Current situation of H9N2 subtype avian influenza in China

PB2 627V and HA 217 sites synergistically affect the lethality of H9N2 in mice

The H9N2 subtype avian influenza virus (AIV) continues to propagate and undergo evolution within China, thereby posing a significant threat to the poultry industry. This study encompassed the collection of 436 samples and swabs in East China over the period spanning 2018 to 2019, from which 31 strains of the H9N2 subtype viruses were isolated and purified. We revealed that the HA and NA genes of the 31 isolates categorized within the Y280 branch, while the PB2 and M genes were associated with the G1 branch, and the remaining genes aligned with the F/98 branch. Despite this alignment, antigenic mapping demonstrated differences between the 2018 and 2019 strains, with the early vaccine strains displaying low serological reactivity toward these isolates. Notably, the CK/SH/49/19 isolate exhibited lethality in mice, characterized by a PB2 E627V mutation and a HA deletion at amino acid position 217. Mechanistically, in vitro studies showed that the influenza virus CK/SH/49/19 carrying PB2 627V and HA 217M mutations displayed enhanced replication capacity, attributed to the heightened activity of the polymerase with PB2 627V. Moreover, the absence of the amino acid at the HA 217 site obstructed viral adsorption and internalization, resulted in lower activation pH, and impeded the virus budding process. Critically, in vivo experiments revealed that CK/SH/49/19 (PB2 627V, HA 217Δ) triggered a robust activation of interferon response and interferon-stimulated genes. This study furnished a theoretical foundation for the scientific prevention and control strategies against H9N2 subtype avian influenza.

Field production efficiency investigation of broilers immunized with a turkey herpesvirus vector vaccine expressing hemagglutinin from H9N2 subtype avian influenza virus

Turkey herpesvirus (HVT) vector vaccine expressing hemagglutinin from the H9N2 AIV, namely HVT-H9, were demonstrated to block H9N2 AIV infection and transmission in chickens. In this study, we evaluated the protection efficiency and production performance of broilers in HVT-H9 field trials in the presence or absence of the H9N2 AIV natural infection. HI titers against H9N2 AIV in broilers harboring maternal antibodies were successfully induced by HVT-H9. In the presence of H9N2 AIV natural infection, immunization with HVT-H9 blocked H9N2 AIV infection and reduced the mortality rate. Importantly, HVT-H9 vaccination slightly increased broiler weight and decreased the feed conversion rate in the absence of the H9N2 AIV natural infection but significantly reduced mortality rates and increased production efficiency during the H9N2 AIV natural infection. In summary, HVT-H9 immunization might block H9N2 AIV infection and improve production efficiency in the field, especially in the presence of H9N2 AIV natural infection.

The PB2 I714S mutation influenced mammalian adaptation of the H3N2 canine influenza virus by interfering with nuclear import efficiency and RNP complex assembly

Avian influenza viruses (AIVs) are the origin of multiple mammal influenza viruses. The genetic determinants of AIVs adapted to humans have been widely elucidated, however, the molecular mechanism of cross-species transmission and adaptation of AIVs to canines are still poorly understood. In this study, two H3N2 influenza viruses isolated from a live poultry market (A/environment/Guangxi/13431/2018, GX13431) and a swab sample from a canine (A/canine/Guangdong/0601/2019, GD0601) were used to investigate the possible molecular basis that determined H3N2 AIV adapting to canine. We found that GD0601 exhibited more robust polymerase activity in cells and higher pathogenicity in mice compared with its evolution ancestor H3N2 AIV GX13431. A series of reassortments of the ribonucleoprotein (RNP) complex showed that the PB2 subunit was the crucial factor that conferred high polymerase activity of GD0601, and the substitution of I714S in the PB2 subunit of GD0601 attenuated the replication and pathogenicity in mammal cells and the mouse model. Mechanistically, the reverse mutation of I714S in the PB2 polymerase subunit which was identified in AIV GX13431 reduced the nuclear import efficiency of PB2 protein and interfered with the interactions of PB2-PA/NP that affected the assembly of the viral RNP complex. Our study reveals amino acid mutation at the position of 714 in the nuclear localization signal (NLS) area in PB2 plays an important role in overcoming the barrier from poultry to mammals of the H3N2 canine influenza virus and provides clues for further study of mammalian adaptation mechanism of AIVs.

H9 Consensus Hemagglutinin Subunit Vaccine with Adjuvants Induces Robust Mucosal and Systemic Immune Responses in Mice by Intranasal Administration

The H9N2 subtype avian influenza viruses mainly cause respiratory symptoms, reduce the egg production and fertility of poultry, and result in secondary infections, posing a great threat to the poultry industry and human health. Currently, all H9N2 avian influenza commercial vaccines are inactivated vaccines, which provide protection for immunized animals but cannot inhibit the spread of the virus and make it difficult to distinguish between the infected animals and vaccinated animals. In this study, a trimeric consensus H9 hemagglutinin (HA) subunit vaccine for the H9N2 subtype avian influenza virus based on a baculovirus expression system was first generated, and then the effects of three molecular adjuvants on the H9 HA subunit vaccine, Cholera toxin subunit B (CTB), flagellin, and granulocyte-macrophage colony-stimulating factor (GM-CSF) fused with H9 HA, and one synthetic compound, a polyinosinic-polycytidylic acid (PolyI:C) adjuvant, were evaluated in mice by intranasal administration. The results showed that these four adjuvants enhanced the immunogenicity of the H9 HA subunit vaccine for avian influenza viruses, and that GM-CSF and PolyI:C present better mucosal adjuvant activity for the H9 HA subunit vaccine. These results demonstrate that we have developed a potential universal H9 HA mucosal subunit vaccine with adjuvants in a baculovirus system that would be helpful for the prevention and control of H9N2 subtype avian influenza viruses.

Recombinant avian-derived antiviral proteins cIFITM1, cIFITM3, and cViperin as effective adjuvants in inactivated H9N2 subtype avian influenza vaccines

Vaccine adjuvants, serving as non-specific immune enhancers, play a pivotal role in the immunoprevention and control of animal diseases. This study utilized prokaryotic expression systems to express and purify chicken-derived cIFITM1, cIFITM3, and cViperin, which were then formulated as adjuvants with H9N2 avian influenza virus antigens to create inactivated vaccines. These vaccines were administered to SPF chickens to investigate their immunopotentiating functions. Additionally, the proteins were assessed for their ability to act as standalone immune enhancers. The results demonstrated that cIFITM1, cIFITM3, and cViperin significantly elevated serum hemagglutination inhibition (HI) antibody titers. Notably, when used individually, these proteins markedly enhanced the antiviral capabilities of challenged chickens, leading to alleviated clinical symptoms, reduced tracheal virus replication, diminished virus shedding, and lessened histopathological damage, with cIFITM1 exhibiting the most pronounced effect. Furthermore, the protective efficacy of two H9N2 recombinant virus inactivated vaccines supplemented with cIFITM1 adjuvant was validated, achieving a 100 % vaccine protection efficiency. In conclusion, cIFITM1, cIFITM3, and cViperin as adjuvants for influenza vaccines effectively inhibit virus replication and shedding, highlighting their significant potential in influenza prevention and control.

Risk distribution of human infections with avian influenza A (H5N1, H5N6, H9N2 and H7N9) viruses in China

Background

This study aimed to investigate epidemiologic characteristics of major human infection with avian influenza and explore the factors underlying the spatial distributions, particularly H5N6 and H9N2, as H9N2 could directly infect mankind and contribute partial or even whole internal genes to generate novel human-lethal reassortants such as H5N6. They pose potential threats to public health and agriculture.

Methods

This study collected cases of H5N1, H5N6, H9N2, and H7N9 in China, along with data on ecoclimatic, environmental, social and demographic factors at the provincial level. Boosted regression tree (BRT) models, a popular approach to ecological studies, has been commonly used for risk mapping of infectious diseases, therefore, it was used to investigate the association between these variables and the occurrence of human cases for each subtype, as well as to map the probabilities of human infections.

Results

A total of 1,123 H5N1, H5N6, H9N2, and H7N9 human cases have been collected in China from 2011 to 2024. Factors including density of pig and density of human population emerged as common significant predictors for H5N1 (relative contributions: 5.3, 5.8%), H5N6 (10.8, 6.4%), H9N2 (11.2, 7.3%), and H7N9 (9.4, 8.0%) infection. Overall, each virus has its own ecological and social drivers. The predicted distribution probabilities for H5N1, H5N6, H9N2, and H7N9 presence are highest in Guangxi, Sichuan, Guangdong, and Jiangsu, respectively, with values of 0.86, 0.96, 0.93 and 0.99.

Conclusion

This study highlighted the important role of social and demographic factors in the infection of different avian influenza, and suggested that monitoring and control of predicted high-risk areas should be prioritized.

