A new strain of the bird flu virus has proven fatal for the first time after it jumped from birds to humans and is worrying scientists.
The latest strain, previously unknown in humans, called H10N8, killed a 73-year-old Chinese woman in December and Chinese authorities last week confirmed a second human case of the new strain of a second woman, who remains critically ill in a hospital.
"We should be especially worried when those viruses show characteristics that suggest they have the capacity to replicate easily or to be virulent or resistant to drugs. This virus ticks several of these boxes and therefore is a cause for concern," said Jeremy Farrar, director of Wellcome Trust and an expert on flu.
Another new strain of bird flu, H7N9, has already infected at least 286 people in China, Taiwan and Hong Kong, killing around 60 of them.
Worrying new strain
Chinese scientists writing in The Lancet medical journal, who conducted a genetic analysis on samples of the H10N8 virus from the woman who died, said it was a new genetic reassortment of other strains of bird flu viruses, including one called H9N2 that is relatively well known in poultry in China.
Somewhat worryingly, the virus like H7N9 has also evolved "some genetic characteristics that may allow it to replicate efficiently in humans", said Yuelong Shu of the Chinese Center for Disease Control and Prevention in Beijing.
According to the scientists' study of her case, the 73-year-old victim, from Nanchang City in eastern China, was admitted to hospital with fever and severe pneumonia on November 30, 2013. Despite being treated with antibiotic and antivirals, she deteriorated rapidly, developed multiple organ failure and died nine days after her symptoms first started.
The source of the infection remains unknown.
Mingbin Liu from Nanchang City Center for Disease Control and Prevention added that the emergence of a second human case of H10N8 in a 55-year-old woman reveals that the newly discovered strain has circulated and could cause more infection.
"It's still an early stage to know whether this virus is going to cause a major threat," Dr. Ben Cowling, Division Head and Associate Professor at the School of Public Health in the University of Hong Kong, told Al Jazeera.
He said that Chinese officials have been very open about their investigation and are putting "a lot of effort into controlling the strain in humans."
Ban on poultry sales
Authorities in eastern China announced a ban last Tuesday on live poultry sales following a spike in the number of people infected with the H7N9 strain of bird flu during the busy Chinese New Year travel period, while Hong Kong began culling 20,000 chickens.
So far this year, that virus has killed 20 people in China out of 96 known infections, according to the official Xinhua News Agency. The deaths were in eastern Shanghai, neighbouring Zhejiang province and southern Guangdong province.
The H7N9 bird flu virus emerged in March last year and has so far infected at least 240 people in China, Taiwan and Hong Kong, according to the Hong Kong Department of Health.
China's official Xinhua news agency, citing the Chinese Centre for Disease Control and Prevention, said 19 people had died of the flu in China this year.