Islamabad - A man in northern Pakistan passed the deadly bird flu virus to two of his brothers, and the virus killed one of them, in the first known human-to-human transmission in Pakistan, a health official said Friday.

"It was definitely person-to-person. That is confirmed," said Maqbool Jan Abbasi, Ministry of Health joint secretary.

He said the World Health Organization confirmed by serological testing from a family in Peshawar, northwest of the capital Islamabad, three brothers had H5N1, the strain of avian influenza that can be deadly in humans.

"Two of the brothers had no contact with birds," Abbasi said.

One brother who did not have contact with birds died and was buried, and his blood could not be tested. For cultural reasons they did not exhume the body to test him for bird flu, Abbasi said. But he added they feel certain he died of bird flu.

"The other two brothers, including the one who culled birds, did have the virus. Now they are okay, clear of all symptoms," he said.

Theirs were the first human cases of bird flu in Pakistan and were reported in November 2007.

The human-to-human transmission of the virus raises the concern about the bird flu danger and the country will have to be more careful, Abbasi said.

Pakistan already has quarantine rooms ready for when people are suspected to have bird flu, he said.

"We will have to be more careful in the future," he said.

Pakistan's poultry population has seen multiple outbreaks of the H5N1 strain since 2006, but still only the one case of humans getting the virus.

The last outbreaks the Pakistani health officials reported was on three farms near the southern city of Karachi last February, they were limited only to fowl with no humans were infected.

Bird flu has killed at least 232 people worldwide from at least 366 cases since 2003. Scientists have long feared the virus may mutate into a form more easily transmissible among humans, possibly killing millions. (dpa)