Improved cellular immune response induced by intranasal boost immunization with chitosan coated DNA vaccine against H9N2 influenza virus challenge

The H9N2 avian influenza virus (AIV) is spreading worldwide. Presence of H9N2 virus tends to increase the chances of infection with other pathogens which can lead to more serious economic losses. In a previous study, a regulated delayed lysis Salmonella vector was used to deliver a DNA vaccine named pYL233 encoding M1 protein, mosaic HA protein and chicken GM-CSF adjuvant. To further increase its efficiency, chitosan as a natural adjuvant was applied in this study. The purified plasmid pYL233 was coated with chitosan to form a DNA containing nanoparticles (named CS233) by ionic gel method and immunized by intranasal boost immunization in birds primed by oral administration with Salmonella strain. The CS233 DNA nanoparticle has a particle size of about 150 nm, with an encapsulation efficiency of 93.2 ± 0.12 % which protected the DNA plasmid from DNase I digestion and could be stable for a period of time at 37°. After intranasal boost immunization, the CS233 immunized chickens elicited higher antibody response, elevated CD4+ T cells and CD8+ T cells activation and increased T-lymphocyte proliferation, as well as increased productions of IL-4 and IFN-γ. After challenge, chickens immunized with CS233 resulted in the lowest levels of pulmonary virus titer and viral shedding as compared to the other challenge groups. The results showed that the combination of intranasal immunization with chitosan-coated DNA vaccine and oral immunization with regulatory delayed lytic Salmonella strain could enhance the immune response and able to provide protection against H9N2 challenge.

Multiple pathways to evaluate the immunoprotective effect of Turkeys Herpesvirus recombinant vaccine expressing HA of H9N2

H9N2 avian influenza virus is a significant poultry pathogen that provides internal genes for multiple zoonotic subtypes of avian influenza, presenting a severe threat to public health. The isolation rate of H9N2 in poultry has increased annually in recent years. In this study, a recombinant Herpesvirus of Turkeys (HVT) vaccine expressing H9-HA was constructed using Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) technology. In the construction of HVT-EGFP-HA recombinant virus, nonhomologous end joining (NHEJ) is a much more efficient strategy compare to Homology-directed recombination (HDR). HVT-HA demonstrated stability and consistent replication with the parent strain. Subcutaneous injection and in-ovo injection of HVT-HA induced different levels of immune response. Compared to in-ovo injection of HVT-HA, subcutaneous injection induced significantly higher neutralizing serum antibodies. This finding is supported by the significantly higher CD4+ T cell response in Peripheral blood mononuclear cell Peripheral blood mononuclear cell (PBMC) in the subcutaneous injection group. However, in-ovo injection of HVT-HA resulted in significantly higher neutralizing antibodies in the Harderian glands. In addition, it significantly inhibited viral shedding after intranasal exposure to H9N2. This phenomenon could be attributed to the mucosal immunity present in the Hadrian gland. Thus, our findings indicate that the in-ovo injection of the HVT-HA recombinant vaccine is a promising method to inhibit the transmission of H9N2 via the upper respiratory tract in chickens.

Analyzing Molecular Traits of H9N2 Avian Influenza Virus Isolated from a Same Poultry Farm in West Java Province, Indonesia, in 2017 and 2023

Background

Indonesia is one of the countries that is endemic to avian influenza virus subtype H9N2. This study aims to compare the molecular characteristics of avian influenza virus (AIV) subtype H9N2 from West Java.

Methods

Specific pathogen-free (SPF) embryonated chicken eggs were used to inoculate samples. RNA extraction and RT-qPCR confirmed the presence of H9 and N2 genes in the samples. RT-PCR was employed to amplify the H9N2-positive sample. Nucleotide sequences were obtained through Sanger sequencing and analyzed using MEGA 7. Homology comparison and phylogenetic tree analysis, utilizing the neighbor-joining tree method, assessed the recent isolate's similarity to reference isolates from GenBank. Molecular docking analysis was performed on the HA1 protein of the recent isolate and the A/Layer/Indonesia/WestJava-04/2017 isolate, comparing their interactions with the sialic acids Neu5Ac2-3Gal and Neu5Ac2-6Gal.

Results

RT-qPCR confirmed the isolate samples as AIV subtype H9N2. The recent virus exhibited 11 amino acid residue differences compared to the A/Layer/Indonesia/WestJava-04/2017 isolate. Phylogenetically, the recent virus remains within the h9.4.2.5 subclade. Notably, at antigenic site II, the recent isolate featured an amino acid N at position 183, unlike A/Layer/Indonesia/WestJava-04/2017. Molecular docking analysis revealed a preference of HA1 from the 2017 virus for Neu5Ac2-3Gal, while the 2023 virus displayed a tendency to predominantly bind with Neu5Ac2-6Gal.

Conclusion

In summary, the recent isolate displayed multiple mutations and a strong affinity for Neu5Ac2-6Gal, commonly found in mammals.

Continued evolution of H10N3 influenza virus with adaptive mutations poses an increased threat to mammals

The H10 subtype avian influenza virus (AIV) poses an ongoing threat to both birds and humans. Notably, fatal human cases of H10N3 and H10N8 infections have drawn public attention. In 2022, we isolated two H10N3 viruses (A/chicken/Shandong/0101/2022 and A/chicken/Shandong/0603/2022) from diseased chickens in China. Genome analysis revealed that these viruses were genetically associated with human-origin H10N3 virus, with internal genes originating from local H9N2 viruses. Compared to the H10N8 virus (A/chicken/Jiangxi/102/2013), the H10N3 viruses exhibited enhanced thermostability, increased viral release from erythrocytes, and accumulation of hemagglutinin (HA) protein. Additionally, we evaluated the pathogenicity of both H10N3 and H10N8 viruses in mice. We found that viral titers could be detected in the lungs and nasal turbinates of mice infected with the two H10N3 viruses, whereas H10N8 virus titers were detectable in the lungs and brains of mice. Notably, the proportion of double HA Q222R and G228S mutations in H10N3 viruses has increased since 2019. However, the functional roles of the Q222R and G228S double mutations in the HA gene of H10N3 viruses remain unknown and warrant further investigation. Our study highlights the potential public health risk posed by the H10N3 virus. A spillover event of AIV to humans could be a foretaste of a looming pandemic. Therefore, it is imperative to continuously monitor the evolution of the H10N3 influenza virus to ensure targeted prevention and control measures against influenza outbreaks.

Effectively Evaluating a Novel Consensus Subunit Vaccine Candidate to Prevent the H9N2 Avian Influenza Virus

The enormous effects of avian influenza on poultry production and the possible health risks to humans have drawn much attention to this disease. The H9N2 subtype of avian influenza virus is widely prevalent among poultry, posing a direct threat to humans through infection or by contributing internal genes to various zoonotic strains of avian influenza. Despite the widespread use of H9N2 subtype vaccines, outbreaks of the virus persist due to the rapid antigenic drift and shifts in the influenza virus. As a result, it is critical to develop a broader spectrum of H9N2 subtype avian influenza vaccines and evaluate their effectiveness. In this study, a recombinant baculovirus expressing the broad-spectrum HA protein was obtained via bioinformatics analysis and a baculovirus expression system (BES). This recombinant hemagglutinin (HA) protein displayed cross-reactivity to positive sera against several subbranch H9 subtype AIVs. An adjuvant and purified HA protein were then used to create an rHA vaccine candidate. Evaluation of the vaccine demonstrated that subcutaneous immunization of the neck with the rHA vaccine candidate stimulated a robust immune response, providing complete clinical protection against various H9N2 virus challenges. Additionally, virus shedding was more effectively inhibited by rHA than by the commercial vaccine. Thus, our findings illustrate the efficacy of the rHA vaccine candidate in shielding chickens against the H9N2 virus challenge, underscoring its potential as an alternative to conventional vaccines.

Diversity of genotypes and pathogenicity of H9N2 avian influenza virus derived from wild bird and domestic poultry

Introduction

The H9N2 subtype is a predominant avian influenza virus (AIV) circulating in Chinese poultry, forming various genotypes (A-W) based on gene segment origins. This study aims to investigate the genotypic distribution and pathogenic characteristics of H9N2 isolates from wild birds and domestic poultry in Yunnan Province, China.

Methods

Eleven H9N2 strains were isolated from fecal samples of overwintering wild birds and proximate domestic poultry in Yunnan, including four from common cranes (Grus grus), two from bar-headed geese (Anser indicus), and five from domestic poultry (Gallus gallus). Phylogenetic analysis was conducted to determine the genotypes, and representative strains were inoculated into Yunnan mallard ducks to assess pathogenicity.

