The death toll from the new strain of bird flu sickening people in eastern China has risen to five, the two latest deaths being reported in the commercial hub of Shanghai.
Chinese officials and state media confirmed the death Thursday of a 48-year-old man who transported poultry for a living. The other victim was not identified.
Chinese officials have now identified 14 cases of the H7N9 virus, which until recently had not been known to affect humans.
Chinese medical experts say it is not clear how people are getting infected since the virus does not appear capable of being transmitted from person to person. Authorities in Shanghai Thursday said they found the virus in a sample taken from a pigeon at a traditional market.
The new strain of bird flu has officials worried.
The World Health Organization's Timothy O'Leary:
"This is a very unique event. H7N9 had not been known previously to infect human beings. We'd seen it before only in birds. So for this virus suddenly to turn up in humans is a great cause for concern.''
Concerns are also spreading across the region. Authorities in Hong Kong have begun monitoring poultry farms and suspending the import of live birds from mainland China.
Japanese Chief Cabinet Secretary Yoshihide Suga says airline passengers from China are being asked to report any influenza-like symptoms.
"I have told the Health Minister to take all possible measures in our response to this virus, bringing together every shred of available information and keeping the Japanese people informed of where it leads.''
Laurie Garrett with the U.S.-based Council for Foreign Relations says a big reason for concern is that so many key questions remain unanswered.
(SOUNDBITE (English) LAURIE GARRETT, SENIOR FELLOW FOR GLOBAL HEALTH AT COUNCIL FOR FOREIGN RELATIONS))
"We need to know how are these people getting infected. Who are they getting it from? We need to know what's the denominator. How many people out there in China are infected right now with this virus harmlessly or with very mild illness? Third, we need to know what species did this come from. Did it come from birds? Did it come from dead pigs? Did it come from other animals of some kind? Until we have those three big questions answered, we have no capacity to speculate about the probability that this will become the next great pandemic.''