Isolation and Genomic Characterization of a Duck-Origin GPV-Related Parvovirus from Cherry Valley Ducklings in China

Genome cloning and genetic evolution analysis of eight duck-sourced novel goose parvovirus strains in China in 2023

Introduction

There are three major categories of waterfowl parvoviruses, namely goose parvovirus (GPV), Muscovy duck parvovirus, and novel goose parvovirus (NGPV). NGPV can infect both Cherry Valley ducks and mule ducks, resulting in short beaks and dwarfism syndrome, and the incidence of short beaks and dwarfism syndrome rises annually, posing a significant threat to the waterfowl breeding and the animal husbandry. Therefore, clarifying the biological characteristics and genetic evolution of NGPV is very important for the prevention and control of NGPV.

Methods

Ducks with short beaks and dwarfism syndrome from Shandong and Henan Province were investigated by dissection and the tissue samples were collected for study. The NGPV genome was amplified by PCR, and the genome was analyzed for genetic evolution.

Results

Eight strains of NGPV were isolated, which were designated as HZ0512, HZ0527, HZ0714, HZ0723, HZ0726, HZ0811, HZ0815, and HN0403. The nucleotide homology among these strains ranged from 99.9% to 100%. The eight strains, along with other NGPVs, belong to GPV. The eight strains showed a 92.5%-98.9% nucleotide homology with the classical GPV, while a 96.0%-99.9% homology with NGPV.Therefore, it can be deduced that there have been no major mutations of NGPV in Shandong and Henan provinces in recent years.

Discussion

This study lays a theoretical foundation for further studying the genetic evolution and pathogenicity of NGPV, thereby facilitating the prevention and control of NGPV.

Virus-Like Particles Based on the Novel Goose Parvovirus (NGPV) VP2 Protein Protect Ducks against NGPV Challenge

Novel goose parvovirus (NGPV), a genetic variant of goose parvovirus, has been spreading throughout China since 2015 and mainly infects ducklings with the symptoms of growth retardation, beak atrophy, and protruding tongue, leading to huge economic losses every year. A safe and effective vaccine is urgently needed to control NGPV infection. In this study, virus-like particles (VLPs) of NPGV were assembled and evaluated for their immunogenicity. The VP2 protein of NGPV was expressed in Spodoptera frugiperda insect cells using baculovirus as vector. The VP2 protein was efficiently expressed in the nucleus of insect cells, and the particles with a circular or hexagonal shape and a diameter of approximately 30 nm, similar to the NGPV virion, were observed using transmission electron microscopy (TEM). The purified particles were confirmed to be composed of VP2 using western blot and TEM, indicating that the VLPs of NGPV were successfully assembled. Furthermore, the immunogenicity of the VLPs of NGPV was evaluated in Cherry Valley ducks. The level of NGPV serum antibodies increased significantly at 1-4 weeks post-immunization. No clinical symptoms or deaths of ducks occurred in all groups after being challenged with NGPV at 4 weeks post-immunization. There was no viral shedding in the immunized group. However, viral shedding was detected at 3-7 days post-challenge in the non-immunized group. Moreover, VLPs can protect ducks from histopathological lesions caused by NGPV and significantly reduce viral load in tissue at 5 days post-challenge. Based on these findings, NGPV VLPs are promising candidates for vaccines against NGPV.

Involvement of Goose Parvovirus in Induction of Angel Wing Syndrome in Muscovy Ducks

Dietary, environmental, and hereditary causes were reported as causative agents of angel wing syndrome in waterfowl. Since 2017, several Muscovy duck flocks at Behira governorate were found to exhibit this syndrome associated with the clinical symptoms of goose parvovirus (GPV) infection. Four strains of goose parvovirus named HS1-HS4 were isolated and identified from diseased ducks at some of these flocks. Phylogenetic analysis revealed clustering of these strains together and within a distinct monophyletic group in relation to GPV strains of Derzsy's disease and short beak and dwarfism syndrome (SBDS). Nucleotide identities with goose parvovirus strain B of Derzsy's disease were 95.7%-96.6%, and with the strain JS1603 of SBDS they were 96.8%-97.4%. However, nucleotide identities with Muscovy duck parvovirus strain FM were 74.1%-74.6%. The disease was reproduced experimentally via oral-route artificial infection with HS1 strain, and both clinical symptoms of goose parvovirus and angel wing syndrome were observed in the artificially infected Muscovy ducks, but with less severity in geese. This study demonstrated clear evidence for induction of angel wing syndrome, at least partially, with GPV infection in Muscovy duck. To the authors' knowledge, this is the first work to mention a viral cause of angel wing syndrome in waterfowl.

Epidemiological Analysis and Genetic Characterization of Parvovirus in Ducks in Northern Vietnam Reveal Evidence of Recombination

In total, 130 tissue-pooled samples collected from ducks in some provinces/cities in north Vietnam were examined for waterfowl parvovirus genome identification. Twenty-six (20%) samples were positive for the parvovirus infection, based on polymerase chain reaction analysis. Of the 38 farms tested, 14 (36.84%) were positive for the waterfowl parvovirus genome. The rate of the parvovirus genome detection in ducks aged 2−4 weeks (37.04%) was significantly (p < 0.05) higher than that at ages <2 weeks (9.09%) and >4 weeks (16.30%). The positive rate on medium-scale farms (9.36%) was significantly (p < 0.05) lower than for small-scale (31.03%) and large-scale (29.73%) farms. The lengths of the four Vietnamese waterfowl parvovirus genomes identified were 4750 nucleotides. Among the four Vietnamese parvovirus genomes, nucleotide identities were from 99.29% to 99.87%. Phylogenetic analysis of the near-complete genomes indicated that the waterfowl circulating in northern Vietnam belonged to the novel goose parvovirus (NGPV) group. The Vietnamese NGPV group was closely related to the Chinese group. Recombination analysis suggested that the Vietnam/VNUA-26/2021 strain was generated by a recombination event. One positive selection site of the capsid protein was detected.

Molecular Identification and Pathogenicity of Novel Duck-Origin Goose Parvovirus Isolated from Beak Atrophy and Dwarfism Syndrome of Waterfowls in the North of Vietnam

The aim of this study is to identify and characterize virus isolates (which are named for Bacgiang Agriculture and Forestry University [BAFU]) from diseased Cherry Valley duck and mule duck flocks and investigate the damage caused by a novel parvovirus-related virus (DuPV) to tissues and organs, including the brain, cerebellum, kidney, liver, lung, spleen, and spinal cord. The results of phylogenetic analysis show that DuPV-BAFU evolved from a goose lineage and duck parvoviruses rather than from Muscovy duck parvoviruses. In the genetic lineages, DuPVs were identified from the DuPV samples analyzed, and DuPV-BAFU was found to be closely clustered with two known goose origin parvoviruses (GPVa2006 and GPV1995) and a duck GPVs. Finally, structural modeling revealed that DuPV-BAFU and the closely related viruses GPVa2006 and GPV1995 possessed identical clusters of receptor-interacting amino acid residues in the VP3 protein, a major determinant of viral receptor binding and host specificity. Significantly, these three viruses differed from DuPVs, Muscovy duck parvoviruses, and other goose parvoviruses at these positions. These results also demonstrated that DuPV-BAFU represents a new variant of goose-origin parvovirus that currently circulates in ducklings and causes beak atrophy and dwarfism syndrome, as noted in the previous reports in Europe, Taiwan, and China. This new finding highlights the need for future surveillance of DuPV-BAFU in waterfowl in order to gain a better understanding of both the evolution and the biology of this emerging parvovirus in waterfowl.