Results

Phylogenetic analysis revealed that five isolates from domestic birds and one from a bar-headed goose belong to genotype S, while the remaining five isolates from wild birds belong to genotype A. These bird-derived strains possess deletions in the stalk domain of NA protein and the N166D mutation of HA protein, typical of poultry strains. Genotype S H9N2 demonstrated oropharyngeal shedding, while genotype A H9N2 exhibited cloacal shedding and high viral loads in the duodenum. Both strains caused significant pathological injuries, with genotype S inducing more severe damage to the thymus and spleen, while genotype A caused duodenal muscle layer rupture.

Discussion

These findings suggest that at least two genotypes of H9N2 are currently circulating in Yunnan, and Yunnan mallard ducks potentially act as intermediaries in interspecies transmission. These insights highlight the importance of analyzing the current epidemiological transmission characteristics of H9N2 among wild and domestic birds in China.

Immunogenicity and protective efficacy of a multivalent herpesvirus vectored vaccine against H9N2 low pathogenic avian influenza in chicken

The application of recombinant herpesvirus of turkey, expressing the H9 hemagglutinin gene from low pathogenic avian influenza virus (LPAIV) H9N2 and the avian orthoavulavirus-1 (AOAV-1) (commonly known as Newcastle Disease virus (NDV)) fusion protein (F) as an rHVT-H9-F vaccine, is an alternative to currently used classical vaccines. This study investigated H9- and ND-specific humoral and mucosal responses, H9-specific cell-mediated immunity, and protection conferred by the rHVT-H9-F vaccine in specific pathogen-free (SPF) chickens. Vaccination elicited systemic NDV F- and AIV H9-specific antibody response but also local antibodies in eye wash fluid and oropharyngeal swabs. The ex vivo H9-specific stimulation of splenic and pulmonary T cells in the vaccinated group demonstrated the ability of vaccination to induce systemic and local cellular responses. The clinical protection against a challenge using a LPAIV H9N2 strain of the G1 lineage isolated in Morocco in 2016 was associated with a shorter duration of shedding along with reduced viral genome load in the upper respiratory tract and reduced cloacal shedding compared to unvaccinated controls.

Modelling the transmission dynamics of H9N2 avian influenza viruses in a live bird market

H9N2 avian influenza viruses (AIVs) are a major concern for the poultry sector and human health in countries where this subtype is endemic. By fitting a model simulating H9N2 AIV transmission to data from a field experiment, we characterise the epidemiology of the virus in a live bird market in Bangladesh. Many supplied birds arrive already exposed to H9N2 AIVs, resulting in many broiler chickens entering the market as infected, and many indigenous backyard chickens entering with pre-existing immunity. Most susceptible chickens become infected within one day spent at the market, owing to high levels of viral transmission within market and short latent periods, as brief as 5.3 hours. Although H9N2 AIV transmission can be substantially reduced under moderate levels of cleaning and disinfection, effective risk mitigation also requires a range of additional interventions targeting markets and other nodes along the poultry production and distribution network.

Low-Temperature Adaptive Single-Atom Iron Nanozymes against Viruses in the Cold Chain

Outbreaks of viral infectious diseases, such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza A virus (IAV), pose a great threat to human health. Viral spread is accelerated worldwide by the development of cold chain logistics; Therefore, an effective antiviral approach is required. In this study, it is aimed to develop a distinct antiviral strategy using nanozymes with low-temperature adaptability, suitable for cold chain logistics. Phosphorus (P) atoms are added to the remote counter position of Fe-N-C center to prepare FeN4P2-single-atom nanozymes (SAzymes), exhibiting lipid oxidase (OXD)-like activity at cold chain temperatures (-20, and 4 °C). This feature enables FeN4P2-SAzymes to disrupt multiple enveloped viruses (human, swine, and avian coronaviruses, and H1-H11 subtypes of IAV) by catalyzing lipid peroxidation of the viral lipid envelope. Under the simulated conditions of cold chain logistics, FeN4P2-SAzymes are successfully applied as antiviral coatings on outer packaging and personal protective equipment; Therefore, FeN4P2-SAzymes with low-temperature adaptability and broad-spectrum antiviral properties may serve as key materials for developing specific antiviral approaches to interrupt viral transmission through the cold chain.

Protection of Chickens against H9N2 Avian Influenza Isolates with a Live Vector Vaccine Expressing Influenza Hemagglutinin Gene Derived from Y280 Avian Influenza Virus

Since the outbreak of the H9N2/Y439 avian influenza virus in 1996, the Korean poultry industry has incurred severe economic losses. A novel possibly zoonotic H9N2 virus from the Y280-like lineage (H9N2/Y280) has been prevalent in Korea since June 2020, posing a threat to the poultry sector. Rapid mutation of influenza viruses urges the development of effective vaccines against newly generated strains. Thus, we engineered a recombinant virus rHVT/Y280 to combat H9N2/Y280. We integrated the hemagglutinin (HA) gene of the H9N2/Y280 strain into the US2 region of the herpesvirus of turkeys (HVT) Fc126 vaccine strain, utilizing CRISPR/Cas9 gene-editing technology. The successful construction of rHVT/Y280 was confirmed by polymerase chain reaction and sequencing, followed by efficacy evaluation. Four-day-old specific pathogen-free chickens received the rHVT/Y280 vaccine and were challenged with the H9N2/Y280 strain A21-MRA-003 at 3 weeks post-vaccination. In 5 days, there were no gross lesions among the vaccinated chickens. The rHVT/Y280 vaccine induced strong humoral immunity and markedly reduced virus shedding, achieving 100% inhibition of virus recovery in the cecal tonsil and significantly lowering tissue viral load. Thus, HVT vector vaccines expressing HA can be used for protecting poultry against H9N2/Y280. The induction of humoral immunity by live vaccines is vital in such cases. In summary, the recombinant virus rHVT/Y280 is a promising vaccine candidate for the protection of chickens against the H9N2/Y280.

Efficacy of an inactivated influenza vaccine adjuvanted with Toll-like receptor ligands against transmission of H9N2 avian influenza virus in chickens

Avian influenza viruses (AIV), including the H9N2 subtype, pose a major threat to the poultry industry as well as to human health. Although vaccination provides a protective control measure, its effect on transmission remains uncertain in chickens. The objective of the present study was to investigate the efficacy of beta-propiolactone (BPL) whole inactivated H9N2 virus (WIV) vaccine either alone or in combination with CpG ODN 2007 (CpG), poly(I:C) or AddaVax™ (ADD) to prevent H9N2 AIV transmission in chickens. The seeder chickens (trial 1) and recipient chickens (trial 2) were vaccinated twice with different vaccine formulations. Ten days after secondary vaccination, seeder chickens were infected with H9N2 AIV (trial 1) and co-housed with healthy recipient chickens. In trial 2, the recipient chickens were vaccinated and then exposed to H9N2 AIV-infected seeder chickens. Our results demonstrated that BPL+ CpG and BPL+ poly(I:C) treated chickens exhibited reduced oral and cloacal shedding in both trials post-exposure (PE). The number of H9N2 AIV+ recipient chickens in the BPL+ CpG group (trial 1) was lower than in other vaccinated groups, and the reduction was higher in BPL+ CpG recipient chickens in trial 2. BPL+ CpG vaccinated chickens demonstrated enhanced systemic antibody responses with high IgM and IgY titers with higher rates of seroprotection by day 21 post-primary vaccination (ppv). Additionally, the induction of IFN-γ expression and production was higher in the BPL+ CpG treated chickens. Interleukin (IL)- 2 expression was upregulated in both BPL+ CpG and BPL+ poly(I:C) groups at 12 and 24 hr post-stimulation.

The Chinese Hamster Ovary Cell-Based H9 HA Subunit Avian Influenza Vaccine Provides Complete Protection against the H9N2 Virus Challenge in Chickens

(1) Background: Avian influenza has attracted widespread attention because of its severe effect on the poultry industry and potential threat to human health. The H9N2 subtype of avian influenza viruses was the most prevalent in chickens, and there are several commercial vaccines available for the prevention of the H9N2 subtype of avian influenza viruses. However, due to the prompt antigenic drift and antigenic shift of influenza viruses, outbreaks of H9N2 viruses still continuously occur, so surveillance and vaccine updates for H9N2 subtype avian influenza viruses are particularly important. (2) Methods: In this study, we constructed a stable Chinese hamster ovary cell line (CHO) to express the H9 hemagglutinin (HA) protein of the major prevalent H9N2 strain A/chicken/Daye/DY0602/2017 with genetic engineering technology, and then a subunit H9 avian influenza vaccine was prepared using the purified HA protein with a water-in-oil adjuvant. (3) Results: The results showed that the HI antibodies significantly increased after vaccination with the H9 subunit vaccine in specific-pathogen-free (SPF) chickens with a dose-dependent potency of the immunized HA protein, and the 50 μg or more per dose HA protein could provide complete protection against the H9N2 virus challenge. (4) Conclusions: These results indicate that the CHO expression system could be a platform used to develop the subunit vaccine against H9 influenza viruses in chickens.

