According to officials in Bangladesh bird flu has killed nearly 500 chickens at a poultry farm in the northeast of the country and as a result another 20,000 chickens have been culled.
Salehuddin Khan, director of the government's livestock department says the outbreak of the disease is the first to occur in that area.
The farm is situated in the Moulavibazar district, about 250 km (155 miles) from the capital Dhaka.
Khan says after bird flu was confirmed the authorities culled almost 800 chickens, ducks and birds in a one-kilometer area around the affected farm.
The H5N1 avian flu virus was first reported near Dhaka in March last year and has since spread mainly to northern districts and authorities have been forced to kill more than 300,000 chickens.
The latest outbreak now means 71 farms in 22 of Bangladesh's 64 districts have been infected with the deadly virus.
According to officials 4 million of the population are in one way or another involved in poultry farming.
Bangladesh is among the most densely populated countries in the world with a high level of poverty; the majority of the population is rural but to date there have been no cases of human infection according to government officials.
In neighbouring Bengal thousands of backyard poultry have died in the west of the country over the last 10 days and tests show they too were infected with bird flu, but officials say as yet it is unclear if it was the H5N1 strain of the virus.
This latest outbreak was in the village of Margram in the Birbhum district.
Birbhum's chief medical officer Sunil Kumar Bhowmik says quarantine measures will be imposed if anyone becomes sick and culling will be intensified.
Three separate outbreaks of the deadly H5N1 virus in Maharastra in 2006 meant that thousands of birds were culled at the time.
Experts fear the H5N1 virus will ultimately mutate, as they do, or else combine with the highly contagious seasonal influenza virus and trigger a pandemic with the potential to kill millions of people.
According to the World Health Organisation the H5N1 bird flu virus has already killed more than 210 people in 12 countries since 2003.