said on saturday. the cases were found at farms around the village of brudzen near the city of plock. officials say the virus was most likely brought to poland by migrating ducks, geese or swans." december 10, 2007: "chinese health authorities said they were hunting for the causal link between a son and his father both struck by bird flu, but have found no evidence that the virus has mutated into a new strain. the 52-year old father was diagnosed with the h5n1 strain of bird flu late last week in the eastern province of jiangsu, days after his 24-year old son died from the disease."