“There are around 3,000 species of the Aedes in the world,” says Dr Prabhakar Patil, medical entomologist. But only two—Aedes aegypti and Aedes albopictus—among the species are harmful.
On June 14, it rained heavily in Jalna district, about an hour's drive from Aurangabad. Dr Shaibal Dasgupta sat in a car, and through the glass window, peered at a large, boxy enclosure with wooden floor and legs. In the heavy rain, the only thing that made it conspicuous was the green net that covered the entire enclosure. “This,” said Dasgupta, “is the world's largest cage for the Aedes aegypti mosquito. There's nothing quite like this anywhere in the world.”
Built on a budget of about 035 lakh, the enclosure is a set of six cages placed on a platform of 580 square metres. Each cage is 6X6X3 metres, enclosed in a cover of 8X8X3 metres, and contains thousands of Aedes aegypti mosquitoes caught from nearby areas. The buzzing insects are fed sucrose—male mosquitoes feed on sugar, female on blood—at regular intervals, and left to multiply. The green cover, imported from Taiwan, protects the insects from extreme temperature and ultraviolet rays, while the ant traps fixed on the wooden legs prevent other insects from infiltrating.
Few among us would reckon that the life of a mosquito holds much value. But inside the warm environs of this laboratory at Gangabishan Bhikulal Investment and Trading Company, the mosquito is an unlikely ally in the war against its own kind—the deadly Aedes aegypti, known to be a carrier of dengue, chikungunya, and as India has learnt lately, the zika virus, too. GBIT started working on the project in 2008 after signing an agreement with Oxitec, a British biotechnology company that specialises in producing genetically-modified insects. As part of the project, GBIT has imported eggs of a genetically modified strain of the Aedes aegypti mosquito. When males of this strain (OX513A) mate with the local mosquito, they produce an offspring that would die before reaching adulthood. Ultimately, it will lead to a reduction in the mosquito population, claim scientists.
Dr Prabhakar Patil, medical entomologist, has been working on the project since its inception in 2008. He shows a brown-coloured paper strip of 15cm X 10cm which contains close to 8,000 eggs.
Every time Patil needs insects for the experiment, he cuts a strip of paper—the 8,000 eggs look like fine ash spread on paper to the naked eye—and immerses it in water. “Once the eggs hatch, the larvae are fed tetramin [larvae feed],” he says. Patil then closely monitors their life cycle, mating habits with the wild strain, and the progeny they produce.
Oxitec's insects have a gene that prevents them from surviving to adulthood. This pest control gene produces a protein called tTAV (tetracycline repressible activator variant) that acts as a switch to control the activity of the other genes. “It is a gene variant that has been optimised to work only in insect cells,” says the Oxitec website. “In the engineered insects, when the tTAV gene is expressed, the non-toxic protein ties up the cell’s machinery so its other genes aren’t expressed. And the insect dies.”
To keep the mosquitoes alive inside the laboratory, and offset the effect of the self-limiting gene, tetracycline, an antibiotic that binds itself to the tTAV protein and disables it, is used.
“There are around 3,000 species of the Aedes in the world,” says Patil, as he shows us around the GBIT lab. However, only two—Aedes aegypti and Aedes albopictus—among the species are harmful.
Controlling the Aedes aegypti mosquito is difficult because of its breeding habits, says Dasgupta, project leader at GBIT, which is owned by Maharashtra Hybrid Seeds Company. Dr Neena Valecha, director of National Malaria Research Institute at Dwarka in New Delhi, shows pictures of old, abandoned tyres at different sites in the city, including those at puncture shops, where the mosquito breeds easily. Which is why scientists like Dasgupta are placing their bet on the transgenic mosquito. The technology has had varying degrees of success in different countries; Oxitec's biggest factory producing mosquitoes is currently being tested in Brazilian neighbourhoods.
This, however, isn't India's first tryst with genetic control of mosquitoes. According to an article published on the website of Third World Network, a transnational alternative policy group, a similar experiment was done in the 1970s in India. In the article, veteran medical entomologist Dr P.K. Rajagopalan highlights how in 1975, the WHO was forced by the Indian government to wind up its Genetic Control of Mosquitoes Unit (GCMU) in New Delhi. The GCMU's planned release of millions of modified Aedes aegypti mosquitoes in urban Sonepat, north of New Delhi, was declared to be “not in the national interest and aborted”.
