Immune-Related Gene Expression in Ducks Infected With Waterfowl-Origin H5N6 Highly Pathogenic Avian Influenza Viruses

Genetic characteristics of waterfowl-origin H5N6 highly pathogenic avian influenza viruses and their pathogenesis in ducks and chickens

Waterfowl, such as ducks, are natural hosts for avian influenza viruses (AIVs) and act as a bridge for transmitting the virus to humans or susceptible chickens. Since 2013, chickens and ducks have been threatened by waterfowl-origin H5N6 subtype AIVs in China. Therefore, it is necessary to investigate the genetic evolution, transmission, and pathogenicity of these viruses. In this study, we determined the genetic characteristics, transmission, and pathogenicity of waterfowl-origin H5N6 viruses in southern China. The hemagglutinin (HA) genes of H5N6 viruses were classified into the MIX-like branch of clade 2.3.4.4h. The neuraminidase (NA) genes belonged to the Eurasian lineage. The PB1 genes were classified into MIX-like and VN 2014-like branches. The remaining five genes were clustered into the MIX-like branch. Therefore, these viruses belonged to different genotypes. The cleavage site of the HA proteins of these viruses was RERRRKR/G, a molecular characteristic of the H5 highly pathogenic AIV. The NA stalk of all H5N6 viruses contained 11 amino acid deletions at residues 58-68. All viruses contained 627E and 701D in the PB2 proteins, which were molecular characteristics of typical bird AIVs. Furthermore, this study showed that Q135 and S23 viruses could replicate systematically in chickens and ducks. They did not cause death in ducks but induced mild clinical signs in them. All the infected chickens showed severe clinical signs and died. These viruses were shed from the digestive and respiratory tracts and transmitted horizontally in chickens and ducks. Our results provide valuable information for preventing H5N6 avian influenza outbreaks.

Natural variant R246K in hemagglutinin increased zoonotic characteristics and renal inflammation in mice infected with H9N2 influenza virus

Considered a potential pandemic candidate, the widespread among poultry of H9N2 avian influenza viruses across Asia and North Africa pose an increasing threat to poultry and human health. The massive epidemic of H9N2 viruses has expanded the host range; however, the molecular basis and characteristic underlying the transmission to poultry and mammals remains unclear. Our previous study has proved that some natural mutations in the HA gene enhanced the binding ability of the H9N2 virus to α-2,6 SA receptors. Here, we systematically analyzed the impact of these natural mutations on zoonotic characteristics and the pathogenicity of H9N2 AIVs in poultry and mammals. Our study demonstrated that mutation R246K increased the replication in human lung epithelial cells in vitro. Mutation R246K increased the virus shedding of oropharyngeal swabs during early-stage infection in chickens. Moreover, mutation R246K displayed stronger pH stability and pathogenicity in mice. The strong renal tropism and inflammatory response may accelerate the pathogenicity. In summary, we found that natural variation R246K in HA of prevalent H9N2 in China promoted the transmissibility in chicken and accelerate the pathogenicity in mice, posing a great concern for zoonotic and pandemic emergence.

Pathogenicity and Transmissibility of Clade 2.3.4.4h H5N6 Avian Influenza Viruses in Mammals

Avian influenza viruses (AIVs) have the potential for cross-species transmission and pandemics. In recent years, clade 2.3.4.4 H5N6 AIVs are prevalent in domestic poultry, posing a threat to the domestic poultry industry and public health. In this study, two strains of H5N6 AIVs were isolated from chickens in Hebei, China, in 2019: A/chicken/Hebei/HB1907/2019(H5N6) and A/chicken/Hebei/HB1905/2019(H5N6). Phylogenetic analysis showed that both viral HA genes clustered in the 2.3.4.4h clade. Receptor binding analysis showed that the HB1905 strain preferentially binds to α-2,3-linked sialic acid (SA) receptors, while the HB1907 strain preferentially binds to α-2,3- and α-2,6-linked sialic acid (SA) receptors. During early infection, the HB1907 strain is highly replicable in MDCK cells, more so than the HB1905 strain. Pathogenicity assays in mice showed that both viruses could replicate in the lungs without prior adaptation, with HB1907 being more highly pathogenic in mice than the HB1905 strain. Significantly, both the HB1905 and HB1907 strains can be transmitted through direct contact among guinea pigs, but the transmission efficiency of the HB1907 strain through contact between guinea pigs is much greater than that of the HB1905 strain. These results strengthen the need for ongoing surveillance and early warning of H5N6 AIVs in poultry.

