The avian flu strain that killed 45 people in Asia last spring is poised to return as poultry flocks swell before Chinese New Year, amplifying the virus that hides undetected in birds.
A 35-year-old man from the eastern Chinese province of Zhejiang is in serious condition after being infected with the new H7N9 flu strain, health authorities said this week. It’s the first confirmed human case in two months, according to the World Health Organization in Geneva.
Human cases of H7N9 were first reported in China in March and spiked in April before agriculture authorities temporarily closed live poultry markets to limit human exposure. The WHO counts 136 laboratory-confirmed cases to date. Three patients remain hospitalized and 88 have been discharged, the United Nations health agency said in an Oct. 16 statement.
“If an H7N9 outbreak starts again now it could spread much further in China and infect a large amount of people unless intensive measures are taken to control the outbreak in birds,” said Ben Cowling, an associate professor of infectious disease epidemiology at the University of Hong Kong’s school of public health, in an interview.
The more people who get infected with H7N9, the greater the chances of the virus mutating into a form that spreads more easily among people, Cowling said.
Even though H7N9 hasn’t mutated to become as contagious as seasonal flu, strains that emerge in China are of special interest to researchers. The 1957-58 Asian Flu and 1968-69 Hong Kong Flu pandemics were first identified in the world’s most populous nation, and an earlier bird flu strain known as H5N1 is thought to have come from the southern province of Guangdong in 1996. Years later, a new seasonal flu was found in neighboring Fujian and triggered explosive epidemics worldwide.
H7N9 has turned up outside mainland China. In late April, officials in Taiwan reported a case in a 53-year-old man who had just returned to Taiwan via Shanghai after a business trip to the eastern city of Suzhou.
The virus can circulate widely in chickens, ducks and geese without causing the mass die-offs characteristic of the H5N1 bird flu virus. Its stealth has made it difficult to track and contain a germ that’s typically more active during the colder winter months, scientists said.
New Year Threat
“We are just heading into re-emergence in November and December,” said Malik Peiris, a virologist at the University of Hong Kong, who was part of an international team of flu scientists that assisted the Chinese government in April identify how people are catching the new virus. “It will of course peak at Chinese New Year because it’s the time of maximum poultry production.”
Chinese New Year is on Jan. 31 next year.
The latest H7N9 case, a man with the surname Liu, sought medical attention on Oct. 8 and is hospitalized in Shaoxing county, the Zhejiang health bureau said on Oct. 15.
Shanghai began reopening poultry markets on June 20 to cater to residents’ demand for live ducks and chickens, the official Xinhua News Agency reported last month. The Shanghai Municipal Commission of Commerce lists 102 live-poultry markets on its website. Shanghai’s largest, the Shuidian market in Hongkou district, reopened on Aug. 30 after glass partitions and separate exhaust pipes for areas used to store and slaughter poultry were installed, Xinhua reported on Sept 10.
Call to Cull
Agriculture authorities are counting on the measures to rebuff calls from health officials for mass culling of poultry to eradicate the virus. Doctors studying disease patterns in humans found that infected poultry are the principal source of the infections in people.
When the Ministry of Agriculture tested 68,060 samples collected from poultry markets, farms and slaughterhouses, they found only 46 -- or 0.07 percent -- tested positive for the virus, the official Xinhua news agency reported in April.
When researchers from the University of Hong Kong conducted their own survey based on 1,341 specimens from chickens, ducks and other birds, as well as 1,006 water and fecal samples from bird markets, they found H7 viruses in 60, or 2.6 percent of them, according to a study published in the journal Nature in August.
“There’s competing interests in China between economic development and human health, and there’s continual pressure on these two essentially competing interests at all levels of government,” said Hong Kong University’s Cowling.
Poultry consumers don’t want the markets to close, said Mao Zhenjin, 70, who was buying live chickens at Shanghai’s Yinghua Market on Wednesday to boil with potatoes and taro -- a local specialty and one of his granddaughter’s favorite dishes.
‘Taste the Difference’
“You can’t make this soup with frozen chicken because it’s not fresh,” Mao said as he handed over 53 yuan ($8.70) for a 1.5 kilogram (3-pound) chicken. “It’s like buying fish dead for a long time -- you can taste the difference.”
Six percent of blood specimens from 396 poultry workers in China were found to have antibodies against H7N9, according to a Sept. 18 report in the Journal of Infectious Diseases. That suggests dozens of people in contact with farmed birds have been exposed to the virus without necessarily getting sick. None of the 1,129 people from the general population had H7N9 antibodies.
“The data support the conclusion that influenza A(H7N9), or a closely related virus, is circulating in live poultry markets and that infected poultry is the principal source for human infections,” wrote the authors, who included researchers from Zhejiang University’s First Affiliated Hospital.
Cooler weather will enable viral particles to remain viable for longer in the environment, such as in the air, on surfaces or in water, Cowling said.
Death by Suffocation
In its severest form, the new strain damages the lungs so badly that it causes suffocation even as other vital organs rapidly shut down, doctors in Shanghai reported in April.
While laboratory experiments using ferrets -- the most-common animal model for human flu infections -- showed the virus is capable of spreading from person to person, the WHO said this week that there is no evidence of sustainable human-to-human transmission so far.
Cases reported to the WHO may represent “the tip of the iceberg,” the University of Hong Kong’s Peiris said in an interview.
In 2009, a novel flu virus known as H1N1 that evolved in pigs touched off the first influenza pandemic in 41 years. The H5N1 bird flu strain, which killed at least 380 people over the past decade, hasn’t acquired the ability to spread easily among people.
If H7N9 starts spreading easily from human to human, “then it’s a different ball game,” he said. “From all the evidence we have this could be much more serious than H1N1 was: looking at human lung tissue experimental studies -- seasonal flu grows on it like a weed, H5N1 really struggles, and H7N9 grows like a bomb.”
— With assistance by Natasha Khan, and Daryl Loo