China - New virulent bird flu viruses in ducks after vaccines largely prevented H7N9 in chickens - study

[Gert van der Hoek]

sept 27, 2018

In response to bird flu pandemics starting in 2013, officials in China introduced a new vaccine for chickens in September 2017. Recent findings suggest that the vaccine largely worked but detected two new genetic variations of the H7N9 and H7N2 subtypes in unvaccinated ducks. These findings will be published in the journal Cell Host & Microbe on September 27.

"It surprised me that the novel, highly pathogenic subtypes had been generated in and adapted so well to ducks, because the original highly pathogenic form of H7N9 has very limited capacity to replicate in ducks," says Hualan Chen, a senior author on the paper and an animal virologist at the Harbin Veterinary Research Institute.

Chen's team collected over 37,928 chickens and 15,956 duck genetic samples 8 months before and 5 months after the vaccine's introduction. They isolated 304 H7N9 viruses before the vaccine's release, and only 17 H7N9 viruses and one H7N2 virus after.

"Our data show that vaccination of chickens successfully prevented the spread of the H7N9 virus in China," says Chen. "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."
The bird flu virus replicates in host cells and often mutates and reassorts over time. When Chen's team looked closely at the genetic types of the disease-causing strains in ducks, they found that an H7N2 and an H7N9 virus had picked up certain gene segments from other duck influenza viruses, improving their ability to infect ducks.

[Gert van der Hoek]

In China, a deadly strain of bird flu now easily infects ducks

A vaccine that protects chickens from the virus works in ducks, too


sept 27, 2018

Some ducks in China now carry a deadly strain of bird flu.

Highly pathogenic versions of H7N9 ? a bird flu strain that?s proven particularly deadly to people ? and H7N2 viruses have turned up in ducks in the Fujian province. These viruses replicate easily in the ducks and can kill them, researchers report September 27 in Cell Host & Microbe.

The discovery is worrisome because the virus made the jump to ducks just ahead of efforts to eliminate H7N9 by vaccinating chickens.
Since H7N9 began sickening people in 2013, a total of 1,625 people have contracted the bird flu strain and 623 have died. Most of those infected had been in contact with chickens (SN Online: 3/11/15). Initially the virus killed about a third of people who caught it. But in 2016, the virus mutated to become even deadlier in both poultry and people, killing about half of people it infected.

A vaccine against the virus protects chickens, and consequently people, the new study found. No human cases of H7N9 have been reported since October 2017.

But ducks weren?t vaccinated because the original H7N9 virus didn?t infect them easily.

Now, they should be to prevent the deadlier virus strains from spreading to other poultry, wild birds and to people, the researchers write.