Genetic variation of the VP1 gene of the virulent duck hepatitis A virus type 1 (DHAV-1) isolates in Shandong province of China

Duck hepatitis a virus: Full-length genome-based phylogenetic and phylogeographic view during 1986-2020

Duck hepatitis A virus (DHAV) is one of key pathogens for duck viral hepatitis, especially in Asian duck industry. Currently, two main genotypes (DHAV-1 and -3) exist. To explore insightfully the evolutionary character, we assessed the available 141 full-length genome sequences of DHAV isolated in 1986-2020 globally and divided DHAV-1 and DHAV-3 into further seven (DHAV-1 a-g) and five (DHAV-3 a-e) sub-clades, respectively. Phylogenetic and phylogeographic network analyses indicated great genetic diversity of DHAV identified in China, where the DHAV-1 cluster and DHAV-3 cluster were linked by virus strain HDHV1-BJ (GenBank ID: FJ157172.1) and Du_CH_LSD_090612 (GenBank ID: JF828995.1) via a long mutational branch and intermediate strains. Several strains previously identified as DHAV-1 according to the partial gene sequences were actually clustered within DHAV-3 in full-length genome-based analysis. Furthermore, we identified 32 recombination events across virus genome with the recombination hotspot at the 5' end and upstream of the capsid coding region. The highest variability of DHAV polyprotein was shown at the upstream region of the N terminus P-loop region, e.g., amino acids 672-716, followed by the aa 334-359 in the Capsid encoding region. The results presented here provides a robust insight into the genetic exchange patterns of DHAV genomes during the past decades, which may be used to map the evolutionary history and facilitate preventive measures of DHAVs.

Nonstructural protein 2A2 from Duck hepatitis A virus type 1 inhibits interferon beta production by interaction with mitochondrial antiviral signaling protein and TANK-binding kinase 1

Type I interferon (IFN-I) is essential for the regulation of host-virus interactions, and viruses have evolved strategies to escape the host immune response. Duck hepatitis A virus type 1 (DHAV-1) causes severe liver necrosis and hemorrhage, neurological symptoms, and high mortality in ducklings. However, how DHAV-1 interacts with the duck innate immune system remains unclear. In this study, DHAV-1-encoded proteins were cloned, and DHAV-1 2A2 was shown to strongly suppress IFN-β-luciferase activity, triggered by Sendai virus and polyriboinosinic polyribocytidylic acid [poly(I:C)], along with the transcription of IFN-β and downstream antiviral genes, including OASL, PKR, and TNF-a. In addition, 2A2 interacts with the central adaptor proteins mitochondrial antiviral signaling (MAVS) and TANK-binding kinase 1 (TBK1) by its N-terminal 1-100 amino acids (aa), thus leading to the inhibition of IFN-β production. Importantly, the deletion of the N-terminal 1-100 aa region of 2A2 abolished inhibition of IFN-I production. Moreover, the transmembrane domain of the MAVS protein and the ubiquitin domain of TBK1 were demonstrated to be required for interaction with DHAV-1 2A2. These findings revealed a novel strategy by which DHAV-1 hijacks cellular immunosurveillance and provided new insights into controlling the disease.

Duck hepatitis A virus type 1 transmission by exosomes establishes a productive infection in vivo and in vitro

Duck hepatitis A virus type 1 (DHAV-1) infection causes an acute and highly fatal disease in young ducklings. Exosomes are nano-sized small extracellular vesicles secreted by various cells, which participate in intercellular communication and play a key role in the physiological and pathological processes. However, the role of exosomes in DHAV-1 transmission remains unknown. In this study, through RT-PCR, WB analysis and TEM observation, the complete DHAV-1 genomic RNA, partial viral proteins, and virions were respectively identified in the exosomes derived from DHAV-1-infected duck embryo fibroblasts (DEFs). The productive DHAV-1 infection was transmitted by exosomes in DEFs, duck embryos, and ducklings, and high titers of neutralizing antibodies completely blocked DHAV-1 infection but did not significantly neutralize exosome-mediated DHAV-1 infection. To the best of our knowledge, this is the first report that exosome-mediated DHAV-1 infection was resistant to antibody neutralization in vivo and in vitro, which might be an immune evasion mechanism of DHAV-1.

