From GM bugs to DDT: It’s an all-out war on mosquitoes now

NYT News Service | Feb 1, 2016, 06.23 AM IST


Every weekday at 7 am, a van drives slowly through the southeastern Brazilian city of Piracicaba carrying a precious cargo -mosquitoes. More than 100,000 of them are dumped from plastic containers out the van’s window, and they fly off to find mates. But these are not ordinary mosquitoes. They have been genetically engineered to pass a lethal gene to their offspring, which die before they can reach adulthood. In small tests, this approach has lowered mosquito populations by 80% or more. The biotech bugs could become one of the newest weapons in the perennial battle between humans and mosquitoes, which kill hundreds of thousands of people a year by transmitting malaria, dengue fever and other devastating diseases and have been called the deadliest animal in the world.

The battle has abruptly become more pressing by what the World Health Organization has called the “explosive” spread of the mosquito-borne Zika virus through Brazil and other parts of Latin America. Experts say that new methods are needed because the standard practices -using insecticides and removing the standing water where mosquitoes breed -have not proved sufficient.

“After 30 years of this kind of fight, we had more than two million cases of dengue last year in Brazil,” said Dr Artur Timerman, an infectious disease expert in Sao Paulo. “New approaches are critically necessary.” But the new efforts have yet to be proved, and it would take some years to scale them up to a meaningful level.

So for now, experts say, the best modes of prevention are to intensify use of the older methods of mosquito control and to lower the risk of being bitten using repellents and by wearing long sleeves.

One old method that is not getting serious attention would be to use DDT, a powerful pesticide that is banned in many countries because of the ecological damage documented in the 1962 book “Silent Spring.” Still, it is being mentioned a bit, and some experts defend its use for disease control.

The mosquito that transmits Zika virus -and also dengue, chikungunya and yellow fever -is Aedes aegypti.The genetically enginee red Aedes aegypti mosquitoes were developed by Oxitec, a British company , to fight dengue, but would also work to curtail the spread of Zika.

Since last April, the mosquitoes have been released in one neighbourhood of Piracicaba populated by about 5,000 people. By the end of 2015, there was a reduction in wild mosquito larvae -as opposed to larvae inheriting the lethal gene -of 82%, the company said. Oxitec and the city said this month that they would extend the project for another year and expand it to cover an area of up to 60,000 people.Oxitec is building a new factory to rear enough mosquitoes to cover an area with 300,000 people. The company calls its creation the “friendly Aedes aegypti” and notes that it releases only male mosquitoes, which do not bite. It says its solution is ecologically friendly because only the one species is targeted, whereas chemical spraying can affect many types of organisms.

Another approach, being tested in Rio de Janeiro, is to infect the mosquitoes with Wolba chia, a bacterium that does not infect them naturally . Once infected, the mosquitoes do not pick up and transmit viruses as easily . The bacteria can be passed to the next generation through eggs, so they spread through the mosquito population.

A new and even more powerful tool may be gene drives, which are genetic mechanisms that rapidly propagate a trait through a wild population. Just in the last few months, scientists have made gene drives that work in mosquitoes in the laboratory. Anthony A James, a professor at the University of California, Irvine, said it would be straightforward to use a gene drive to spread something like a sterility trait through the Aedes aegypti population to kill them off.