It is felt that conventional techniques to control mosquito-borne diseases like malaria, chikungunya and dengue are not going to be enough. Scientists across the world have begun working on the premise that in addition to spraying insecticides, controlling breeding sites and promoting bed-nets, genetic strategies also need to be evolved to control the entire spectrum of diseases transmitted by mosquitoes.

Genetic strategies include two methods: mosquito population replacement and population suppression. The one reported in PNAS is that of replacement. In India, there is a proposal pending with the Review Committee on Genetic Manipulation (RCGM) to import a batch of GM mosquitoes for fully-contained trials. This one works on a technology which suppresses the population of Aedes mosquitoes that carry dengue and chikungunya.

The Johns Hopkins University has worked on a replacement strategy for malaria-carriers: they have reported that the engineered mosquitoes have a higher survival rate than non-resistant ones, meaning they could eventually replace the ones that can carry the disease. When they fed on malaria-infected mice, the resistant mosquitoes were able to outdo the non-resistant ones. Starting with the same number of resistant and non-resistant mosquitoes, they found that after nine generations, the resistant type made up 70 per cent of the population.

Though tests with the human form of malaria is yet to be done, scientists are touting it as a step that might one day help block the spread of an illness that has claimed millions of lives around the world. An estimated 2.7 million people die of malaria each year. In India, there are 1 million cases each year though the number of deaths have fallen considerably.

Several laboratories have been trying to develop resistant mosquitoes. Oxitec, a spin-off company of Oxford University, has decided to collaborate with Chennai-based International Institute for Biotechnology and Toxicology (IIBAT).

S S Vasan, Oxitec’s head of public health, said: “We are collaborating with the IIBAT to test our dengue and chikungunya-control technology involving local experts. The main objective is to test the fitness of our Aedes mosquitoes against the wild type in a small room under total containment.”

IIBAT’s director P Balakrishna Murthy said: “Our proposal has been cleared by the Institutional Biological Safety Committee that has nominees from the DBT, and is now being deliberated by RCGM. It is our hope that it will be approved.”

In population replacement, a mosquito is genetically altered to become resistant to a given disease, say malaria. If somehow this GM mosquito replaces the mosquito in the wild, then you will still have mosquitoes — mosquitoes which bite — but are unable to transmit malaria. So far, the problem was that GM mosquitoes are generally not as fit as those in the wild, so they won’t be able to spread and replace the wild type. The Johns Hopkins scientists seem to have got around that problem for mice under certain conditions.