Vietnamese sisters may have caught bird flu from brother

BANGKOK, Thailand -- Two Vietnamese sisters who died from bird flu may have caught the disease from their brother, which would be the first known case involving human-to-human transmission in the outbreak now sweeping Asia, the World Health Organization said Sunday.

The source of the sisters' infection has not been identified, but investigations have failed to find a specific event, such as contact with sick poultry, or an environmental source to explain the cases, WHO spokesman Bob Dietz said in Hanoi.

"Limited human-to-human transmission from the brother to his sisters is one possible explanation," he said.

No other cases of people catching the virus from other people have been suspected anywhere else.

Bird flu has killed millions of chickens in 10 Asian countries and jumped to humans in Thailand and Vietnam, killing at least 10 people.

Limited human-to-human transmission of the virus is not the real danger. What experts fear is the virus mutating into a form that passes easily between people -- a pandemic strain that is a hybrid of the bird virus and a normal human influenza variety.

There is no evidence that a new strain has emerged, WHO spokeswoman Maria Cheng said. Results from tests comparing the genetic makeup of the virus found in the two Vietnamese sisters with that found in other people are expected from Hong Kong in several days, she said.

"This may be an isolated incident. These were very close contacts, family members," she said.

"We wouldn't be surprised if we saw more of these cases, especially where you cannot trace the contacts back to chickens."

The two women, ages 30 and 23, from Vietnam's northern Thai Binh province became sick after attending their brother's wedding reception. Their 31-year-old brother died shortly afterward but his body was cremated, so no samples were available to determine whether he had bird flu.

The sisters died Jan. 23. Their sister-in-law also was hospitalized with an unidentified respiratory illness but she recovered.

Bird flu spread between humans in a 1997 outbreak in Hong Kong that killed six people.

Then, the virus passed from infected people to health workers but soon lost its punch and failed to transmit further. Symptoms were very mild or nonexistent in those who caught it from patients rather than birds.

The six who died in 1997 all contracted the virus from chickens. All cases of human-to-human transmission recovered, raising doubts about whether the Vietnamese sisters caught the lethal strain from their brother.

Experts believe Hong Kong may have averted a global pandemic that year by slaughtering its entire chicken population in three days.

The U.N. health agency welcomed tests showing that bird flu has been in Asia since at least April, saying the virus has not succeeded in infecting humans on a large scale despite having many more months of opportunity than originally believed.

Efforts to stamp out the disease are aimed at heading off a global human flu pandemic.

Scientists warn that pigs also may play a role in helping the virus jump from birds to humans. Pigs have been implicated in human flu epidemics in the past, they often are housed with poultry in traditional family farms in Asia and they are more similar genetically to humans than birds.

"Pigs can be a mixing bowl of chicken viruses and human viruses. I wouldn't exclude the pig yet from the whole thing," said John Oxford, a flu expert from Queen Mary School of Medicine in London.

The epidemic has struck Asia's economies hard, with tens of millions of chickens killed by the virus or destroyed to prevent its spread. Governments are keen to restore public confidence.

The disease is being battled in Cambodia, China, Indonesia, Japan, Laos, Pakistan, South Korea, Taiwan, Thailand and Vietnam. However, the strain of bird flu striking Taiwan and Pakistan is different from the one hitting the other countries and is not considered a serious threat to humans.