As bird flu spread continues, why the recent jump to pigs raises worries

Bird flu has spread far and wide, infecting a range of species like chickens, skunks, cows, foxes and polar bears. But it's the pigs that have experts on high alert.

Bird flu has spread far and wide, infecting a range of species like chickens, skunks, cows, foxes and polar bears and renewing questions about what level of risk it poses to people as a B.C. teenager remains in critical condition in hospital after being infected.

But it’s the recent jump to pigs that has experts on high alert, as swine offer the perfect conditions for the virus to mutate, making it a potential threat to human health.

Last month, United States health officials reported the first case of avian influenza A(H5N1) in a pig on a backyard farm in Oregon, marking the first time the virus had been detected in pigs in the country. Days later, officials confirmed a second pig on the farm had also tested positive.

“With every species it jumps to, it elevates the risk,” said Kerry Bowman, a professor of bioethics and global health at the University of Toronto. “But pigs are particularly worrisome species. The risk has risen yet again.”

Pigs represent a particular concern for the spread of bird flu because they can become co-infected with bird and human viruses, which could swap genes to form a new, more dangerous virus that can more easily infect humans.

“Pigs can work as a mixing vessel, as they can have both bird flu and human flu simultaneously. And these things could recombine,” Bowman said, adding that this could result in the emergence of a new influenza A virus with different properties.

These “mixing vessel” events have happened in pigs in the past; it is believed to have caused the 2009 influenza A(H1N1) pandemic, Bowman said.

Currently, the risk of bird flu remains low, but Bowman said every time the virus jumps to a new species, it raises the risk.