Deaths spark new bird flu fears

Vietnam has continued disinfecting

Health experts are examining the possibility that bird flu may have passed between humans for the first time in the current outbreak in Asia.

Two sisters in Vietnam died after possibly contracting the flu from their brother, a World Health Organization (WHO) spokesman said on Sunday.

The brother died from a respiratory illness which was not identified.

However, the WHO said this appeared to be an anomaly - the virus was not being transmitted to the wider public.

Health experts have been worried that if the virus mixed with a regular human influenza strain, it might create a mutant form that was able to pass between humans, triggering a human flu pandemic.

At least 10 people have died from the H5N1 virus.

• China on Sunday reported 10 new suspected cases - indicating the disease was spreading.

• Thai Prime Minister Thaksin Shinawatra - who has been accused of a cover-up - appeared on state television to say bird flu was controllable in Thailand.

'Only a possibility'

The two Vietnamese sisters, aged 23 and 30, died on 23 January in the northern province of Thai Binh.

They, their brother and his wife all suffered from a respiratory illness.

The brother died shortly before his sisters were admitted to hospital and no samples were available from him.

Limited human-to-human transmission, from the brother to his sisters, is one possible explanation WHO

His wife has recovered - but it is not clear she had bird flu.

"The investigation failed to reveal a specific event, such as contact with sick poultry, or an environmental source to explain these cases," the WHO said referring to the sisters' deaths.

"At the same time, such exposures cannot be discounted, either."

"However, WHO considers that limited human-to-human transmission, from the brother to his sisters, is one possible explanation."

Bird flu has affected 10 Asian countries

But the WHO sought to calm fears, saying there was "no evidence of efficient human-to-human transmission of H5N1 occurring in Vietnam or elsewhere".

WHO spokesman Bob Dietz told the BBC the Vietnam situation had many unknowns - but was more likely to be an anomaly.

And a similar case had occurred in Hong Kong in 1997, when a doctor treating a patient with the H5N1 virus had himself contracted the disease.

But that case was never resolved - and there was a likelihood a question mark would remain on the Vietnam case, too, Mr Dietz said.

He said there was no evidence of human-to-human transmission reaching the public at large.