The bird flu virus endemic in Asia appears to be evolving in ways that increasingly favour the start of a deadly human influenza outbreak, the World Health Organisation (WHO) warned on Thursday. The situation "may resemble that leading to the 1918 pandemic", which killed more than 40 million people, it said in its latest report on preparedness for an influenza pandemic.
The United Nations health agency - which fears that the H5N1 bird flu virus could mutate into a deadly human form - again urged countries and drugs companies to speed development and production of a vaccine. The death toll in Asia stands at 38 - 26 in Vietnam and 12 in Thailand - from the latest outbreak, but so far there are no signs that the virus is being transmitted easily between people, the agency's greatest fear.
But recent epidemiological and laboratory studies revealed unusual features that "suggest that the virus may be evolving in ways that increasingly favour the start of a pandemic", the agency said in a report to its bi-annual executive board, which is meeting this week.
The WHO has forecast a potential death toll of two million to seven million as a "best case scenario" for an outbreak, which it says is overdue. The last one, which claimed between one million and four million lives, was in 1968.
The deadly virus has become "hardier", surviving several days longer in the environment. Evidence also suggested that the virus is expanding its range of mammal hosts, including captive tigers and experimentally-infected domestic cats, it added.
Migratory birds and domestic ducks show no symptoms but excrete the highly pathogenic virus, indicating an "important silent role in maintaining transmission".