Infectious laryngotracheitis virus (ILTV) causes severe respiratory disease in chickens and results in huge economic losses in the poultry industry worldwide. To correlate the genomic difference with the replication and pathogenicity, phenotypes of three ILTVs isolated from chickens in China from 2016 to 2018 were sequenced by high-throughput sequencing. Based on the entire genome, the isolates GD2018 and SH2017 shared 99.9% nucleotide homology, while the isolate SH2016 shared 99.7% nucleotide homology with GD2018 and SH2017, respectively. Each virus genome contained 82 ORFs encoding 77 kinds of protein, 31 of which share the same amino acid sequence in the three viruses. GD2018 and SH2017 shared 57 proteins with the same amino acid sequence, while SH2016 shared 42 and 41 proteins with the amino acid sequences of GD2018 and SH2017, respectively. SH2016 propagated efficiently in allantoic fluid and on chorioallantoic membranes (CAMs) of SPF chicken embryo eggs, while GD2018 and SH2017 proliferated well only on CAMs. GD2018 propagated most efficiently on CAMs and LMH cells among three isolates. SH2016 caused serious clinical symptoms, while GD2018 and SH2017 caused mild and moderate clinical symptoms in chickens, although the sero of the chickens infected with those three isolates were all positive for anti-ILTV antibody at 14 and 21 days after challenge. Three ILTVs with high genetic homology showed significant differences in the replication in different culture systems and the pathogenicity of chickens, providing basic materials for studying the key determinants of pathogenicity of ILTV.

Avian viral arthritis (AVA), caused by avian reovirus (ARV), is a viral disease in chickens that has led to significant economic losses in the poultry industry. Recent studies have shown that traditional ARV vaccines based on the S1133 strain fail to protect against emerging ARV variants. In this study, we isolated and characterized three ARV strains (G4, YV, WF) from immunized chicken flocks with respiratory and arthritic symptoms. Genomic analysis revealed that the σC genes of G4, YV, and WF shared only 55.5%, 55.7%, and 58.7% sequence homology, respectively, with the S1133 strain. Phylogenetic analysis placed them in different branches, indicating they are variant strains. YV and WF belong to genotype III, and G4 falls into genotype VI. Whole genome analysis revealed gene segment reassortment among the variants. Pathogenicity testing in three-week-old SPF chickens showed that G4 (genotype VI) caused swelling of footpads, whereas WF (genotype III) did not. G4-infected chickens exhibited significantly higher viral loads in the thymus, lungs, spleen, and bursa of Fabricius than those in the WF-infected chickens, indicating viruses from different genotypes showed various pathogenesis. These results suggested an urgent need for new updates of vaccines against the variant ARVs, especially the genotype VI virus.

Pigs serve as a mixing vessel for influenza viruses and can independently promote the emergence of pandemic strains in humans. During our surveillance of pig populations from 2021 to 2023 in China, 11 H1 subtype swine influenza viruses (SIVs) were isolated. All viruses were reassortants, possessing internal genes of identical origins (PB2, PB1, PA, NP, M: pdm09/H1N1 origin, NS: North American triple reassortant origin). The H1N1 isolates were all the dominant G4 EA H1N1 viruses in China. Two H1N2 isolates carried early human pdm09/H1N1 HA genes, suggesting a possible pig-to-human transmission route. Mutations that dictate host range specificity were identified in all isolates, a phenomenon which may enhance the affinity to human receptors. These H1 subtype viruses effectively replicated both in vivo and in vitro without prior adaptation and exhibited different pathogenicity and growth characteristics. Some of the H1 viruses were even found to cause lethal infections in mice. Taken together, our study indicates that the H1 subtype SIVs recently circulating in China pose a potential threat to human health and emphasizes the importance of continuing to closely monitor their evolution and spread.

During the life cycle of the influenza virus, viral RNPs (vRNPs) are transported to the nucleus for replication. Given that a large number of progeny viral RNA occupies the nucleus, whether there is any host protein located in the nucleus that recognizes the viral RNA and inhibits the viral replication remains largely unknown. In this study, to explore the role of hnRNPH1 in influenza virus infection, we knocked down and over-expressed the hnRNPH1 proteins in 293T cells, then infected the cells with the influenza virus. The results showed that the host hnRNPH1 inhibits the replication of H1N1 and H9N2 influenza viruses by restraining the polymerase activity of viruses. hnRNPH1 contains two RNA recognition motifs (RRM1) and RRM2. Further studies indicated that hnRNPH1 specifically binds to the viral RNA of the PB1, PA, and NP genes. Mutation of the key residues tryptophan and tyrosine in RRM1 and RRM2 abolished the binding affinity to viral RNA and the suppression of polymerase activity of the influenza virus. All the results suggested that hnRNPH1 suppresses polymerase activity and replication of the influenza virus by binding viral RNA.

Duck hepatitis A virus type 3 (DHAV-3), an avian-specific pathogen primarily impacting ducklings, poses a significant threat to the duck farming industry by causing high mortality rates. A DHAV-3 strain SH52 was isolated from the diseased ducks and phylogenetic analysis of the whole genome revealed that the DHAV-3 SH52 belongs to the prevalent strains in China. The DHAV-3 SH52 strain replicates at high levels in various organs of 8-day-old specific pathogen-free (SPF) shelducks, causing pathological damage and leading to high lethality in 8-day-olds following intramuscular infection. The findings of this study provide an ideal animal challenge model for evaluating the efficacy of DHAV-3 vaccines in the future.

In 2014, Duck Adenovirus type 3 (DAdV-3) emerged in Muscovy ducks and has since spread rapidly across China, causing significant economic losses to the duck industry. Given this situation, the development of reliable diagnostic tools is crucial for effective disease control. In this study, a neutralizing monoclonal antibody (mAb) 2F12 specific to DAdV-3 was generated, which showed a blocking rate of over 70% and a neutralization titer of up to 1:794. A blocking enzyme-linked immunosorbent assay (b-ELISA) was further developed based on mAb 2F12 to efficiently detect neutralizing antibodies against DAdV-3. The cut-off values of percent inhibition (PI) were set based on testing 84 negative duck serum samples, with a value below 16.79% (mean ($\overline{X}$) + 2 standard deviations (SD)) for negative sera and over 21.62% ($\overline{X}$ + 3SD) for positive sera. The b-ELISA exhibited a high specificity, reacting exclusively with DAdV-3 positive serum and showing no cross-reactivity with other representative positive sera tested. Additionally, the b-ELISA showed significantly higher sensitivity than the serum neutralization test (SNT), detecting antibodies 16-fold greater than the endpoint dilution of the SNT. The established b-ELISA, validated with 90 field serum samples from six duck farms, was well-suited for clinical detection of DAdV-3 antibodies and for monitoring post-vaccination antibody levels, representing a significant advancement in DAdV-3 detection and prevention.