An experimental trial to reduce the number of mosquitoes in a Brazilian town by releasing genetically modified mosquitoes has not gone as planned. Traces of the mutated insects have been detected in the natural population of mosquitoes, which was never supposed to happen.
The deliberate release of 450,000 transgenic mosquitoes in Jacobina, Brazil has resulted in the unintended genetic contamination of the local population of mosquitoes, according to new research published last week in Scientific Reports. Going into the experimental trial, the British biotech company running the project, Oxitec, assured the public that this wouldn’t happen. Consequently, the incident is raising concerns about the safety of this and similar experiments and our apparent inability to accurately predict the outcomes.
The point of the experiment was to curb the spread of mosquito-borne diseases, such as yellow fever, dengue, chikungunya, and Zika, in the region. To that end, Oxitec turned to OX513A—a proprietary, transgenically modified version of the Aedes aegypti mosquito. To create its mutated mosquito, Oxitec took a lab-grown strain originally sourced from Cuba and genetically mixed it with a strain from Mexico.
The key feature of these bioengineered mosquitoes is a dominant lethal gene that (supposedly) results in infertile offspring, known as the F1 generation. By releasing the OX513A mosquitoes into the wild, Oxitec hoped to reduce the population of mosquitoes in the area by 90 percent, while at the same time not affecting the genetic integrity of the target population. The OX513A strain is also equipped with a fluorescent protein gene, allowing for the easy identification of F1 offspring.
Starting in 2013, and for a period of 27 consecutive months, Oxitec released nearly half a million OX513A males into the wild in Jacobina. A Yale research team led by ecologist and evolutionary biologist Jeffrey Powell monitored the progress of this experiment to assess whether the newly introduced mosquitoes were affecting the genes of the target population. Despite Oxitec’s assurances to the contrary, Powell and his colleagues uncovered evidence showing that genetic material from OX513A did in fact trickle to the natural population.
“The claim was that genes from the release strain would not get into the general population because offspring would die,” Powell, the senior author of the new study, said in a press release. “That obviously was not what happened.”
That genetic material from OX513A has bled into the native species does not pose any known health risks to the residents of Jacobina, but it is the “unanticipated outcome that is concerning,” said Powell. “Based largely on laboratory studies, one can predict what the likely outcome of the release of transgenic mosquitoes will be, but genetic studies of the sort we did should be done during and after such releases to determine if something different from the predicted occurred.”
Indeed, lab tests conducted by Oxitec prior to the experiment suggested that around 3 to 4 percent of F1 offspring would survive into adulthood, but it was presumed these lingering mosquitoes would be too weak to reproduce, rendering them infertile. These predictions, as the new research shows, were wrong.