GENEVA (Reuters) - The World Health Organization (WHO) confirmed on Thursday a single case of human-to-human transmission of the H5N1 bird flu virus in a family in Pakistan but said there was no apparent risk of it spreading wider.

A poultry farm with chickens infected with the H5N1 strain of bird flu is seen on the outskirts of Islamabad on May 22, 2007. The World Health Organization (WHO) confirmed on Thursday a single case of human-to-human transmission of the H5N1 bird flu virus in a family in Pakistan but said there was no apparent risk of it spreading wider. REUTERS/Stringer

A statement from the U.N. agency said tests in its special laboratories in Cairo and London had established the “human infection” through presence of the virus “collected from one case in an affected family.”

But it said a WHO team invited to Pakistan to look into an outbreak involving up to nine people, from late October to December 6 had found no evidence of sustained or community human-to-human transmission.

No identified close contacts of the people infected, including health workers and other members of the affected family, had shown any symptoms and they had all been removed from medical observation, the WHO added.

The outbreak followed a culling of infected chickens in the Peshawar region, in which a veterinary doctor was involved. Subsequently he and three of his brothers developed proven or suspected pneumonia.

The brothers cared for one another and had close personal contact both at home and in the hospital, a WHO spokesman in Geneva said. One of them, who was not involved in the culling, died on November 23.

His was the human-to-human transmission case confirmed by the WHO. The others all recovered.

“All the evidence suggests that the outbreak within this family does not pose a broader risk,” the WHO spokesman told Reuters. “But there is already heightened surveillance and there is a need for ongoing vigilance.”

It was the first human-to-human case of H5N1 transmission in Pakistan, while others have been confirmed in Indonesia and Thailand in similar circumstances of what the WHO calls close contacts in a very circumscribed area.

Global health experts fear the virus -- which has killed 211 people out of 343 infections reported since 2003 -- could mutate into a form that spreads easily from one person to another, possibly triggering a pandemic that could kill millions.