H7N9 and H7N2 highly pathogenic viruses detected in ducks

H7N9 low pathogenic Influenza A viruses emerged in China in 2013 and mutated to highly pathogenic strains in 2017, resulting in human infections and disease in chickens. To control spread, a bivalent H5/H7 inactivated vaccine was introduced in poultry (mainly chickens) in September 2017. Recent findings suggest that the vaccine largely worked, but researchers report in Cell Host & Microbe that they have detected two new genetic variations of the H7N9 and H7N2 subtypes in unvaccinated ducks.

“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 252 H7N9 low pathogenic viruses, 69 H7N9 highly pathogenic viruses, and one H7N2 highly pathogenic virus, of which two low pathogenic and 14 highly pathogenic strains were collected after vaccine introduction.

“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.”

Influenza viruses replicate in host cells and often mutate and reassort 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.

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

To prevent further human infection, Chen and her team believe that the virus should be eliminated in ducks as soon as possible.

“Fortunately, our study indicates that the current vaccine will work well in ducks, so we do not need to develop a new one,” says Chen. “We suggest applying the H7 vaccine in ducks immediately.”

Article: Rapid Evolution of H7N9 Highly Pathogenic Viruses that Emerged in China in 2017 by Jianzhong Shi, Guohua Deng, Shujie Ma, Xianying Zeng, Xin Yin, Mei Li, Bo Zhang, Pengfei Cui, Yan Chen, Huanliang Yang, Xiaopeng Wan, Liling Liu, Pucheng Chen, Yongping Jiang, Yuntao Guan, Jinxiong Liu, Wenli Gu, Shuyu Han, Yangming Song, Libin Liang, Zhiyuan Qu, Yujie Hou, Xiurong Wang, Hongmei Bao, Guobin Tian, Yanbing Li, Li Jiang, Chengjun Li, Hualan Chen, published in Cell Host & Microbe, online 27 September 2018, doi: 10.1016/j.chom.2018.08.006

[SOURCE: Cell Press]