Long Noncoding RNA Expression Rofiles Elucidate the Potential Roles of lncRNA- XR_003496198 in Duck Hepatitis A Virus Type 1 Infection

Duck hepatitis A virus type 1 (DHAV-1) is a highly lethal virus that severely affects the duck industry worldwide. Long noncoding RNAs (lncRNAs) exert crucial roles in pathogen attacks. Here, we conducted deep transcriptome analysis to investigate the dynamic changes of host lncRNAs profiles in DHAV-1-infected duck embryo fibroblasts. We identified 16,589 lncRNAs in total and characterized their genomic features. Moreover, 772 and 616 differentially expressed lncRNAs (DELs) were screened at 12 and 24 h post-infection. Additionally, we predicted the DELs’ cis- and trans-target genes and constructed lncRNA-target genes regulatory networks. Functional annotation analyses indicated that the putative target genes of DELs participated in diverse vital biological processed, including immune responses, cellular metabolism, and autophagy. For example, we confirmed the dysregulation of pattern recognition receptors (TLR3, RIG-I, MDA5, LGP2, cGAS), signal transducers (STAT1), transcription factors (IRF7), immune response mediators (IL6, IL10, TRIM25, TRIM35, TRIM60, IFITM1, IFITM3, IFITM5), and autophagy-related genes (ULK1, ULK2, EIF4EBP2) using RT-qPCR. Finally, we confirmed that one DHAV-1 induced lncRNA-XR_003496198 is likely to inhibit DHAV-1 replication in DEFs. Our study comprehensively analyzed the lncRNA profiles upon DHAV-1 infection and screened the target genes involved in the innate immune response and autophagy signaling pathway, thereby revealing the essential roles of duck lncRNAs and broadening our understanding of host-virus interactions.

Integrated miRNA and mRNA Expression Profiles Reveal Differentially Expressed miR-222a as an Antiviral Factor Against Duck Hepatitis A Virus Type 1 Infection

Duck hepatitis A virus 1 (DHAV-1) is a highly contagious etiological agent that causes acute hepatitis in young ducklings. MicroRNAs (miRNAs) play important regulatory roles in response to pathogens. However, the interplay between DHAV-1 infection and miRNAs remains ambiguous. We characterized and compared miRNA and mRNA expression profiles in duck embryo fibroblasts cells (DEFs) infected with DHAV-1. In total, 36 and 96 differentially expressed (DE) miRNAs, and 4110 and 2595 DE mRNAs, were identified at 12 and 24 h after infection. In particular, 126 and 275 miRNA-mRNA pairs with a negative correlation were chosen to construct an interaction network. Subsequently, we identified the functional annotation of DE mRNAs and target genes of DE miRNAs enriched in diverse Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, which may be important for virus resistance, cell proliferation, and metabolism. Moreover, upregulated miR-222a could negatively regulate DHAV-1 replication in DEFs and downregulate integrin subunit beta 3 (ITGB3) expression by targeting the 3' untranslated region (3'UTR), indicating that miR-222a may modulate DHAV-1 replication via interaction with ITGB3. In conclusion, the results reveal changes of mRNAs and miRNAs during DHAV-1 infection and suggest miR-222a as an antiviral factor against DHAV-1.

Construction of Recombinant Lactococcus lactis Strain Expressing VP1 Fusion Protein of Duck Hepatitis A Virus Type 1 and Evaluation of Its Immune Effect

With the continuous development of duck farming and the increasing breeding density, the incidence of duck hepatitis A virus type 1 (DHAV-1) has been on the rise, seriously endangering the development of duck farming. To reduce the use of antibiotics in duck breeding, susceptibility risks and mortality, and avoid virulence recovery and immune failure risk, this study aims to develop a new type of mucosal immune probiotics and make full use of molecular biology techniques, on the level of genetic engineering, to modify Lactococcus lactis (L. lactis). In this study, a secretory recombinant L. lactis named MG1363-VP1 with an enhanced Green Fluorescent Protein (eGFP) and translation enhancer T7g10L was constructed, which could express the VP1-eGFP fusion protein of DHAV-1. The animal experiment in ducklings was performed to detect the immune response and protection effect of oral microecologics by recombinant L. lactis. The results showed that oral L. lactis MG1363-VP1 significantly induced the body’s humoral immune system and mucosal immune system to produce specific anti-VP1 IgG antibodies and mucosal secretory immunoglobulin A (sIgA) for DHAV-1 in ducklings, and cytokines including interleukin-2 (IL-2), interleukin-4 (IL-4), interleukin-10 (IL-10), and interferon gamma (IFN-γ). The mortality rate was monitored simultaneously by the natural infestation in the process of production and breeding; notably, the ducklings vaccinated with L. lactis MG1363-VP1 were effectively protected against the nature infection of DHAV-1. The recombinant L. lactis MG1363-VP1 constructed in this study provides a new means of preventing and controlling DHAV-1 infection in the future.

