A few years ago, a virus was spreading in South America that for a long time received little attention. In 2016, more than one million people in Brazil became infected with Zika. The epidemic had devastating consequences: pregnant women gave birth to children with severe birth defects and some people died.
The disease was transmitted by a mosquito of the species Aedes aegypti. Originally from Central Africa, the Egyptian tiger mosquito also transmits other viruses such as yellow fever or dengue. Therefore, researchers have been working on methods for a long time to prevent the spread of the animals.
Biotec company Oxitec had already genetically modified and abandoned mosquitoes before the Zika epidemic with the help of the Bill and Melinda Gates Foundation in northern Brazil. If the bred mosquitoes continued to live on free-living females, their offspring would already die in the larval or pupal stage.
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Although the mosquito populations in the field trials should have been decimated by up to 80 percent. But critics had already noted that the intervention in the ecosystem risks. Maybe the death-gene could switch off again with some mosquitoes or mutations have an influence.
A study now shows that those doubts were not entirely unfounded. Because there are still traces of the gene mosquitoes - some have apparently survived. Depending on the sample, ten to 60 percent of Aedes aegypti in the village of Jacobina in northeastern Brazil have corresponding traces in the genome, scientists write in the journal "Scientific Reports".
Paulo Whitaker / REUTERS
View into the Oxitec laboratory in Piracicaba
Oxitec had released around 450,000 Egyptian tiger mosquitoes weekly from 2013 to 2015. The genetically modified animals are a mix of mosquito strains from Cuba and Mexico. The now found in the field specimens thus carry genetic material from three tribes.
The consequences of the transfer of the genetically modified genome to future generations of tiger mosquitoes is still unclear, according to the journal Scientific Reports.
The mosquitoes may be resistant to insecticides
The genetic engineering mosquitoes may be more robust and resistant to insecticides, the team around Jeffrey Powell of Yale University in New Haven (USA) speculates in the study. Powell emphasizes: "These results demonstrate the importance of a GMO exposure monitoring program to avoid unanticipated consequences."
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Meanwhile, Oxitec has changed its strategy. The second generation of genetically modified mosquitoes is programmed so that not all offspring die. Only the female offspring are not viable. By contrast, male male males can survive, mate with wild females, and pass on the deadly genes again.
In the new program, the survival of genetically modified yellow fever mosquitoes is intentionally aimed at curbing the population of dangerous females. Only they transmit the pathogens (read more about the technique here).
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