A rooster puts his head out of a bag before being culled along with other poultry by health workers in China’s Guangdong province on Sunday. (Reuters)

Hanoi, Feb. 1 (Reuters): Two Vietnamese sisters have died from bird flu, possibly after contracting the deadly virus from their brother in the epidemic’s first recorded human-to-human transmissions, the UN health agency said today.

The deaths brought to 10 the number of people known to have died after the virus, which has decimated poultry flocks across Asia, made the leap to humans.

Scientists believed, and health officials hoped, that the disease could only be contracted through exposure to infected birds or droppings, and not from person to person.

The World Health Organisation (WHO) said it could not be entirely be sure of how the Vietnamese sisters contracted the disease, because their brother had died earlier of respiratory ailments before any tests could be conducted on him.

But it said it “considers that limited human-to-human transmission, from the brother to the sisters, is one possible explanation”.

With the disease taking a foothold in 10 Asian nations, China’s state television today reported five more areas with suspected cases of bird flu in the world’s most populous country.

The Vietnamese sisters, aged 23 and 30, died on January 23, the WHO said. Hanoi’s National Institute for Hygiene and Epidemiology said last week it was certain bird flu was the cause of death. But the WHO waited for tests at a laboratory in Hong Kong to confirm the results. It said an investigation into the family’s illness failed to uncover any contact with sick poultry or “an environmental source”.

“At the same time, such exposures cannot be discounted, either,” it said.

Six other people have died from bird flu in Vietnam. The disease has killed two boys in Thailand, and two other Vietnamese have been confirmed as having the virus but have either recovered or are still in hospital.

The WHO said it saw no evidence of “efficient” transmission of the H5N1 strain of the bird flu virus between people “in Vietnam or elsewhere”. Human transmission is not unprecedented. The WHO noted that in the 1997 Hong Kong outbreak, there were cases of “limited” human-to-human infection, but said it never “developed into a significant public health threat.”

Vietnam has stepped up its fight against the disease, banning the transport of poultry nationwide. Others nations are also battling to contain the virus. Bird flu fears in Bangladesh eased today when the health ministry said US tests had identified a mysterious illness which killed 23 people last month as encephalitis.