Reuters reports that animal health authorities will cull 55,000 hens in the northern town of Slavyianovo after a bird flu outbreak was confirmed at a industrial farm there, the fourth since February 3, the food safety agency said late on Monday 8 February.

The agency said the four farms have been hit by highly pathogenic avian influenza type A, but did not disclose the strain of the disease.

The predominant strain in Europe at present is H5N8.

Some 160,000 ducks and 99,000 have been culled at three farms in Slavyianovo, some 190 km northeast of Sofia, this month as authorities try to contain the spread of the disease.

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