It’s been several months since the H7N9 avian flu virus emerged in China, infecting an estimated 132 people and leaving at least 39 of them dead. But while there have been no reported cases of the disease since the middle of June, infectious disease experts say it is not time to let down their guard.
Writing in the journal mBio, Anthony Fauci, the head of NIAID, the National Institute of Allergy and Infectious Diseases, says the lull in H7N9 infections in China is good news. But he says this is no reason to think the virus could not reemerge, posing a future threat.
H7N9 can cause pneumonia, acute respiratory distress syndrome and multiple organ failure.
Fauci and two other leading infectious disease scientists at NIAID note that H7N9 is not transmitted easily from chickens to humans or among people. But H7 subtypes have been responsible for a number of devastating poultry outbreaks in Canada, Mexico, the Netherlands and Italy, which eventually affected people.
That’s because H7 viruses have the ability to mutate from a low-level infection in birds into a highly contagious avian pathogen, which Fauci says could lead to human exposure through poultry markets and large scale culling of diseased flocks.
“You always need to be concerned about the possibility that this virus or these viruses that can attain the capability of more efficient spread. And if that happens, there will be a problem," said Fauci.
One cause for concern is H7N9-infected pigs. Swine, which are physiologically more like humans than chickens, are considered a so-called “mixing vessel” for viruses, a place where viral DNA could mutate, making it easier for the pathogen to infect people. That's what happened in 2009, with the H1N1 "swine flu" influenza pandemic.
Given the unknowns about H7N9, and the fact that it killed almost one-third of those who were infected in China, Fauci says the outbreak should prompt enhanced research efforts to better understand the mutation of avian and swine flu viruses into diseases that infect humans.