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Disease outbreaks highlight India's poor mosquito control

October 9, 2006 By Killugudi Jayaraman This article courtesy of Nature News.

Officials fear yellow fever may hit in wake of raging outbreaks.

BANGALORE A series of outbreaks of the viral diseases dengue and chikungunya in India are being blamed on the collapse of mosquito control programmes and poorly planned urbanization.

The worrying spread of disease has left virologists wondering whether the country would be able to cope with an outbreak of yellow fever. This deadly mosquito-borne disease is currently absent in India, but is transmitted by the same species of mosquito, Aedes Aegypti, as are dengue and chikungunya.

"The situation is serious, but there is no epidemic," a statement from the health ministry declared on 7 October. But other countries in the region are not taking chances. Malaysia has issued precautionary travel advice to its citizens, and officials at the World Health Organization in New Delhi say they are keeping a careful eye on the situation.

Government figures released on 8 October put the number of suspected chikungunya cases at 1.32 million, and dengue at 3,407 cases, with 47 associated deaths, 23 of them in the nation's capital, New Delhi. The Indian Medical Association says the numbers could be much higher, because as much as 80% of cases treated by private doctors go unreported. There have been 90 chikungunya deaths reported in Kerala alone, though the cause of death has not been confirmed and may be due to West Nile virus.

Disease outbreaks of 200-300 are not unusual after the annual monsoons. But the numbers this year are already staggering. Dengue has occurred among army personnel and in the family of Prime Minister Manmohan Singh.

And the emergence of chikungunya after 32 years of dormancy in India has surprised public-health experts. "It is a new strain, much more pathogenic than what we saw in the 1960s," says Brij Kishore Tyagi, director of the Madurai-based centre for research in medical entomology run by the Indian Council of Medical Research.


Blaming the outbreaks on "rains and sanitation problems", Indian health minister Anbumani Ramadoss promised to revive the vector control centre in Kerala state that was closed down in 1996, and to set up a third virus research laboratory in southern India.

But Palakkad Krishnaiyer Rajagopalan, former chief of the Vector Control Research Centre in Pondicherry, says that beefing up research won't solve the problem. It is operational failures that are at fault, he says, not a lack of study. "Nobody wants to do fieldwork," he told Nature. "Our scientists are happy devising mosquito control strategies using molecular-biology tools and sitting in air-conditioned rooms."

Rajagopalan says that 90% of the chikungunya cases in Kerala state have occurred in a town from which his team totally eradicated mosquitoes infected with parasitic nematodes some 20 years ago. They achieved this simply by closing every breeding pit and introducing larva-eating fish into ponds and wells. "Such control activities have ended, and there is no surveillance for mosquitoes or viruses," he says. A disease-surveillance network mooted soon after the plague outbreak of 1994 was never put in place because of bureaucratic wrangling.

Breeding sites

Akilesh Mishra, director of the National Institute of Virology in Pune, blames the outbreaks on urbanization. Widespread construction of both homes and roads, along with improper water management, is compounding the problem, says Kalyan Banerjee, Mishra's predecessor. "Discarded rubber tyres on roadsides are ideal places for Aedes mosquitoes to breed," he adds.

Banerjee says the reason India has never experienced outbreaks of yellow fever is unclear, given the presence of A. Aegypti mosquitoes, monkeys that can act as hosts for the virus, and a susceptible population. It is assumed that the virus has not reached India because of the country's stringent quarantine measures.

But Banerjee warns that "it may come any day". Former chief of the Indian Council of Medical Research, Sriram Prasad Tripathy, agrees: "True, we do not have yellow fever now, but no one has said it will never come. We cannot afford to neglect vector control."

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