Some fowl infected with bird flu in Indonesia appear healthy, making it difficult to detect outbreaks of the virus which is often deadly for humans, an official said Monday.
Indonesia, the country worst hit by bird flu, with 79 fatalities, has been struggling to control H5N1 outbreaks across its vast archipelago.
"From our observations during 2007 we have found that chickens infected by bird flu have not been showing the usual symptoms," Memed Zulkarnaen, director of the agriculture ministry's bird flu campaign management unit, told AFP.
"This is a problem for Indonesia's fight against bird flu.... It is difficult for us to detect the infected chickens."
He added, however, that no change in the virus had been detected. He said the ministry was responding by reinforcing vaccination programmes for fowl and boosting public awareness of the virus.
Bird flu first appeared in humans in Indonesia just over two years ago. Since then, 99 human infections have been recorded and the virus has become widespread among fowl across all but two of Indonesia's 33 provinces.