Reproduction and pathogenesis of short beak and dwarfish syndrome in Cherry Valley Pekin ducks infected with the rescued novel goose parvovirus

Since the outbreak of short beak and dwarfish syndrome (SBDS) in Cherry Valley Pekin ducks in China, novel goose parvovirus (NGPV) has been isolated. Till now, little is known about the NGPV pathogenesis toward Cherry Valley Pekin ducks. Besides, due to detection of duck circovirus co-infection in SBDS clinical cases, whether sole NGPV infection can reproduce all the typical symptoms of SBDS remains unclear. In this study, based on the NGPV isolate SDJN19, an infectious plasmid clone pJNm containing the entire SDJN19 genome was constructed. Transfection of pJNm in embryonated duck eggs resulted in generation of the infectious virus carrying the genetic marker, named rJNm. rJNm infection of 2-day-old Cherry Valley Pekin ducks reproduced all the typical signs of SBDS, including beak atrophy, tongue protrusion, and growth retardation. rJNm can infect Cherry Valley Pekin ducks through the horizontal transmission route, and the infected ducks exhibited the characteristic SBDS symptoms. A high level of serum precipitation antibodies (above 5log₂) were induced in the surviving ducks, however, high viral loads were still detected in the duck organs, suggesting persistent NGPV infection in ducks. By incorporating the homologous Rep1 and VP1 gene from classical GPV, two chimeric viruses rJN-cVP1 and rJN-cRep1 were generated. Duck infection tests revealed that the non-structural protein Rep1 played a crucial role in the NGPV pathogenicity. The present result lays a solid foundation for further exploring how the Rep protein contributes to the NGPV pathogenesis.

Characterizing two novel goose parvoviruses with different origins

Outbreaks of short beak dwarf syndrome caused by novel goose parvovirus (NGPV) have been prevalent in China since 2015, resulting in a high mortality rate of ducks. Herein we evaluated differences between two NGPV strains: Muscovy duck-origin (AH190917-RP: MD17) and Cherry Valley duck-origin (JS191021-RP: CVD21) NGPV. Both of them showed certain level of pathogenicity to primary duck embryo fibroblasts, Cherry Valley duck embryos and ducklings. CVD21 showed comparatively stronger pathogenicity than MD17. Only CVD21 caused obvious cytopathic effect (CPE), characterized by cell shedding; further, the virus titer of MD17 and CVD21 was 10^2.571 ELD₅₀ (i.e., median embryo lethal dose)/0.2 mL and 10^6.156 ELD₅₀ /0.2 mL, respectively, and the mortality rate of CVD21- and MD17-infected Cherry Valley ducklings was 100% and 80%, respectively. In addition, CVD21 had a greater influence on the growth and development of ducklings. Futhermore, we found that MD17 could infect Muscovy duck embryos and produce lesions similar to Cherry Valley duck embryos, but it could not infect Muscovy duck embryo fibroblasts (MDEFs,) and Muscovy ducklings. MDV21 had no infection to MDEFs, Muscovy duck embryo and Muscovy ducklings. We then sequenced the complete genome of the two isolates to enable genomic characterization. The complete genome of MD17 and CVD21 was 5,046 and 5,050 nucleotides in length, respectively. Nucleotide alignment, amino acid analysis, and phylogenetic tree analysis revealed that MD17 showed higher homology to goose parvovirus (GPV), while CVD21 demonstrated stronger similarity with NGPV. Moreover, the two isolates shared 95.8% homology, with encoded proteins showing multiple amino acid variations. Our findings indicate that Muscovy ducks seem to have played a crucial role in the evolution of GPV to NGPV. We believe that our data should serve as a foundation for further studying the genetic evolution of waterfowl parvoviruses and their pathogenic mechanisms. This article is protected by copyright. All rights reserved.

Advances in research on genetic relationships of waterfowl parvoviruses

Derzsy’s disease and Muscovy duck parvovirus disease have become common diseases in waterfowl culture in the world and their potential to cause harm has risen. The causative agents are goose parvovirus (GPV) and Muscovy duck parvovirus (MDPV), which can provoke similar clinical symptoms and high mortality and morbidity rates. In recent years, duck short beak and dwarfism syndrome has been prevalent in the Cherry Valley duck population in eastern China. It is characterised by the physical signs for which it is named. Although the mortality rate is low, it causes stunting and weight loss, which have caused serious economic losses to the waterfowl industry. The virus that causes this disease was named novel goose parvovirus (NGPV). This article summarises the latest research on the genetic relationships of the three parvoviruses, and reviews the aetiology, epidemiology, and necropsy characteristics in infected ducks, in order to facilitate further study.

Molecular Characterization and Pathogenicity of the Novel Recombinant Muscovy Duck Parvovirus Isolated from Geese

Simple Summary

Waterfowl parvoviruses are important pathogens that cause severe disease in young waterfowl. Waterfowl parvoviruses can be divided into goose parvovirus (GPV)- and Muscovy duck parvovirus (MDPV)-related groups. New variant strains can be generated from genomic recombination between different waterfowl parvoviruses and result in new epidemics. Recently, a novel recombinant MDPV (rMDPV) derived from recombination between GPVs and MDPV was reported. This virus caused high morbidity and mortality rates in ducklings and was circulating in waterfowl in mainland China. In this study, a novel rMDPV was isolated in Taiwan from a goose flock that experienced a high mortality. The complete genome of this goose-origin rMDPV was sequenced. Phylogenetic and recombination analyses were performed to elucidate its molecular characteristics. The virulence of this rMDPV was evaluated using experimental infection goose embryos and goslings. This study was the first report showing the pathogenicity of rMDPV in geese.

Abstract

Goose parvovirus (GPV) and Muscovy duck parvovirus (MDPV) are the main agents associated with waterfowl parvovirus infections that caused great economic losses in the waterfowl industry. In 2020, a recombinant waterfowl parvovirus, 20-0910G, was isolated in a goose flock in Taiwan that experienced high morbidity and mortality. The whole genome of 20-0910G was sequenced to investigate the genomic characteristics of this isolate. Recombination analysis revealed that, like Chinese rMDPVs, 20-0910G had a classical MDPV genomic backbone and underwent two recombination events with classical GPVs at the P9 promoter and partial VP3 gene regions. Phylogenetic analysis of the genomic sequence found that this goose-origin parvovirus was highly similar to the circulating recombinant MDPVs (rMDPVs) isolated from duck flocks in China. The results of experimental challenge tests showed that 20-0910G caused 100% mortality in goose embryos and in 1-day-old goslings by 11 and 12 days post-inoculation, respectively. Taken together, the results indicated that this goose-origin rMDPV was closely related to the duck-origin rMDPVs and was highly pathogenic to young geese.

Molecular characteristics and phylogenetic analysis of novel goose parvovirus strains associated with short beak and dwarfism syndrome

Short beak and dwarfism syndrome (SBDS) emerged in Cherry Valley duck flocks in China in 2015, and novel goose parvovirus (NGPV) was shown to be the etiological agent of SBDS. To date, it is not known whether SBDS-related NGPV isolates possess common molecular characteristics. In this study, three new NGPV strains (namely, SDHT16, SDJN19, and SDLC19) were isolated from diseased ducks showing typical signs of SBDS and successfully passaged in embryonated goose or Cherry Valley duck eggs. The complete genome sequences of these NGPV strains were 98.9%-99.7% identical to each other but showed slightly less similarity (95.2%-96.1% identity) to classical GPV strains. A total of 16 common amino acid substitutions were present in the VP1 proteins of six NGPV strains (SDHT16, SDJN19, SDLC19, QH, JS1, and SDLC01) compared with the classical Chinese GPV strains, nine of which were identical to those found in European GPV strain B. The non-structural protein Rep1 of the six NGPV strains had 12 common amino acid substitutions compared with the classical GPV strains. Phylogenetic analysis indicated that the Chinese NGPV strains clustered with the European SBDS-related NGPV strains, forming a separate branch that was distinct from the group formed by the classical GPV strains. The present study shows the common molecular characteristics of NGPV isolates and suggests that the Chinese NGPV isolates probably share a common ancestor with European SBDS-related NGPV strains.

