The buzz about mutating mosquitoes

Standard repellents are fast proving to be ineffective as mosquitoes mutate and adapt to new environs, leading to higher health risks


Government health authorities spray insecticides and pesticides on stagnant water and other mosquito habitats. But even those are fast proving to be ineffective, as mosquitoes mutate and adapt to new environs, although this is disputed by manufacturers. Photo: AFP
Government health authorities spray insecticides and pesticides on stagnant water and other mosquito habitats. But even those are fast proving to be ineffective, as mosquitoes mutate and adapt to new environs, although this is disputed by manufacturers. Photo: AFP

Blame it on the warm climate or dirty environment, but it’s a fact that mosquito bites are fast becoming fatal—in India and elsewhere.

The global burden of the mosquito-borne viral infection dengue is a case in point. Nearly 2.4 million cases were reported in 2010, according to a World Health Organization (WHO) factsheet published in February.

In India, 131 people died of dengue in 2014, as against 96 in 2009, according to data from the government’s National Vector-Borne Disease Control Programme.

The UN health body clearly states that about half the world’s population is at risk and that there is no specific treatment for dengue except early detection. The only effective way to rein it in is to check mosquito proliferation, especially the Aedes aegypti, the so-called yellow fever mosquito, which can spread dengue fever, chikungunya and yellow fever viruses.

India accounts for 35% of the over one billion people who are affected by neglected tropical diseases such as dengue, chikungunya and filariasis, according to the Global Network for Neglected Tropical Diseases. For the vast majority of Indians, especially those living in crowded cities, the common ways to escape mosquito bites are to use lotions, repellents—electric vaporizers or coils that are burnt—or mosquito nets.

Government health authorities, on the other hand, spray insecticides and pesticides on stagnant water and other mosquito habitats. But even those are fast proving to be ineffective, as mosquitoes mutate and adapt to new environs, although this is disputed by manufacturers.

Mutating, adapting

Although rising global temperatures have endangered many species of plants and animals, mosquitoes, through genetic mutation, have been able to adapt to deforestation and depleting water sources, thereby becoming more virulent. In human habitations, the insects have long braved the onslaught of pesticides. For instance, mosquitoes are thought to have developed resistance to DDT, an insecticide that is used in India but is banned in several countries such as the US for its toxicity.

“Mosquitoes are fast gaining resistance to commonly used insecticides and repellents and it is inevitable that diseases transmitted by mosquitoes will become more severe, and there are also chances for new diseases to emerge,” says Utpal Tatu, a professor and researcher at the Indian Institute of Science, Bengaluru.

Worse may be in store, according to scientists. Newer viruses—such as trypanosoma, or sleeping sickness, and coma-causing Japanese encephalitis—are likely to be transmitted through mosquitoes. “Host receptivity through odour-sensing has evolved in the newer species of mosquitoes and their ability to act as a vector for more diseases has increased due to mutations in the mosquito immunity,” says Tatu.

Avoiding repellents

According to Ashwani Kumar, scientist and officer-in-charge at the National Institute of Malaria Research in Panaji, mutating mosquitoes are changing their behaviour as they learn to avoid repellents. “Many species of mosquitoes bite indoors and rest indoors in dark and damp places. But if the surface on which they rest is sprayed with any kind of insecticide, they would avoid it as a survival strategy and rest outdoors on bushes,” he says.

In Mumbai, one of the most populous cities in the world, the Municipal Corporation of Greater Mumbai has deployed 2,300 workers to spray pesticides in public spaces, up from 1,500 five years ago. “Since 2010, we have stepped up our fight and everything is being done at optimum level. But the major problem we are facing is indoors. We can’t enter every home. If people don’t implement the mosquito-fighting means in their homes, these diseases taking epidemic proportion can’t be ruled out,” says Rajan A. Naringrekar, insecticide officer at the public health department of the civic body.

Meanwhile, the repellent market has steadily expanded and is today worth around Rs.3,200 crore. Godrej Consumer Products Ltd (GCPL), which has captured around half of this market, in the last 20 years introduced as many as nine innovative solutions to fight mosquitoes. The latest is a repellent card that can be burned and extinguished in a flash and can be used in houses with no electricity. For houses without electricity in rural India, this is a great relief.

“We decided (a couple of years back) that we now need to take the R&D (research and development) and the team to the next level, so we put in a programme,” says Sunder Mahadevan, executive vice-president, R&D, at GCPL. “In terms of the sheer talent that we have brought on board, our incremental cost is a 50% increase over what we were having in the last two years.”

Competitor Reckitt Benckiser (India) Ltd (RB), which has launched an automatic insect control system using natural extracts, is also working on new products. “Mosquitoes are changing their behaviour, like biting and resting at micro level, to suit the sleeping and living habits of humans,” says Nitish Kapoor, managing director at RB. “Their adaptability to survive is fascinating. We at RB study them closely and incorporate the learning in our product development strategies.”

Genetically modified army

With mosquitoes managing to keep a step ahead of scientific innovations, government officials are examining an application that seems to have come out of the world of science fiction.

The proposal, before the genetic engineering approval committee under the ministry of environment, forests and climate change, involves releasing genetically modified mosquitoes in the environment to slow down the spread of dengue-causing Aedes aegypti mosquitoes. According to the proposal mooted in India by Oxitec Ltd, a UK-based biotechnology company that is a spin-off of Oxford University, genetically modified mosquitoes will be released in the environment to fight against dengue.

The company has created genetically modified mosquitoes by injecting two genes in their eggs: one is a colouring gene to help track them and the other is a gene that makes the larvae of the mosquitoes overproduce protein, which in turn interferes with their cell function and eventually kills them before they become adults.

Male mosquitoes carrying the two genes are released in the environment to mate with female Aedes aegypti mosquitoes so that their offspring do not survive, thus drastically reducing the insect’s birthrate.

“This was an adaptation to the sterile insect technique, SIT, which has been used around the world for more than 50 years—it uses radiation to sterilize insects,” says Kevin Gorman, senior field operations manager at Oxitec. “Oxitec came up with a new way to create the same ‘sterilization’ result [effectively] without using radiation.”

Oxitec’s technology has been tested in places such as Cayman Islands, Brazil and Panama. In Brazil, the national biosafety group, CTNBio, has approved the so-called Oxitec mosquito for commercial release. It now awaits approvals for trials in other countries, including India and the US. In India, Oxitec is working with GBIT, the seed company that founded Maharashtra Hybrid Seeds Co. Ltd.

The plan, if approved, will involve releasing genetically modified mosquitoes for 6-9 months in two villages of Maharashtra, which Oxitec has not named, with a combined population of about 5,000 people.

The proposal comes when much of the world is debating the wisdom of using genetically modified organisms (GMO). The argument against GMOs is that they may harm the ecology, especially if they disrupt the food chain—mosquitoes, for instance, are food to frogs and birds.

“If such a thing is permitted, it will have to be technically examined for evidence of their impact on disease in a pilot project in the community and regulatory okays, political clearance and social acceptability would be needed,” says Kumar of the National Institute of Malaria Research.

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