Insights into the Genetic Evolution of Duck Hepatitis A Virus in Egypt

Duck hepatitis virus (DHV) is one of the commercially important diseases of ducklings worldwide. It is an acute and highly infectious disease of ducklings caused by three different serotypes (1-3) of duck hepatitis A virus (DHAV), and serotype 1 is the most common in poultry. To date, little is known about the prevalence and genetic characterisation of DHAV-1 in Egypt. In the current study, isolation and complete genomic analyses of DHAVs circulating in commercial duck farms in different Egyptian governorates were conducted. A total of eighteen samples were collected from six Egyptian governorates of 3-11 days old ducklings (Pekin and Mullard) with a history of nervous signs and high mortality rates. Five out of eighteen (5/18) samples were screened positive for the DHAV-1 based on the VP1 gene. These samples were individually used for virus isolation in embryonated duck embryos (EDE), followed by complete genome sequencing. Phylogenomic analyses showed that DHAV serotype I; genotype I were diversified into four different groups (1-4). Most of the recent circulating Egyptian DHAV strains are clustered within group 4, while isolates characterised within this study were clustered within group 1. Recombination analyses revealed that the emergence of a new recombinant virus-DHAV-1 strain Egypt-10/2019-through recombination. Likewise, the selective pressure analyses showed the existence, inside or near areas of the viral attachment or related functions, of positive scores highlighting the importance of natural selection and viral evolution mechanism at different protein domains. The findings of this study provide updated information on the epidemiological and genetic features of DHAV-1 strains and underscore the importance of DHAV surveillance as well as re-evaluation for currently used vaccines.

Dual Circulation of Duck Hepatitis A Virus Genotypes 1 and 3 in Egypt

Duck hepatitis A virus (DHAV) causes acute hepatitis and mortality, resulting in high economic losses in the duck farm industry. The current study describes the outbreak of DHAV in vaccinated duck farms in North Egypt during 2019 and molecular characterization of the 3' untranslated region (UTR) and viral protein VP1 genes. The 30 samples were collected from 7- to 28-day-old commercial Pekin ducks that showed a history of nervous signs and sudden deaths and were on farms in 6 governorates. DHAV was typed by reverse transcription-polymerase chain reaction (RT-PCR) for 3' UTR and VP1 genes and revealed 20 positive farms, with the first detection of DHAV genotype 3 (DHAV-3) in 18 samples and the classic DHAV-1 in 2 samples. The phylogenetic analysis of VP1 and 3' UTR genes of the nine selected strains representative of six governorates revealed that seven strains were clustered with DHAV-3 Chinese and Korean-Vietnamese strains within different subgroups with 92.4%-93.7% amino acid identity; such strains were distinguishable from the vaccine strain of DHAV-1 used in Egypt with 74.4% amino acid identity. The other strains were closely related to the DHAV-1 Asian strain and the vaccine strain used in Egypt with 98.7%-99.6% amino acid identity for the VP1 gene with different clustering than that of recently isolated DHAV-1 Egyptian strains. The VP1 gene of DHAV-3 had 1 hypervariable region (HVR) with 10 amino acid mutations compared with DHAV3/DN2/Vietnam/2011, but DHAV-1 had 3 HVRs with 1 amino acid mutation in HVRII compared with the DHAV-1 vaccine strain. In conclusion, a new introduction of DHAV-3 with the classical DHAV-1 was recorded in Pekin duck farms in North Egypt that is genetically distant from the vaccinal strain.

