WHO concern over 'one of the most lethal bird flu viruses'

The World Health Organisation's (WHO) top influenza expert, Dr. Keiji Fukuda, said that people appear to catch the latest 'bird flu' virus, H7N9, from birds more easily than the H5N1 strain that began ravaging poultry across Asia in 2003.

Health experts are concerned about H7N9's ability to jump to humans, as well as the strain's capacity to infect birds without causing noticeable symptoms - making it difficult to monitor its spread.

"This is definitely one of the most lethal influenza viruses we have seen so far," Dr Fukuda said. But he added that experts are still trying to understand the virus, and that there might be a large number of mild infections that are going undetected.

The H7N9 bird flu virus has infected more than 100 people in China, seriously sickening most of them and killing more than 20, mostly near the eastern coast around Shanghai.