The Variation of Duck RIG-I-Mediated Innate Immune Response Induced by Different Virulence Avian Influenza Viruses

In recent years, the emerging highly pathogenic avian influenza (HPAI) A(H5N8) virus has been reported with features of widely spread, an expanding host range, and cross-species transmission, attracting wide attention. The domestic duck plays a major role in the epidemiological cycle of the HPAI H5N8 virus, but little is known concerning innate immune responses during influenza infection in duck species. In this study, we used two wild-bird-origin viruses, H5N8 and H4N6, to conduct duck infection experiments, and detect the load of the two viruses, and retinoic acid-inducible gene I (RIG-I) and interferon β (IFN-β) in the host's natural immune response. Through comparison, it is found that the expression levels of RIG-I and IFN-β are both fluctuating. The innate immunity starts rapidly within 6 h after infection and is inhibited by the virus to varying degrees. The expression of RIG-I and IFN-β decreased on 1-2 days post-infection (dpi). The HPAI H5N8 virus has a stronger inhibitory effect on RIG-I than the low pathogenic avian influenza (LPAI) H4N6 virus and is the strongest in the lungs. After infection with HPAI H5N8 virus, 2 dpi, viral RNA replicates in large amounts in the lungs. It has been proven that RIG-I and IFN-β play an important role in the innate immune response of ducks to HPAI H5N8 virus infection, especially in the lungs. The main battlefield of RIG-I and IFN-β after infection with the LPAI H4N6 virus is in the rectum. Both viruses have been effectively controlled after 7 dpi. These results will help to understand the transmission mechanisms of avian influenza virus in wild ducks and help effectively prevent and control avian influenza.

Highly pathogenic avian influenza virus H5N6 (clade 2.3.4.4b) has a preferable host tropism for waterfowl reflected in its inefficient transmission to terrestrial poultry

Highly-pathogenic avian influenza virus (HPAIV) H5N6 (clade 2.3.4.4b) incurred into Europe in late 2017 and was predominantly detected in wild birds, with very few terrestrial poultry cases. Pekin ducks directly-infected with a UK virus (H5N6-2017) were donors of infection to investigate contact transmission to three recipient species: Ducks, chickens and turkeys. H5N6-2017 transmission to ducks was 100% efficient, but transmission to in-contact galliforme species was infrequent and unpredictable, thereby reflecting the European 2017-2018 H5N6 epidemiology. Although only two of 28 (7%) infected ducks died, the six turkeys and one chicken which became infected all died and displayed systemic H5N6-2017 dissemination, while pathogenesis in ducks was generally milder. Analysis of H5N6-2017 progeny in the contacts revealed no emergent polymorphisms in an infected duck, but the galliforme species included changes in the polymerase (PB2 A199T, PA D347A), matrix (M1 T218A) and neuraminidase genes (T88I). H5N6-2017 environmental contamination was associated with duck shedding.

Differences in Highly Pathogenic H5N6 Avian Influenza Viral Pathogenicity and Inflammatory Response in Chickens and Ducks

Infection with H5N6 highly pathogenic avian influenza virus caused high mortality in chickens, while ducks often appear to be asymptomatic. But, some recent H5Nx subtype viruses could cause high mortality in ducks. The variation between different species and the mechanisms by which some H5Nx viruses cause death in ducks requires investigation to identify the key processes in influenza susceptibility and pathogenesis. Here, we characterized two representative H5N6 viruses, A/Pavo cristatus/Jiangxi/JA1/2016 (JA1) and A/Anas crecca/shanghai/SH1/2016 (SH1), and compared their pathogenicity and expression profiles of immune-related genes in chickens and ducks to identify the elements of the host immune-related response that were involved in disease lethality. Results suggested that H5N6 HPAIVs had higher pathogenic and inflammatory effect in chickens than in ducks. Importantly, the TNF-α, IL-6, IFN-γ and iNOS levels were significantly higher in the lung of SH1 infected chickens compared to those of ducks. And we found higher systemic levels of IL-6 induced by JA1 in chickens than in ducks. In addition, our experiments demonstrated that JA1 was associated with greater pathogenicity in ducks were accompanied by the excessive expression of iNOS in the brain. These results are helpful to understand the relationship between the pathogenicity of H5N6 AIVs and inflammatory responses to them in chickens and ducks.