Evidence of possible vertical transmission of duck hepatitis A virus type 1 in ducks

Duck hepatitis A virus (DHAV) causes a highly contagious and acute disease in ducklings younger than 3 weeks of age and spreads rapidly by horizontal transmission to all susceptible ducklings in the flock. To date, there is no evidence of vertical transmission of DHAV-1. In a previous study, we identified a novel DHAV type 1 (DHAV-1) isolate that could infect adult ducks and induce laying drop. In this study, 30 non-embryonated duck eggs and 60 17-day-old embryos were collected from three breeding duck flocks with egg drop syndrome caused by DHAV-1 in China, and 30 17-day-old embryos were randomly selected from the 60 embryos and allowed to hatch. DHAV-1 RNA was detected by RT-PCR in 10 of 30 non-embryonated eggs, 9 of 30 17-day-old embryos, 5 of 7 dead embryos and 5 of 23 newly hatched ducklings. Overall, 29 of 90 (32.2%) eggs and embryos were positive for DHAV-1. Three DHAV-1 strains were isolated from the dead duck embryos of the three breeding duck flocks, respectively. Pathogenicity studies showed that the three DHAV-1 isolates had median embryo lethal doses but were highly pathogenic to healthy ducklings. Compared with the DHAV reference strains, there were two specific amino acid mutation sites (F₁₆₉ and S₂₂₀ ) in VP1 of the three isolates. To the best of our knowledge, this is the first report that DHAV-1 is isolated from duck embryos. The findings provide evidence of possible vertical transmission of DHAV-1 from breeding ducks to ducklings.

Development and evaluation of an indirect ELISA based on recombinant structural protein VP2 to detect antibodies against duck hepatitis A virus

An indirect enzyme-linked immunosorbent assay (I-ELISA) based on the VP2 protein of duck hepatitis A virus type 3 (DHAV-3) was established in this study. The optimal dilutions of antigen, serum and goat anti-duck IgG conjugate were 1:1600 (2.23 μg/mL), 1:160 and 1:2000, respectively. The optimal blocking buffer was 1% skim milk. The cut-off value for the method was 0.25, and the analytical sensitivity of the method was 1:5120. The results of specific evaluation showed that except for DHAV-1, DHAV-3 antisera did not cross-react with any other common duck-sensitive pathogens, indicating that this method can be used to detect DHAV-3 and DHAV-1 antibodies. The coefficients of variation (CVs) were lower than 10 %. The coincidence rate between the VP2-DHAV-3-ELISA and the neutralization test was 93.3 %. In summary, the I-ELISA method based on VP2 protein has high sensitivity, specificity, and coincidence rate compared with the neutralization test and has advantages in serum monitoring. The I-ELISA method based on VP2 protein provides a simple and rapid method for the detection of anti-DHAV antibodies and the epidemiological monitoring of DHAV.

Comparative Pathogenicity of Duck Hepatitis A Virus-1 Isolates in Experimentally Infected Pekin and Muscovy Ducklings

Duck hepatitis virus (DHV) has always been considered one of the threats endangering duck farming in Egypt since the 1960s. In the current study, suspected DHV samples (n = 30) were obtained from commercial Pekin, Mulard (hybrid), and Muscovy duck farms and backyards in Beheira, Alexandria, Gharbia, Kafr El-Sheikh, and Giza provinces between 2012 and 2017. Diseased 3–21-day-old ducklings showed a clinical history of high mortality rates and nervous signs. Samples were screened by RT-PCR targeting the 5′UTR region and VP1 gene. The PCR-confirmed samples (n = 7) were isolated via allantoic route inoculation onto 9-day-old specific-pathogen-free embryonated chicken eggs. Embryos showed stunting, subcutaneous hemorrhages, and liver necrotic greenish-yellow foci. Duck hepatitis A virus-1 (DHAV-1) isolates were genetically analyzed in comparison to other field and vaccine strains. Phylogenetic analyses of the full-length VP1 gene sequences revealed that the obtained DHAV-1 field isolates clustered into genetic group 4 alongside other Egyptian strains isolated during the same period (95.9–99.72% similarity). Amino acid substitutions in the carboxyl-terminal of VP1 (I180T, G184E, D193N, and M213I) were identified in two strains. Also, deletion mutation at I189 was detected in three DHAV-1 strains. Additionally, the two amino acid residues E205 and N235 were common among the isolated strains and other virulent DHAV-1 strains. Two DHAV-1 isolates originated from Pekin source were selected for conducting the comparative pathogenicity testing based on detected point mutations at C-terminus of VP1. We evaluated the pathogenicity of these isolates by investigating clinical signs, mortality rates, and gross pathological and microscopic lesions. The study revealed that experimentally infected Pekin and Muscovy ducklings showed similar clinical signs including squatting down, lateral recumbency, and spasmodic kicking. Muscovy showed milder pathological changes in the liver compared to Pekin ducklings. Histopathological findings supported the gross pathological lesions detected in both breeds. In conclusion, these data provide updated information on the genetic diversity and pathotyping of Egyptian DHAV-1 strains. To the best of our knowledge, this is the first report of comparative pathogenicity of recent DHAV-1 strains in Pekin and Muscovy ducklings in Egypt and the Middle East region.

