Alarm over a sixth death from a strain of lethal bird flu never before seen in humans has led Chinese authorities to slaughter more than 20,000 birds at a poultry market in Shanghai.
The city stopped sales of live fowl and slaughtered all poultry at the market after the virus was detected in pigeons being sold for meat.
With stock markets taking fright, leading to a sell-off in Hong Kong, medical experts said the outbreak was worrying and demonstrated global vulnerability to a new disease.
However, the World Health Organisation (WHO) moved to insist there is no evidence of “sustained human-to-human transmission” while awaiting laboratory tests on a further two deaths suspected to have been caused by the virus.
Sixteen cases of infection with the H7N9 strain have been confirmed by the WHO in the last week, and 520 people who have been in close contact with confirmed victims were being closely monitored.
Avian flu strains infecting humans such as H5N1 have emerged in China before because the Chinese habit of sharing domestic accommodation with poultry provides ideal conditions for new virus mutations in one species to jump to the other.
Alan Hampson, an influenza expert and chair of the Australian Influenza Specialist Group, said the reports were “certainly concerning.”
“There is a virus out there which, like the H5N1 strain, appears to be causing serious illness, but how widespread that illness is at this very early stage, we don’t know”, he said.
“If a virus starts to transmit among humans then there’s no telling how quickly it might travel and where it might travel to... Does it have pandemic potential? Yes, any influenza that jumps from an animal species to a human has pandemic potential. If it learns to spread in humans then it’s a high likelihood it will become pandemic.”
With six deaths among 16 cases, the virus appears to have a high mortality rate. But it may be that there are many unidentified cases of mild infection, which are unrecorded because the individuals do not seek medical help.
However lethal the virus is, if it does not spread among humans, or spreads only with difficulty, it is much less of a threat.