A woman weeps as she gives away her ducks for culling in Hooghly on Thursday. Picture by Debabrota Biswas

New Delhi, Jan. 24: A failure to define the focal points of the bird flu outbreak in the state is stretching human surveillance activities to endurance limits and delaying action to contain the virus, experts and officials said.

Working with the state’s machinery for poultry disease surveillance, the central Department of Animal Husbandry has been listing blocks in each of Bengal’s nine districts affected by the H5N1 virus.

But in some blocks, according to sources, it is still unclear in which villages or which households the virus struck first. With such outbreak foci still invisible, health teams tasked with door-to-door surveillance of people exposed to poultry have to cover enormous ground, village after village, the sources in Delhi and Bengal said.

The health ministry has sent seven teams to Bengal to screen people who are exposed to poultry and who live up to 10km from the affected zones. The teams examine people to ensure there is no human case of avian influenza.

“If focal points had been provided, we could concentrate human surveillance activities to the 10km zone around those points,” a source said. “Health teams could quickly complete the task and move to the next zone.”

In Birbhum, the 10km zone has a population of nearly 500,000. Health teams had covered only 250,000 people by last night. In Nadia, only 10,000 among a total population of 90,000 had been examined.

Animal husbandry officials said it was difficult to pinpoint the exact location of the first unusual mortality in backyard poultry. “The poultry samples that we get for diagnosis sometimes do not indicate their origin — the household remains unknown.”

But experts argue that meticulous disease surveillance demands that every sample sent for diagnosis have a label specifying its origin.

When multiple sites report an outbreak, the experts said, it is important to work towards rapid containment, followed by deployment of staff to a different site.

But with large activity zones, poultry culling and human surveillance have been delayed, the experts said. Among Bengal’s nine affected districts, surveillance of people is now under way in only five — Birbhum, South Dinajpur, Nadia, Murshidabad, and Burdwan.

In Burdwan, the human population in the 10km zone is 920,000, but health surveillance workers had been able to examine only 60,000 people by yesterday.

Experts believe slow action allows the virus to move. “We need to stay ahead of the virus. Unfortunately, the virus is moving ahead of us,” an official said.

The slow progress may also lead to fatigue and frustration, an expert in infectious diseases deputed to one of the affected districts told The Telegraph. “The smoothest operations are fast.… The longer this takes, the greater the chance of fatigue.”