Outbreaks of Duck Hepatitis A Virus in Egyptian Duckling Flocks

During 2015, duck farms (n = 27) in Sharkia Province, Egypt, experienced several disease outbreaks leading to mortality and nervous manifestations. Upon necropsy, the affected ducklings showed liver lesions, such as hemorrhage or necrosis, suggestive of duck virus hepatitis (DVH). Reverse transcription-PCR (RT-PCR), on the basis of the 3D gene, found duck livers from 21 farms to be positive for duck hepatitis A virus serotype 1 (DHAV-1). All duck breeds (Pekin, Mallard, and Muscovy) were infected. The virus was isolated in embryonated chicken eggs, which showed embryonic mortality (40%-80%) within 5-7 days, stunting or dwarfing (69.6%), and necrotic liver foci (60.9%). The VP1 gene of 11 DHAV-1 strains was characterized by RT-PCR and Sanger sequencing. All study strains were clustered in a monophyletic branch within subclade B2 of Group 4 and were separated from the Egyptian vaccine strain. Several amino acid (aa) residues, such as V129, S142 (only in four strains), L181, G184, and K217, were related to virus attenuation. However, two aa residues (N193 and E205), found in virulent DHAV-1 strains, were also observed in our strains. This study confirms the circulation of DHAV-1 (subclade B2) in Lower Egypt and elucidates the phylogenetic characters of the VP1 genes, which will be useful in following the local trends of DHAV-1 infections. Further studies are indicated to determine the correlation between these mutations and the virulence of the Egyptian DHAV-1 isolates.

Quantitative Proteomic Analysis Uncovers the Mediation of Endoplasmic Reticulum Stress-Induced Autophagy in DHAV-1-Infected DEF Cells

Autophagy is a tightly regulated catabolic process and is activated in cells in response to stress signals. Despite extensive study, the interplay between duck hepatitis A virus type 1 (DHAV-1) and the autophagy of host cells is not clear. In this study, we applied proteomics analysis to investigate the interaction mechanism between DHAV-1 and duck embryo fibroblast (DEF) cells. In total, 507 differentially expressed proteins (DEPs) were identified, with 171 upregulated proteins and 336 downregulated proteins. The protein expression level of heat shock proteins (Hsps) and their response to stimulus proteins and zinc finger proteins (ZFPs) were significantly increased while the same aspects of ribosome proteins declined. Bioinformatics analysis indicated that DEPs were mainly involved in the “response to stimulus”, the “defense response to virus”, and the “phagosome pathway”. Furthermore, Western blot results showed that the conversion of microtubule-associated protein 1 light chain 3-I (LC3-I) to the lipidation form of LC3-II increased, and the conversion rate decreased when DEF cells were processed with 4-phenylbutyrate (4-PBA). These findings indicated that DHAV-1 infection could cause endoplasmic reticulum (ER) stress-induced autophagy in DEF cells, and that ER stress was an important regulatory factor in the activation of autophagy. Our data provide a new clue regarding the host cell response to DHAV-1 and identify proteins involved in the DHAV-1 infection process or the ER stress-induced autophagy process.

