Despite major efforts to control the avian influenza in Indonesia, the country worst hit by the virus, the situation there remains "grave," the United Nations Food and Agriculture Organization (FAO) warned on Tuesday. The bird flu has become "deeply entrenched" in Indonesia, effecting 31 out of 33 provinces according to United Nations estimates.

The virus is endemic in Java, Sumatra, Bali and southern Sulawesi with sporadic outbreaks reported from other areas. In February, five people living in the west of Java, Indonesia's most populous island, died after contracting the H5N1 virus, responsible for outbreaks of bird flu around the world in recent years.

"The human mortality rate from bird flu in Indonesia is the highest in the world and there will be more human cases if we do not focus more on containing the disease at source in animals," FAO Chief Veterinary Officer Joseph Domenech said.

Domenech warned that the high circulation levels could create conditions for the virus to mutate and to finally cause a human influenza pandemic. Among the major constraints the country is facing in tackling the virus are a highly decentralized administration, lack of engagement with commercial poultry producers and lack of resources for veterinary services.

"Indonesia is facing an uphill battle against a virus that is difficult to contain," Domenech noted. "Major human and financial resources, stronger political commitment and strengthened coordination between the central, province and district authorities are required to improve surveillance and control measures."

He stressed that the major challenge will be to implement the components of a successful national avian influenza control strategy.