sampled the mosquito population in the target area in Brazil six, 12 and 30 months after releases commenced and concluded there was “clear evidence” that portions of the Oxitec genome had been incorporated into the natural population.
“Our data clearly show that release of the OX513A has led to significant transfer of its genome (introgression) into the natural Jacobina population of Ae. Aegypti,” the researchers wrote.
They go on to caution that such releases need more robust monitoring.
“These results highlight the importance of having in place a genetic monitoring program during such releases to detect unanticipated outcomes,” the authors wrote.
According to the research paper, hybrid offspring of the GM mosquitoes and the natural population were able to reproduce in nature, meaning the modified genome persisted even after the releases had stopped.
The authors reported between 10% and 60% of individuals had some evidence of the OX513A genome, depending on the sample and criterion used.
They said it is not known what impact that would have on disease control or transmission.
The authors did note a reduction in the prevalence of the Oxitec gene over time, suggesting the modified mosquitoes were at a “selective disadvantage” over the longer term.
They also noted that the mosquitoes did not carry any greater risk of infectivity for dengue or Zika, though they cautioned that they noted they may be more resistant to insecticide and may have contributed to a generally more genetically robust mosquito population.
Oxitec CEO Grey Frandsen said the company had not yet had time to review the paper but “looks forward to doing so soon”.