Genetic characterization and phylogenetic analysis of duck-derived waterfowl parvovirus in Anhui province, eastern China

Recently, a novel duck-origin goose parvovirus (N-GPV) was reported to cause short beak and dwarfism syndrome in ducks. In this study, we performed complete genome sequencing and analyzed three different duck-derived parvoviruses that infected different breeds of ducks. Phylogenetic trees based on gene sequences indicated that they were classical goose parvovirus (C-GPV), Muscovy duck parvovirus (MDPV), and N-GPV. Furthermore, potential recombination events were found. These results improve our understanding of the diversity of duck-derived parvoviruses in Anhui province, eastern China, and provide a reference for the prevention of associated diseases.

VP2 virus-like particles elicit protective immunity against duckling short beak and dwarfism syndrome in ducks

Duckling short beak and dwarfism syndrome virus (SBDSV), an emerging goose parvovirus, has caused short beak and dwarfism syndrome (SBDS) in Chinese duck flocks since 2015. Presently, there is no commercial vaccine against SBDS. In the present study, a virus-like particle (VLP)-based candidate vaccine was developed against this disease. A baculovirus expression system was used to express the SBDSV VP2 protein in Sf9 cells. Immunofluorescence assay, sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting were used to confirm protein expression. Furthermore, transmission electron microscopy was used to observe the formation of VLPs. VLPs were formulated into an oil-adjuvanted maternal vaccine to evaluate humoral responses in breeding ducks via latex particle agglutination inhibition assay (LPAI) and microneutralization assay. The offspring were challenged with SBDSV to test the protective efficacy. A single dose of SBDSV was able to induce the high level of LPAI antibodies in ducks, with LPAI and neutralization peak titres of 4.9 ± 1.20 log2 and 7.1 ± 1.20 log2, respectively, at 4 weeks post-vaccination (wpv). The average LPAI titre of yolk antibodies in duck eggs receiving 2 doses (first and boost doses) of the vaccine was 5.3 ± 1.09 log2 at 4 weeks post-boost. The protective efficacy of the maternal vaccine was 87.5%-100%. These results indicate that SBDSV VLPs can be a promising vaccine candidate for controlling SBDS.

An altered gut microbiota in duck-origin parvovirus infection on cherry valley ducklings is associated with mucosal barrier dysfunction

Duck-origin parvovirus disease is an epidemic disease mainly caused by duck-origin goose parvovirus (D-GPV), which is characterized by beak atrophy and dwarfism syndrome. Its main symptoms are persistent diarrhea, skeletal dysplasia, and growth retardation. However, the pathogenesis of Cherry Valley ducks infected by D-GPV has not been studied thoroughly. To perceive the distribution of D-GPV in the intestinal tract, intestinal morphological development, intestinal permeability, inflammatory cytokines in Cherry Valley ducks, and expression of tight junction protein, the D-GPV infection was given intramuscularly. Illumina MiSeq sequencing technology was used to analyze the diversity and structure of ileum flora and content of short-chain fatty acids of its metabolites. To investigate the relationship between intestinal flora changes and intestinal barrier function after D-GPV infection on Cherry Valley ducks is of great theoretical and practical significance for further understanding the pathogenesis of D-GPV and the structure of intestinal flora in ducks. The results showed that D-GPV infection was accompanied by intestinal inflammation and barrier dysfunction. At this time, the decrease of a large number of beneficial bacteria and the content of short-chain fatty acids in intestinal flora led to the weakening of colonization resistance of the intestinal flora and the accumulation of potentially pathogenic bacteria, which would aggravate the negative effect of D-GPV damage to the intestinal tract. Furthermore, a significant increase in Unclassified_S24-7 and decrease in Streptococcus was observed in D-GPV persistent, indicating the disruption in the structure of gut microbiota. Notably, the shift of microbiota was associated with the transcription of tight-junction protein and immune-associated cytokines. These results indicate that altered ileum microbiota, intestinal barrier, and immune dysfunction are associated with D-GPV infection. Therefore, there is a relationship between the intestinal barrier dysfunction and dysbiosis caused by D-GPV, but the specific mechanism needs to be further explored.

A TaqMan-based real-time PCR assay for specific detection of novel duck reovirus in China

BACKGROUND

In China, Newly emerging duck reovirus (NDRV) variants have been causing major disease problems in cherry valley ducks. NDRV has the potential to cause high morbidity and 5-50% mortality rates. Severe hemorrhagic-necrosis in the liver and spleen were commonly seen in NDRV affected ducks. The availability of upgraded methods for rapid diagnosis of newly emerging DRV variants is crucial for successful DRV infection control and prevention.

RESULTS

In this study, we present a TaqMan-based real-time PCR assay (RT-qPCR) for the detection of NDRV infection. Using the conserved regions within the NDRV genome, we designed the specific primers and probe. The lower limit of detection for NDRV infection was 10 copies/μL (Ct values: 38.3) after the optimization of the RT-qPCR conditions. By cross-checking with other duck viral pathogens, no cross-reactivity was observed confirming the assay was highly specific for the detection of NDRV. Reproducibility of the RT-qPCR was confirmed by intra- and inter-assay variability was less than 2.91%(Intra-assay variability of Ct values: 0.07-1.48%; Interassay variability of Ct values: 0.49-2.91%). This RT-qPCR and conventional PCR (cPCR) detected one hundred and twenty samples of NDRV infection from different regions. The result shows that the positive rates were 94.17 and 84.17% respectively. The detection rate of RT-qPCR rapid detection assay was 10% higher than that of the cPCR method.

CONCLUSION

This research developed a highly sensitive, specific, reproducible and versatile of RT-qPCR for quantitatively detecting NDRV. It can be used to study the pathogenesis and epidemiology investigation of NDRV.

Simultaneous detection of duck circovirus and novel goose parvovirus via SYBR green I-based duplex real-time polymerase chain reaction analysis

Beak atrophy and dwarfism syndrome (BADS) is commonly caused by co-infection with duck circovirus (DuCV) and novel goose parvovirus (NGPV). Therefore, concurrent detection of both viruses is important for monitoring and limiting BADS, although such a diagnostic test has not been reported. In this study, we developed a duplex, SYBR Green I-based real-time polymerase chain reaction (PCR) assay to enable the simultaneous detection of DuCV and NGPV. The assay readily distinguished between the two viruses, based on their different melting temperatures (Tm), where the Tm for DuCV was 80 °C and that for NGPV was 84.5 °C. Other non-target duck viruses that were tested did not show melting peaks. The detection limit of the duplex assay was 10¹ copies/μL for both viruses. This method exhibited high repeatability and reproducibility, and both the inter-assay and intra-assay variation coefficients were <1.6%. Thirty-one fecal samples were collected for clinical testing using real-time PCR analysis, and the results were confirmed using sequencing. The rate of co-infection was 6.5%, which was consistent with the sequencing results. This duplex real-time PCR assay offers advantages over other tests, such as rapid, sensitive, specific, and reliable detection of both viruses in a single sample, which enables the quantitative detection of DuCV and NGPV in clinical samples. Using this test may be instrumental in reducing the incidence of BADS and the associated economic losses in the duck and goose industries.

