Laboratory studies using GM mosquitoes have been carried out in India since 2012

Outdoor caged trials to demonstrate the efficiency of genetically modified mosquitoes to suppress wild female Aedes aegypti mosquito populations that causes dengue, chinkungunya and Zika were launched on January 23 in Dawalwadi, Badnapur in  Maharashtra’s Jalna district.

Based on the results of the caged trials, which use the Release of Insects carrying Dominant Lethal genes (RIDL) technology, and permission from Indian regulatory authorities, Gangabishan Bhikulal Investment and Trading Limited (GBIT) and Oxitec, plan to conduct open field trials in the country.

The announcement was made on January 23 after the field cage facility was inaugurated by Dr. Soumya Swaminathan, Director General of the Indian Council of Medical Research.

Laboratory-based studies have already been carried out in India since 2012 by GBIT and Oxitec and these studies have demonstrated the compatibility of Aedes aegypti mosquitoes. “The efficiency to kill offspring was over 99% and male mosquitoes imported from the U.K were able to mate with locally available wild female mosquitoes and the longevity of imported mosquitoes was the same as the wild ones,” says Dr. Shaibal Dasgupta, Project Leader, GBIT, Delhi.

Oxitec’s technology uses genetically modified male Aedes aegypti mosquitoes that carry a dominant lethal gene. When male GM mosquitoes mate with wild female mosquitoes the lethal gene is passed on to offspring. The lethal gene in the offspring produces a protein that stops their cells from functioning normally and prevents other genes essential for survival from turning on. This causes the mosquito larvae to die before reaching adulthood.

Since male mosquitoes do not bite humans, the release of genetically modified males will not increase the risk of dengue, chinkungunya and Zika.

“The caged trials, which will last 50-55 weeks, will study the efficiency of vector suppression and mating capacity,” Dr. Dasgupta says. “Surveillance [to undertake open field studies] to gather data on predominance of Aedes mosquitoes in the wild has already started. The open field studies, which will be of one-year duration, will be conducted in two villages and two control villages in close vicinity of the caged study area in Jalna.”

“It is a promising technology and India must certainly look at new vector control methods,” says Dr. Swaminathan. “From studies carried out in other countries we know the safety is beyond doubt, but efficiency has to be proved, especially in big cities and towns.”

“There are practical problems of raising large number of mosquitoes needed for vector control — 100-150 [GM] mosquitoes are needed per person for months together. So some innovation in breeding techniques is needed,” says Dr. Swaminathan.

In the case of the RIDL technology, the genetically altered male mosquitoes have to be released in large numbers at regular intervals. Only then can they compete with the wild normal male insects for mating. Since the larvae die before reaching adulthood, the technology is a “self-limiting approach (the genetic modifications are not perpetuated in wild populations)”, notes a piece published in The Lancet (February 1, 2016).

The first open field trial by Oxitec was carried out in 2010 in the Caribbean island of Grahnd Cayman. The trial was successful in reducing the mosquito population by 80%. Similar trials have since been carried out in west Panama, Malaysia and more recently in Brazil with at least 90% reduction in vector population.

Another alternative

“India is looking at another alternative. We are about to sign a memorandum of understanding next month with Monash University for vector control using Wolbachia-infected A. aegypti mosquitoes,” she says. Pilot studies of mosquitoes harbouring the Wolbachia bacterium are being conducted in Colombia, Brazil, Australia, Vietnam and Indonesia to help control the spread of dengue virus.

Vector control using Wolbachia-infected A. aegypti mosquitoes is achieved by using the life-shortening bacteria strain in both male and female mosquitoes. Uninfected wild females embryos fertilised by Wolbachia-infected males fail to develop, while embryos from infected females fertilised by infected or uninfected wild males survive. As Wolbachia is maternally inherited, the bacteria are passed on to offspring immaterial of which male mosquito the female mosquito mated with. Dengue, Zika or chikunguya viruses cannot replicate when mosquitoes have Wolbachia and hence cannot be transmitted to humans when the mosquito bites.

Unlike the RIDL technology, a salient feature of Wolbachia is that it is self-sustainable, making it a very low-cost intervention to mosquito vector control. The downside is that the release of even a single female mosquito infected with Wolbachia bacteria could “potentially lead to the alien Wolbachia spreading in the target population” says a June 2013 report in the journal Pathogens and Global Health.

Published in The Hindu on January 25, 2017