As China gets ready to usher in the Year of the Horse on Friday, millions of them will find it hard to buy chicken for traditional Lunar New Year feasts. That's a mark of the nation's growing anxiety about a poultry-borne flu virus called H7N9.
On Tuesday, Hong Kong agricultural workers will begin destroying 20,000 chickens. The bird flu virus H7N9 was found in a single live bird from a farm in neighboring Guangdong Province.
"The Department (of Food and Health) has declared the wholesale poultry market as an infected place," Hong Kong's top health official, Dr. Ko Wing-man, said at a press conference on Monday.
Poultry won't be imported into Hong Kong from mainland farms until Feb. 18 at the earliest.
Because of its isolation, the former British colony has long used mass poultry culling as its main defense against the spread of new types of flu. Elsewhere across China, poultry outbreaks aren't so easily contained.
And this bird virus, which emerged last spring in southeastern China, is particularly vexing to human and animal health authorities, because it doesn't make birds visibly sick. Thus, it takes laborious sampling and testing to spot infection. And poultry farmers are resistant to mass culling of apparently healthy birds.
As an alternative, live poultry markets have been shut down nearly 700 miles away in eastern Zhejiang Province, the epicenter of H7N9 cases so far. Neighboring Shanghai plans to close down its live poultry markets this Friday until April.
As another indication of how widely H7N9 has spread throughout Chinese poultry flocks, a human case of the bird flu was recently reported in Beijing, 800 miles north of Shanghai, in a man hospitalized after buying and preparing pigeons for dinner.
Shutting down live bird markets seemed to damp down last spring's H7N9 cases among people. But those outbreaks didn't overlap with Chinese New Year festivities, when hundreds of millions of people travel to ancestral homes, often bearing gifts of poultry, alive or dead.
Human H7N9 cases in China have topped 200 since December and killed about a third of those infected. Most of the others have been hospitalized in serious or critical condition. The current outbreak is on track to surpass last spring's debut.
There's still no evidence that this bird flu virus has acquired the ability to pass readily from person to person. If there has been occasional human-to-human transmission, the virus hasn't touched off chains of infection.
Moreover, the World Health Organization says H7N9 doesn't appear to be evolving genetically, a somewhat reassuring sign that it's not drifting toward a virus that could cause widespread human illness – and possibly a devastating pandemic.
The patterns of disease caused by H7N9 have not changed much either since last year's appearance, although there has been a predominance of cases among men, and a somewhat lower death rate.
But flu researchers are concerned. "I've been worried all the time about H7N9," Prof. John McCauley of a London-based WHO lab on influenza told the BBC last week. "It's highly virulent, and the case fatality (rate) is about one-in-three, so it poses a threat."
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