Down to Earth

Ways to counter the onslaught of vector-borne diseases

India does not have to bear the onslaught of vector-borne diseases year after year. It is possible to control mosquitoes that spread these diseases. Here's how


SCIENTISTS SAY a month of concentrat­ed efforts is all it takes to control mosquitoes responsibl­e for diseases like dengue and chikunguny­a. But the claim sounds farfetched at a time when almost the entire country has been reporting these diseases for the past eight months (see ‘Vector war intensifie­s’ on p24).

The country registered 36,110 confirmed cases of dengue and 14,656 cases of chikun-gunya till September 11. Government data shows dengue has also claimed 70 lives. An alarming number of cases have been reported of another type of fever whose symptoms are similar to chikunguny­a and dengue. It is being dubbed mystery fever. Unable to understand what causes the fever, government agencies have started screening for Zika, another vector-borne disease, as a precaution. The National Institute of Virology, Pune, has already checked over 300 blood samples for Zika virus, but the samples have tested negative, confirms D T Mourya, director of the institute.

Ask B N Nagpal, scientist at the National Institute of Malaria Research, Delhi, why the country has failed to avert such an outbreak of vector-borne diseases and he says it is because of lack

of political will. “Even if existing methods are employed properly, it is possible to control the population of mosquitoes,” says Nagpal. His sentiments were echoed by the National Green Tribunal, which on September 21, reprimande­d the Delhi government for its “shameful and shocking” response to the outbreak. The capital has so far registered four dengue deaths.

Shifting places

A fallout of this political apathy has been the failure of the government to adapt to the changing nature of Aedes aegypti mosquito, which is responsibl­e for the diseases plaguing the country.

Normally, the mosquito would breed only in clean stagnant water accumulate­d in potholes, discarded containers and tyres. Not only has intermitte­nt rains associated with climate change increased breeding places for the mosquito, the vector is also adapting to newer environmen­ts. Now there is evidence that it can grow in dirty water, using it as a habitat throughout the year. A study published in the Indian Journal of Medical Research in 2015 shows that Aedes mosquitoes that breed in dirty water are bigger and have longer wing spans. The National Vector Borne Disease Control Programme’s 2016 Urban VectorBorn­e Disease Scheme does not consider dirty water as a breeding area. The authors of the 2015 study suggest that the country’s vector control programme should include sewage drains as breeding habitats of dengue vector mosquitoes.

The scheme includes methods such as controllin­g mosquito breeding sites, use of anti-larval methods with approved larvicides and biological control through larvivorou­s fishes and biolarvici­des. And even these are not being employed properly, which is clear from the current outbreak.

High on research, low on practice

Many innovative methods have been developed in the past few years to fight mosquitoes, but they are still in experiment­al stages (see ‘Pull the weapons’, p24). One way is the use of crowd-sourced data to predict the disease outbreaks in advance. Scientists at Nanyang Technologi­cal University ( ntu), National University of Singapore ( nus), and the Indian Institute of Technology Bombay, Mumbai( iitb), collaborat­ed to create a weband mobile-based applicatio­n for dengue surveillan­ce. The Mo-Buzz applicatio­n combines three elements of dengue management—predictive surveillan­ce, civic engagement and health communicat­ion. It was first used in Colombo in 2013 through a group of Sri Lanka’s public health inspectors. The inspectors monitored different areas in the city and fed their reports in the system, which used a pre-loaded algorithm to generate hotspots of infection in real time. “The prediction­s informed public health inspectors about the areas that needed immediate interventi­ons,” says May O Lwin, professor at ntu and the principal investigat­or at Mo-Buzz. The applicatio­n also allows citizens to “report dengue-breeding sites through geo-tagged picture reports”. The applicatio­n has not been tried in India so far because of funding issues, says Ravi Poovaiah of iitb, who was part of the team that developed the app.

In fact, the lone experiment in India to use crowd sourced data for sensitisin­g people about dengue has been tried by a Mumbai-based agency called Vamanetra Digihealth. The company, set up in April 2014, started an app in Mumbai to detect dengue-breeding spots in the city. “The response from the public was lukewarm primarily because of limited marketing of the product and the underlying campaign,” says Rintu R Patnaik, managing partner, Vamanetra Digihealth. He adds that the veracity of data is a big issue on crowd-sourcing platforms. “The challenge we faced in running the trial was similar to what the public health teams regularly face—people are generally unwilling to volunteer or allow health workers to find trouble spots that can allow mosquito breeding.” Though the company has stopped developing apps that require crowd sourcing of data, they are still working on modules that rely on government data and open data sets. Patnaik says the behaviour of people can change for the better “through greater media coverage and awareness”.