Identification of a functional nuclear localization signal in 3Dpol/3CD of duck hepatitis A virus 1

The nuclear localization signals (NLS) were usually composed of basic residues (K and R) and played an important role in delivery of genomes and structural protein into nucleus. In this research, we identified that 3D^pol/3CD entered into nucleus during viral propagation of duck hepatitis A virus type 1 (DHAV-1). To investigate the reason that 3D^pol/3CD entered into nucleus, the amino acid sequence of 3CD was analyzed through NLS Mapper program. The basic region ¹⁷PRKTAYMRS²⁵ was subsequently proved to be a functional NLS to guide 3D^pol/3CD into nucleus. ¹⁸R, ¹⁹K and ²⁴R were found essential for maintaining the nuclear targeting activity, and exchange between ²⁴R and ²⁴K had no impact on cellular localization of 3D^pol. Since the entry of 3D^pol/3CD into nucleus was essential for shutoff of host cell transcription and maintaining the viral propagation of picornavirus numbers, our study provided new insights into the mechanism of DHAV-1 propagation.

A novel picornavirus in feces of a rainbow lorikeet (Trichoglossus moluccanus) shows a close relationship to members of the genus Avihepatovirus

A novel picornavirus, named "lorikeet picornavirus 1" (LoPV-1), was detected in a fecal sample from rainbow lorikeets using viral metagenomic analysis, and its complete genome sequence was determined and analyzed. The genome of LoPV-1 is 7862 nt long, including a 617-nt 5' UTR, a type IV IRES 5'UTR with an '8-like' motif, a 7032-nt polyprotein ORF, and a 213-nt 3' UTR. Phylogenetic analysis and pairwise asequence comparisons based on the amino acid sequences of P1, P2, and P3 indicated that LoPV-1 showed the closest relationship to two picornaviruses that were isolated recently from red-crowned cranes and clustered together with members of the genus Avihepatovirus.

The Functional Role of the 3' Untranslated Region and Poly(A) Tail of Duck Hepatitis A Virus Type 1 in Viral Replication and Regulation of IRES-Mediated Translation

The duck hepatitis A virus type 1 (DHAV-1) is a member of Picornaviridae family, the genome of the virus contains a 5′ untranslated region (5′ UTR), a large open reading frame that encodes a polyprotein precursor and a 3′ UTR followed by a poly(A) tail. The translation initiation of virus proteins depends on the internal ribosome-entry site (IRES) element within the 5′ UTR. So far, little information is known about the role of the 3′ UTR and poly(A) tail during the virus proliferation. In this study, the function of the 3′ UTR and poly(A) tail of DHAV-1 in viral replication and IRES-mediated translation was investigated. The results showed that both 3′ UTR and poly(A) tail are important for maintaining viral genome RNA stability and viral genome replication. During DHAV-1 proliferation, at least 20 adenines were required for the optimal genome replication and the virus replication could be severely impaired when the poly (A) tail was curtailed to 10 adenines. In addition to facilitating viral genome replication, the presence of 3′ UTR and poly(A) tail significantly enhance IRES-mediated translation efficiency. Furthermore, 3′ UTR or poly(A) tail could function as an individual element to enhance the DHAV-1 IRES-mediated translation, during which process, the 3′ UTR exerts a greater initiation efficiency than the poly(A)₂₅ tail.

Novel duck hepatitis A virus type 1 isolates from adult ducks showing egg drop syndrome

Generally, duck hepatitis A virus type 1 (DHAV-1) only infects young ducklings. Since December 2016, severe outbreaks of duck viral infection with egg drop, feed consumption decline, and ovary-oviduct disease have occurred in some laying duck flocks in Shandong Province of China. DHAV-1 isolated from the affected ducks was confirmed as the causative pathogen of the egg drop. Compared with other DHAV-1 strains, the novel isolate has three special amino acid mutation points in the most variable regions at the C-terminus of VP1. The experimental infection in laying ducks indicated that successful immunization with DHAV-1 vaccine could protect laying duck from infection. To the best of our knowledge, this is the first reported incidence of a severe duck disease outbreak involving egg drop syndrome caused by DHAV-1.

