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Plan to Crush Native Mosquito Population With Gene-Edited Strain Fails

Even the best laid plans can go awry—and one public health initiative in Brazil is a case in point. The project in question involved releasing an army of gene-edited mosquitoes into the wild in order to stop the spread of vector-borne diseases, from yellow fever and dengue to the Zika virus. But instead of depleting the population, the experiment may have made the mosquitoes even stronger.

It was thought that by short-circuiting certain parts of the insect's DNA, researchers could squash the target population's size without affecting its genetics. This is a plan being put to the test in various regions plagued by the disease-riddled bugs—apparently with varying levels of success.

In the case in Brazil, researchers edited strains of Aedes aegypti with a defective gene to limit their fertility—or at the very least ensure any offspring produced would be too weak to progress into adulthood and reproduce themselves. According to researchers writing in Scientific Reports, this particular strain (OX513A) has previously resulted in declines of native Ae. aegypti by 85 percent.

And so, in the largest project of its kind to date, approximately 450,000 male Ae. aegypti OX513A were released every week, starting from June 2013 and ending in September 2015. This weekly event took place at sites across the city of Jacobina in the Brazilian state of Bahia. Theoretically—and if things had gone to plan—levels of disease-carrying mosquitoes in the area should have plummeted afterwards. This was not the case.

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