KOLKATA, 17 January 2008 — Veterinary workers began killing thousands of chickens in eastern India yesterday following what the World Health Organization said was the worst outbreak of bird flu in the country.

Officials said it could take up to a week to cull about 350,000 birds in three districts of West Bengal.

The WHO’s India office said the fourth bird flu outbreak in India since 2006 presented its toughest challenge yet.

“More serious risk factors are associated with this current outbreak than previously encountered, including that the affected areas are more widespread,” Indrani Dasgupta, a WHO India official, wrote in an e-mail.

But Pradeep Kumar, India’s animal husbandry secretary, emphasized that the outbreak was “localized” and under control. “There is no need for a scare,” he told a news conference in New Delhi.

Kumar acknowledged some of the difficulties containing the threat. He said the West Bengal government took too long to tell New Delhi about suspicious bird deaths in the state.

And in Birbhum, the worst-affected district, where nearly half the adult population is illiterate and few own a television, it has been difficult to get villagers to observe stringent hygiene practices that might limit the spread of infection.

Local men wearing only cotton wraps around their waist were seen carrying dead birds with their bare hands and dropping them in shallow pits.

In some villages inside the quarantine zone, a Reuters photographer saw backyard poultry roaming in farmlands and mud roads as villagers said they were unaware about a culling operation and had let them loose. “It is a very densely populated area ... it is not easy to create awareness,” Kumar said.

The WHO said that while the central government was very well-prepared to deal with the disease, that may not always be the case at the state and district level.

Preliminary tests showed the highly contagious H5N1 strain had infected birds in the area, Health Ministry officials have said. H5N1 is the strain that scientists worry could mutate into a form easily passed between humans.

However, India’s animal husbandry department said its laboratory confirmed only that it was an H5 strain, and establishing the N-type would take a few more days.

India has never reported a case of human infection, but health workers were checking people in affected areas for flu symptoms. In some villages, people queued up at local health centers for a checkup.

Experts from the West Bengal’s animal husbandry department were also investigating the southern fringes of the state capital, Kolkata, after reports of backyard poultry deaths in the area.

In neighboring Bangladesh, bird flu spread to another district forcing authorities to cull more than 1,500 birds, officials said yesterday.

The H5N1 bird flu virus was reported in backyard poultry in the southern coastal district Barisal, a Livestock Department official said.

“After the confirmation of bird flu, authorities culled more than 1,531 chickens, ducks and birds in a one-kilometer area around the affected backyard poultry,” the official said.

Suspected outbreaks were also reported at a farm in northwestern Rajshahi district and another farm in northern Rangpur district, where the virus has been confirmed in fowl previously.

“The preliminary tests showed some birds at the farm have died from bird flu, but we still don’t know whether it is the deadly H5N1 strain,” the official told Reuters, referring to the farm in Rajshahi.