After being criticised for their poor handling of the slaughter of over a million chickens in order to eliminate a deadly "bird-flu" virus, Hong Kong authorities face the appalling prospect that the source carriers may not be chickens at all - but ducks.
Hong Kong newspapers have reported that ducks and geese are now considered the most likely conveyor of the virus. They may have been passed over because they do not show any symptoms when infected.
In the culling operation which began on Monday, a few ducks and geese were killed, but only if found near chickens.
Migrating ducks carry different strains of influenza, which they give to tame ducks, and thence to pigs and humans, experts say. There are about a million ducks, geese, pigeons and quail in the territory which has 60 duck farms.
Of 21 confirmed and suspected human cases of "bird flu", some had contact with ducks, although not within the incubation period, a health official said.
In Taiwan, 400 chickens died on a farm of an unknown cause, raising fears that the H5N1 virus which causes avian flu had crossed the South China Sea.
Another appalling prospect - though there is no evidence of it yet - is that the badly conducted operation of killing the chickens may have allowed the virus, which has killed four people, to pass to dogs.
Local television showed dogs carrying off chicken carcasses from uncollected plastic bags, and other bin liners left torn open with carcasses inside. Chickens have also been found wandering in housing estates.
Test results this week will show whether ducks have been infected, but in the meantime a warning has already been issued to people working with ducks and geese to take extra precautions, such as wearing gloves if they touch ducks or their excrement.
"If there's one duck found with the virus, the slaughter will immediately have to be extended to them," a senior Hong Kong health official told Reuters. "We need to be absolutely sure that the virus will not spread to other animals and that no animals infected with the disease will be at large because they could be another transmission source.
"If we don't take further steps to look into the potential natural reservoir of the disease our efforts in killing all chickens will be in vain."
He added that if the virus was found in duck excrement, it was possible it could spread to chickens and then to humans, or it could also be transmitted to humans directly from ducks.
A 19-year-old woman admitted to Yan Chai Hospital two weeks ago was yesterday confirmed to be infected with bird flu. She is in a critical condition.
The Hong Kong Director of Health, Dr Margaret Chan Fung Fu-chun, said proof of the success of the chicken slaughter in curbing the disease would be shown if no new cases were found in the first two weeks in January. The incubation period is estimated at seven days.
"If we double the incubation period to January 14th and there are no more new cases of H5N1, the action can be regarded as effective," she said in a radio interview.