Genetically modified mosquitoes thrive in Brazil, surprising researchers

Mosquitos around the world are known to carry dangerous and potentially fatal human diseases such as West Nile virus, yellow fever, dengue, malaria and zika. In recent years, as scientists moved away from the dangerous insecticides of the past, they turned to genetic modification to make it a more effective and less dangerous means of controlling mosquito populations. But the new results published in Scientific reports Yale researchers show that this new plan of attack is not without bugs, literally.

The paper, released Tuesday, summarizes the results of a study conducted between June 2013 and September 2015 in the Brazilian city of Jacobina. In collaboration with British biotech company Oxitec, researchers have presented 450,000 genetically mutated men Aedes aegypti mosquitoes a week in order to reduce the resident mosquito population.

In theory, these genetically modified mosquitoes would mate with native female mosquitoes and produce weak offspring that would die before transmitting their mutant genes. But the reality was very different.

Instead of producing low offspring, these genetically modified male mosquitoes mated with native females and produced robust offspring. Jeffrey Powell, Ph.D., lead author and professor of ecology and evolutionary biology at Yale, said that these descendants then continued to spread their genetic material beyond the initial breeding ground.

"The assertion was that liberation strain genes would not enter the population because the offspring would die," said Powell. Yale News "This is obviously not what happened."

According to the authors of the study, approximately 10 to 60% of the Jacobina mosquito population now contains a fragment of the genome genome. Before conducting the study, the initial estimate of the number of offspring that would survive even until birth was 3-4%.

And to add to the wounds, not only did the genes of these genetically modified mosquitoes spread unexpectedly, but the introduction of these mosquitoes into the indigenous population did not even reduce the total population mosquitoes, contrary to what the team was hoping for. While the total population decreased slightly during the first months of the trial, the researchers wrote in the 18th month that the population had returned to a level comparable to that observed before release.

So how did it go so badly?

Part of the problem, said Powell Yale Newswas that expectations based on isolated laboratory results did not really translate into the field.

"…[I]It's the unplanned result that's worrisome, "said Powell. "Based largely on laboratory studies, we can predict what will be the likely outcome of the spread of transgenic mosquitoes, but genetic studies of the type we have done should be conducted during and after these releases to determine whether an event different from that which had been planned took place.

However, Powell pointed out that even if these results were unexpected, they pose no additional risk to the health of the human population. However, with regard to future work to reduce the impact of human-caused diseases caused by mosquitoes, the study also mentions that the results of this genetic mix could increase insecticide resistance in these new offspring – exactly what they were trying to avoid in the future. first place.

As scientists return to the drawing board, it is unclear what will be the future of these new genetically mixed mosquitoes.

Abstract: In order to control mosquito-borne diseases, yellow fevers, dengue fever, chikungunya fever and Zika fever, a strain of Aedes aegypti mosquitoes containing a dominant lethal gene were developed by a trading company, Oxitec Ltd. If the lethality is complete, the spread of this strain should only reduce the size of the population and not affect the genetics of the target populations. Approximately 450,000 males of this strain were released weekly for 27 months in Jacobina, Bahia, Brazil. We genotyped the release strain and the target Jacobina population before the onset of release for over 21,000 nucleotide polymorphisms (SNPs). Genetic sampling in the target population six, 12 and 27-30 months after the start of the releases clearly shows that portions of the genome of the transgenic strain have been incorporated into the target population. Clearly, the rare viable hybrids between the strain to be released and the Jacobina population are robust enough to reproduce in the wild. The release strain was developed using a strain originally from Cuba, then crossed with a Mexican population. So, Jacobina Ae. aegypti are now a mixture of three populations. It is unclear how this can affect the transmission of the disease or affect other efforts to control these dangerous vectors. These results highlight the importance of setting up a genetic monitoring program during these releases to detect unexpected results.