Adaptive Immune Responses following Senecavirus A Infection in Pigs

Senecavirus A (SVA), an emerging picornavirus of swine, causes vesicular disease (VD) that is clinically indistinguishable from foot-and-mouth disease (FMD) in pigs. Many aspects of SVA interactions with the host and the host immune responses to infection, however, remain unknown. In the present study, humoral and cellular immune responses to SVA were evaluated following infection in pigs. We show that SVA infection elicited an early and robust virus-neutralizing (VN) antibody response, which coincided and was strongly correlated with VP2- and VP3-specific IgM responses. Notably, the neutralizing antibody (NA) responses paralleled the reduction of viremia and resolution of the disease. Analysis of the major porcine T-cell subsets revealed that during the acute/clinical phase of SVA infection (14 days postinfection [p.i.]), T-cell responses were characterized by an increased frequency of αβ T cells, especially CD4⁺ T cells, which were first detected by day 7 p.i. and increased in frequency until day 14 p.i. Additionally, the frequency of CD8⁺ and double-positive CD4⁺ CD8⁺ T cells (effector/memory T cells) expressing interferon gamma (IFN-γ) or proliferating in response to SVA antigen stimulation increased after day 10 p.i. Results presented here show that SVA elicits B- and T-cell activation early upon infection, with IgM antibody levels being correlated with early neutralizing activity against the virus and peak B- and T-cell responses paralleling clinical resolution of the disease. The work provides important insights into the immunological events that follow SVA infection in the natural host.IMPORTANCE Senecavirus A (SVA) has recently emerged in swine, causing outbreaks of vesicular disease (VD) in major swine-producing countries around the world, including the United States, Brazil, China, Thailand, and Colombia. Notably, SVA-induced disease is clinically indistinguishable from other high-consequence VDs of swine, such as FMD, swine vesicular disease, vesicular stomatitis, and vesicular exanthema of swine. Despite the clinical relevance of SVA-induced VD, many aspects of the virus infection biology remain unknown. Here, we assessed host immune responses to SVA infection. The results show that SVA infection elicits early B- and T-cell responses, with the levels of VN antibody and CD4⁺ T-cell responses paralleling the reduction of viremia and resolution of the disease. SVA-specific CD8⁺ T cells are detected later during infection. A better understanding of SVA interactions with the host immune system may allow the design and implementation of improved control strategies for this important pathogen of swine.

Construction and characterization of an improved DNA-launched infectious clone of duck hepatitis a virus type 1

Background

DNA-launched infectious system is a useful tool with high rescue efficiency that allows the introduction of mutations in specific positions to investigate the function of an individual viral element. Rescued virus particles could be harvested by directly transfecting the DNA-launched recombinant plasmid to the host cells, which will reduce labor and experimental cost by skipping the in vitro transcription assay.

Methods

A total of four overlapping fragments covering the entire viral genome were amplified and then were assembled into a transformation vector based on pIRES2-EGFP to establish the DNA-launched infectious system of duck hepatitis A virus type 1 (DHAV-1), named pIR-DHAV-1. Reverse transcription polymerase chain reaction (RT-PCR) detection, quantitative real-time polymerase chain reaction (qRT-PCR), western blotting assay and indirect immunofluorescence (IFA) were conducted for rescued virus identification. A total of 4.0 μg of recombinant plasmid of pIR-DHAV-1 and in vitro transcribed product of 4.0 μg of RNA-launched infectious clone named pR-DHAV-1 were transfected into BHK-21 cells to analyze the rescue efficiency. Following that, tissue tropism of rescued virus (rDHAV-1) and parental virus (pDHAV-1) were assayed for virulence testing in 1-day-old ducklings.

Results

Rescued virus particles carry the designed genetic marker which could be harvested by directly transfecting pIR-DHAV-1 to BHK-21 cells. The qRT-PCR and western blotting results indicated that rDHAV-1 shared similar growth characteristics with pDHAV-1. Furthermore, DNA-launched infectious system possessed much higher rescue efficiency assay compared to RNA-launched infectious system. The mutation at position 3042 from T to C has no impact on viral replication and tissue tropism. From 1 h post infection (hpi) to 48 hpi, the viral RNA copies of rDHAV-1 in liver were the highest among the six tested tissues (with an exception of thymus at 6 hpi), while the viral RNA copy numbers in heart and kidney were alternately the lowest.

