Juan Pu^a,^b,¹, Shuoguo Wang^c,¹, Yanbo Yin^d,¹, Guozhong Zhang^a, Robert A. Carter^c, Jinliang Wang^a, Guanlong Xu^a, Honglei Sun^a, Min Wang^a, Chu Wen^a, Yandi Wei^a, Dongdong Wang^d, Baoli Zhu^e, Gordon Lemmon^c, Yuannian Jiao^c, Susu Duan^b, Qian Wang^a, Qian Du^a, Meng Sun^a, Jinnan Bao^a, Yipeng Sun^a, Jixun Zhao^a, Hui Zhang^f, Gang Wu^c, Jinhua Liu^a,², and Robert G. Webster^b,²

Significance

The emergence of human infection with a novel H7N9 avian influenza reassortant in China raises a pandemic concern. However, it is not fully understood how these H9N2 chicken viruses facilitated the genesis of the novel H7N9 viruses. Here we show that a “fittest” genotype (G57) emerged with changed antigenicity and improved adaptability in chickens. It became predominant in vaccinated farm chickens and caused widespread outbreaks before the H7N9 virus emergence, increasing reassortment between H9N2 and other subtype viruses and finally providing all of their internal genes to the novel H7N9 viruses. The prevalence and variation of H9N2 influenza virus in farmed poultry could provide an important early warning of the emergence of novel reassortants with pandemic potential.

Abstract

The emergence of human infection with a novel H7N9 influenza virus in China raises a pandemic concern. Chicken H9N2 viruses provided all six of the novel reassortant’s internal genes. However, it is not fully understood how the prevalence and evolution of these H9N2 chicken viruses facilitated the genesis of the novel H7N9 viruses. Here we show that over more than 10 y of cocirculation of multiple H9N2 genotypes, a genotype (G57) emerged that had changed antigenicity and improved adaptability in chickens. It became predominant in vaccinated farm chickens in China, caused widespread outbreaks in 2010–2013 before the H7N9 viruses emerged in humans, and finally provided all of their internal genes to the novel H7N9 viruses. The prevalence and variation of H9N2 influenza virus in farmed poultry could provide an important early warning of the emergence of novel reassortants with pandemic potential.

See http://www.pnas.org/content/112/2/548.abstract

PNAS January 13, 2015 vol. 112 no. 2: 548-553  

Fig. 1. Isolation rate (%) of H9N2 influenza viruses during 2010–2013 on chicken farms reporting illness in our investigated regions. Histogram indicates monthly isolation rates; red horizontal line (connected with dots) indicates mean annual isolation rates; and gray horizontal dashed line indicates 95% CI.