Phylogenetic and Molecular Characterization of H9N2 Influenza Isolates from Chickens in Northern China from 2007–2009

Abstract

The repeated transmission to pigs and humans, and the long-term endemicity in terrestrial poultry of H9N2 viruses in China lend urgency to the study of their ecology and pathogenicity. In the present paper, we reported an H9N2 virus sublineage isolated from chickens in northern China from 2007 to 2009 has high lethality for mice. Phylogenetic analysis of the full genome indicated that six representative H9N2 isolates shared high homology to each other, and they clustered in the same sublineage with other H9N2 viruses isolated recently in northern China. The isolates were double-reassortant viruses containing M genes similar to A/Quail/Hong Kong/G1/97 (H9N2) and the other seven gene segments from A/Chicken/Shanghai/F/98 (H9N2). These six isolates were capable of replicating in the lungs of infected chickens without producing observable clinical signs of disease or death. However, they were highly lethal to mice with mortality rates as high as 100% (14/14) without prior adaptation. The affected mice exhibited severe respiratory syndromes and diffuse lung injury. The H9N2 viruses could be detected in multiple organs of the infected mice, including hearts, livers, spleens, lungs and kidneys. Our findings demonstrated that H9N2 viruses isolated from the chickens in northern China have established a stable sublineage with enhanced pathogenicity to mice, suggesting that urgent attention will need to be paid to the transmission of H9N2 viruses from chickens to mammals.

Evolution of the H9N2 influenza genotype that facilitated the genesis of the novel H7N9 virus

“…By comparison of their shedding time (Fig. 4C), G57 viruses had longer shedding time until 7 dpi in contact vaccinated chickens with high antibody titers (10)(11)(12). Although the shedding time of ZB/07 was similar with those of G57 viruses, the numbers of H9N2-positive chickens was less (Fig.…”

“…The vaccinated chickens were divided into groups with low antibody levels (HI titer,(6)(7)(8)(9) and high antibody levels (HI titer,(10)(11)(12). Nine viruses used in the above unvaccinated chicken experiment (Fig.…”

“…In 1994, the H9N2 subtype was first identified in chicken farms in the Guangdong province of south China (7); it has since become widespread in chickens and has caused great economic loss from reduced egg production and highly lethal coinfections (8)(9)(10)(11). To reduce the impact of H9N2 infection in chickens, the flocks have been vaccinated since 1998 with commercial inactivated vaccines, such as A/chicken/Guangdong/SS/1994 (Ck/GD/ SS/94), A/chicken/Shandong/6/1996 (Ck/SD/6/96), and A/chicken/ Shanghai/F/1998 (Ck/SH/F/98) (8,12,13).…”

“…These H9N2 vaccines initially limited the outbreaks and virus spread. However, despite multiple doses, the H9N2 vaccines became less effective, especially after 2007, and H9N2 influenza virus continues to circulate in vaccinated chicken flocks and has caused sporadic disease outbreaks (8,10,(12)(13)(14)(15)(16)(17)(18)(19)(20). However, the recent prevalence and molecular evolution of the H9N2 viruses in chickens especially in the flocks receiving large-scale vaccination, and their role in the emergence of human H7N9 virus, are not fully understood.…”

Different outcomes of infection of chickens and ducks with a duck-origin H9N2 influenza A virus

“…Since the first isolation from terrestrial birds (quails) in 1988, H9N2 became prevalent in China and, occasionally, infected a wide range of species, including humans, dogs, cats, pigs, and a wide variety of domesticated birds (Peiris et al, 1999;Xu et al, 2004;Bi et al, 2010;Zhang et al, 2013). It has been reported that H9N2 might provide internal genes to the lethal 1997 Hong Kong H5N1 viruses that caused six fatal cases out of 18 infected patients (Guan et al, 1999).…”