A six-month long trial using genetically engineered mosquitoes brought down the population of  Aedes aegypti that bite to cause dengue fever in humans. The trial was carried out on a 16-hectare plot in Mosquito Control and Research Unit located in  Caribbean island of Grand Cayman.

Dengue fever infects 50 million people every year and causes an annual death toll of 25,000. The only method of prevention used till now is to kill and control the infective mosquitoes. Unlike similar disease malaria also caused by mosquito bites, dengue fever cannot be cured by vaccination, therapeutic and preventive drugs. Dengue infections contained for last 65 years have reappeared in US and Southern Europe.  At present, the disease is a threat to 40% of world's population. The mosquitoes breed in stagnated waters.

Combating measures currently in use are limited to only control measures like spraying insecticides and restricting mosquito breeding by carefully monitoring water sources.

The new and more effective approach reported here uses the male mosquitoes (incapable of causing dengue fever) containing tTA gene alteration for mating with disease causing females. tTA is capable of overcommitting the gene reading machinery in larva and pupa, leading to their insufficient growth and premature death. The normal lifecycle of the mosquito is brought to abrupt termination with the progeny 's death before reaching adulthood.

Eggs laid on randomly dispersed jam-jar-sized pots placed in trial ground were counted. The initial 60% increase in the proportion of pots with at least one egg observed during the first three months fell to a 10% low by end of the study. The researchers give death of female larvae and depletion of resources due to competition between the dying and alive larvae as the reasons for observed reduction in the number of eggs.

With the trial having ended now, researchers are determining the time taken for the population to recover. With this they will be able to calculate the exact number of males required to suppress the natural population.

Oxitec conducted one trial in Malaysia and has gained approval to conduct these trials in Brazil, France, India, the US, Thailand, Singapore and Vietnam.