A cluster of human bird flu cases among relatives and possibly health workers in Vietnam may show the virus is changing into a form that can be passed on by humans, the World Health Organization said.

The WHO is worried that bird flu, which has killed 47 people in Asia, could mutate into an easily spread form that sparks the next influenza pandemic, killing millions.

 

“Such cases can provide the first signal that the virus is altering its behavior in human populations and thus alert authorities to the need to intervene quickly,” the WHO said in a statement seen on Monday.

The main concern of the WHO is a series of cases of the deadly H5N1 bird flu virus in a family in the northern Vietnam province of Thai Binh and the possible infection of two nurses who cared for one of the patients.

It also said it had received confirmation of an additional 10 cases of human infections from Vietnam’s Health Ministry.

“Full information on new cases, including those that may be closely related in time and place, is critical to ongoing assessment of the pandemic risk posed by the H5N1 virus,” the U.N health agency said in a statement.

The new cases were detected in early March or through re-examination of older cases, some of which dated back to late January and three of which had been fatal, the WHO said.

Since the H5N1 virus, which spread across much of Asia in late 2003, erupted again in Vietnam in December, 24 cases have been confirmed and 13 people have died.

Earlier, there was only one probable case of human-to-human transmission of the virus, that of a Thai woman who cradled her infected and dying daughter in her arms for hours.

Now, medical experts are investigating whether two nurses who treated a bird flu victim in Thai Binh caught it from their patient.

In the Thai Binh cases, one male nurse tested positive for bird flu after tending a patient who drank raw duck blood.

At the weekend, Thai Binh health officials said a second nurse who tended the patient was in hospital with symptoms of the disease and they were awaiting the results of tests being conducted in Hanoi.

The patient, whose 14-year-old sister and grandfather were also infected, remained in a critical condition, but his sister was recovering and his grandfather had shown no signs of illness despite testing positive.

The H5N1 virus has killed 34 Vietnamese, 12 Thais and a Cambodian and has recurred several times despite the slaughter of millions of poultry.