Influenza A(H7N9) may already have adapted to humans

The emergence of the Influenza A(H7N9) virus in humans in Eastern China has raised concerns that a new influenza pandemic could occur. For that to happen the virus must be able to easily spread via an air-born route in humans. At the moment this is not yet the case.

Avian influenza A H7 viruses normally circulate amongst avian populations with some variants known to cause infections in humans but this is an uncommon occurrence, though there have been confirmed infections in people who have direct contact with infected birds. At the moment person-to-person infections do happen but only in cases where there was close, prolonged and intensive contact between patients.

[Foto: China Navis]

But the influenza virus is known for its rapid genetic change and Influenza A(H7N9) virus may be just one step away from becoming a doomsday virus. We too are mammals so scientists[1] infected ferrets and pigs to see how these animals would react to the virus. It transpired that the virus transmits well among ferrets and even sometimes spreads among them by the airborne route. While the airborne spread wasn’t highly efficient, the work suggests this virus is more closely adapted to person-to-person spread than other avian influenza viruses.

In another interesting aspect of the study, the researchers experimentally infected pigs. Pigs are susceptible to influenza viruses. And because they can be infected with both bird and human flu strains, they are thought to play a key role in the formation of new hybrid strains.

The researchers also noted that pigs could become infected with the Influenza A(H7N9) virus, but didn’t pass the virus from infected animal to healthy animal. What this data would suggest is that it is unlikely that this virus came from pigs.

Ron Fouchier, a Dutch virologist, commented that “This virus is already well on its way. … It is poorly transmissible, but it can transmit. So there are reasons to date to take this virus seriously.”

[1] Zhu et al: Infectivity, Transmission, and Pathology of Human H7N9 Influenza in Ferrets and Pigs in Science - 2013