A dangerous influenza virus spreading in China's live poultry markets has the potential to become a worldwide pandemic, researchers say. They are calling for these markets to be permanently closed to protect global public health.
H7N9 flu has infected roughly 650 people, mostly in China. Almost all of those patients had contact with poultry. Nearly 40 percent of them have died, an unusually high rate for influenza. Those who died generally had other medical problems.
While the virus does not spread easily from person to person, experts say the more opportunity the virus has to evolve, the greater the chances it will get better at infecting people.
In a study in Nature, researchers found H7N9 influenza virus in chickens at markets in several southern Chinese cities that had been unaffected in the first wave of the outbreak in 2013.
They also found the virus had evolved since then into at least three subtypes, including exchanging some genetic material with H9N2 virus, a strain that spreads fairly easily from person to person.
Yi Guan, director of the University of Hong Kong Center of Influenza Research, noted that it took just two years for H7N9 to infect nearly 650 people. By contrast, it took more than 10 years for H5N1 — known commonly as bird flu — to infect about 800 people.
“If you compare these numbers, you will know this virus is even more dangerous than H5N1,” Guan said.
Experts are concerned that this virus could spark a pandemic because people have not been exposed to it before and therefore have not had the opportunity to build up immunity.
Scientists are looking for evidence that H7N9 has been circulating undetected, said Greg Poland, director of vaccine research at the Mayo Clinic.
“They’re not finding it. So, it is a novel virus for humans,” he said.
However, Poland cautioned, “I don’t think there’s any reason to sound the alarm and run the red flag up the pole yet. What we have is evidence that this virus could become of pandemic potential. What it has not done yet is demonstrate the ability to easily infect humans and transmit from human to human.”
H7N9 first appeared in Shanghai in early 2013. That first wave infected 132 people and killed 44.
“During the first wave of the outbreak, China did a great job,” Guan said. “They closed the market in Shanghai and in many of the provinces of the affected region. The human cases dramatically reduced and eventually stopped.”
But the virus turned up again in Zhejiang and Guangdong provinces late that year.
“If we really want to stop the circulation of this H7N9 virus,” Guan said, “we should consider a complete stop of the live poultry market system.”