Hemagglutinin affects replication, stability and airborne transmission of the H9N2 subtype avian influenza virus

H9N2 subtype avian influenza virus (AIV) can transmit by direct as well as airborne contacts. It has been widespread in poultry and continued to contribute to zoonotic spillover events by providing its six internal genes for the reassortment of novel influenza viruses (eg, H7N9) that infect poultry and humans. Compared to H7N9, H9N2 virus displays an efficient airborne transmissibility in poultry, but the mechanisms of transmission difference have been insufficiently studied. The Hemagglutinin (HA) and viral polymerase acidic protein (PA) have been implicated in the airborne transmission of influenza A viruses. Accordingly, we generated the reassortant viruses of circulating airborne transmissible H9N2 and non-airborne transmissible H7N9 viruses carrying HA and/or PA gene. The introduction of the PA gene from H7N9 into the genome of H9N2 virus resulted in a reduction in airborne transmission among chickens, while the isolated introduction of the HA gene segment completely eliminated airborne transmission among chickens. We further showed that introduction of HA gene of non-transmissible H7N9 did not influence the HA/NA balance of H9N2 virus, but increased the threshold for membrane fusion and decreased the acid stability. Thus, our results indicate that HA protein plays a key role in replication, stability, and airborne transmission of the H9N2 subtype AIV.

Reported human infections of H9N2 avian influenza virus in China in 2021

Introduction

The continued emergence of human infections of H9N2 avian influenza virus (AIV) poses a serious threat to public health. The prevalent Y280/G9 lineage of H9N2 AIV in Chinese poultry can directly bind to human receptors, increasing the risk of spillover infections to humans. Since 2013, the number of human cases of H9N2 avian influenza has been increasing continuously, and in 2021, China reported the highest number of human cases, at 25.

Methods

In this study, we analyzed the age, geographic, temporal, and sex distributions of humans with H9N2 avian influenza in 2021 using data from the National Influenza Center (Beijing, China). We also conducted evolutionary, gene homology, and molecular characterization analyses of the H9N2 AIVs infecting humans.

Results

Our findings show that children under the age of 12 accounted for 80% of human cases in 2021, and females were more frequently affected than males. More cases occurred in winter than in summer, and most cases were concentrated in southern China. Human-infecting H9N2 viruses showed a high level of genetic homology and belonged to the prevalent G57 genotype. Several additional α2,6-SA-binding sites and sites of mammalian adaptation were also identified in the genomes of human-infecting H9N2 viruses.

Discussion

Therefore, continuous monitoring of H9N2 AIV and the implementation of further measures to control the H9N2 virus in poultry are essential to reduce the interspecies transmission of the virus.

The emergence of new antigen branches of H9N2 avian influenza virus in China due to antigenic drift on hemagglutinin through antibody escape at immunodominant sites

Vaccination is a crucial prevention and control measure against H9N2 avian influenza viruses (AIVs) that threaten poultry production and public health. However, H9N2 AIVs in China undergo continuous antigenic drift of hemagglutinin (HA) under antibody pressure, leading to the emergence of immune escape variants. In this study, we investigated the molecular basis of the current widespread antigenic drift of H9N2 AIVs. Specifically, the most prevalent h9.4.2.5-lineage in China was divided into two antigenic branches based on monoclonal antibody (mAb) hemagglutination inhibition (HI) profiling analysis, and 12 antibody escape residues were identified as molecular markers of these two branches. The 12 escape residues were mapped to antigenic sites A, B, and E (H3 was used as the reference). Among these, eight residues primarily increased 3`SLN preference and contributed to antigenicity drift, and four of the eight residues at sites A and B were positively selected. Moreover, the analysis of H9N2 strains over time and space has revealed the emergence of a new antigenic branch in China since 2015, which has replaced the previous branch. However, the old antigenic branch recirculated to several regions after 2018. Collectively, this study provides a theoretical basis for understanding the molecular mechanisms of antigenic drift and for developing vaccine candidates that contest with the current antigenicity of H9N2 AIVs.

Construction and Immunogenicity Evaluation of Recombinant Bacillus subtilis Expressing HA1 Protein of H9N2 Avian Influenza Virus

The H9N2 subtype of the avian influenza virus (AIV) is one of the main subtypes of low pathogenic AIV, and it seriously affects the poultry breeding industry. Currently, vaccination is still one of China's main strategies for controlling H9N2 avian influenza. In this study, we selected MW548848.1 on the current popular main branch h9.4.2.5 as the reference strain, and we optimized the amino acid sequence of HA1 to make it suitable for expression in Bacillus subtilis. The B. subtilis expression vector showed good safety and stress resistance; therefore, this study constructed a recombinant B. subtilis expressing H9N2 HA1 protein and evaluated its immunogenicity in mice. The following results were obtained: the sIgA level of HA1 protein in small intestine fluid and the IgG level of PHT43-HA1/B. subtilis in serum were significantly improved (P < 0.01); PHT43-HA1/B. subtilis can cause a special immune response in mice; and cytokine detection interferon-gamma (IFN-γ) (P < 0.05) and Interleukin 2 (IL-2) (P < 0.01) expressions significantly increased. Additionally, the study found that PHT43-HA1/B. subtilis can alleviate the attack of H9N2 AIV in the spleen, lungs, and small intestine of mice. This study was the first to use an oral recombinant B. subtilis-HA1 vaccine candidate, and it provides theoretical data and technical reference for the creation of a new live vector vaccine against H9N2 AIV.

Virulence and transmission characteristics of clade 2.3.4.4b H5N6 subtype avian influenza viruses possessing different internal gene constellations

Clade 2.3.4.4 H5N6 avian influenza virus (AIV) has been predominant in poultry in China, and the circulating haemagglutinin (HA) gene has changed from clade 2.3.4.4h to clade 2.3.4.4b in recent years. In 2021, we isolated four H5N6 viruses from ducks during the routine surveillance of AIV in China. The whole-genome sequencing results demonstrated that the four isolates all belonged to the currently prevalent clade 2.3.4.4b but had different internal gene constellations, which could be divided into G1 and G2 genotypes. Specifically, G1 possessed H9-like PB2 and PB1 genes on the H5-like genetic backbone while G2 owned an H3-like PB1 gene and the H5-like remaining internal genes. By determining the characteristics of H5N6 viruses, including growth performance on different cells, plaque-formation ability, virus attachment ability, and pathogenicity and transmission in different animal models, we found that G1 strains were more conducive to replication in mammalian cells (MDCK and A549) and BALB/c mice than G2 strains. However, G2 strains were more advantageously replicated in avian cells (CEF and DF-1) and slightly more transmissible in waterfowls (mallards) than G1 strains. This study enriched the epidemiological data of H5 subtype AIV to further understand its dynamic evolution, and laid the foundation for further research on the mechanism of low pathogenic AIV internal genes in generating novel H5 subtype reassortants.

Emergence of a new designated clade 16 with significant antigenic drift in hemagglutinin gene of H9N2 subtype avian influenza virus in eastern China

H9N2 avian influenza viruses (AIVs) pose an increasing threat to the poultry industry worldwide and have pandemic potential. Vaccination has been principal prevention strategy to control H9N2 in China since 1998, but vaccine effectiveness is persistently challenged by the emergence of the genetic and/or antigenic variants. Here, we analysed the genetic and antigenic characteristics of H9N2 viruses in China, including 70 HA sequences of H9N2 isolates from poultry, 7358 from online databases during 2010-2020, and 15 from the early reference strains. Bayesian analyses based on hemagglutinin (HA) gene revealed that a new designated clade16 emerged in April 2012, and was prevalent and co-circulated with clade 15 since 2013 in China. Clade 16 viruses exhibited decreased cross-reactivity with those from clade 15. Antigenic Cartography analyses showed represent strains were classified into three antigenic groups named as Group1, Group2 and Group3, and most of the strains in Group 3 (15/17, 88.2%) were from Clade 16 while most of the strains in Group2 (26/29, 89.7%) were from Clade 15. The mean distance between Group 3 and Group 2 was 4.079 (95%CI 3.605-4.554), revealing that major switches to antigenic properties were observed over the emergence of clade 16. Genetic analysis indicated that 11 coevolving amino acid substitutions primarily at antigenic sites were associated with the antigenic differences between clade 15 and clade 16. These data highlight complexities of the genetic evolution and provide a framework for the genetic basis and antigenic characterization of emerging clade 16 of H9N2 subtype avian influenza virus.