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SYBR Green based PCR to simultaneously detect duck circovirus and goose parvovirus.

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The assay had specificity, sensitivity and reproducibility.

Effect of Goose Parvovirus and Duck Circovirus Coinfection in Ducks

Introduction

Coinfection of goose parvovirus (GPV) and duck circovirus (DuCV) occurs commonly in field cases of short beak and dwarfism syndrome (SBDS). However, whether there is synergism between the two viruses in replication and pathogenicity remains undetermined.

Material and Methods

We established a coinfection model of GPV and DuCV in Cherry Valley ducks. Tissue samples were examined histopathologically. The viral loads in tissues were detected by qPCR, and the distribution of the virus in tissues was detected by immunohistochemistry (IHC).

Results

Coinfection of GPV and DuCV significantly inhibited growth and development of ducks, and caused atrophy and pallor of the immune organs and necrosis of the liver. GPV and DuCV synergistically amplified pathogenicity in coinfected ducks. In the early stage of infection, viral loads of both pathogens in coinfected ducks were significantly lower than those in monoinfected ducks (P < 0.05). With the development of the infection process, GPV and DuCV loads in coinfected ducks were significantly higher than those in monoinfected ducks (P < 0.05). Extended viral distribution in the liver, kidney, duodenum, spleen, and bursa of Fabricius was consistent with the viral load increases in GPV and DuCV coinfected ducks.

Conclusion

These results indicate that GPV and DuCV synergistically potentiate their replication and pathogenicity in coinfected ducks.

Coinfection of novel goose parvovirus-associated virus and duck circovirus in feather sacs of Cherry Valley ducks with feather shedding syndrome

Since 2017, an infectious disease, named feather shedding syndrome (FSS), has consistently broken out in Cherry Valley ducks in East China. The sick ducks showed the new clinical symptoms of feather shedding and being plucked off with difficulty after slaughter. The high incidence rate of 20 to 70% predominantly happened in ducks of 4 to 5 wk of age, and nearly 40% mortality rate was observed in infected ducks. To explore the possible role of novel goose parvovirus–associated virus (NGPV) and duck circovirus (DuCV) in this disease, a total of 540 feather sac samples were collected from sick ducks with FSS. The infection rates of NGPV and DuCV in samples were 82.78 and 78.89%, respectively, and the coinfection rate of the 2 viruses was 70.00%. Notably, ducks of 4 to 5 wk of age usually presented obvious and severe FSS in the flocks with high codetection rate of NGPV and DuCV. Furthermore, 9 NGPV strains were isolated from feather sacs and 5 synchronous amino acid mutations were demonstrated in VP3 protein. These results indicated that coinfection of NGPV and DuCV might play an important role in duck FSS disease.

Coinfection of parvovirus and astrovirus in gout-affected goslings

Outbreaks of gosling gout have occurred in China since 2017 and caused a considerable economic impact on the poultry industry. While gosling astrovirus (GoAstV) is believed to be the main causal pathogen of gout, the full-blown disease of gout cannot be well reproduced by infecting the goslings with GoAstV, suggesting the possibility of other infectious agents being involved with the development of gosling gout. To assess other possible infectious agents, we collected tissues from gout-affected goslings in 12 goose farms in China, followed by PCR detection of GoAstV, goose reovirus (GRV), goose parvovirus (GPV), fowl adenovirus (FAdV), goose circovirus (GcoV), Tembusu virus (TMUV) and goose haemorrhagic polyomavirus (GHPV). Our data showed that all gout-affected goslings carried both of GoAstV and GPV determined by PCRs, and this was further confirmed by fluorescence multiplex immunohistochemical staining, and phylogenetic analysis of ORF2 gene of GoAstV and VP3 gene of GPV. In addition to the haemorrhage in the kidney, liver, spleen and lung of the gout-affected goslings, histological examinations showed also extensive infiltration of heterophil myelocytes in the kidney, liver, spleen, bursa of Fabricius, thymus, lungs and pancreas. Our findings strongly suggest that coinfection of GoAstV and GPV increases the severity of gout. While this is the first study to report GPV in gout-affected goslings, further studies including infection model are warranted to investigate the role of GPV and its coinfection with GoAstV in the development of gosling gout.

Identification of a common conserved neutralizing linear B-cell epitope in the VP3 protein of waterfowl parvoviruses

Waterfowl parvoviruses (WPVs) including goose parvovirus (GPV), novel GPV-related virus (NGPV) and Muscovy duck parvovirus (MDPV) cause significant economic losses and epizootic threat to the waterfowl industries, and little is known about the B-cell epitopes of WPVs. In this study, a monoclonal antibody (mAb) 5B5 against the VP3 protein of NGPV was used to identify the possible epitope in the three kinds of WPVs. The mAb 5B5 had neutralizing activities to the three viruses, and reacted with the conserved linear B-cell epitopes of ⁴³⁸LHNPPP⁴⁴³ in VP3 protein of GPV, NGPV and MDPV. To the authors' best knowledge, this is the first report on identification of the common conserved neutralizing linear B-cell epitope on VP3 protein of three different WPVs, which would facilitate the development of a novel immunodiagnostic assay for rapid detection of WPV infection.

Molecular Characterization and Comparative Pathogenicity of Goose Parvovirus Isolated from Jilin Province, Northeast China

Goose parvovirus (GPV) is a highly contagious disease caused by GPV in goslings and young Muscovy ducklings. In recent years, frequent GPV outbreaks have occurred in many regions of Jilin Province, China. In this study, to understand the immune-related characteristics of the currently prevailing GPV strains in some regions of Jilin Province, six GPV strains were isolated from six different regions of Jilin Province in 2016-2018. The results of phylogenetic analysis, clinical signs, and histopathologic analysis showed that four strains were virulent and two strains were attenuated. Specifically, we found that the two attenuated strains have the same amino acid mutation at the same position in the virus protein 3 (VP3) gene, and the virulent strains have more mutation sites than the attenuated strains. This finding suggests that changes in these sites may result in GPV replication or reduction in the immune response in goslings, thereby producing strong pathogenicity, and that attenuated strains are more conservative than virulent strains.

Detection and Molecular Characterization of Two Genotypes of Goose Parvoviruses Isolated from Growing Period Geese and Cherry Valley Ducks in China

Goose parvovirus (GPV) is the etiologic pathogen of Derzsy's disease, causing great economic losses in the waterfowl industry. A novel GPV-related virus (NGPV), which caused short beak and dwarfism syndrome, has occurred in China since 2015. In this study, two GPV strains (RC45 and RC70) were isolated from diseased growing period geese (45 days old and 70 days old), and one NGPV strain GXN45 was isolated from a 45-day-old Cherry Valley duck in China. To better understand the genetic diversity between GPVs isolated from growing period waterfowls and other classical waterfowl parvoviruses, the complete genomes and main genes were sequenced and analyzed. Full-length genomic sequence alignments demonstrated that both RC45 and RC70 showed the highest identity with classical GPVs YZ99-6 and SHFX1201, whereas GXN45 shared the highest identity with NGPV SDLC01. Sequence alignment of the inverted terminal repeat region showed that GXN45, RC45, and RC70 had two 14-nucleotide (nt) deletions compared with the classical GPV virulent B strain and one 14-nt deletion compared with mule duck-origin NGPV M15 strain. Phylogenetic tree analysis of nonstructural and VP1 genes showed that GXN45 was clustered into a branch with NGPV QH15 strain except for the VP1 amino acid tree. Although both RC45 and RC70 formed one separate branch distinct from classic GPV isolates, they were in one large phylogenetic tree branch. This study will contribute to a better understanding of the genetic diversity and molecular characterization of three isolated parvoviruses and lay the foundation to further study the relationship between mutations of virus genome and viral pathogenicity.

