Highly Pathogenic Avian Influenza A(H5Nx) Virus of Clade 2.3.4.4b Emerging in Tibet, China, 2021

Impaired influenza A virus replication by the host restriction factor SAMHD1 which inhibited by PA-mediated dephosphorylation of the host transcription factor IRF3

BACKGROUND

Influenza A virus (IAV) can cause severe and life-threatening illness in humans and animals. Therefore, it is important to search for host antiviral proteins and elucidate their antiviral mechanisms for the development of potential treatments. As a part of human innate immunity, host restriction factors can inhibit the replication of viruses, among which SAM and HD domain containing deoxynucleoside triphosphate triphosphohydrolase 1 (SAMHD1) can restrict the replication of viruses, such as HIV and enterovirus EV71. Viruses also developed countermeasures in the arms race with their hosts. There are few reports about whether SAMHD1 has a restriction effect on IAV.

METHODS

To investigate the impact of IAV infection on SAMHD1 expression in A549 cells, we infected A549 cells with a varying multiplicity of infection (MOI) of IAV and collected cell samples at different time points for WB and RT-qPCR analysis to detect viral protein and SAMHD1 levels. The virus replication level in the cell culture supernatant was determined using TCID50 assay. Luciferase assay was used to reveal that H5N1 virus polymerase acidic protein (PA) affected the activity of the SAMHD1 promoter. To assess the antiviral capacity of SAMHD1, we generated a knockdown and overexpressed cell line for detecting H5N1 replication.

RESULTS

In this study, we observed that SAMHD1 can restrict the intracellular replication of H5N1 and that the H5N1 viral protein PA can downregulate the expression of SAMHD1 by affecting SAMHD1 transcriptional promoter activity. We also found that SAMHD1's ability to restrict H5N1 is related to phosphorylation at 592-tyrosine.

CONCLUSIONS

In conclusion, we found that SAMHD1 may affect the replication of IAVs as a host restriction factor and be countered by PA. Furthermore, SAMHD1 may be a potential target for developing antiviral drugs.

Epidemiology and phylodynamics of multiple clades of H5N1 circulating in domestic duck farms in different production systems in Bangladesh

Waterfowl are considered to be natural reservoirs of the avian influenza virus (AIV). However, the dynamics of transmission and evolutionary patterns of AIV and its subtypes within duck farms in Bangladesh remain poorly documented. Hence, a cross-sectional study was conducted in nine districts of Bangladesh between 2019 and 2021, to determine the prevalence of AIV and its subtypes H5 and H9, as well as to identify risk factors and the phylodynamics of H5N1 clades circulating in domestic duck farms. The oropharyngeal and cloacal swab samples were tested for the AIV Matrix gene (M-gene) followed by H5, H7, and H9 subtypes using rRT-PCR. The exploratory analysis was performed to estimate AIV and its subtype prevalence in different production systems, and multivariable logistic regression model was used to identify the risk factors that influence AIV infection in ducks. Bayesian phylogenetic analysis was conducted to generate a maximum clade credibility (MCC) tree and the maximum likelihood method to determine the phylogenetic relationships of the H5N1 viruses isolated from ducks. AIV was detected in 40% (95% CI: 33.0-48.1) of the duck farms. The prevalence of AIV was highest in nomadic ducks (39.8%; 95% CI: 32.9-47.1), followed by commercial ducks (24.6%; 95% CI: 14.5-37.3) and backyard ducks (14.4%; 95% CI: 10.5-19.2). The H5 prevalence was also highest in nomadic ducks (19.4%; 95% CI: 14.0-25.7). The multivariable logistic regression model revealed that ducks from nomadic farms (AOR: 2.4; 95% CI: 1.45-3.93), juvenile (AOR: 2.2; 95% CI: 1.37-3.61), and sick ducks (AOR: 11.59; 95% CI: 4.82-32.44) had a higher risk of AIV. Similarly, the likelihood of H5 detection was higher in sick ducks (AOR: 40.8; 95% CI: 16.3-115.3). Bayesian phylogenetic analysis revealed that H5N1 viruses in ducks belong to two distinct clades, 2.3.2.1a, and 2.3.4.4b. The clade 2.3.2.1a (reassorted) has been evolving silently since 2015 and forming at least nine subgroups based on >90% posterior probability. Notably, clade 2.3.4.4b was introduced in ducks in Bangladesh by the end of the year 2020, which was genetically similar to viruses detected in wild birds in Japan, China, and Africa, indicating migration-associated transmission of an emerging panzootic clade. We recommend continuing AIV surveillance in the duck production system and preventing the intermingling of domestic ducks with migratory waterfowl in wetlands.