Evaluation of the Virulence of Low Pathogenic H9N2 Avian Influenza Virus Strains in Broiler Chickens

Our study aimed to investigate the virulence of three recent H9N2 LPAIV strains belonging to the G1 lineage, isolated from field infections in North Africa and the Middle East. Three-week-old commercial broiler chickens (in total 62) were included and randomly allocated into three infected test groups and one control group. Each test group was inoculated intranasally/intratracheally with one of the three H9N2 isolates at a dose of 108 EID50 virus. The control group received phosphate-buffered saline (PBS) via the same route of application. The pathogenicity was evaluated based on clinical signs and gross pathological and histopathological lesions, the viral antigen load was assessed through immunohistochemistry staining (IHC), and a semi-quantitative detection of the genetic material was conducted via a real-time PCR. Our findings confirmed the obvious respiratory tract tropism of the virus strains with variable renal tropism. In contrast to the highly pathogenic AIVs, the tested H9N2 strains did not show replication in the central nervous system. The virus presence and lesions, mainly in the respiratory tract, were predominant on dpi 5 and significantly reduced or disappeared by dpi 11. A clear difference was demonstrated among the three isolates: the A/chicken/Morocco/2021/2016 strain proved to be significantly more virulent than the Egyptian and Saudi Arabian ones, which showed no remarkable difference.

Base composition, adaptation, and evolution of goose astroviruses: codon-based investigation

Goose astroviruses (GoAstVs) are causative agents that account for fatal infection of goslings characterized by visceral urate deposition, resulting in severe economic losses in major goose-producing regions in China since 2017. In this study, we sought to unravel the intrinsic properties associated with adaptation and evolution in the host environment of GoAstVs. Consistent results from phylogenetic analysis and correspondence analysis performed on the codon usage patterns (CUPs) reveal 2 clusters of GoAstVs, namely, GoAstV-1 and GoAstV-2. However, multiple similar compositional characteristics were found, despite the high divergence between GoAstV-1 and GoAstV-2. Studies on the base composition of GoAstVs reveal an A/U bias, indicating a compositional constraint, while natural selection prevailed in determining the CUPs in the virus genome based on our neutrality plot analysis, reflecting high adaptive pressure to fit the host environment. Codon adaptation index (CAI) analysis revealed a higher degree of fitness to the CUPs of the corresponding host for GoAstVs than avian influenza virus and betacoronaviruses, which may be a favorable factor contributing to the high pathogenicity and wide distribution of GoAstVs in goslings. In addition, GoAstVs were less adapted to ducks and chickens, with significantly lower CAI values than to geese, which may be a reason for the different prevalence of GoAstVs among these species. Extensive investigations on dinucleotide distribution revealed a significant suppression of the CpG and UpA motifs in the virus genome, which may facilitate adaptation to the host's innate immune system by evading surveillance. In addition, our study reported the trends of increasing fitness to the host's microenvironment for GoAstVs through increasing adaptation to host CUPs and ongoing reduction of CpG motifs in the virus genome. The present analysis deepens our understanding of the basic biology, pathogenesis, adaptation and evolutionary pattern of GoAstVs, and contributes to the development of novel antiviral strategies.

Alteration of the Chicken Upper Respiratory Microbiota, Following H9N2 Avian Influenza Virus Infection

Several studies have highlighted the importance of the gut microbiota in developing immunity against viral infections in chickens. We have previously shown that H9N2 avian influenza A virus (AIV) infection retards the diversity of the natural colon-associated microbiota, which may further influence chicken health following recovery from infection. The effects of influenza infection on the upper respiratory tract (URT) microbiota are largely unknown. Here, we showed that H9N2 AIV infection lowers alpha diversity indices in the acute phase of infection in the URT, largely due to the family Lactobacillaceae being highly enriched during this time in the respiratory microbiota. Interestingly, microbiota diversity did not return to levels similar to control chickens in the recovery phase after viral shedding had ceased. Beta diversity followed a similar trend following the challenge. Lactobacillus associate statistically with the disturbed microbiota of infected chickens at the acute and recovery phases of infection. Additionally, we studied age-related changes in the respiratory microbiota during maturation in chickens. From 7 to 28 days of age, species richness and evenness were observed to advance over time as the microbial composition evolved. Maintaining microbiota homeostasis might be considered as a potential therapeutic target to prevent or aid recovery from H9N2 AIV infection.

Loss of amino acids 67-76 in the neuraminidase protein under antibody selection pressure alters the tropism, transmissibility and innate immune response of H9N2 avian influenza virus in chickens

H9N2 virus has become the most widespread subtype of avian influenza in Chinese poultry. Although many studies have been published on this disease, the pathogenesis of the H9N2 virus remains to be fully understood. In our previous work, we identified 44 viral strains with 67-76 amino acid deletions in the neuraminidase protein (NA∆67-76) from trachea and lung tissues after 20 successive generations in vaccinated chickens. Interestingly, these 10 amino acid deletions are located in the stalk of the NA protein, and all mutations were unique to the viruses under the selection pressure of vaccine antibodies. To investigate the effect of NA∆67-76 on the H9N2 virus, the NA∆67-76 deletion mutant (rF/NAΔ67-76) was constructed in the H9N2 virus A/Chicken/Shanghai/F/98 (F/98) to assess the phenotypic changes between the parental and mutant strains. The results showed that the recombinant virus rF/NAΔ67-76 had no significantly effect on the antigenicity of the virus or on the infectivity of the host cells, but it significantly inhibited the release of virions from host cells. In addition, rF/NAΔ67-76 efficiently enhanced the neuraminidase activity and improved the receptor binding ability of the virus, indicating that the influence of receptor binding ability on the rF/NAΔ67-76 virus is much greater than that of neuraminidase activity. Furthermore, this study revealed that rF/NAΔ67-76 reduced the viral replication ability at 6 and 12 h post-infection, but improved it at 24, 48, and 72 h post-infection. Chicken experiments showed that rF/NAΔ67-76 exhibits a much higher tissue tropism for the trachea rather than lung tissue. rF/NAΔ67-76 still had the ability to infect the upper respiratory tract through aerosol, but its cloaca replication capacity was significantly reduced. Both in vivo and in vitro experiments confirmed that rF/NAΔ67-76 could produce a stronger innate immune response after infecting cells and chickens, especially significantly enhancing the transcription levels of TLR3, TLR4, TLR7, TLR21, MDA5, and NLRP3. Altogether, the results of this study propose that antibody selection pressure plays an important role in the evolution of H9N2 avian influenza virus.

Engineering an Optimal Y280-Lineage H9N2 Vaccine Strain by Tuning PB2 Activity

H9N2 avian influenza A viruses (AIVs) cause economic losses in the poultry industry and provide internal genomic segments for the evolution of H5N1 and H7N9 AIVs into more detrimental strains for poultry and humans. In addition to the endemic Y439/Korea-lineage H9N2 viruses, the Y280-lineage spread to Korea since 2020. Conventional recombinant H9N2 vaccine strains, which bear mammalian pathogenic internal genomes of the PR8 strain, are pathogenic in BALB/c mice. To reduce the mammalian pathogenicity of the vaccine strains, the PR8 PB2 was replaced with the non-pathogenic and highly productive PB2 of the H9N2 vaccine strain 01310CE20. However, the 01310CE20 PB2 did not coordinate well with the hemagglutinin (HA) and neuraminidase (NA) of the Korean Y280-lineage strain, resulting in a 10-fold lower virus titer compared to the PR8 PB2. To increase the virus titer, the 01310CE20 PB2 was mutated (I66M-I109V-I133V) to enhance the polymerase trimer integrity with PB1 and PA, which restored the decreased virus titer without causing mouse pathogenicity. The reverse mutation (L226Q) of HA, which was believed to decrease mammalian pathogenicity by reducing mammalian receptor affinity, was verified to increase mouse pathogenicity and change antigenicity. The monovalent Y280-lineage oil emulsion vaccine produced high antibody titers for homologous antigens but undetectable titers for heterologous (Y439/Korea-lineage) antigens. However, this defect was corrected by the bivalent vaccine. Therefore, the balance of polymerase and HA/NA activities can be achieved by fine-tuning PB2 activity, and a bivalent vaccine may be more effective in controlling concurrent H9N2 viruses with different antigenicities.

