Carcasses with H5 found on Lantau may be from mainland Guangdong will be asked to check if there has been a recent undetected bird flu outbreak along the Pearl River after strong indications that the carcasses of three birds with H5 bird flu found on Lantau Island may have drifted ashore from the mainland. Secretary for Food and Health York Chow Yat-ngok yesterday said there was no evidence so far that the carcasses had been dumped by local villagers who had broken the law banning people from keeping poultry at their homes. Dr Chow also said he was concerned over whether the means of bird flu transmission had changed following reports of eight H5N1 bird flu cases on the mainland in the past month. The carcasses of a goose and a duck were found on Thursday on a beach at Sha Lo Wan, near the airport on Lantau. Officers from the Agriculture, Fisheries and Conservation Department collected another dead duck from the same spot on Saturday. Preliminary tests showed the birds had H5 bird flu. Dr Chow said: 'We shall inform the mainland authorities so that they can follow up on the dead bird cases along the Pearl River. 'We all understand that the risk of bird flu is especially high during winter. In the past month, eight people have been infected with bird flu on the mainland. But these cases are not related to a major bird flu outbreak. 'Of course, we are concerned whether that means a change in how birds react to the virus. In the past, many birds would die after being infected with the virus, and then the bird flu would spread to humans. But this time not many birds died. This may imply that some birds which carry the virus show no symptoms.' Sha Lo Wan village head Lee Chi-fung, who is also an Islands district councillor, said: 'Our village faces the Pearl River estuary and there is often rubbish and animal carcasses drifting along the river. There is no one keeping poultry in Sha Lo Wan. We obey the law.' A spokesman for the Guangdong health department told TVB news: 'If all dead birds are from the mainland, there should have been reports of outbreaks here. But, we have not heard anything.' Lo Wing-lok, an expert on infectious disease and a Centre for Health Protection scientific committee member, said: 'From the small number being picked up, it could be due to people bringing a few of them to the village on Lantau or being brought in by fishing boats from the mainland. 'There is something happening on the mainland. The problem with the poultry there is definitely a cause for concern.' Ornithologist Martin Williams also believed the birds might have been washed up from the Pearl River. Wild geese were rare in Hong Kong, he said. 'I have not seen a wild duck on Lantau, so they were likely farm birds,' he said. Eighteen people who had potential contact with the dead waterfowl had been placed under medical surveillance, said a Centre for Health Protection spokesman. A driver, 26, who helped collect the dead birds developed fever and symptoms of upper respiratory tract infection. But the centre spokesman said he was unlikely to be infected with bird flu because he had developed the symptoms two days before the collection.