The Aedes Aegypti mosquito is responsible for a variety of diseases, including yellow fever, Zika, malaria and dengue fever, resulting in robust offspring. Jeffrey Powell, Ph.D., senior author and professor of ecology and evolutionary biology at Yale, said that these offspring would then have spread their genetic material beyond the original breeding ground.
"The claim was that genes from the release strain would not get into the general population because offspring would die," Powell said to Yale News The authors of the study estimated that 10 to 60 percent of the mosquito population in Jacobina is now one piece of the genetically modified genome. Before the study was conducted, the initial estimate of how many offspring would even survive until birth was 3 to 4 percent.
And to further insult the injury, the genes of these genetically modified mosquitoes not only spread in unexpected ways, but the introduction of these mosquitoes into the native population did not even reduce the entire mosquito population as the team would have hoped. While the overall population dipped slightly in the first few months of the experiment, researchers wrote until the 18th month that the population had returned to a level close to pre-release.
So, how did it go so wrong?
Powell said Yale News that expectations based on isolated laboratory results did not really translate into the field.
"… [I] This is the unexpected result is worrisome," said Powell. "Based mainly on laboratory studies, it can be predicted how the release of transgenic mosquitoes is likely to impact, but genetic testing, as we did, should be done during and after such releases to see if anything else but that predicted occurred. "
Powell emphasized, however, that these results, while unexpected, do not pose an additional health risk to the human population. However, with regard to future work to reduce the impact of mosquito-borne diseases on humans, the study also notes that the results of this genetic mixing could lead to increased insecticide resistance in these new offspring – exactly what they said in the study avoid trying first place.
As the scientists return to the drawing board, it is unclear what the future of these new, genetically mixed mosquitoes will look like.
Abstract: In an attempt to combat mosquito-borne yellow fever, dengue, Chikungunya and Zika fever, a strain of transgenic modified Aedes aegypti mosquitoes, which is a dominant lethal gene included, were developed by a commercial company, Oxitec Ltd., population size and did not affect the genetics of the target populations. Approximately 450,000 men of this variety were released weekly in Jacobina, Bahia, Brazil, for 27 months. We genotyped the release strain and the target Jacobina population prior to release for> 21,000 single nucleotide polymorphisms (SNPs). Genetic sampling from the target population at six, twelve and 27 to 30 months after initiation of release clearly indicates that portions of the genome of the transgenic strain have been incorporated into the target population. Obviously, rare viable hybrid progeny between the release strain and the Jacobina population are sufficiently robust to reproduce in nature. The release strain was developed using a strain originally from Cuba and then crossed over to a Mexican population. So Jacobina Ae. Aegypti are now a mix of three populations. It is unclear how this may affect disease transmission or other efforts to control these dangerous vectors. These results demonstrate the importance of establishing a genetic monitoring program during such releases to identify unexpected results.