China bird flu: third person dies from new H7N9 virus
A third man has died in China from a new strain of bird flu not previously known in humans.
The death, in the eastern province of Zhejiang, follows the death of two others in Shanghai in March.
A total of nine cases of the infection have now been reported across China, according to the Xinhua news agency.
It is unclear how the H7N9 strain is spread but the men in Shanghai did not infect each other or any close contacts, officials say.
A woman of 35 who caught the virus in the eastern province of Anhui is said to be critically ill.
According to China's National Health and Family Planning Commission, the men who died in Shanghai became ill with coughs and fevers before developing pneumonia.
Commission experts said on Saturday the cause had been identified as H7N9, a strain of avian flu not thought to have been transmitted to humans before.
There is no vaccine against the strain, the commission said, adding it was currently testing to assess its ability to infect humans.
Scientists around the world who are investigating the strain suggested the virus could be hard to track because it shows no symptoms in poultry but can be fatal in humans.
"We speculate that when this virus is maintained in poultry the disease will not appear... so nobody recognizes the infection in animals around them, then the transmission from animal to human may occur,'' said Dr Masato Tashiro, director of the World Health Organization's influenza research centre.
The bird flu outbreak coincides with the tenth anniversary of the Sars (Severe Acute Respiratory Syndrome) outbreak that killed at least 349 people in China.
Media in China have called on authorities - who were criticised for their response to Sars, to openly release information on the spread of the disease.
"The H7N9 bird flu is currently approaching," Yang Yu, a commentator with state broadcaster CCTV, said in a post on his microblog.
"Ten years ago, the lesson learned in fighting SARS was: The greatest enemy is not the virus, but covering up the truth; the best medicine is not steroids, but transparency and trust."
Another strain of bird flu, H5N1, has led to more than 360 confirmed human deaths since 2003 and the deaths of tens of millions of birds.
The World Health Organization says that most avian flu viruses do not infect humans and the majority of H5N1 cases have been associated with contact with infected poultry.