Genetically and Antigenically Divergent Influenza A(H9N2) Viruses Exhibit Differential Replication and Transmission Phenotypes in Mammalian Models

Abstract

Low pathogenicity avian influenza A(H9N2) viruses, enzootic in poultry populations in Asia, are associated with fewer confirmed human infections but higher rates of seropositivity compared to A(H5) or A(H7) subtype viruses. Co-circulation of A(H5) and A(H7) viruses leads to the generation of reassortant viruses bearing A(H9N2) internal genes with markers of mammalian adaptation, warranting continued surveillance in both avian and human populations. Here, we describe active surveillance efforts in live poultry markets in Vietnam in 2018 and compare representative viruses to G1 and Y280 lineage viruses that have infected humans. Receptor binding properties, pH thresholds for HA activation, in vitro replication in human respiratory tract cells, and in vivo mammalian pathogenicity and transmissibility were investigated. While A(H9N2) viruses from both poultry and humans exhibited features associated with mammalian adaptation, one human isolate from 2018, A/Anhui-Lujiang/39/2018, exhibited increased capacity for replication and transmission, demonstrating the pandemic potential of A(H9N2) viruses. IMPORTANCE A(H9N2) influenza viruses are widespread in poultry in many parts of the world, and for over twenty years, have sporadically jumped species barriers to cause human infection. As these viruses continue to diversify genetically and antigenically, it is critical to closely monitor viruses responsible for human infections, to ascertain if A(H9N2) viruses are acquiring properties that make them better suited to infect and spread among humans. In this study, we describe an active poultry surveillance system established in Vietnam to identify the scope of influenza viruses present in live bird markets and the threat they pose to human health. Assessment of a recent A(H9N2) virus isolated from an individual in China in 2018 is also reported and was found to exhibit properties of adaptation to humans and, importantly, show similarities to strains isolated from the live bird markets of Vietnam.

Antigenic and molecular characterization of low pathogenic avian influenza A(H9N2) viruses in sub-Saharan Africa from 2017 through 2019

“…Ghana [14]. The human strain A/Hong Kong/1073/99 used in kinetics replication as control was also characterized in ferrets and did not show any increased virulence or airborne transmission ability [30]. These results suggest a similar zoonotic potential of Sub-Saharan…”

“…At least 59 human cases of H9N2 have been reported in the world [2]. In Africa, ferrets [12,14,30]. Algerian viruses did not show any increase of virulence or airborne transmission ability in ferrets [12].…”

“…Nevertheless, the virus from Benin (Bn/145) showed a decrease of replicative fitness in human cells compared to other African and Asian viruses tested. In vivo characterizations were not performed since closely related viruses from Algeria and Ghana, and the human strain A/Hong Kong/1073/99 had already been characterized in chickens or ferrets [ 12 , 14 , 30 ]. Algerian viruses did not show any increase of virulence or airborne transmission ability in ferrets [ 12 ].…”

“…Similar results were observed in chicken with viruses from Ghana [ 14 ]. The human strain A/Hong Kong/1073/99 used in kinetics replication as control was also characterized in ferrets and did not show any increased virulence or airborne transmission ability [ 30 ]. These results suggest a similar zoonotic potential of Sub-Saharan African viruses with H9N2 isolated in human, except for the viruses from Benin which showed an antigenic dritft and a decrease of replication in human cells.…”

Avian influenza overview May – August 2020

“…Gross and microscopic pathology for the dead bird included congestion and haemorrhages of the lungs and ovarian follicles with oedema and mononuclear cell infiltration, hypertrophy of the liver with necrosis and mononuclear cell infiltration, and spleen atrophy with necrosis and lymphocyte infiltration. Belser et al (2020) reported the detection of 163 A(H9N2) positive oropharyngeal swabs and environmental (feces and water) samples collected between September 2018 and September 2019 in live poultry markets in Vietnam. 55 complete genome sequences were obtained: all clustered with Y280/G9 lineage A(H9N2) viruses and were grouped in two large sublineages named A and B in this study, and respectivrly related to candidate vaccine viruses A/chicken/Hong Kong/G9/1997 and A/Hong Kong/308/2014 or A/Anhui-Lujiang/39/2018.…”