Specific detection and differentiation of classic goose parvovirus and novel goose parvovirus by TaqMan real-time PCR assay, coupled with host specificity

Background

Classic goose parvovirus (cGPV) causes high mortality and morbidity in goslings and Muscovy ducklings. Novel GPV (N-GPV) causes short beak and dwarfism syndrome (SBDS) in Cherry Valley ducks, Pekin ducks and Mule ducks. Both cGPV and N-GPV have relatively strict host specificity, with obvious differences in pathogenicity. Specific detection of cGPV and N-GPV may result in false positives due to high nucleotide similarity with Muscovy duck parvovirus (MDPV). The aim of this study was to develop a highly specific, sensitive, and reliable TaqMan real-time PCR (TaqMan qPCR) assay for facilitating the molecular detection of cGPV and N-GPV.

Results

After genetic comparison, the specific conserved region (located on the NS gene) of cGPV and N-GPV was selected for primer and probe design. The selected regions were significantly different from MDPV. Through a series of optimization experiments, the limit of detection was 50.2 copies/μl. The assay was highly specific for the detection of cGPV and N-GPV and no cross-reactivity was observed with E. coli., P.M., R.A., S.S., MDPV, N-MDPV, DAdV-A, DEV, GHPV, DHAV-1, DHAV-3, ATmV, AIV, MDRV and N-DRV. The assay was reproducible with an intra-assay and inter-assay variability of less than 2.37%. Combined with host specificity, the developed TaqMan qPCR can be used for cGPV and N-GPV in differential diagnoses. The frequency of cGPV in Muscovy duckling and goslings was determined to be 12 to 44%, while N-GPV frequency in Mule ducks and Cherry Valley ducks was 36 to 56%. Additionally, fluorescence-positive signals can be found in Mule duck embryos and newly hatched Mule ducklings. These findings provide evidence of possible vertical transmission of N-GPV from breeding Mule ducks to ducklings.

Conclusions

We established a quantitative platform for epidemiological investigations and pathogenesis studies of cGPV and N-GPV DNA that was highly sensitive, specific, and reproducible. N-GPV and cGPV infections can be distinguished based on host specificity.

Molecular evidence of goose-parvovirus-related abnormal molting in Pekin ducks

Since January 2019, abnormal molting has been observed frequently in approximately 40-day-old Pekin ducks in China. To investigate the possible involvement of a virus, we tested the prevalence of duck circovirus (DuCV), goose hemorrhagic polyomavirus (GHPyV), and goose parvovirus (GPV) in 11 molt cases in two provinces. GPV was detected in all cases, particularly in all samples collected from the feather area. The complete genome sequences of three GPV strains were determined and found to have 52 nucleotide changes relative to GPVs associated with short beak and dwarfism syndrome of Pekin ducks. These data will enhance our understanding of GPV diversity and outcomes of GPV infection in Pekin ducks.

Novel goose parvovirus in domestic Linwu sheldrakes with short beak and dwarfism syndrome, China

Recently, short beak and dwarfism syndrome (SBDS) had a sudden outbreak in Cherry Valley duck flocks, followed by Pekin ducks and mule ducks in various regions of mainland China. This widely spreading infectious disease was characterized by growth retardation, smaller beak and tarsus with high morbidity and low mortality rate. In this study, we identified and characterized virus from domestic Linwu sheldrakes (namely as HuN18) with SBDS. HuN18 isolates shared high nucleotide identity with novel goose parvovirus (N-GPV). A 5110-nucleotide full-length genome sequence of HuN18 was found with no deletion in ITR region. Alignment studies of HuN18 showed 96.8%-99.0% identity with other N-GPVs and 92.9%-96.3% identity with classic GPV. According to the recombination analysis, HuN18 showed the potential major parent was the N-GPV sdlc01 strain, the potential minor parent was the classical GPV Y strain, and the secondary potential minor parent was the SYG61v strain. To the best of our knowledge, this is the first report of N-GPV in domestic Linwu sheldrakes with SBDS; these data provide evidence that attenuated live viruses are involved in genetic recombination with prevailing wild parvoviruses, which contributes to the novel emerging variants of waterfowl parvoviruses.

Diagnosis and characterization of duck beak atrophy and dwarfism syndrome in Chongqing of China

Duck beak atrophy and dwarfism syndrome (BADS) is a newly emerged disease in China since 2015. In October 2017, an unidentified disease occurred in Cherry Valley ducks, Chongqing municipality, the southwest of China. The affected birds showed short beak and growth retardation clinical signs. The disease caused approximately 20.00% morbidity and serious weight loss due to retarded growth. In order to identify the causative agent of BADS, liver, spleen, lung and heart samples were collected for virus isolation, hemagglutination test, PCR identification, and partial gene sequencing. The isolated virus was tentatively named SC16. Hemagglutination test indicated that the virus was negative to chicken red blood cells. Based on the PCR and sequencing results, the causative agent of BADS was a novel duck-origin goose parvovirus (DGPV) while no another co-infection pathogen was found in this case. Further analysis could provide insights into the control strategies of DGPV in ducks.

Impacts of Duck-Origin Parvovirus Infection on Cherry Valley Ducklings From the Perspective of Gut Microbiota

Duck-origin goose parvovirus (D-GPV) is the causative agent of beak atrophy and dwarfism syndrome (BADS), characterized by growth retardation, skeletal dysplasia, and persistent diarrhea. However, the pathogenic mechanism of D-GPV remains undefined. Here, we first reported the gut microbiome diversity of D-GPV infected Cherry Valley ducks. In the investigation for the influence of D-GPV infection on gut microbiota through a period of infection, we found that D-GPV infection caused gut microbiota dysbiosis by reducing the prevalence of the dominant genera and decreasing microbial diversity. Furthermore, exfoliation of the intestinal epithelium, proliferation of lymphocytes, up-regulated mRNA expression of pro-inflammatory TNF-α, IL-1β, IL-6, IL-17A, and IL-22 and down-regulated mRNA expression of anti-inflammatory IL-10 and IL-4 occurred when D-GPV targeted in cecal epithelium. In addition, the content of short chain fatty acids (SCFAs) in cecal contents was significantly reduced after D-GPV infection. Importantly, the disorder of pro-inflammatory and anti-inflammatory cytokines was associated with the decrease of SCFAs-producing bacteria and the enrichment of opportunistic pathogens. Collectively, the decrease of SCFAs and the enrichment of pathogen-containing gut communities promoted intestinal inflammatory injury. These results may provide a new insight that target the gut microbiota to understand the progression of BADS disease and to research the pathogenic mechanism of D-GPV.

Identification and genomic analysis of two novel duck-origin GPV-related parvovirus in China

Background

Since early 2015, mule duck and Cherry Valley duck flocks have been suffering from short beak and dwarfism syndrome. This widely spreading infectious disease is characterized by growth retardation, smaller beak and tarsus with high morbidity and low mortality rate. For better understanding, we identified and characterized virus isolates named AH and GD from diseased Cherry Valley duck and mule duck flocks and investigated the damage caused by novel parvovirus-related virus (NGPV) to tissues and organs, including kidney, brain, pancreas, liver, spleen, bursa of fabricius and myocardial tissues.

