Via The Globe and Mail, a fascinating report by Stephanie Nolen: Buzz kill: Taking a bite out of dengue fever with genetically modified mosquitoes.
Piracicaba: As the morning sky slowly lightened above this central Brazilian city, biologist Guilherme Trivellato settled into the back of a van and got ready. He sat surrounded by hundreds of small plastic containers, each holding 1,158 thrumming mosquitoes, give or take a bug or two. To his left, a jury-rigged tabletop held a Dyson bladeless fan, taped to a plastic tube feeding out the window.
While a colleague drove the van slowly through the quiet streets, Mr. Trivellato opened each pot in front of the fan, sending the mosquitoes tumbling out into the world. A colleague kept a hair dryer, plugged into the dashboard, trained on him to blast out any stragglers.
Up and down each street they went, for two hours, until 250,000 new Aedes aegypti mosquitoes were released to seek out the dark corners of closets and garages all through the neighbourhood.
The plastic pots and hair dryer are the ultra-low-tech delivery method for the most sophisticated effort in the world to wipe out this mosquito, and the diseases it carries. The mosquitoes in the pot were bred in a lab by a British biotechnology company called Oxitec. They were all males, genetically altered to fly out, find a female, have sex and die – essentially the normal life plan of a male mosquito – but along the way pass on their altered genes to their offspring. These too will die, as larvae: before they can fly, or, if female, bite – and contract and then pass on a virus such as dengue fever or chikungunya to humans.
The Oxitec method is the most complex new weapon in Brazil’s arsenal in its war on the mosquito. Aegypti, as it is known to its reluctant admirers, spreads dengue and other viruses around the world – an estimated 390 million cases a year of dengue alone, according to a recent study in Nature, of which 96 million made people significantly ill. Brazil, which has both a heavy burden of the disease and a strong public health system, is the locus of innovation in the fight to wipe dengue out.
In addition to the transgenic mosquito, there is also a project to infect mosquitoes with a bacterium that keeps them from being able to pass on dengue; an effort to lure mosquitoes to lay eggs on a tape that prevents them from hatching; an experiment with a mosquito-toxic fungus spread in homes; and a study that is hanging curtains made of insecticide-soaked fabric in schools and hospitals.
But it is the Oxitec method that has garnered the most attention, and provoked the most debate. It is built on the fact that an Aegypti mosquito travels no more than 200 metres in its lifetime – so by flooding the zone with transgenic males, it makes it highly likely a female will mate with one of them, and lay the doomed eggs.
The company bills it as the most ecological solution: Currently, to fight dengue, Brazil spends more than $120-million (Can.) a year on millions of tons of insecticides to kill off Aegypti – but the mosquito grows more resistant all the time to the chemicals, which also end up in the water and food chain.
Oxitec monitors mosquito population (by checking eggs in the lab for absolute numbers and for how many hatch into their modified larvae) and says that in trials in two sites in Brazil, as well as in Panama and the Cayman Islands, its method has lowered the population by at least 90 per cent.