Dengue fever is carried in the tropics all around the world by the mosquito Aedis aegypti. The disease passes from person to person via these mosquitoes. Dengue doesn’t exist in forests and fields, only where people live, so it’s particularly prevalent in towns.

Dengue is endemic in Brazil. The only weapon against it is chemical spray. But it’s hard to catch the mozzies as they lurk in the tiniest pool of water. Also, once you get infected with Dengue (symptoms ranging from mild-flu-like to bedridden ‘breakbone fever’) all subsequent infections just get worse. It’s why the Brazilians are desperate to find a new way of stopping Dengue – for which there is no vaccine.

That’s the reason Brazil is the first country in the world to run a GM mosquito public health programme. They already have facilities for producing vast numbers of sterile mosquitoes – though they produce them via irradiation. Last summer we reported on caged outdoor trials in Mexico of mosquitoes genetically modified to fight Dengue.

In Brazil in February this year, UK company Oxitec, in collaboration with the University of Sao Paolo and a company called Moscamed in Brazil, started doing test releases in the city of Juazeiro, in Bahia province of N E Brazil. (Juazeiro is close to Brazil’s major tropical fruit exporting city of Petrolina). The test was to see whether the GM mozzies would survive and do their job in the wild, which they seemed to.