Transmission of H7N9 Influenza Viruses with a Polymorphism at PB2 Residue 627 in Chickens and Ferrets

Abstract

Poultry exposure is a major risk factor for human H7N9 zoonotic infections, for which the mode of transmission remains unclear. We studied the transmission of genetically related poultry and human H7N9 influenza viruses differing by four amino acids, including the host determinant PB2 residue 627. A/Silkie chicken/HK/1772/2014 (SCk1772) and A/HK/3263/14 (HK3263) replicated to comparable titers in chickens, with superior oropharyngeal over cloacal shedding; both viruses transmitted efficiently among chickens via direct contact but inefficiently via the airborne route. Interspecies transmission via the airborne route was observed for ferrets exposed to the SCk1772-or HK3263-infected chickens, while low numbers of copies of influenza viral genome were detected in the air, predominantly at particle sizes larger than 4 m. In ferrets, the human isolate HK3263 replicated to higher titers and transmitted more efficiently via direct contact than SCk1772. We monitored "intrahost" and "interhost" adaptive changes at PB2 residue 627 during infection and transmission of the Sck1772 that carried E627 and HK3263 that carried V/K/E polymorphism at 60%, 20%, and 20%, respectively. For SCk1772, positive selection for K627 over E627 was observed in ferrets during the chicken-to-ferret or ferret-to-ferret transmission. For HK3263 that contained V/K/E polymorphism, mixed V627 and E627 genotypes were transmitted among chickens while either V627 or K627 was transmitted to ferrets with a narrow transmission bottleneck. Overall, our results suggest direct contact as the main mode for H7N9 transmission and identify the PB2-V627 genotype with uncompromised fitness and transmissibility in both avian and mammalian species. IMPORTANCEWe studied the modes of H7N9 transmission, as this information is crucial for developing effective control measures for prevention. Using chicken (SCk1772) and human (HK3263) H7N9 isolates that differed by four amino acids, including the host determinant PB2 residue 627, we observed that both viruses transmitted efficiently among chickens via direct contact but inefficiently via the airborne route. Chicken-to-ferret transmission via the airborne route was observed, along with the detection of viral genome in the air at low copy numbers. In ferrets, HK3263 transmitted more efficiently than SCk1772 via direct contact. During the transmission of SCk1772 that contained E and HK3263 that contained V/K/E polymorphism at PB2 residue 627, positive selections of E627 and K627 were observed in chickens and ferrets, respectively. In addition, PB2-V627 was transmitted and stably maintained in both avian and mammalian species. Our results support applying intervention strategies that minimize direct and indirect contact at the poultry markets during epidemics.

Mammalian Pathogenesis and Transmission of H7N9 Influenza Viruses from Three Waves, 2013-2015

“…Mutations in the polymerase genes highlighted in Table 2 may have increased in frequency as a result of selection during circulation in poultry, but they appear to have minimal impact on virus replication and transmission in mammals. The limited transmissibility by respiratory droplets of second-and third-wave H7N9 viruses in ferrets tested here aligns with other studies which have reported transmission primarily among cohoused animals (52). Importantly, the similar transmission profile of H7N9 viruses between first-wave isolates and viruses isolated during the second and third waves suggest that vaccine and antiviral candidates which limit the transmissibility of the commonly employed Anhui/1/13 virus would maintain a comparable efficacy against more recently detected H7N9 viruses (53).…”

“…While potential correlations between ocular tropism detected in the murine model and human susceptibility to influenza viruses following ocular exposure still are poorly understood, these data underscore the necessity of evaluating influenza viruses for the capacity to cause mammalian infection following alternate inoculation routes, even in the absence of a demonstrated tropism outside the respiratory tract. As observed in this study with shv/Egypt/07 virus, H7N9 viruses isolated from poultry from multiple waves have demonstrated reduced transmissibility in the ferret model compared with viruses isolated from humans (30,31,52). While this can be explained in part by sequence differences often present between poultry-and human-isolated viruses (notably at PB2 residue 627), further examination of how these viruses diverge will allow for a more precise understanding of the adaptation these viruses have undergone to cause human disease.…”

H7N9 Influenza Virus in China

“…Guinea pigs and ferrets are two well-established animal models for the evaluation of transmissibility of influenza viruses (Gao et al 2009;Steel et al 2009;Herfst et al 2012;Imai et al 2012;Zhang et al 2013b). The H7N9 viruses, especially the human isolates, transmitted efficiently among guinea pigs or ferrets via direct contact (Belser et al 2013;Zhu et al 2013;Gabbard et al 2014;Luk et al 2015;Sun et al 2018). Compared with natural H5N1 viruses, which have never acquired respiratory droplet transmissibility, many studies have reported that both H7N9 LPAIV and HPAIV can transmit via respiratory droplets in guinea pigs and ferrets, although the efficiency of virus transmis- All six low pathogenic viruses and five of the six highly pathogenic viruses bound well to both human-type and avian-type receptors, whereas one of the six highly pathogenic viruses bound only to avian-type receptors.…”

Mutations Driving Airborne Transmission of A/H5N1 Virus in Mammals Cause Substantial Attenuation in Chickens only when combined

“…Other parameters than the duration or level of shedding influencing transmission efficacy include stability in the environment (in feces, water, dust or air) as well as the infectious dose necessary to infect a naïve animal. It would also be interesting to assess whether INDO AT6 could be better transmitted to mammals than INDO WT by performing chicken to ferret airborne transmission 65 , 66 .…”