Rajagopalan, former director of Vector Control Research Centre and WHO consultant, is a strong opponent of the genetic sterile male technique. He argues that releasing competitive, sterile males [to overwhelm the wild males] has worked in the case of insects such as screw worm and Mediterranean fruit flies, because the females cause no damage, and sex separation systems are not required. For the mosquito, however, it is essential to ensure that no females, not even sterile ones, are released because the female (even if sterile) bites and transmits diseases. In the GCMU experiment, Rajagopalan says that a “contamination” of 2 to 5 per cent females was observed with the males.
Experts at GBIT, however, insist no females would be released, and even if they were the probability of them transmitting infection is next to nil. Studies carried out by the GCMU show that the sterile males were unable to compete with wild males, says Rajagopalan.
Also, there is no way to ensure that the synthetic DNA would not cause any harm when transferred into humans by the transgenic mosquitoes.
In the laboratories of the Vector Control Research Centre in Puducherry, the stage is being set for another innovative method. A fresh batch of Aedes mosquito eggs, infected with a bacteria, is set to be imported from Australia, as part of an agreement between the Indian Council of Medical Research and the Monash University. Scientists will test whether the bacteria can help reduce the ability of the mosquitoes to be infected by the dengue virus. Unlike the GBIT project, this project does not aim to reduce population. Instead, it aims to stop the virus from growing inside the vector.
Researchers part of the Eliminate Dengue Programme at the Monash University told THE WEEK that the bacteria approach worked in two ways. It boosts the immune system of the mosquito to make it harder for it to support the dengue or zika infection. “The other way is by competing for key molecules like cholesterol, which both the virus and wolbachia [a bacteria] need. When wolbachia is there, it consumes those molecules and makes it harder for the viruses to grow. If the viruses can’t grow, they can’t be transmitted,” say the researchers.
The imported eggs would be hatched in clean water. Simultaneously, colonies of wild mosquitoes will also be raised, and the two strains will be backcrossed (cross a hybrid with one of its parents or an organism with the same genetic characteristics as one of the parents). “The wolbachia infection is inherited maternally. We will experiment with 5 to 6 generations of the mosquito before we know how it will work,” says Dr P. Jambulingam, director of VCRC. The mosquitoes will be fed on dengue virus, and the experiment will check whether the virus reaches the salivary gland of the insect from where it is passed on to others, he says. Wolbachia is safe for humans and the environment, insist experts. Unlike the Oxitec technique, this effect is self-sustaining in the mosquito population, making it an affordable, long-term intervention.
The success of these strategies will rest on community engagement, says Dr Soumya Swaminathan, director of ICMR. According to Dr T. Mariappan, scientist at the ICMR-Centre for Research in Medical Entomology in Madurai, improving sanitation and increasing awareness would play a key role. “It is being predicted that by 2025, diseases such as dengue and chikungunya will overtake malaria. There is no vaccine that protects against the four dengue virus strains. The fight against the mosquito is not the government's alone,” says Mariappan. It is everyone's fight.
WHY INDIA NEEDS TO WAIT FOR A DENGUE VACCINE
Last year, 245 people died of dengue in India. This year, 11,402 cases have been reported so far. Finding a vaccine is the need of the hour. There are two candidates in the fray—an indigenous tetravalent vaccine being developed by scientists at International Centre for Genetic Engineering and Biotechnology, and another vaccine developed by France–based Sanofi Pasteur.
There are four serotypes of the dengue virus. Our vaccine protects against all four, says Dr Navin Khanna, group leader, recombinant gene products at ICGEB.
The other vaccine, Dengvaxia, has been approved in 16 countries (in Asia and Latin America), but is currently under review in India, according to Jean-Pierre Baylet, country head, South Asia, Sanofi Pasteur. “It is the only dengue vaccine to have completed three phases of development and is now approved for use in 16 dengue-endemic countries,” says Baylet.
However, according to World Health Organisation's position paper on dengue vaccine, “in defining populations to be targeted for vaccination, prior infection with dengue virus of any serotype, as measured by seroprevalence, should be approximately 70 per cent or greater in the age group targeted for vaccination in order to maximise public health impact and cost-effectiveness”. The paper that was published in July 2016 says that “vaccination of populations with seroprevalence between 50 per cent and 70 per cent is acceptable but the impact of the vaccination programme may be lower”.
Dr Soumya Swaminathan, director of Indian Council of Medical Research, says that over the next year, a seroprevalence study for dengue virus would be conducted in ten states with about 70,000 to 80,000 samples, before the introduction of a vaccine can be considered. “We need to invest more in development of a vaccine. Since it is a complex area that requires a lot of research and development, not many good vaccine companies are willing to invest in it,” she says. “The mosquito is adapting much faster, and more research in this area is needed.”