Results

AH and GD isolates shared high nucleotide identity with goose parvovirus (GPV). Alignment studies of AH and GD isolates showed 94.5–99.2% identity with novel parvovirus-related virus (NGPV), 98.7–91.5% identity with GPV and 79.9–83.7% with muscovy duck parvovirus (MDPV). Compared with other NGPV, classical GPV and MDPV sequences, a four 14-nucleotide-pair insertion in GD isolate was found in left open reading frame (ORF) (87–100 nt and 350–363 nt) and in right ORF (4847–4861 nt and 5122–5135 nt). However, in AH isolate, a five 14-nucleotide-pair deletions similar to other NGPV were found. The complete genome sequence comparison of eleven NGPV isolates from mule ducks and cherry valley ducks revealed no remarkable difference between them. Notably, the myocardium and bursa of fabricius of both disease and healthy animals are perfectly normal while other tissues have inflammatory cells exudation.

Conclusions

The AH and GD strains are novel parvovirus-related virus that isolates from mule ducks or cherry valley ducks which DNA sequence has no remarkable difference. The histopathology of tissues and organs such as kidney, brain etc. revealed non-significant changes in experimental and control animals. Overall, this study has contributed better understanding of molecular biology of NGPV strains and will help to develop the candidate strain for vaccine preparation to get better protection against these viral infections.

Growth characteristics of the novel goose parvovirus SD15 strain in vitro

Background

Short beak and dwarfism syndrome (SBDS) was caused by novel goose parvovirus (NGPV)--a variant of goose parvovirus (GPV). Ducks infected with NGPV shows clinical signs including growth retardation and protrusion of the tongue from an atrophied beak. SBDS outbreak was first reported at the northern coastal provinces of China during 2015 and it was again reported in Sichuan, an inland province of China in 2016. The disease caused a huge economic loss in Chinese duck feeding industry.

Results

The SD15 strain of NGPV was isolated from liver and intestinal tract tissue samples of infected ducks. Real-time quantitative PCR (qPCR) was used to estimate viral load in embryonated eggs and cells infected with adapted virus. The data showed that duck embryo fibroblasts (DEFs) were permissive to NGPV, while goose embryo fibroblasts (GEFs) cells were not, and the copy numbers of SD15 in the allantoic fluid of infected eggs remained at 10^5.0–10^6.5 copies/ml. The adaption procession of the virus was determined via qPCR, and viral proliferation was detected through indirect fluorescent antibody assay (IFA) in DEFs. It was further determined that viral copy numbers peaked at 96 h post-inoculation (hpi), which is the best time to harvest the virus in DEFs. Cytotoxic effects and cell death were observed at 72 hpi in SD15 infected DEFs, yet SD15 did not induce apoptosis.

Conclusions

The growth characteristics of SD15 strain of NGPV determined would be beneficial for further molecular characterization of these viruses and develop potential vaccines if required.

Development of a PCR assay for detection and differentiation of Muscovy duck and goose parvoviruses based on NS gene characterization

Muscovy duck parvovirus (MDPV) and goose parvovirus (GPV) have both been found to cause high mortality and morbidity in Muscovy ducklings. Specific detection is often rife with false positives due to high identity at the genomic nucleotide level and antigenic similarity between MDPVs and GPVs. In this study, significantly variable regions were found, via non-structural (NS) comparison, between MDPV and GPV NS genes; however, NS genes were conserved within the MDPV and GPV groups. A polymerase chain reaction (PCR) assay for detecting and differentiating MDPVs and GPVs was developed with more specificity based on the NS gene characterization. The assay detected as low as 10³ DNA copies of both the MDPV and GPV strains, along with 549 separate base pairs (bp). No bands of the same size from other duck pathogens, including duck circovirus, duck enteritis virus, egg drop syndrome virus, duck-origin goose hemorrhagic polyomavirus, Escherichia coli, Salmonella, Riemerella anatipestifer and Pasteurella multocida were amplified. This indicates that this method for performing PCR provides a useful and reliable alternative tool for more precise differentiation of MDPV and GPV infection in clinical samples.

Specific detection of Muscovy duck parvovirus infection by TaqMan-based real-time PCR assay

BACKGROUND

Muscovy duck parvovirus (MDPV) causes high mortality and morbidity in Muscovy ducks, with the pathogenesis of the virus still unknown in many respects. Specific MDPV detection is often rife with false positive results because of high identity at the genomic nucleotide level and antigenic similarity with goose parvovirus (GPV). The objective of this study was to develop a sensitive, highly specific, and repeatable TaqMan-based real-time PCR (qPCR) assay for facilitating the molecular detection of MDPV.

RESULTS

The specific primers and probe were designed based on the conserved regions within MDPVs, but there was a variation in GPVs of the nonstructural (NS) genes after genetic comparison. After the optimization of qPCR conditions, the detection limit of this qPCR assay was 29.7 copies/μl. The assay was highly specific for the detection of MDPV, and no cross-reactivity was observed with other non-targeted duck-derived pathogens. Intra- and inter-assay variability was less than 2.21%, means a high degree of repeatability. The diagnostic applicability of the qPCR assay was proven that MDPV-positive can be found in cloacal swabs samples, Muscovy duck embryos and newly hatched Muscovy ducklings.

CONCLUSIONS

Our data provided incidents that MDPV could be possible vertically transmitted from breeder Muscovy ducks to Muscovy ducklings. The developed qPCR assay in the study could be a reliable and specific tool for epidemiological surveillance and pathogenesis studies of MDPV.

Microbiological identification and analysis of waterfowl livers collected from backyard farms in southern China

In total, 985 livers were collected from 275 backyard waterfowl farms distributed in seven provinces of southern China. The virus that was most commonly isolated was avian influenza virus, with a 12.1% positivity rate. Of the other positive samples, 10.6% tested positive for avian Tembusu virus, 6.8% for duck hepatitis A virus, 3.8% for duck plague virus, 3.4% for Muscovy duck parvovirus, 3.1% for goose parvovirus, 1.0% for mycoplasma and 0.9% for respiratory enteric orphan virus. The bacterium that was most commonly isolated was Escherichia coli, with a 47.1% positivity rate. This survey suggests that backyard waterfowl in southern China could be an important vector for the storage, variation, and transmission of various pathogens.

Pathogenicity of a variant goose parvovirus, from short beak and dwarfism syndrome of Pekin ducks, in goose embryos and goslings

The pathogenicity of a variant goose parvovirus (GPV), isolated from short beak and dwarfism syndrome of Pekin ducks (strain Cherry Valley), was investigated in embryonating goose eggs and goslings. The virus was easily grown in GPV antibody-free goose embryos and caused high mortality and severe lesions of goose embryos, indicating that the variant GPV has good adaptation and high pathogenicity to embryonated goose eggs similar to the classical GPV. Like the third egg-passage virus (strain H) of a classical GPV, the third egg-passage virus (strain JS1) of the variant GPV caused Derzsy's disease in 2-day-old goslings with high mortality. The findings suggest that the variant GPV strain, which had specifically adapted to Pekin ducks, still retained high pathogenicity for its original host. The mortality (73.3-80%) caused by the first and third egg-passages of the variant GPV was somewhat lower than that (93.3%) caused by the third passage virus of the classical GPV, reflecting the higher pathogenicity of the classical GPV for its original host. These findings are likely to reinforce the importance of surveillance for parvoviruses in different waterfowl species and stimulate further study to elucidate the impact of mutations in the GPV genome on its pathogenicity to goslings and ducks.