Immunoadjuvant efficacy of CpG plasmids for H9N2 avian influenza inactivated vaccine in chickens with maternal antibodies

Maternal-derived antibodies (MDAs) are one of reasons why vaccination with the H9N2 inactivated whole virus (IWV) vaccine failed in poultry. Unmethylated CpG motif-containing oligodeoxynucleotides (CpG ODN) shows great potential to overcome MDAs interference in mammals, but whether it has similar characteristics in poultry is still unknown. In the present study, different classes and various copies of CpG ODN motifs were cloned into two different plasmids (pCDNA3.1 or T vector). Immunomodulatory activities and immunoadjuvant efficacy of these CpG ODN plasmids were tested in vitro and in vivo in the presence of passively transferred antibodies (PTAs) that were used to mimic MDAs. Results showed that the T vector enriched with 30 copies of CpG-A ODN and 20 copies of CpG-B ODN (T-CpG-AB) significantly up-regulated mRNA expression of chicken-interferon-α (ch-IFN-α), chicken-interferon-β (ch-IFN-β) and chicken-interleukin-12 protein 40 (ch-IL-12p40). When administered as adjuvant of the H9N2 IWV vaccine, the minimal dose of T-CpG-AB plasmid was 30 µg per one-day-old chicken, which could induce strong humoral immune responses in the presence of PTAs. Furthermore, T-CpG-AB plasmid-based vaccine triggered both strong humoral immune responses and cytokines expression in the presence of PTAs in chickens. Overall, our findings suggest that T-CpG-AB plasmid can be an excellent adjuvant candidate for the H9N2 IWV vaccine to overcome MDAs interference in chickens.

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.

Monoclonal antibody targeting a novel linear epitope on nucleoprotein confers pan-reactivity to influenza A virus

Nucleoprotein (NP) functions crucially in the replicative cycle of influenza A virus (IAV) via forming the ribonucleoprotein complex together with PB2, PB1, and PA proteins. As its high conservation, NP ranks one of the hot targets for design of universal diagnostic reagents and antiviral drugs for IAV. Here, we report an anti-NP murine monoclonal antibody (mAb) 5F10 prepared from traditional lymphocyte hybridoma technique with the immunogen of a clade 2.3.4.4 H5N1 subtype avian influenza virus. The specificity of mAb 5F10 to NP protein was confirmed by immunofluorescence assay and western blotting, and the mAb 5F10 could be used in immunoprecipitation and immunohistochemistry assays. Importantly, mAb 5F10 possessed broad-spectrum reactivity against H1~H11 subtypes of avian influenza viruses, including various HA clades of H5Nx subtype. In addition, mAb 5F10 also showed good affinity with H1N1 and H3N2 subtype influenza viruses of swine and human origin. Furthermore, the recognized antigenic epitope of mAb 5F10 was identified to consist of the conserved amino acid motif ⁸¹EHPSA⁸⁵ in the second flexible loop region of NP protein through screening the phage display peptide library. Collectively, the mAb 5F10 which recognizes the novel universal NP linear B-cell epitope of IAV with diverse origins and subtypes will be a powerful tool for NP protein-based structural, functional, and mechanistic studies, as well as the development of detection methods and universal vaccines for IAV. KEY POINTS: • A broad-spectrum mAb against various subtypes and sources of IAV was developed • The mAb possessed good reactivity in IFA, western blot, IP, and IHC assays • The mAb targeted a novel conserved linear B-cell epitope involving ⁸¹EHPSA⁸⁵ on NP protein.

An efficient double-fluorescence approach for generating fiber-2-edited recombinant serotype 4 fowl adenovirus expressing foreign gene

Recently, the infection of serotype 4 fowl adenovirus (FAdV-4) in chicken flocks has become endemic in China, which greatly threatens the sustainable development of poultry industry. The development of recombinant FAdV-4 expressing foreign genes is an efficient strategy for controlling both FAdV-4 and other important poultry pathogens. Previous reverse genetic technique for generating the recombinant fowl adenovirus is generally inefficient. In this study, a recombinant FAdV-4 expressing enhanced green fluorescence protein (EGFP), FA4-EGFP, was used as a template virus and directly edited fiber-2 gene to develop an efficient double-fluorescence approach to generate recombinant FAdV-4 through CRISPR/Cas9 and Cre-Loxp system. Moreover, using this strategy, a recombinant virus FAdV4-HA(H9) stably expressing the HA gene of H9N2 influenza virus was generated. Chicken infection study revealed that the recombinant virus FAdV4-HA(H9) was attenuated, and could induce haemagglutination inhibition (HI) titer against H9N2 influenza virus at early time points and inhibit the viral replication in oropharynx. All these demonstrate that the novel strategy for constructing recombinant FAdV-4 expressing foreign genes developed here paves the way for rapidly developing attenuated FAdV-4-based recombinant vaccines for fighting the diseases caused by both FAdV-4 and other pathogens.

Avian Influenza Virus Tropism in Humans

An influenza pandemic happens when a novel influenza A virus is able to infect and transmit efficiently to a new, distinct host species. Although the exact timing of pandemics is uncertain, it is known that both viral and host factors play a role in their emergence. Species-specific interactions between the virus and the host cell determine the virus tropism, including binding and entering cells, replicating the viral RNA genome within the host cell nucleus, assembling, maturing and releasing the virus to neighboring cells, tissues or organs before transmitting it between individuals. The influenza A virus has a vast and antigenically varied reservoir. In wild aquatic birds, the infection is typically asymptomatic. Avian influenza virus (AIV) can cross into new species, and occasionally it can acquire the ability to transmit from human to human. A pandemic might occur if a new influenza virus acquires enough adaptive mutations to maintain transmission between people. This review highlights the key determinants AIV must achieve to initiate a human pandemic and describes how AIV mutates to establish tropism and stable human adaptation. Understanding the tropism of AIV may be crucial in preventing virus transmission in humans and may help the design of vaccines, antivirals and therapeutic agents against the virus.

Effect of Avian Influenza Virus subtype H9N2 on the expression of complement-associated genes in chicken erythrocytes

The H9N2 subtype avian influenza virus can infect both chickens and humans. Previous studies have reported a role for erythrocytes in immunity. However, the role of H9N2 against chicken erythrocytes and the presence of complement-related genes in erythrocytes has not been studied. This research investigated the effect of H9N2 on complement-associated gene expression in chicken erythrocytes. The expression of complement-associated genes (C1s, C1q, C2, C3, C3ar1, C4, C4a, C5, C5ar1, C7, CD93 and CFD) was detected by reverse transcription-polymerase chain reaction (RT-PCR). Quantitative Real-Time PCR (qRT-PCR) was used to analyse the differential expression of complement-associated genes in chicken erythrocytes at 0 h, 2 h, 6 h and 10 h after the interaction between H9N2 virus and chicken erythrocytes in vitro and 3, 7 and 14 d after H9N2 virus nasal infection of chicks. Expression levels of C1q, C4, C1s, C2, C3, C5, C7 and CD93 were significantly up-regulated at 2 h and significantly down-regulated at 10 h. Gene expression levels of C1q, C3ar1, C4a, CFD and C5ar1 were seen to be different at each time point. The expression levels of C1q, C4, C1s, C2, C3, C5, C7, CFD, C3ar1, C4a and C5ar1 were significantly up-regulated at 7 d and the gene expression of levels of C3, CD93 and C5ar1 were seen to be different at each time point. The results confirmed that all the complement-associated genes were expressed in chicken erythrocytes and showed the H9N2 virus interaction with chicken erythrocytes and subsequent regulation of chicken erythrocyte complement-associated genes expression. This study reported, for the first time, the relationship between H9N2 and complement system of chicken erythrocytes, which will provide a foundation for further research into the prevention and control of H9N2 infection.

Amino Acid Variation at Hemagglutinin Position 193 Impacts the Properties of H9N2 Avian Influenza Virus

Despite active control strategies, including the vaccination program in poultry, H9N2 avian influenza viruses possessing mutations in hemagglutinin (HA) were frequently isolated. In this study, we analyzed the substitutions at HA residue 193 (H3 numbering) of H9N2 and investigated the impact of these mutations on viral properties. Our study indicated that H9N2 circulating in the Chinese poultry have experienced frequent mutations at HA residue 193 since 2013, with viruses that carried asparagine (N) being replaced by those with alanine (A), aspartic acid (D), glutamic acid (E), glycine (G), and serine (S), etc. Our results showed the N193G mutation impeded the multiple cycles of growth of H9N2, and although most of the variant HAs retained the preference for human-like receptors as did the wild-type N193 HA, the N193E mutation altered the preference for both human and avian-like receptors. Furthermore, these mutations substantially altered the antigenicity of H9N2 as measured by both monoclonal antibodies and antisera. In vivo studies further demonstrated that these mutations showed profound impact on viral replication and transmission of H9N2 in chicken. Viruses with D, E, or S at residue 193 acquired the ability to replicate in lungs of the infected chickens, whereas virus with G193 reduced its transmissibility in infected chickens to those in direct contact. Our findings demonstrated that variations at HA residue 193 altered various properties of H9N2, highlighting the significance of the continued surveillance of HA for better understanding of the etiology and effective control of H9N2 in poultry. IMPORTANCE H9N2 are widespread and have sporadically caused clinical diseases in humans. Extensive vaccinations in poultry helped constrain H9N2; however, they might have facilitated the evolution of the virus. It is therefore of importance to monitor the variation of the circulating H9N2 and evaluate its risk to both veterinary and public health. Here, we found substitutions at position 193 of HA from H9N2 circulated since 2013 and assessed the impact of several mutations on viral properties. Our data showed these mutations resulted in substantial antigenic change. N193E altered the binding preference of HA for human-like to both avian and human-like receptors. More importantly, N193G impaired the growth of H9N2 and its transmission in chickens, whereas mutations from N to D, E, and S enhanced the viral replication in lungs of chickens. Our study enriched the knowledge about H9N2 and may help implement an effective control strategy for H9N2.

