GM MOSQUITO TRIALS TO CONTROL DENGUE AND OTHER WATER BORNE DISEASES

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Outdoor caged trials to demonstrate the efficiency of genetically modified (GM) mosquitoes to suppress wild female Aedes aegypti mosquito populations that transmit dengue, chikungunya and zika were launched recently in Dawalwadi and Badnapur towns, in Maharashtra’s Jalna district.

Based on the results of the 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.

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 UK 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 kills the larvae before they reach adulthood. Since male mosquitoes do not bite humans, the release of GM males will not increase the risk of dengue, chikungunya and zika.

“The caged trials will last 50-55 weeks,” 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 will be conducted for about a year in two villages in Jalna.”

“It is a promising technology and India must certainly look at new vector control methods,” says Dr. Soumya Swaminathan, Director General of the Indian Council of Medical Research. “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 a large number of mosquitoes needed for vector control – 100-150 [GM] mosquitoes are needed per person for months together,” says Dr. Swaminathan.
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Large numbers of GM male mosquitoes have to be released at regular intervals to compete with wild normal males for mating. Since the larvae die before reaching adulthood, the technology is a ‘self-limiting approach’. India is looking to sign a memorandum of understanding next month with Monash University for vector control using Wolbachia-infected A. aegypti mosquitoes.

Vector control using A. aegypti infected with the bacterium Wolbachia is achieved by using the life-shortening bacteria strain in both male and female mosquitoes. Uninfected wild female mosquito 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 anyway passed on to offspring. Dengue, zika or chikungunya viruses cannot replicate, when mosquitoes have Wolbachia. Unlike the RIDL technology, a feature of Wolbachia is that it is self-sustaining, making it a low-cost intervention. The downside is that the release of even a single female mosquito infected with Wolbachia could potentially lead to the alien bacteria spreading in the target population, which could be dangerous.

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