Pattern Recognition Receptor Signaling and Innate Responses to Influenza A Viruses in the Mallard Duck, Compared to Humans and Chickens

Mallard ducks are a natural host and reservoir of avian Influenza A viruses. While most influenza strains can replicate in mallards, the virus typically does not cause substantial disease in this host. Mallards are often resistant to disease caused by highly pathogenic avian influenza viruses, while the same strains can cause severe infection in humans, chickens, and even other species of ducks, resulting in systemic spread of the virus and even death. The differences in influenza detection and antiviral effectors responsible for limiting damage in the mallards are largely unknown. Domestic mallards have an early and robust innate response to infection that seems to limit replication and clear highly pathogenic strains. The regulation and timing of the response to influenza also seems to circumvent damage done by a prolonged or dysregulated immune response. Rapid initiation of innate immune responses depends on viral recognition by pattern recognition receptors (PRRs) expressed in tissues where the virus replicates. RIG-like receptors (RLRs), Toll-like receptors (TLRs), and Nod-like receptors (NLRs) are all important influenza sensors in mammals during infection. Ducks utilize many of the same PRRs to detect influenza, namely RIG-I, TLR7, and TLR3 and their downstream adaptors. Ducks also express many of the same signal transduction proteins including TBK1, TRIF, and TRAF3. Some antiviral effectors expressed downstream of these signaling pathways inhibit influenza replication in ducks. In this review, we summarize the recent advances in our understanding of influenza recognition and response through duck PRRs and their adaptors. We compare basal tissue expression and regulation of these signaling components in birds, to better understand what contributes to influenza resistance in the duck.

Host Innate Immune Response of Geese Infected with Clade 2.3.4.4 H5N6 Highly Pathogenic Avian Influenza Viruses

Since 2014, highly pathogenic avian influenza (HPAI) H5N6 viruses have circulated in waterfowls and caused human infections in China, posing significant threats to the poultry industry and the public health. However, the genetics, pathogenicity and innate immune response of H5N6 HPAIVs in geese remain largely unknown. In this study, we analyzed the genetic characteristic of the two H5N6 viruses (GS38 and DK09) isolated from apparently healthy domestic goose and duck in live poultry markets (LPMs) of Southern China in 2016. Phylogenetic analysis showed that the HA genes of the two H5N6 viruses belonged to clade 2.3.4.4 and were clustered into the MIX-like group. The MIX-like group viruses have circulated in regions such as China, Japan, Korea, and Vietnam. The NA genes of the two H5N6 viruses were classified into the Eurasian sublineage. The internal genes including PB2, PB1, PA, NP, M, and NS of the two H5N6 viruses derived from the MIX-like. Therefore, our results suggested that the two H5N6 viruses were reassortants of the H5N1 and H6N6 viruses and likely derived from the same ancestor. Additionally, we evaluated the pathogenicity and transmission of the two H5N6 viruses in domestic geese. Results showed that both the two viruses caused serious clinical symptoms in all inoculated geese and led to high mortality in these birds. Both the two viruses were transmitted efficiently to contact geese and caused lethal infection in these birds. Furthermore, we found that mRNA of pattern recognition receptors (PRRs), interferons (IFNs), and stimulated genes (ISGs) exhibited different levels of activation in the lungs and spleens of the two H5N6 viruses-inoculated geese though did not protect these birds from H5N6 HPAIVs infection. Our results suggested that the clade 2.3.4.4 waterfowl-origin H5N6 HPAIVs isolated from LPMs of Southern China could cause high mortality in geese and innate immune-related genes were involved in the geese innate immune response to H5N6 HPAIVs infection. Therefore, we should pay more attention to the evolution, pathogenic variations of these viruses and enhance virological surveillance of clade 2.3.4.4 H5N6 HPAIVs in waterfowls in China.