Officials in Shanghai addressed questions about the H7N9 bird flu. At least… (AFP / Getty Images )
It appears that seven people in China have been sickened by H7N9 bird flu -- a strain that until now had been known to infect only birds, the World Health Organization reported Wednesday.
Because this is the first time H7N9 has been seen in people -- and two of the victims have died from their infections -- the WHO and the U.S. Centers for Disease Control will monitor this flu outbreak closely, the agencies said this week.
So far, the WHO is not calling for any travel or trade restrictions related to the disease, which does not seem to pass easily from person to person. According to the WHO, close contacts of people who fell ill have not developed symptoms of respiratory illness.
"It's wait and see" for scientists, said virologist Earl Brown, executive director of the Emerging Pathogens Research Centre at the University of Ottawa in Canada. But he added that the lineage of this particular H7N9 strain was worrisome.
Influenza mutates quickly, with new strains sometimes emerging through a process called reassortment: a single animal is infected by two or more flu viruses at the same time, and those viruses swap genes to create a new strain.
Judging from the new flu's genetic sequence, which has been posted online, the H7N9 virus that infected the Chinese people appears to be a combination of an H7N9 strain and an H9N2 strain, Brown said.
The H7N9 involved is not a form of the virus that kills a lot of birds. It does not have mutations in a protein on its surface called hemagglutinin (that's the "H" in H7N9) known to make it fuse aggressively to host cells.
Usually, virologists wouldn't expect such a virus to jump over and kill people, Brown said, but "this one breaks the rule." The key to its ability to do so, he added, may have to do with the H9N2 with which it combined, which has been deadly in people in the past.
"It has some features about it that make it more virulent," Brown said. "Now you've transferred the history of that lineage to the H7N9." (The deadly H5N1 bird flu also has a similar genealogy, he said.)
Brown said that he and other scientists would continue to study the sequence of the new H7N9 strain to figure out exactly how it evolved to become deadly in people. Already, he said, people have detected changes in various parts of the virus that have been associated with the jump from birds to mammals in the past.
He said he was concerned that Chinese health officials had not shared everything they knew about the outbreak and might be trying to minimize reports of its severity.
The Chinese Center for Disease Control and Prevention posted a FAQ about H7N9 on March 31, the same day officials reported three illnesses and two deaths. News of the additional four cases emerged Wednesday, reportedly after a hospital staffer leaked a patient's diagnosis on social media.
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