"The key to the public health response is surveillance," said Peter Cordingley, spokesman for the WHO Western Pacific region in Manila. "If we do actually get to the cases with antiviral early on, the health outcome is a lot better."

WHO experts arrived in Pakistan to try to sort out cases reported there, South Asia's first human infections. They were expected to visit a hospital and affected areas today, said WHO country representative Khalif Bile in Islamabad.

"They are here to get more information and to provide more support in the case of any potential risk," he said, adding that the Health Ministry, Agriculture Ministry and WHO are now working closely together following a "communication gap" when the government did not immediately report suspected cases to the WHO.

Four brothers and two cousins fell ill last month in Abbotabad, a small city north of Islamabad, while three others who slaughtered poultry in the same area and a nearby town tested positive for the H5N1 bird flu virus earlier this month.

Two of the brothers died, but specimens were collected from only one.

The cases were positive for H5N1 in initial government testing, but WHO will conduct further analysis to confirm the results.

WHO spokesman Gregory Hartl in Geneva said on Sunday human-to-human transmission had not been ruled out, but added that poultry outbreaks had earlier been reported in the area and it was unclear if all patients had links to sick birds or infected surroundings.

A doctor who cared for the brothers also experienced mild flu-like symptoms, but more testing needs to be carried out to determine if she was infected, Hartl said.

Two poultry farms near Abbotabad have been closed and health workers are taking temperatures of those living in the affected area twice a day, but no new suspected cases have been reported, said Minhajul Haq, a district health officer.

"We are on high alert, though we still await any confirmation of human-to-human transmission," he said.

At least 208 people have died from the virus, which began plaguing Asian poultry stocks in late 2003. It remains hard for people to catch, but scientists worry it could mutate into a form that spreads easily among people, potentially sparking a pandemic.

With fresh poultry outbreaks reported in a number of countries, including Germany over the weekend, WHO urged nations to be vigilant in identifying and reporting cases in both birds and humans.

Two outbreaks of H5N1 cases among poultry were also discovered in Benin earlier this month north of the capital Porto Novo and on a farm in the commercial capital Cotonou, a government statement said on Sunday.

Myanmar's first human case was reported on last Friday in a 7-year-old girl who fell ill last month and survived, while Indonesia, the country hardest hit by the virus, has announced its 93rd death from the virus.

Two human cases were also recently confirmed in China, one of whom died.

The H5N1 virus often flares during the winter months. In some countries, like Indonesia, poultry outbreaks and human cases are reported year round, but many countries experience a flurry of activity when temperatures drop.

Further Reading

- You can visit the Avian Flu information page by clicking here.