Bird flu has spread to 13 of West Bengals 19 districts, with samples of dead chickens testing positive in two new districts, officials said on Monday. In neighbouring Bangladesh, the disease has spread to 29 of its 64 districts.
Experts fear the H5N1 strain found in both countries could mutate into a form easily transmitted from person to person, leading to a pandemic, but there have been no reported human infections in India yet.
It is very difficult to contain the virus among backyard poultry as villagers hide their chickens and even smuggle them to homes of far-away relatives, said Anisur Rahaman, the states animal resources minister. Officials said they were worried about the disease spreading to the crowded state capital, Kolkata, after bird flu hit the South 24 Parganas district on Sunday, only 20 km (12.5 miles) from the city.
Surveillance was in place to stop infected poultry from being smuggled into one of Indias biggest cities, they said.