Bird flu switches from chickens to ducks

The H7N9 pathogen that triggered the 2013 global bird flu pandemic has pivoted away from chickens and has now colonised ducks, a study has found.

Chinese researchers say its absence in chickens is evidence that a new vaccine is successful – and they are confident that a vaccination campaign in ducks will be similarly effective, providing it happens quickly.

The duck infections are surprising, the researchers say, because the original highly-pathogenic form of H7N9 has very limited capacity to replicate in ducks.

They found that the bird flu virus mutates very rapidly, and H7N9 managed to pick up certain gene segments from other duck influenza viruses, allowing it to infect them more easily.

“Influenza viruses mutate as long as they replicate, but it’s very difficult to predict when the H7N9 virus will obtain a particular harmful mutation,” says lead author animal virologist Hualan Chen from the Harbin Veterinary Research Institute.

“It is possible that the virus may adapt in other species in the future if it cannot be eliminated soon.”

Chen’s team collected genetic samples from more than 37,928 chickens and 15,956 ducks eight months before and five months after the vaccine’s introduction in September 2017. They isolated 304 H7N9 viruses before its release, and only 17 H7N9 viruses and one H7N2 virus afterwards.

“Our data show that vaccination of chickens successfully prevented the spread of the H7N9 virus in China,” he says. “The fact that human infection has not been detected since February 2018 indicates that consumers of poultry have also been well-protected from H7N9 infection.”

Chinese consumers eat an estimated three billion ducks and 14 billion chickens a year.

The paper is published in the journal Cell Host & Microbe.