HANOI, Feb 1: Two Vietnamese sisters have died from bird flu, possibly after contracting the virus from their brother in the epidemic's first recorded human-to-human transmissions, the World Health Organization said on Sunday.

The deaths brought to 10 the number of people known to have died after the virus 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.

The WHO said it could not be sure of how the 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 on Sunday reported five more areas with suspected cases of bird flu in the country.

The Vietnamese sisters, aged 23 and 30, died on Jan 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.

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."

Bird flu fears in Bangladesh eased on Sunday when the health ministry said US tests had identified an illness which killed 23 people last month as encephalitis. -Reuters