Evolutionary Origin, Genetic Recombination, and Phylogeography of Porcine Kobuvirus

The newly identified porcine Kobuvirus (PKV) has raised concerns owing to its association with diarrheal symptom in pigs worldwide. The process involving the emergence and global spread of PKV remains largely unknown. Here, the origin, genetic diversity, and geographic distribution of PKV were determined based on the available PKV sequence information. PKV might be derived from the rabbit Kobuvirus and sheep were an important intermediate host. The most recent ancestor of PKV could be traced back to 1975. Two major clades are identified, PKVa and PKVb, and recombination events increase PKV genetic diversity. Cross-species transmission of PKV might be linked to interspecies conserved amino acids at 13-17 and 25-40 residue motifs of Kobuvirus VP1 proteins. Phylogeographic analysis showed that Spain was the most likely location of PKV origin, which then spread to pig-rearing countries in Asia, Africa, and Europe. Within China, the Hubei province was identified as a primary hub of PKV, transmitting to the east, southwest, and northeast regions of the country. Taken together, our findings have important implications for understanding the evolutionary origin, genetic recombination, and geographic distribution of PKV thereby facilitating the design of preventive and containment measures to combat PKV infection.

Current situation and control strategies of H9N2 avian influenza in South Korea

The H9N2 avian influenza (AI) has become endemic in poultry in many countries since the 1990s, which has caused considerable economic losses in the poultry industry. Considering the long history of the low pathogenicity H9N2 AI in many countries, once H9N2 AI is introduced, it is more difficult to eradicate than high pathogenicity AI. Various preventive measures and strategies, including vaccination and active national surveillance, have been used to control the Y439 lineage of H9N2 AI in South Korea, but it took a long time for the H9N2 virus to disappear from the fields. By contrast, the novel Y280 lineage of H9N2 AI was introduced in June 2020 and has spread nationwide. This study reviews the history, genetic and pathogenic characteristics, and control strategies for Korean H9N2 AI. This review may provide some clues for establishing control strategies for endemic AIV and a newly introduced Y280 lineage of H9N2 AI in South Korea.

Immunogenicity of engineered probiotics expressing conserved antigens of influenza virus and FLIC flagellin against H9N2 AIVinfection in mice

Avian influenza virus (AIV)is easy to cause diseases in birds and humans.It causes great economic losses to the poultry farms and leads to public health problems. Using vaccines is the main approach to control the prevalence of AIV. In our previously published article, a recombinant Lactobacillus plantarum (L. plantarum) expressing the NP-M2 peptide ofH9N2 AIV was generated, and its protective effect was evaluated in a chicken model. In this study, the protective effect was estimated in mice model. Humoral and cellular immune response parameters were measured using flow cytometry adding to body weight loss, survival rate, virus load, and histopathological changes in the lung. The obtained results elucidated that, the recombinant L. plantarum can promote the activation of dendritic cells (DC), proliferation of T and B cells adding to eliciting protective secretory IgA (sIgA) and humeral IgG level in mice model. Accordingly, it could be used as a patent vaccine to control the AIV infection.

Genetic characterization and pathogenicity of a Eurasian avian-like H1N1 swine influenza reassortant virus

BACKGROUND

Swine influenza viruses (SIV), considered the "mixing vessels" of influenza viruses, posed a significant threat to global health systems and are dangerous pathogens. Eurasian avian-like H1N1(EA-H1N1) viruses have become predominant in swine populations in China since 2016.

METHODS

Lung tissue samples were obtained from pregnant sows with miscarriage and respiratory disease in Heilongjiang province, and pathogens were detected by Next-generation sequencing (NGS) and PCR. The nucleic acid of isolates was extracted to detect SIV by RT-PCR. Then, SIV-positive samples were inoculated into embryonated chicken eggs. After successive generations, the isolates were identified by RT-PCR, IFA, WB and TEM. The genetic evolution and pathogenicity to mice of A/swine/Heilongjiang/GN/2020 were analyzed.

RESULTS

The major pathogens were influenza virus (31%), Simbu orthobunyavirus (15%) and Jingmen tick virus (8%) by NGS, while the pathogen that can cause miscarriage and respiratory disease was influenza virus. The SIV(A/swine/Heilongjiang/GN/2020) with hemagglutination activity was isolated from lung samples and was successfully identified by RT-PCR, IFA, WB and TEM. Homology and phylogenetic analysis showed that A/swine/Heilongjiang/GN/2020 is most closely related to A/swine/Henan/SN/10/2018 and belonged to EA-H1N1. Pathogenicity in mice showed that the EA-H1N1 could cause lethal or exhibit extrapulmonary virus spread and cause severe damage to respiratory tracts effectively proliferating in lung and trachea.

CONCLUSION

A/swine/Heilongjiang/GN/2020 (EA-H1N1) virus was isolated from pregnant sows with miscarriage and respiratory disease in Heilongjiang province, China. Clinical signs associated with influenza infection were observed during 14 days with A/swine/Heilongjiang/GN/2020 infected mice. These data suggest that A/swine/Heilongjiang/GN/2020 (EA-H1N1) had high pathogenicity and could be systemic spread in mice.

Human infection of avian influenza A H3N8 virus and the viral origins: a descriptive study

BACKGROUND

The H3N8 avian influenza virus (AIV) has been circulating in wild birds, with occasional interspecies transmission to mammals. The first human infection of H3N8 subtype occurred in Henan Province, China, in April, 2022. We aimed to investigate clinical, epidemiological, and virological data related to a second case identified soon afterwards in Hunan Province, China.

METHODS

We analysed clinical, epidemiological, and virological data for a 5-year-old boy diagnosed with H3N8 AIV infection in May, 2022, during influenza-like illness surveillance in Changsha City, Hunan Province, China. H3N8 virus strains from chicken flocks from January, 2021, to April, 2022, were retrospectively investigated in China. The genomes of the viruses were sequenced for phylogenetic analysis of all the eight gene segments. We evaluated the receptor-binding properties of the H3N8 viruses by using a solid-phase binding assay. We used sequence alignment and homology-modelling methods to study the effect of specific mutations on the human receptor-binding properties. We also conducted serological surveillance to detect the H3N8 infections among poultry workers in the two provinces with H3N8 cases.

FINDINGS

The clinical symptoms of the patient were mild, including fever, sore throat, chills, and a runny nose. The patient's fever subsided on the same day of hospitalisation, and these symptoms disappeared 7 days later, presenting mild influenza symptoms, with no pneumonia. An H3N8 virus was isolated from the patient's throat swab specimen. The novel H3N8 virus causing human infection was first detected in a chicken farm in Guangdong Province in December, 2021, and subsequently emerged in several provinces. Sequence analyses revealed the novel H3N8 AIVs originated from multiple reassortment events. The haemagglutinin gene could have originated from H3Ny AIVs of duck origin. The neuraminidase gene belongs to North American lineage, and might have originated in Alaska (USA) and been transferred by migratory birds along the east Asian flyway. The six internal genes had originated from G57 genotype H9N2 AIVs that were endemic in chicken flocks. Reassortment events might have occurred in domestic ducks or chickens in the Pearl River Delta area in southern China. The novel H3N8 viruses possess the ability to bind to both avian-type and human-type sialic acid receptors, which pose a threat to human health. No poultry worker in our study was positive for antibodies against the H3N8 virus.

INTERPRETATION

The novel H3N8 virus that caused human infection had originated from chickens, a typical spillover. The virus is a triple reassortment strain with the Eurasian avian H3 gene, North American avian N8 gene, and dynamic internal genes of the H9N2 viruses. The virus already possesses binding ability to human-type receptors, though the risk of the H3N8 virus infection in humans was low, and the cases are rare and sporadic at present. Considering the pandemic potential, comprehensive surveillance of the H3N8 virus in poultry flocks and the environment is imperative, and poultry-to-human transmission should be closely monitored.

FUNDING

National Natural Science Foundation of China, National Key Research and Development Program of China, Strategic Priority Research Program of the Chinese Academy of Sciences, Hunan Provincial Innovative Construction Special Fund: Emergency response to COVID-19 outbreak, Scientific Research Fund of Hunan Provincial Health Department, and the Hunan Provincial Health Commission Foundation.

