Trials conducted by British start-up Oxitec, Ltd showed that genetically modified mosquitoes could eradicate dengue fever. The scientific team inserted two genes into the Aedes aegypt mosquito, a sterility gene, which prevents male mosquitoes' offspring from growing past the larva stage, and a fluorescent tag gene, which allows researchers to easily identify larvae that have inherited the sterility gene. Sterility is achieved by employing tetracycline-controlled transcriptional activation (tTa). The tTa gene produces a protein that then acts as a transcription factor for the tTa gene, triggering further production of the protein in a positive-feedback cycle, which forces the cell's resources away from synthesizing other proteins, eventually leading to the cell's death. The antibiotic tetracycline stops the positive-feedback cycle. Mosquitoes raised in the laboratory are exposed to tetracycline, so they can survive to adulthood and then mate with female mosquitoes when released in the wild. By mating with females that would have ordinarily mated with normal males, the genetically modified mosquitoes reduce the percentage of viable offspring, thus decreasing the population of the next generation of mosquitoes.
The first trial, which was conducted in 2009, introduced the modified mosquitoes equivalent to 16% of the population in the Grand Cayman study area, and the fluorescent marker was found in 10% of the larvae, demonstrating that the mosquitoes were effective sexual competitors, although not quite as competitive of their normal counterparts. A second as-yet-unpublished trial in 2010 saw an 80% reduction of mosquito population in the target area on Grand Cayman island. These trials show much promise compared to previous methods such as using radiation to sterilize the mosquitoes, which reduced the mosquitoes ability to compete with wild males. One issue that needs to be dealt with is keeping any females from being released; unlike males, females bite humans, and the effects of a genetically engineered mosquito's bite on humans is unknown. Future trials will hopefully show promise of genetically modified insects to eliminate all insect-borne diseases, including dengue fever and malaria.