Pathogenicity and Transmissibility of Goose-Origin H5N6 Avian Influenza Virus Clade 2.3.4.4h in Mammals

Throughout the last decade, H5N6 avian influenza viruses (AIVs) circulating in poultry and infecting humans have caused increasing global concerns that they might become a pandemic threat to global health. Since AIVs could occasionally cause asymptomatic infections in geese, virus monitoring in such a host should be critical to the control of cross-species infection. In addition, previous studies showed that clade 2.3.4.4h H5N6 AIVs could infect mammals without adaptation. However, the pathogenicity and transmissibility of goose-origin clade 2.3.4.4h H5N6 AIVs in mammals remain unknown. In this study, two H5N6 AIVs were isolated from a domestic chicken (A/chicken/Hebei CK05/2019 (H5N6)) and a goose (A/goose/Hebei/GD07/2019(H5N6)). This study is the first to evaluate the pathogenicity and transmissibility of goose-origin clade 2.3.4.4h H5N6 AIVs in mammals by comparison with chicken-origin 2.3.4.4h H5N6 AIVs. The CK05 virus had an affinity for α-2,3-receptors, while the GD07 virus had an affinity for both α-2,3-and α-2,6-receptors. The GD07 virus had a higher replication capacity in vitro and more severe pathogenicity in mice than the CK05 virus. The CK05 virus could not be transmitted effectively among guinea pigs, whereas the GD07 virus could be transmitted through direct contact among guinea pigs. The results of this study indicated the potential health threat of clade 2.3.4.4h H5N6 AIVs to mammals and emphasized the importance of continuous monitoring of H5N6 AIVs, especially in waterfowl.

Highly Pathogenic Avian Influenza A (H5N1) Virus in Swans, Central China, 2021

Six highly pathogenic avian influenza (HPAI) H5N1 viruses (clade 2.3.4.4b) were detected in migratory birds in Hubei Province in November 2021. Phylogenetic analysis indicated that the viruses in the study included two different reassortants between H5N1 viruses that were circulating in Eurasia and low-pathogenic avian influenza viruses (LPAIVs). Several amino acid substitutions that contributed to the enhanced replication or virulence in mammals were observed in these viruses, suggesting a potential threat of the H5N1 viruses to human health. IMPORTANCE Here, we obtained the whole-genomes of six H5N1 viruses from dead or rescued wild birds in Hubei Province. These viruses were divided into two genotypes and had different evolutionary trajectories from previously reported H5N1 viruses in China. Extensive reassortment events between high-pathogenic (HP) and low-pathogenic (LP) avian influenza viruses (AIVs) were observed in these viruses. Moreover, a key amino acid analysis also suggests a potential threat of H5N1 viruses to public health. Our work explored the prevalent patterns of H5N1 viruses in wild birds and replenished the viral population data of H5N1 viruses in central China.

Seroprevalence of pullorum disease in chicken across mainland China from 1982 to 2020: A systematic review and meta-analysis

Pullorum disease (PD), caused by the bacterium Salmonella pullorum, severely threatens the health of chickens worldwide, especially in China, and generating concerns for public health safety. Greater awareness of the seroprevalence may facilitate the prevention and control of this disease. We conducted systematic review and meta-analysis on the seroprevalence of PD in chicken flocks across mainland China. The results show that the overall pooled estimates of PD seroprevalence in chicken flocks was 18.2%. Furthermore, during 38-year period the seroprevalence of PD was markedly high in all seven regions, being at least 14.9% in central China. Our results suggest PD was highly prevalent in autumn, followed by winter. Chickens older than 120 days (22.6%, CI₉₅: 14.5%-31.9%) had a significantly higher positive rate of PD than those <120 days in age (9.4%, CI₉₅: 3.7%-17.4%). Additionally, the rearing mode used is a risk factor associated with the seroprevalence of PD, it being considerably lower for caged chickens (13.7%, CI₉₅: 7.1%-22.0%) than free-range chickens (30.4%, CI₉₅: 17.3-45.4%). Our findings demonstrate that PD still poses a major threat to poultry industries in mainland China, and therefore comprehensive and stringent strategies are needed to prevent and control this disease.