Transcriptome analysis of pre-immune state induced by interferon gamma inhibiting the replication of H9N2 avian influenza viruses in chicken embryo fibroblasts

Interferon (IFN), a critical antiviral cytokine produced by pathogens-induced cells, plays an important role in host innate immune system. In this study, to investigate the inhibition effect of IFN on avian influenza virus (AIV), Chicken Embryo Fibroblasts (CEFs) was infected by H₉N₂ AIV. The pre-immune state and transcriptome analysis have been observed and performed. The result showed chicken interferon gamma (chIFN-γ) have the most inhibitory effect on H₉N₂ virus among three types of chicken interferons (chIFNs). Inhibition of chIFN-γ on H₉N₂ virus was verified by indirect immunofluorescence, RT-qPCR and western blot. The possible signaling pathways induced by chIFN-γ with or without virus were analyzed by transcriptome. The transcriptome data were compared among H₉N₂-infected, chIFN-γ-treated, chIFN-γ + H₉N₂-treated, and Control groups. In summary, RNA-sequencing (RNA-seq) data suggested that H₉N₂ virus infection resulted in corresponding response of certain defensive, inflammatory and metabolism pathways to the virus replication in CEFs. Furthermore, while CEFs were treated with chIFN-γ, many immune-related signaling pathways in cells are affected and altered. Antiviral genes involved in these immune pathways such as interferon regulatory factors, chemokines, interferon-stimulated genes (ISGs) and transcription factors were significantly up-regulated, and showed significant antiviral responses. Compared with virus infected CEFs alone, pretreatment with IFN induced the expression of antiviral genes and activated related antiviral pathways, inhibited the viral replication as result. Our study provided functional annotations for antiviral genes and the basis for studying the mechanism of chIFN-γ mediated response against H₉N₂ AIV.

A dominant internal gene cassette of high pathogenicity avian influenza H7N9 virus raised since 2018

The zoonotic H7N9 avian influenza virus emerged with the H9N2-origin internal gene cassette. Previous studies have reported that genetic reassortments with H9N2 were common in the first five human H7N9 epidemic waves. However, our latest work found that the circulating high pathogenicity H7N9 virus has established a dominant internal gene cassette and has decreased the frequency of reassortment with H9N2 since 2018. This dominant cassette of H7N9 was distinct from the cocirculating H9N2, although they shared a common ancestor. As a result, we suppose that this dominant cassette may benefit the viral population fitness and promote its continuous circulation in chickens.

Rapid emergence of a PB2 D701N substitution during adaptation of an H9N2 avian influenza virus in mice

H9N2 avian influenza viruses (AIVs) have been isolated frequently from multiple avian species and, occasionally, from humans. To explore the potential molecular basis of cross-species transmission of H9N2 AIVs, an H9N2 AIV (A/chicken/Zhejiang/221/2016) was serially passaged in mouse lung. The results showed that the mouse-adapted H9N2 virus exhibited higher virulence and replicated more efficiently in mouse lung and liver. Whole-genome sequencing showed an amino acid substitution, D701N, in the PB2 protein, which is likely associated with the increased replicative ability of H9N2 virus in mice. The rapid emergence of adaptive substitutions indicates the necessity of continuous monitoring of H9N2 virus in poultry.

Proteomic Analysis Reveals Zinc-finger CCHC-type Containing Protein 3 as a Factor Inhibiting Virus Infection by Promoting Innate Signaling

Influenza a virus exploits host machinery to benefit its replication in host cells. Knowledge of host factors reveals the complicated interaction and provides potential targets for antiviral treatment. Here, instead of the traditional proteomic analysis, we employed a 4D label free proteomic method to identify cellular factors in A549 cells treated with avian H9N2 virus. We observed that 425 proteins were upregulated and 502 proteins were downregulated. Western blotting and quantitative real-time PCR results showed that the zinc-finger CCHC-type containing protein 3 (ZCCHC3) levels were markedly induced by H9N2 infection. Transient expression assay showed that ZCCHC3 expression decreased NP protein levels and viral titers, whereas knockdown of ZCCHC3 enhanced viral growth. Specifically, ZCCHC3 promoted the expression of IFN-β, leading to the increased transcription of IFN downstream antiviral factors. Surprisingly, viral NS1 protein was able to antagonize the antiviral effect of ZCCHC3 by downregulating IFN-β. Eventually, we observed that chicken finger CCCH-type containing protein 3, named ZC3H3, could also suppress the replication of H9N2 virus and the coronavirus-infectious bronchitis virus (IBV) in DF-1 cells. Together, our results showed the cellular proteomic response to H9N2 infection and identified ZCCHC3 as a novel antiviral factor against H9N2 infection, contributing to the understanding of host-virus interaction.

Hemagglutinin Subtype Specificity and Mechanisms of Highly Pathogenic Avian Influenza Virus Genesis

Highly Pathogenic Avian Influenza Viruses (HPAIVs) arise from low pathogenic precursors following spillover from wild waterfowl into poultry populations. The main virulence determinant of HPAIVs is the presence of a multi-basic cleavage site (MBCS) in the hemagglutinin (HA) glycoprotein. The MBCS allows for HA cleavage and, consequently, activation by ubiquitous proteases, which results in systemic dissemination in terrestrial poultry. Since 1959, 51 independent MBCS acquisition events have been documented, virtually all in HA from the H5 and H7 subtypes. In the present article, data from natural LPAIV to HPAIV conversions and experimental in vitro and in vivo studies were reviewed in order to compile recent advances in understanding HA cleavage efficiency, protease usage, and MBCS acquisition mechanisms. Finally, recent hypotheses that might explain the unique predisposition of the H5 and H7 HA sequences to obtain an MBCS in nature are discussed.

Glycine Nano-Selenium Enhances Immunoglobulin and Cytokine Production in Mice Immunized with H9N2 Avian Influenza Virus Vaccine

This study was performed to investigate the immune enhancement effect of glycine nano-selenium, a microelement on H9N2 avian influenza virus vaccine (H9N2 AIV vaccine) in mice. Fifty (50) Specific Pathogen Free Kunming mice aged 4−6 weeks (18−20 g Body weight) were randomly divided into five groups: control normal group, which received no immunization + 0.5 mL 0.9% normal saline, positive control group, which received H9N2 AIV vaccine + 0.5 mL 0.9% normal saline, 0.25 mg/kg selenium group, which received H9N2 AIV vaccine + 0.5 mL 0.25 mg/kg selenium solution, 0.5 mg/kg selenium group, which received H9N2 AIV vaccine + 0.5 mL 0.5 mg/kg selenium solution, and 1 mg/kg selenium group, which received H9N2 AIV vaccine + 0.5 mL 1 mg/kg selenium solution. Hematoxylin and eosin staining, enzyme linked immunosorbent assay (ELISA), and quantitative real time polymerase chain reaction (qRT-PCR) methods were used to investigate the pathological changes, immunoglobulin levels, and cytokine gene expressions in this study. The results showed that all tested doses (0.25 mg/kg, 0.5 mg/kg and 1.00 mg/kg) of glycine nano-selenium did not lead to poisoning in mice. In addition, when compared to the positive control group, glycine nano-selenium increased the immunoglobin indexes (IgA, IgG, IgM and AIV-H9 IgG in serum) as well as the mRNA levels of IL-1β, IL-6 and INF-γ in the liver, lungs, and spleen (p < 0.05). In summary, glycine nano-selenium could enhance the efficacy of avian influenza vaccine.

Efficacy of recombinant Newcastle disease virus expressing HA protein of H9N2 Avian influenza virus in respiratory and intestinal tract

H9N2 subtype avian influenza virus (AIV) is a low pathogenic AIV, which is widely prevalent all over the world. The infection of H9N2 AIV often leads to secondary infection with other pathogens, causing serious economic losses to poultry industry. Up to now, several recombinant Newcastle disease viruses (NDV) expressing H9N2 AIV hemagglutinin (HA) protein had been developed. However, the efficacy of recombinant virus on tracheal and intestinal injury caused by H9N2 AIV was rarely reported. The aim of this study was to evaluate the efficacy of recombinant NDV expressing H9N2 AIV HA protein in respiratory and intestinal tract. In this study, based on Red/ET homologous recombination technology, H9N2 AIV HA gene was embedded into the genome of NDV LaSota vaccine strain to obtain the recombinant virus rNDV-H9. The recombinant virus rNDV-H9 showed similar replication kinetic characteristics with the parent LaSota strain and had good genetic stability. The immunization result showed that rNDV-H9 induced high HI antibody titer against H9N2 AIV. In the H9N2 AIV challenge experiment, rNDV-H9 could significantly reduce the virus shedding in trachea and cloaca. In addition, rNDV-H9 protected the barrier function of chicken intestinal mucosal epithelial cells and reduced the virus-induced inflammatory response to a certain extent, so as to inhibit the abnormal proliferation of E. coli. This study suggests that rNDV-H9 is a promising vaccine candidate against H9N2 AIV.