Conclusion

We have constructed a genetically stable and highly pathogenic DNA-launched infectious clone, from which the rescued virus could be harvested by direct transfection with recombinant plasmids. rDHAV-1 shared similar growth characteristics and tissue tropism with pDHAV-1. The DNA-launched infectious system of DHAV-1 possessed higher rescue efficiency compared to the traditional RNA-launched infectious system.

First isolation and genetic characteristics of porcine sapeloviruses in Hunan, China

Outbreaks of diarrhea in piglets cause serious economic consequences in China. Diarrhetic fecal samples from 20 Hunan farm piglets were tested and found to be positive for porcine epidemic diarrhea virus (PEDV) by RT-PCR, although incubation with porcine kidney (PK-15) cells failed to produce infectious PEDV. Four porcine sapelovirus (PSV) strains (designated as PSV-HuNs) were isolated from four of the samples. Genomic sequence analysis revealed open reading frames encoding polyproteins of 2,331 (HuN1, 2 and 3) and 2,332 (HuN4) amino acids. Homology comparisons of the VP1 gene of the four Hunan strains with previously reported PSV strains revealed nucleotide sequence identities ranging from 74.2 to 98.6%, and deduced amino acid sequence identities from 79.5 to 98%. Phylogenetic analyses based on full-length and partial VP1 gene sequences showed that 3 of the PSV-HuN strains (HuN2, 3 and 4) clustered within a clade distinct from HuN1 as well as from all PSVs previously isolated in China, thereby showing that genetic diversity exists within Chinese PSVs. In addition, recombination analysis among PSVs indicates that a recombinant (HuN2 strain) exist in China.

Detection, differentiation, and VP1 sequencing of duck hepatitis A virus type 1 and type 3 by a 1-step duplex reverse-transcription PCR assay

Duck hepatitis A virus (DHAV) is an infectious pathogen causing fatal duck viral hepatitis in ducklings. Although both the inactivated vaccines and live attenuated vaccines have been used to protect ducklings, DHAV-1 and DHAV-3 still cause significant serious damage to the duck industry in China and South Korea. For rapid detection, differentiation, and epidemic investigation of DHAV in China, a genotype-specific 1-step duplex reverse-transcription (RT) PCR assay was established in this study. The sensitivity and specificity of the developed RT-PCR assay was evaluated with nucleic acids extracted from 2 DHAV reference strains, and 9 other infectious viruses and bacteria. The genotype-specific primers amplified different size DNA fragments encompassing the complete VP1 gene of the DHAV-1 or DHAV-3. The assay detected the liver samples collected from experimentally infected ducklings and dead ducklings collected from different regions of China. Sequence analysis of these DNA fragments indicated that VP1 sequences of DHAV-1 can be used to distinguish wild type and vaccine strains. The phylogenetic analysis of VP1 sequences indicated that the developed RT-PCR assay can be used for epidemic investigation of DHAV-1 and DHAV-3. The developed RT-PCR assay can be used as a specific molecular tool for simultaneous detection, differentiation, and sequencing the VP1 gene of DHAV-1 and DHAV-3, which can be used for understanding the epidemiology and evolution of DHAV.

Apoptosis induction in duck tissues during duck hepatitis A virus type 1 infection

To investigate the role of apoptosis in duck viral hepatitis pathogenesis, 4- and 21-d-old ducks were inoculated with duck hepatitis A virus serotype 1 and killed at 2, 6, 12, 24, and 48 h postinfection. TdT-mediated dUTP nick-end labeling was used to detect apoptosis cells. Expression profiles of apoptosis-related genes including caspase-3, -8, -9, and Bcl-2 in spleen, bursa of Fabricius, liver, and the quantity of virus in blood were examined using real-time PCR. The TdT-mediated dUTP nick-end labeling analysis indicated there was a significant difference of apoptotic cells between treatments and controls. The same difference also appeared in virus amount variation in blood during infection. Gene expression analysis revealed that the apoptosis-related gene expression profile was different in the 2 groups, and also different between various organs. This study suggested that apoptosis may play an important role in duck hepatitis A virus serotype 1 infection, and apoptosis suppression might facilitate virus multiplication, resulting in the highest virus concentration in the host.