Chickens at a poultry farm in Bangladesh\'s Meherpur district, some 240 km west of capital Dhaka, have been tested positive for the highly pathogenic H5N1 bird flu, an official said Tuesday. Ataur Rahman, an assistant director at the control room of Fisheries and Live Stock Department, told Xinhua that \"Some 1,803 birds of the commercial farm were culled on Monday night.\" Some 994 eggs were also destroyed following the outbreak of the disease, he said. This is the fourth case in Bangladesh since the middle of November that mass poultry culling has occurred following the detection of the avian flu virus. Officials said in some cases there was a particularly infective strain. Prior to the latest culling and destroying incident, Rahman had said Bangladesh\'s authorities culled nearly 14,000 chickens and destroyed about 50,000 eggs from three farms since this season\'s first outbreak of bird flu was detected last month in a farm. The disease has so far spread to four Bangladesh districts, including central Manikganj and western Rajbarbi, since its resurrection last month. About a week ago, a farm in Southern Bagerhat district was the scene of the latest case of bird flu in this season. The subsequent spread of the virus is being called a pandemic by some veterinary experts. An official of the Fisheries and Live Stock Department said last week \"although we don\'t expect that there will be a massive outbreak of avian flu this time, we can\'t rule out the possibility of major resurrection of the disease in the dangerous winter season, which is the high time for the outbreak of the disease.\" The official who did not like to be named said the department has also instructed its officials to motivate farmers for adopting all required preventive measures since the disease was found reemerging last month to contain its outbreak. There is also an instruction for field-level officials for proper culling, destruction, disposal and decontamination immediately after diagnosis, he added. Bangladesh is considered a high-risk country with respect to Highly Pathogenic Avian Influenza (HPAI) as the South Asian nation of over 160 million people is especially vulnerable to virus perpetuation because of insufficient biosecurity, rearing of chickens and ducks together, selling of live birds, and deficient disease surveillance. Bangladesh\'s poultry farmers during winter season in 2009 and 2010 had suffered to some extent from the outbreak of the disease. The disease was first detected in Bangladesh in a poultry farm near capital Dhaka in March 2007. The situation deteriorated later on as the virus spread fast across the country which was reported in 47 districts between December 2007 and March 2008. The first bird flu in human body in Bangladesh was detected on May 21, 2008, when the Center for Disease Control and Prevention of the United States diagnosed a 16-month-old Bangladesh child as being infected with H5N1. The child recovered later.