The deadly H7N9 bird flu virus has the potential to be easily transmitted from human to human, a new study suggests.
Chinese scientists have found that the virus is highly transmissible between ferrets, a mammal often used to study possible virus transmission between humans. This discovery could portend a time where the virus might become pandemic, the researchers added.
"The situation raises many urgent questions and global public health concerns," said study co-author Hualan Chen, director of the National Avian Influenza Reference Laboratory at Harbin Veterinary Research Institute.
So far, more than more 130 people in China have been infected with the H7N9 flu, and at least 37 have died, the researchers noted.
However, one US expert stressed that it isn't known whether a large-scale spread among humans will actually occur.
Hard to track
"We already know H7N9 can spread human-to-human," said Dr Marc Siegel, an associate professor of medicine at NYU Langone Medical Center in New York City. "So far, however, we are not seeing large outbreaks. That's not an accident. You can see something in a test tube or in a ferret that doesn't reproduce in real life."
The new study shows that the H7N9 virus does not sicken poultry, Chen said. This can make the virus hard to track as it infects people, since they can be around infected birds without being aware of it.
Replication in humans, however, provides opportunities for the virus to acquire more mutations and become more virulent and transmissible in mammals, she explained.
"Our results suggest that the H7N9 virus is likely to transmit among humans, and immediate action is needed to prevent an influenza pandemic caused by this virus," Chen said.
The new report was published July 18 in the online edition of the journal Science.
The US Centers for Disease Control and Prevention is keeping a close eye on the H7N9 virus.
"Any time a new flu virus emerges, especially one that can cause severe disease in humans, it's a virus we get very interested in," said Dr Joseph Bresee, chief of the epidemiology and prevention branch in the CDC's Influenza Division.
Bresee noted that, so far, the H7N9 virus does not spread easily from human to human, but it is still a matter of concern.
"It can cause severe disease and deaths in humans. The one thing that gives us comfort so far is that it doesn't seem to be able to spread efficiently between humans, and that's what allows a flu virus to develop into a pandemic virus," he said.
Not only is the CDC watching this virus, Bresee said: "The whole world is watching."
Within the United States, the CDC has told state health departments what to look for and how to test for H7N9, Bresee said.
The agency is studying the virus, watching for mutations and trying to understand what medicines work against it. Moreover, the CDC is developing a vaccine against the H7N9 flu, he said.
"When the virus was first discovered and we got our samples here at CDC, we started vaccine development right away," Bresee said. "The US government is developing and testing vaccines just in case we need to use them at some point."
The Chinese researchers investigated the virus from a variety of sources.
Chen's team identified dozens of H7N9 strains from more than 10 000 samples taken from poultry markets, poultry farms, wild bird habitats and slaughterhouses across China.
The researchers looked at the genetic makeup of these strains, comparing them with the genetic makeup of five of the strains found in people.
All strains of the virus could go to airway receptors in humans, and some could be transmitted to birds as well.
All of the H7N9 strains from birds easily went to chickens, ducks and mice without causing any disease. The human strains, however, caused mice to lose up to 30% of their body weight, the researchers said.
In addition, one of the human strains easily went from ferret to ferret.
Whether the virus will mutate, making it easier to transmit from human to human, is not assured, Siegel said.
"That's probably better left to science fiction, because mutations also occur that make something more benign," he said.
To learn more about the H7N9 flu, visit the U.S. Centers for Disease Control and Prevention.