JACOBINA, BRAZIL — Researchers from Yale University have found that an experiment to release transgenic mosquitoes in Brazil as a way to reduce the mosquito population has backfired.

Millions of genetically modified male Aedes aegypti mosquitoes were released over more than two years in Jacobina, Brazil, according to a Yale University news release. The mosquito strain carried a dominant lethal gene that meant to render them unable to produce viable offspring with wild female mosquitoes.

According to the Yale news release, the experiment was aimed at lowering the local mosquito population to reduce the public's risk of contracting diseases such as Zika, dengue, and yellow fever.

In a study published in Scientific Reports, gene samples of both the transgenic and wild mosquitoes were analyzed before and after the release of the modified males.

Researchers found that some of the wild species retained genes from the transgenic strain, despite initial claims that the genes would not enter the general population, as any offspring was expected to die.

The mosquito population initially declined after the transgenic mosquitoes were released into the wild, but increased again after about 18 months, according to the news release.

Researchers say the local population is now likely more resilient since the population has mixed with strains from Cuba and Mexico that were crossed together to create genetically modified males.

Senior author of the study, Jeffrey Powell hypothesized that population may have bounced back after local female mosquitoes learned and started avoiding mating with the modified males.

Powell said in the news release that the mixed mosquitoes pose no known health risks.