Dec. 16 (Bloomberg) -- Five members of a family in Pakistan are among eight people who may be the country's first human cases of bird flu, the World Health Organization said. At least one brother died.

Pakistan's national laboratory found the lethal H5N1 avian flu strain caused the infections in three brothers and two cousins from the same family, according to information from a WHO statement today and Gregory Hartl, a WHO spokesman in Geneva. Another brother and his son from the U.S., who attended a funeral for one of the victims, tested negative for the virus at a hospital in Nassau County, New York, Hartl said.

Medical teams have been sent to Pakistan to assist local authorities in investigating the cases, in which two people had only mild symptoms, Hartl said. Avian flu has infected at least one person a month in Asia and Africa during the past three years, and doctors are monitoring for signs it may be adapting to humans by killing fewer people, fostering its spread.

``It's too early to make any definitive conclusions'' about the outbreak, Hartl said in a telephone interview today. ``We are still in the middle of it.''

Voluntary Isolation

New York State health officials were informed Dec. 7 that a man from Nassau County had returned from Pakistan with flu symptoms, said Claudia Hutton, director of public affairs for the state department of health. The man told his doctor he might have been exposed to bird flu, Hutton said in telephone interview.

The man went into voluntary isolation at home, Hutton said. Then his son began developing flu-like symptoms. Samples from both the man and his son were tested at state laboratories and at the U.S. Centers for Disease Control and Prevention in Atlanta.

The samples came back negative for H5N1 bird flu earlier this week, and the man and his son are no longer in isolation, Hutton said.

``The man did a courteous thing by seeing his physician and saying `I might have been exposed,''' Hutton said. ``In the end, no one in New York is sick.''

Hutton said she didn't know whether the man or his son received antiviral medications. Drugs such as Roche Holding AG's Tamiflu are believed to fight bird flu.

Pakistan Teams

Hutton said that there were erroneous reports on the Internet that another brother of the H5N1-infected family members in Pakistan has returned to the U.S. and tested positive.

``That's not true,'' she said. ``At this point there's no risk to the public or the individuals.''

CDC officials referred all questions to the New York State health department.

The remaining suspected cases in Pakistan include a man and his niece, and a male who worked on a farm about 12 miles (20 kilometers) away.

Doctors from WHO in Geneva and Cairo, and from the U.S. Navy Medical Research Unit No. 3 in Cairo will arrive in Pakistan during the next two days to track and stem the disease's spread, and to analyze specimens for any genetic mutations in the virus.

340 Human Cases

Pakistan has reported 44 H5N1 outbreaks in poultry to the World Organization for Animal Health since early 2006. The most recent occurred on Nov. 27 and Nov. 28 in the states of Punjab and North-West Frontier Province, killing almost 20,000 chickens.

The suspected Pakistan cases occurred in the Peshawar area of the country and were detected following a series of culling operations in response to outbreaks of H5N1 in poultry, according to the WHO statement. Samples from the cases are being sent to a WHO reference laboratory in Cairo for confirmation and further analysis.

At least 340 people in 13 countries have contracted the virus since 2003, WHO said yesterday. Three of every five cases were fatal and most were caused by contact with infected poultry, such as children playing with them or adults butchering them or plucking feathers, according to the Geneva-based agency. It says millions could die if the virus becomes as contagious as seasonal flu and touches off a global pandemic.

To contact the reporter on this story: Jason Gale in Singapore at j.gale@bloomberg.net

Last Updated: December 15, 2007 16:34 EST