Comparative genetic analysis and pathological characteristics of goose parvovirus isolated in Heilongjiang, China

BACKGROUND

Goose parvovirus (GPV) causes acute enteritis, hepatitis, myocarditis and high morbidity and mortality in geese and ducks. GPV H strain was isolated from a Heilongjiang goose farm where the geese were showing signs of hemorrhage in the brain, liver, and intestinal tract. In this study, we explored the genetic diversity among waterfowl parvovirus isolates and the pathological characteristics of GPV H in Shaoxing ducklings.

METHODS

The complete capsid protein (VP) and non-structural (NS) sequences of the isolated H strain were sequenced, and phylogenetic trees of VP and NS were constructed in MEGA version 5.05 using the neighbor-joining method. Three-day-old Shaoxing ducklings were inoculated with GPV and were euthanized at 1, 2, 4, 6, and 8 days post-inoculation (PI), and their organs were removed and collected. The organs of 6-day PI ducklings were fixed in formalin, embedded in paraffin, sectioned for histology, stained with HE and analyzed for pathological lesions. The distribution of the GPV H strain in the tissues of the inoculated ducklings was detected using the polymerase chain reaction (PCR) method.

RESULTS

Genetic analysis of the NS and VP genes indicated that the H strain was closely related to strains circulating in China during 1999-2014, and the nucleic acid identity of those strains was 98%-99%. Classical symptoms were observed in the inoculated ducklings. GPV remained in many tissues and replicated in a majority of the tissues, leading to histopathological lesions in four tissues.

CONCLUSIONS

We first reported the distribution and histopathological lesions of a Chinese strain of GPV in infected shaoxing ducklings. This H strain was moderate pathogenic for Shaoxing ducklings.

Duck "beak atrophy and dwarfism syndrome" disease complex: Interplay of novel goose parvovirus-related virus and duck circovirus?

As a newly emerged infectious disease, duck "beak atrophy and dwarfism syndrome (BADS)" disease has caused huge economic losses to waterfowl industry in China since 2015. Novel goose parvovirus-related virus (NGPV) is believed the main pathogen of BADS disease; however, BADS is rarely reproduced by infecting ducks with NGPV alone. As avian circovirus infection causes clinical symptoms similar to BADS, duck circovirus (DuCV) is suspected the minor pathogen of BADS disease. In this study, an investigation was carried out to determine the coinfection of NGPV and DuCV in duck embryos and in ducks with BADS disease. According to our study, the coinfection of emerging NGPV and DuCV was prevalent in East China (Shandong, Jiangsu and Anhui province) and could be vertical transmitted, indicating their cooperative roles in duck BADS disease.

Development of a Quantitative Loop-Mediated Isothermal Amplification Assay for the Rapid Detection of Novel Goose Parvovirus

An infectious disease characterized with short bills and protruding tongues has attacked to meat ducks in China since March 2015, which has caused ducks poor growth and enormous economic losses to duck industry of China. It was eventually proved to be caused by parvovirus after pathogen isolation and identification. As the genomic sequence analysis showed, this pathogen shared 90.8-94.6% of nucleotide identity with goose parvovirus (GPV), and it was called duck-origin novel goose parvovirus (N-GPV). In this study, a quantitative loop-mediated isothermal amplification (qLAMP) assay was developed for the rapid diagnosis of N-GPV. A set of four specific primers, two inner and two outer, were designed targeting at VP3 gene, which could be completed within 60 min at 65°C in water bath or on a real-time PCR instrument for quantitative analysis. Specificity test of LAMP assay showed that there was no cross-reactivity between N-GPV and other duck pathogens, and the detection limit of qLAMP assay was 1.0 × 10² copies/μL. The repeatability of this method was confirmed by inter-assay and intra-assay tests with variability ranging from 0.74 to 2.25%. The results have indicated that the qLAMP assay was a simple, rapid, accurate, sensitive, and specific method for detecting N-GPV, especially on field detection.

Epidemiological investigation of H9 avian influenza virus, Newcastle disease virus, Tembusu virus, goose parvovirus and goose circovirus infection of geese in China

To deepen the knowledge about epidemic prevalence in the goose breeding field, a triplex PCR assay was established, and 478 samples were collected from scaled goose farms in 11 provinces in China. The results of this epidemiological investigation showed that incidence rates of H9 avian influenza and goose circovirus were the highest among five infectious diseases that were evaluated. In addition, the triplex PCR assay established remarkable sensitivity, rapidity and versatility compared to other diagnostic methods. Dual infection comprised a large proportion of the co-infections in the field, of which the combinations of H9/Tembusu, H9/goose circovirus and goose circovirus/Tembusu co-infected cases were more common. Epidemics were more severe in winter and spring. Additionally, significant differences in the prevalence of these infectious diseases were observed in association with different age groups. In addition, phylogenetic analysis, determined by the neighbour-joining method, was carried out to investigate the evolution of these viruses during the study period. For the most part, virus strains isolated during the study were consistent with most goose-origin strains isolated from the Chinese mainland over the past few years. However, mutations were observed between isolated H9 avian influenza virus strains and sequences available from GenBank, which should draw much attention.

Development of a duplex semi-nested PCR assay for detection of classical goose parvovirus and novel goose parvovirus-related virus in sick or dead ducks with short beak and dwarfism syndrome

Duck short beak and dwarfism syndrome (SBDS) is an emerging infectious disease caused by a novel goose parvovirus-related virus (NGPV) in China. Until now, it remains uncertain whether the Cherry Valley ducks and mule ducks with SBDS are co-infected with classical goose parvovirus (GPV) and NGPV. In this study, a duplex semi-nested PCR assay with high specificity and sensitivity was developed for detection of the two viruses. Using the duplex PCR assay, NGPV was tested positive in all the 15 duck flocks with SBDS, whereas classical GPV was not detected in all the 133 sick and dead ducks collected from East China. A total of 87 (91.58%) Cherry Valley ducks aged from 5 to 18days and 35 (92.11%) mule ducks aged from 17 to 25days were detected positive for NGPV. In the NGPV-positive ducks, the virus detection rates were 81.97% to 8.20% in heart, liver, spleen, lung, kidney, pancreas, bile, thymus, bursa of Fabricius, and brain. The results indicated that NGPV was prevalent in the duck flocks of East China, whereas classical GPV was not detected in Cherry Valley ducks and mule ducks with SBDS. NGPV has extensive tissue tropism in Cherry Valley duck and mule duck, which could invade both the central and peripheral immune organs and break through the blood-brain barrier of ducks.

Goose Parvovirus and Circovirus Coinfections in Ornamental Ducks

Clinical observations and diagnostic procedures carried out to elucidate the cause of high mortality in 2-8-wk-old ornamental ducks (mandarin, wood, falcated, and silver teal ducks) are described. At necropsy, ducklings showed general pallor of skeletal and heart muscles, subcutaneous gelatinous transudates, pericarditis, ascites, and severe edema and hyperemia of lungs. Histopathologic examination revealed that the most important changes were located in the crop, bursa of Fabricius, and lungs with presence of amorphic basic intracytoplasmic inclusions. No bacteria or fungi could be detected from affected organs and ascitic fluid. Viral diagnosis included molecular detection for the presence of goose parvovirus (GPV), circovirus, avian influenza, herpesviruses, paramyxovirus, reovirus, and polyomavirus. Both GPV and circovirus could be detected by real-time PCR and nested broad-spectrum PCR, respectively. Phylogenetically, full-length nucleotide sequence of GPV showed a close similarity ranging from 95.6% to 97.9% with European and Asian pathogenic GPV. On the other hand, the detected circovirus showed nucleotide identity of 90% to 98% with goose circoviruses (GoCVs). This is the first report of GoCVs and GPV in ornamental ducks. The concurrence of GPV and GoCV infections is thought to contribute to the high mortality.

