New Delhi, Oct. 11: The repeated resurgence of dengue over the past decade and the rapid spread of chikungunya this year reflect India’s failure to tackle a tiger-striped mosquito blessed with tricky breeding and biting habits, health experts have said.

The outbreaks also highlight holes in India’s disease surveillance network and the absence of public health systems and community participation to prevent massive outbreaks, according to medical researchers tracking infections spread by mosquitoes.

“We’ve had warnings over the past decade,” said Vinod Sharma, former director of the Malaria Research Centre. “But it’s only during outbreaks that we see attempts to manage the crisis. At other times, there’s little focus on prevention.”

“Instead of regular surveillance of mosquitoes to assess the risk of outbreaks in advance, we’re only fire-fighting after a large number of infections have occurred,” said P.K. Das, director of the Vector Control Research Centre (VCRC) in Pondicherry.

The number of patients with confirmed chikungunya crossed 1,600 yesterday, among over 1.32 million suspected cases. The number of dengue deaths has climbed to 52. The chikungunya and dengue viruses are spread by Aedes aegypti, a mosquito with peculiar breeding and biting behaviour that makes it difficult to control.

All it needs is a tiny pool of fresh water to lay its eggs. While other mosquitoes are known to lay 200 to 300 eggs clustered together in the form of “egg-rafts”, the Aedes aegypti lays just 15 to 20 eggs in one pool of water, another small bunch in another pool, laying its eggs at many sites, a senior scientist at the VCRC said.

Such distributed breeding allows more eggs to survive, hatch into larvae, and produce adult mosquitoes because fumigation may not reach all breeding sites, he said.

Studies on the Aedes aegypti’s feeding habits show that it is a shy feeder. In its effort to get a full bloodmeal — about 40 microlitres of blood — an Aedes aegypti might bite several people. “The slightest disturbance such as a slight movement of the body will make it fly off and look for another victim,” said the VCRC scientist.

Such biting habits increase the chance of spreading infection.

Researchers have also questioned the inability of the disease surveillance network to pick up signs of the outbreak at its earliest stages. “By the time doctors and hospitals begin reporting a spurt in cases, it’s only the tip of the iceberg,” said Das.

He said early signals of chikungunya should have come in by December 2005 or early 2006 when Karnataka had begun to report unusual spikes in the number of patients with high fever and joint pains. The surveillance network is expected to look for unusual sickness and alert central authorities for rapid action.

Delhi had experienced a large dengue outbreak in 1996 with nearly 9,000 patients. More than 12,000 patients had dengue around India during 2003 and over 11,000 last year.

“After the big outbreak of 1996, there should have been intensive health education to motivate the public to prevent the breeding of mosquitoes in homes,” said Sharma.

Insect control experts say the absence of a strong public health system has meant not just little emphasis on sanitation, but also haphazard application of insecticides.

“After the first cases are detected, houses should be fumigated inside and outside,” said Das. “Instead, fumigation done without thinking across neighbourhoods, pushes mosquitoes inside houses where they might even pick up the virus from infected people to spread it further,” he said.