Bengaluru: Oxitec, a UK-based biotechnology company, plans to release genetically modified mosquitoes in the Florida Keys islands off the US this month as part of a trial to curb mosquito-borne diseases like dengue and the one caused by the Zika virus.
This is the latest genetic engineering experiment targeting mosquitoes that is aimed at tackling diseases that continue to kill thousands every year — an approach that has critics as well as backers.
Only females of mosquitoes bite, while males feed on all nectar.
The mosquitoes Oxitec plans to release will all be male, carrying a protein that will kill all their female offspring.
The exact locations where the mosquitoes will be released have not been made public.
The objective over time is to reduce the population of the Aedes aegypti mosquito, which spreads both the above-mentioned diseases as well as chikungunya and yellow fever.
Mosquito populations in Florida are believed to have grown resistant to a common group of insecticides, prompting worries.
Oxitec plans to release around 750 million male mosquitoes to breed with females in the wild over a period of two years.
While the plan has drawn concern from some environmental groups about its potential impact on ecology, the company says it sees no risk from the experiment. Oxitec claims to have released over a billion genetically modified mosquitoes over the years in other trials.
How transgenic mosquitoes work
There are two approaches to genetically modifying mosquitoes that are being experimented with. One is to modify both males and females to become resistant to diseases, thus reducing their ability to transmit them to other species.
The other is to modify the reproductive ability of the males so that they either can’t reproduce or only produce sterile offspring.
The second method aims to lower the population of mosquitoes with the ultimate objective of eliminating them from a region. Since the genetic modification passes from a parent to offspring, it is called “transgenic”, and this is the technology that Oxitec is attempting to test. The first-generation mosquitoes will be called OX513A.
Oxitec genetically engineers mosquitoes in its UK labs to give them a ‘self-limiting’ gene. The gene will make females dependent on an antibiotic for life — if they don’t get that antibiotic, they will die.
Eggs laid by these mosquitoes will be shipped to Florida Keys, where they will be soaked in water, which mosquitoes need to hatch.
When females hatch, they will not have access to the antibiotic and die. But males will survive and carry the gene, which will again kick in when they mate with females in the wild. This is expected to reduce the local female mosquito population.
The company has already tried the approach in field trials in Brazil, Cayman Islands, and Malaysia. The results were reportedly promising, showing a reduction of up to 95 per cent in mosquito populations and a drop of over 90 per cent in dengue cases in the area.
Why trials are opposed
Many voices have been raised against the Oxitec trials. Some ecologists say the loss of mosquitoes is not likely to have any long-term consequences on the ecosystem as they are not a keystone species that others depend on, but others claim it is unwise to draw such a conclusion.
The company has also come under criticism for allegedly not being transparent about their and the US regulatory authority Environment Protection Agency’s review process, which Oxitec has rebutted.
There have also been concerns that the experiment may not turn out as it is supposed, as happened in a trial at Brazil, which saw some seemingly sterile offspring reproduce and survive to adulthood.
The WHO has expressed support for investigating genetically modified mosquitoes as a tool to fight mosquito-borne diseases. “More than 80 per cent of the global population lives in areas at risk of at least one major vector-borne disease. Taken together, these diseases exact an immense toll on economies and can impede both rural and urban development,” the agency said in an October 2020 statement.
It, however, cautioned that the use of the technology “raises concerns and questions around ethics, safety, governance, affordability and cost–effectiveness that must be addressed”. Research into the technology “should be conducted through a step-wise approach and supported by clear governance mechanisms to evaluate any health, environmental and ecological implications”, it said.
(Edited by Sunanda Ranjan)