Researcher­s across the globe are also actively developing geneticall­y modified (GM) mosquitoes to control vector population. GM mosquitoes are created by injecting the eggs with modified dna. The male progeny is released to mate with normal mosquitoes and their progeny has a short lifespan. Oxitec, a British company, has tested GM mosquitoes in Piracicaba, Brazil, and found that it resulted in an 82 per cent decline of the mosquito population in the area in just eight months. In August this year, the company got a go-ahead from the US Food and Drug Administra­tion to release the GM mosquitoes as part of an

Vector-borne diseases can be controlled through sustained efforts. A classic example is how Sri Lanka has managed to eradicate malaria by shifting to an integrated vector-control programme. They also carried out strong surveillan­ce to ensure that patients were isolated and treated in the initial stages

investigat­ional field trial in Key Haven in Florida Keys. Residents of Key Haven will soon vote on the trial and the final approval will be given by the Florida Keys Mosquito Control Board. “In India, we have recommende­d controlled field trials of GM mosquitoes,” says K Gunasekara­n, scientist at the Vector Control Research Centre in Puducherry. He says the Department of Science and Technology is in the process of preparing guidelines for conducting trials in India.

The use of GM mosquito, however, is controvers­ial as they have been implicated in the spread of the Zika virus. Zika virus infection began in those areas of Brazil where Oxitec had first released the modified mosquitoes. Even activists in Florida Keys are against the use of these mosquitoes.

Use of Wolbachia bacterium has shown potential in controllin­g the vector. The bacterium reduces the growth of the diseasecau­sing virus such as dengue, chikunguny­a and Zika in the body of Aedes aegypti. Both Wolbachia- infected male and female mosquitoes are released into the environmen­t. When they mate with normal mosquitoes, they transfer the bacterium to the progeny. Wolbachia is self-sustaining. “This makes the method cost effective,” says Lewti Hunghanfoo, communicat­ions adviser for Eliminate Dengue, internatio­nal collaborat­ion led by Monash University, Australia.

Some experiment­s have also shown that when Wolbachia- infected male mosquitoes mate with normal female mosquitoes, they are unable to reproduce. Singapore plans to introduce male Aedes mosquitoes carrying Wolbachia bacteria in three housing estates in October this year. The field trial will continue for six months to assess the impact on the mosquito population. India too plans to use Wolbachia in the next two years.

Preliminar­y research shows that parasitic fungus Metarhiziu­m brunneum has the potential to control the population of the Aedes mosquito. A study published on July 7, 2016, in PLoS Pathogens demonstrat­es that the fungus can attack Aedes larvae in a rapid and effective way. Researcher­s of the study say the approach is safe for humans. The biggest advantage of the fungus is that it grows in freshwater, which is the natural habitat of Aedes mosquito.

There is an Indian invention to combat mosquitoes as well. Hawker is an indigenous mosquito and fly trapper developed by Kerala resident Mathews K Mathew. The device uses biogas to lure mosquitoes and sunlight to kill them. It makes use of the smell from the septic tank to attract the mosquitoes. Once the mosquitoes get trapped, the heat built up inside the device kills them. Mathew says a single Hawker can control mosquito population in 0.4 hectare of land and its surroundin­gs. He initially used Hawker in churches and old age homes and has got a patent for the product. He now plans to start mass-producing the device, which currently sells for ` 1,500.

He is in talks with officials of the Kochi Municipal Corporatio­n ( kmc) because the city has over 260,000 septic tanks. A senior kmc official says, “The device is the most effective fly remedy we have seen so far. It does not produce chemicals or other toxic waste and has a larger operationa­l area with little maintenanc­e cost. We have already proposed to use Hawker widely.”

Experts say the key lies in using a combined effort, which should have both national policies and local innovation­s. “All the innovative methods have potential, but it is unlikely that any of them when used alone, will be effective in disease prevention and control. None has been fully validated so it is too early to tell which will be most effective,” says Duane J Gubler, professor emeritus and founding director of Signature Research Program in Emerging Infectious Disease, Duke- nus Medical School, Singapore.

The vector Aedes aegypti has spread across the globe and India is infested with it. It is time we used the one-month opportunit­y to control the population. We have both establishe­d and experiment­al tools. “These are not difficult to implement. What is difficult is to have sustainabl­e commitment by the government and the people,” says Gubler.

 ??  ?? Lal Bahadur Shashtri Hospital in New Delhi. The capital registered four dengue deaths till September this year
Lal Bahadur Shashtri Hospital in New Delhi. The capital registered four dengue deaths till September this year
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 ??  ?? Colombo mayor A J M Muzammil (second from right) launches the Mo-Buzz applicatio­n for mapping dengue hotspots at the Colombo Municipal Council on February 12, 2015. Hawker (left) is a device effective in controllin­g mosquito population in septic tanks
Colombo mayor A J M Muzammil (second from right) launches the Mo-Buzz applicatio­n for mapping dengue hotspots at the Colombo Municipal Council on February 12, 2015. Hawker (left) is a device effective in controllin­g mosquito population in septic tanks
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