Pathogenicity of Pekin duck- and goose-origin parvoviruses in Pekin ducklings

Goose parvovirus (GPV) usually affects goslings and Muscovy ducks but not Pekin ducks. Earlier works showed that a variant GPV can cause short beak and dwarfism syndrome (SBDS) in Pekin ducks. Here, we investigated the pathogenicity of a variant GPV of Pekin duck-origin (JS1) and a classical GPV of goose-origin (H) in Pekin ducklings. Following intramuscular infection at two days of age, both JS1 and H strains influenced weight gain and development of beaks and bones of wings and legs, and caused microscopic lesions of internal organs of ducks. However, the clinical signs typical of SBDS could only be replicated with the JS1 isolate. The findings suggest that both variant and classical GPVs are pathogenic for Pekin ducklings, while the former is more virulent than the latter. Using a quantitative real-time PCR assay, high levels of viral load were detected from bloods, internal organs, leg muscles, and ileac contents in JS1- and H-infected ducks from 6h to 35days postinfection (DPI). Using a GPV VP3-based ELISA, antibodies in sera of JS1- and H-infected ducks were detectable at 1 DPI and then persistently rose during the subsequent five weeks. These results suggest that both variant and classical GPVs can infect Pekin ducklings. The present work contributes to the understanding of pathogenicity of GPV to Pekin ducks and may provide clues to pathogenesis of GPV-related SBDS.

Selection of an aptamer against Muscovy duck parvovirus for highly sensitive rapid visual detection by label-free aptasensor

Muscovy duck parvovirus (MDPV) causes high mortality and morbidity in ducks. This study investigated a novel aptamer-based, label-free aptasensor detection of MDPV. In this study, we developed an ssDNA aptamer using the filtration partition and lambda exonuclease method with an affinity-based monitor and counter-screening process. After 15 rounds of SELEX (systematic evolution of ligands by exponential enrichment), the ssDNA aptamer Apt-10, which specifically bound to MDPV with high affinity (K_d = 467nM) was successfully screened, and the aptamer was also found to be good specific to MDPV. The selected Apt-10 aptamer can be used to distinguish MDPV and goose parvovirus (GPV). Three-dimensional structural analysis of the Apt-10 aptamer indicated that it folded into a compact stem-loop motif, which was related to its high affinity. Finally, a label-free detection method based on unmodified gold nanoparticles and Apt-10 aptamer was developed for MDPV determination. The concentration of Apt-10 aptamer at 5μM was optimal for MDPV determination in the label-free aptasensor. Excellent linearity was acquired and the lowest detection limit was 1.5 or 3 EID₅₀ (50% egg infection dose) of MDPV, respectively, depending upon spectrophotometry or the naked eye were used. These results show the potential of the aptamer for the rapid detection of MDPV and antiviral research.

Complete Genome Sequence of a Novel Goose Parvovirus Isolated in Sichuan Province, China, in 2016

Here, we report the complete genome sequence of the novel goose parvovirus (NGPV) strain SC16 (NGPV-SC16), which was isolated from Sichuan Province, China, in 2016 and is a cause of the newly emerging beak atrophy and dwarfism syndrome in ducklings and a moderately pathogenic GPV-related parvovirus. The whole genome of strain NGPV-SC16 was 5,109 nucleotides long.

Development of a taqman-based real-time PCR assay for the rapid and specific detection of novel duck- origin goose parvovirus

A real-time PCR assay was developed for specific detection of novel duck-origin goose parvovirus (N-GPV), the etiological agent of duck beak atrophy and dwarfism syndrome (BADS). The detection limit of the assay was 10² copies. The assay was useful in the prevention and control of BADS.

Analysis of Evolutionary Processes of Species Jump in Waterfowl Parvovirus

Waterfowl parvoviruses are classified into goose parvovirus (GPV) and Muscovy duck parvovirus (MDPV) according to their antigenic features and host preferences. A novel duck parvovirus (NDPV), identified as a new variant of GPV, is currently infecting ducks, thus causing considerable economic loss. This study analyzed the molecular evolution and population dynamics of the emerging parvovirus capsid gene to investigate the evolutionary processes concerning the host shift of NDPV. Two important amino acids changes (Asn-489 and Asn-650) were identified in NDPV, which may be responsible for host shift of NDPV. Phylogenetic analysis indicated that the currently circulating NDPV originated from the GPV lineage. The Bayesian Markov chain Monte Carlo tree indicated that the NDPV diverged from GPV approximately 20 years ago. Evolutionary rate analyses demonstrated that GPV evolved with 7.674 × 10^-4 substitutions/site/year, and the data for MDPV was 5.237 × 10^-4 substitutions/site/year, whereas the substitution rate in NDPV branch was 2.25 × 10^-3 substitutions/site/year. Meanwhile, viral population dynamics analysis revealed that the GPV major clade, including NDPV, grew exponentially at a rate of 1.717 year^-1. Selection pressure analysis showed that most sites are subject to strong purifying selection and no positively selected sites were found in NDPV. The unique immune-epitopes in waterfowl parvovirus were also estimated, which may be helpful for the prediction of antibody binding sites against NDPV in ducks.

Immune-Related Gene Expression Patterns in GPV- or H9N2-Infected Goose Spleens

Goose parvovirus (GPV) and avian influenza virus subtype H9N2 are single-stranded DNA (ssDNA) and single-stranded RNA (ssRNA) viruses, respectively, both of which can spread in goslings and cause a significant economic loss. To explore the comprehensive transcriptome of GPV- or H9N2-infected goose spleens and to understand the immune responses induced by a DNA virus (GPV) or a RNA virus (H9N2), RNA-seq was performed on the spleens of goslings at the fifth day post infection. In the present study, 2604 and 2409 differentially expressed unigenes were identified in the GPV- and H9N2-infected groups, respectively. Through KEGG pathway enrichment analyses, the up-regulated transcripts in the two virus-infected groups were mainly involved in immune-related pathways. In addition, the two virus-infected groups displayed similar expression patterns in the immune response pathways, including pattern-recognition receptor signaling pathways, the antigen processing and presentation pathway, the NF-κB signaling pathway and the JAK-STAT signaling pathway, as well as cytokines. Furthermore, most of the immune-related genes, particularly TLR7, TRAF3, Mx, TRIM25, CD4, and CD8α, increased in response to GPV and H9N2 infection. However, the depression of NF-κB signaling may be a mechanism by which the viruses evade the host immune system or a strategy to achieve immune homeostasis.

Isolation and characterization of a distinct duck-origin goose parvovirus causing an outbreak of duckling short beak and dwarfism syndrome in China

Many mule duck and Cherry Valley duck flocks in different duck-producing regions of China have shown signs of an apparently new disease designated "short beak and dwarfism syndrome" (SBDS) since 2015. The disease is characterized by dyspraxia, weight loss, a protruding tongue, and high morbidity and low mortality rates. In order to characterize the etiological agent, a virus designated SBDSV M15 was isolated from allantoic fluid of dead embryos following serial passage in duck embryos. This virus causes a cytopathic effect in duck embryo fibroblast (DEF) cells. Using monoclonal antibody diagnostic assays, the SBDSV M15 isolate was positive for the antigen of goose parvovirus but not Muscovy duck parvovirus. A 348-bp (2604-2951) VP1gene fragment was amplified, and its sequence indicated that the virus was most closely related to a Hungarian GPV strain that was also isolated from mule ducks with SBDS disease. A similar disease was reproduced by inoculating birds with SBDSV M15. Together, these data indicate that SBDSV M15 is a GPV-related parvovirus causing SBDS disease and that it is divergent from classical GPV isolates.