May 23, 2013 at 3:03 PM ET
The H7N9 bird flu can spread from one mammal to another – meaning it could also spread person to person, an international team of researchers reported Thursday.
Researchers haven’t been exactly sure how H7N9 is spreading. They know it can infect people – it’s infected more than 130 people and killed more than 30 of them – but they have suspected most of the victims had some sort of contact with infected poultry.
The research team, led by Yi Guan of the University of Hong Kong, tried infecting ferrets – the animals closest to humans when it comes to catching flu.
The animals could infect one another by direct contact in cages. And one ferret kept in a separate cage was infected as well, they report in this week’s issue of the journal Science.
“Under appropriate conditions human-to-human transmission of the H7N9 virus may be possible,” they wrote.
Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, says he is not too worried by the findings. “We already know you can infect mammals,” said Fauci, who was not involved in the research.
“That is what influenza does. We know that. You are talking about a handful of ferrets. You can’t make major extrapolations.”
Officials are keeping a close eye on H7N9 because it has the potential to cause a human pandemic. So far, it doesn’t seem to infect people easily and people who are infected do not seem to spread it to others much, if at all. But influenza viruses change quickly and unpredictably and if one starts passing easily from one person to another, it could spread.
The experiment also showed that the ferrets could pass the infection before they started showing symptoms. Human flu does this too – that’s why it spreads so quickly and easily every year, because people are out and about, touching others, before they know they are sick.
“If this virus acquires the ability to efficiently transmit from human-to-human, extensive spread of this virus may be inevitable, as quarantine measures will lag behind its spread,” the researchers wrote in Science.
“Assuming that poultry is the source of the H7N9 virus, continued prevalence of this virus could lead to it becoming endemic in poultry as has occurred with the Asian highly pathogenic H5N1 and H9N2 virus lineages," they added. Endemic viruses are established and cause constant outbreaks.
"If so, the opportunities for the H7N9 virus to evolve to acquire human-to-human transmissibility, or to be introduced to pigs, would greatly increase. To prevent this happening, it may be advisable to reconsider the management of live poultry markets, especially in the urban areas.”
New H7N9 infections appear to have trailed off in China. World Health Organization officials say it might be because officials are closing poultry markets and cleaning them. Or it could be because it’s spring and influenza tends to die down in the spring.
Marc-Alain Widdowson of the U.S. Centers for Disease Control and Prevention says the virus doesn’t make poultry sick, so it could spread quietly and easily.
“One thing that we are particularly worried about is there is a tremendous amount of poultry that goes from China into Vietnam,” said Widdowson, who visited China with a CDC team to investigate the outbreak.
“One of the things we are looking at is ramping up surveillance in bird markers and in the population.”
People who buy an infected chicken won’t know, because H7N9 doesn’t make the birds sick they way H5N1 does, Widdowson says. “It worries me substantially,” he said.
“There’s absolutely no doubt it has got some very concerning mutations which suggest it may be adapting to human receptors. These make it closer to what we are all fearing, which is a virus that can spread sustainably humans to human and cause severe disease.”