KOLKATA, India (Reuters) - India's worst outbreak of birdflu appears to be under control, with a massive cull of poultryto contain the disease almost completed, health officials saidon Tuesday.

More than 3.4 million birds have been culled in WestBengal, where 13 of the 19 districts have been affected by theH5N1 bird flu virus since the disease was first reported lastmonth, state officials said.

"Culling is almost over and we are now conducting moppingup operations in the infected areas," Anisur Rahaman, thestate's animal resources minister, told Reuters.

Disinfecting villages affected by avian influenza couldcontinue for several weeks, he said.

"But the overall situation is totally under control,"Rahaman added.

India said tests of at least 23 people, including severalveterinary staff, who were held in isolation wards withsymptoms of influenza had turned out negative for H5N1.

"But we are still keeping a close watch," Sanchita Bakshi,the director of health services in West Bengal, said.

India has not reported any human infections of the H5N1bird flu virus in its four outbreaks of avian influenza since2006.

Experts fear the H5N1 strain could mutate into a formeasily transmitted from person to person, leading to a pandemicthat could kill millions worldwide.

About 60 percent of India's 1 billion plus people live inrural areas close to livestock, just like in many other partsof Asia, raising the risks of the bird flu virus infectingpeople.

In West Bengal's state capital, Kolkata, one of the biggestcities in India, authorities encouraged people to eat chickento help the poultry industry as many people opted for fish andmutton dishes following the outbreak.

Egg exports from the world's second largest producer havealso dropped about 50 percent, leaving the industry with lossesof around $20 million, trade officials said.

India said culling would also take place in statesbordering West Bengal and a special watch was in place indistricts bordering Bangladesh.

Authorities said the virus could have originated fromBangladesh, where officials were struggling to contain amassive outbreak of bird flu.

"We are keeping a watch on our borders with Bangladesh andother states as the idea is to minimize the chances of bird fluspreading," Rahaman said.

Many unwilling villagers resisted the authorities efforts,letting most of their backyard poultry free when culling teamsarrived. There were reports that some chickens and ducks weresmuggled out at night from infected districts.

(Editing by Alistair Scrutton and Alex Richardson)