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.

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.

Tembusu virus (TMUV) is an emerging mosquito-borne flavivirus, primarily transmitted by Culex spp. mosquitoes. The 2010 outbreak of TMUV in ducks revealed that the virus had acquired direct contact and aerosol transmission routes, enabling its rapid spread in duck farms. Recently, cluster 3 TMUV has increasingly been isolated from chickens, ducks and geese. In this study, we examined the pathogenicity and transmission routes of the cluster 3 TMUV Shandong 2021 (SD) strain in ducks and chickens. Our results show that TMUV SD can infect both species, but only in ducks could TMUV be detected in throat and cloacal swabs. In ducks, the virus can spread without mosquito involvement to co-housed naïve birds, demonstrating direct transmission capability. Conversely, no virus shedding and direct transmission were observed in chickens, suggesting that mosquitoes are required for virus transmission between chickens. Indeed, Culex pipiens mosquitoes could become infected by biting chickens infected with the TMUV SD and transmit the virus to naïve chickens. Our results, for the first time, provide direct evidence that TMUV can be transmitted by mosquitoes in a laboratory setting. Furthermore, our findings indicate that viral excretion through the respiratory tract and/or digestive tract is essential for direct contact transmission of TMUV, which is a critical factor in the epidemic spread of TMUV. These insights into the transmission dynamics of a cluster 3 TMUV emphasize the importance of effective vector control and biosecurity measures in managing and preventing outbreaks.

Background: Maternal-derived antibody (MDA) interferes with immune responses, leading to the failure of H9N2 avian influenza vaccinations in poultry. So far, none of the commercially available H9N2 avian influenza vaccines used in poultry have been able to overcome MDA interference. Methods: To develop a vaccine that can overcome MDA interference, one or multiple copies of the minimum-binding domain (P29) from the complement protein C3d were inserted in between the signal peptide and the head domain of the hemagglutinin (HA) protein on a H9N2 avian influenza virus (A/Chicken/Shanghai/H514/2017, named H514). Results: The HA proteins containing P29 stimulated stronger type I interferences than wild-type HA proteins in vitro. The modified viruses with the HA proteins containing one copy of P29 (rH514-P29.1) and two copies of P29.2 (rH514-P29.2) were successfully rescued using reverse genetics. The inactivated vaccines developed with rH514-P29.1 or rH514-P29.2 induced higher and faster humoral immune responses than the vaccine developed with rH514 in specific pathogen-free (SPF) chickens. To evaluate the vaccines’ efficacy in the presence of MDA and to ensure a uniform level of MDA, passively transferred antibody (PTA) was used as a model to mimic MDA in 1-day-old SPF chickens. Our results showed that the rH514-P29.2 inactivated vaccine induced significantly higher HI titers than the rH514 inactivated vaccine in the presence of PTA. More importantly, it reduced viral shedding after being challenged with H514 in the presence of PTA. Conclusions: Our results suggest that vaccine antigens fused with two copies of P29 can decrease the interference of MDA on immunity in chickens. Overall, our results provide a new strategy for overcoming MDA interference.