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

Short beak and dwarfism syndrome among Pekin ducks: First detection, full genome sequencing, and immunohistochemical signals of novel goose parvovirus in tongue tissue

Novel goose parvovirus (NGPV) is continuously threatening the global duck industry, as it causes short beak and dwarfism syndrome among different duck breeds. In this study, we investigated the viral pathogenesis in the tongue of affected ducks, as a new approach for deeper understanding of the syndrome. Seventy-three, 14- to 60-day-old commercial Pekin ducks were clinically examined. Thirty tissue pools of intestine and tongue (15 per tissue) were submitted for molecular identification. Clinical signs in the examined ducks were suggestive of parvovirus infection. All examined ducks had short beaks. Necrotic, swollen, and congested protruding tongues were recorded in adult ducks (37/73, 51%). Tongue protrusion without any marked congestion or swelling was observed in 20-day-old ducklings (13/73, 18%), and no tongue protrusion was observed in 15-day-old ducklings (23/73, 32%). Microscopically, the protruding tongues of adult ducks showed necrosis of the superficial epithelial layer with vacuolar degeneration. Glossitis was present in the nonprotruding tongues of young ducks, which was characterized by multifocal lymphoplasmacytic aggregates and edema in the propria submucosa. Immunohistochemical examination displayed parvovirus immunolabeling, mainly in the tongue propria submucosa. Based on polymerase chain reaction, goose parvovirus was detected in 9 out of 15 tongue sample pools (60%). Next-generation sequencing confirmed the presence of a variant goose parvovirus that is globally named NGPV and closely related to Chinese NGPV isolates. Novel insights are being gained from the study of NGPV pathogenesis in the tongue based on molecular and immunohistochemical identification.

Interactions between avian viruses and skin in farm birds

This article reviews the avian viruses that infect the skin of domestic farm birds of primary economic importance: chicken, duck, turkey, and goose. Many avian viruses (e.g., poxviruses, herpesviruses, Influenza viruses, retroviruses) leading to pathologies infect the skin and the appendages of these birds. Some of these viruses (e.g., Marek's disease virus, avian influenza viruses) have had and/or still have a devasting impact on the poultry economy. The skin tropism of these viruses is key to the pathology and virus life cycle, in particular for virus entry, shedding, and/or transmission. In addition, for some emergent arboviruses, such as flaviviruses, the skin is often the entry gate of the virus after mosquito bites, whether or not the host develops symptoms (e.g., West Nile virus). Various avian skin models, from primary cells to three-dimensional models, are currently available to better understand virus-skin interactions (such as replication, pathogenesis, cell response, and co-infection). These models may be key to finding solutions to prevent or halt viral infection in poultry.

Development and application of a multiplex PCR method for simultaneous detection of waterfowl parvovirus, duck enteritis virus and goose astrovirus

Waterfowl parvovirus, duck enteritis virus and goose astrovirus have become serious pathogens in waterfowl farming. Co-infections occasionally occur, and as a result, it is much harder to rapidly and simultaneously identify several pathogens using conventional PCR. According to the characteristics of the goose parvovirus (GPV) and muscovy duck parvovirus (MDPV) genome sequences, a universal PCR primer was designed using Rep1 as the target gene. The specific detection primers were designed based on the specific conserved regions of UL54 of the duck enteritis virus (DEV) gene and ORF1a of the goose astrovirus (GAstV) gene. The PCR reaction system and conditions were optimized, and the optimal annealing temperature was found to be 56.2 ℃. The volume ratio of the GPV-MDPV, GAstV and DEV primers (20 μM) was 1:4:5. The established multiplex PCR detection method can simultaneously detect GPV, MDPV, DEV and GAstV within one reaction, and be negative for duck Tembusu virus, muscovy duck reovirus, duck hepatitis A virus type 3 and duck circovirus. The method with excellent sensitivity, specificity and repeatability was successfully applied to clinical samples, it is a useful platform for identifing co-infections of GPV, MDPV, DEV and GAstV in waterfowl.

Development and Evaluation of NanoPCR for the Detection of Goose Parvovirus

Simple Summary

Gosling plague (GP), an acute, virulent infectious disease caused by goose parvovirus (GPV), is a serious problem for livestock and poultry breeding. At present, there is no effective treatment available. The disease is vertically transmitted in geese, and some infected pregnant females are often recessive carriers of the virus, making it very difficult for farmers to detect GPV in the clinical setting. Although there are many clinical testing methods for GPV, some of them still suffered from shortcomings such as being time-consuming and labor-intensive. In this study, gold nanoparticles were put into a conventional PCR reaction system, and the first nanoPCR reaction was successfully established to detect infected GPV in the clinic, thus providing a practical method for the detection of GPV clinical infection.

Abstract

Gosling plague (GP) is an acute and hemorrhagic infectious disease caused by goose parvovirus (GPV). The goose industry suffers significant economic losses as a result of GP, which is found to be widespread worldwide, with high rates of morbidity and mortality. Our group developed a novel technique for detecting GPV nanoparticle-assisted polymerase chain reaction (nanoPCR) and the characterization of its specificity and sensitivity. It was developed by using the traditional polymerase chain reaction (PCR) and nanoparticles. The findings of this study revealed that GPV nanoPCR products were 389 bp in length, and the lower limit of the nanoPCR assay was 4.68 × 10² copies/μL, whereas that of the conventional PCR assay was 4.68 × 10⁴ copies/μL. A total of 230 geese suspected of GPV were detected using nanoPCR, with a positive rate of 83.0% and a specificity of 73%, respectively. Overall, we present a hitherto undocumented method for identifying GPV by using nanoPCR to aid in the evaluation of subclinical illness.

Immunogenicity of an inactivated novel goose parvovirus vaccine for short beak and dwarfism syndrome in Cherry Valley ducks

Duck short beak and dwarfism syndrome (SBDS) is a viral infectious disease caused by novel goose parvovirus (NGPV), which has been responsible for serious economic losses to the Chinese duck industry in recent years. Currently, there is no effective vaccine against this disease. In this study, we developed an inactivated virus vaccine candidate for SBDS based on NGPV strain DS15 isolated from a duck in China. Immune efficacy was evaluated in 112 ducks, which were randomly divided into vaccination, challenge-control, vaccination-challenge, and blank control groups (28 per group). Clinical characteristics, antibodies, virus excretion, viremia, and pathological changes were monitored. No morbidity or death was observed in the immunized ducks, which showed normal weight and a good mental state. High levels of serum antibodies (optical density at 450 nm of ~ 0.63) were detected in ducks immunized with the inactivated vaccine at 7 days post-vaccination (dpv), and the titer of virus-neutralizing antibodies increased from 1:2³ to 1:2^8.5 from 7 to 42 dpv. Measurement of the viral load in anal swab, serum, and tissue samples showed that vaccination significantly inhibited the replication of NGPV in immunized ducks. Moreover, NGPV could not be isolated from the spleens of immunized or vaccinated and challenged ducks. Collectively, these results demonstrate that the newly developed inactivated NGPV vaccine, administered in an oil emulsion adjuvant, possesses good immunogenicity and represents a potentially powerful tool for SBDS prevention and control.

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.

Short Beak and Dwarfism Syndrome in Ducks in Poland Caused by Novel Goose Parvovirus

Short beak and dwarfism syndrome (SBDS), which was previously identified only in mule ducks, is now an emerging disease of Pekin ducks in China and Egypt. The disease is caused by the infection of ducks with a genetic variant of goose parvovirus-novel goose parvovirus (nGPV). In 2019, SBDS was observed for the first time in Poland in eight farms of Pekin ducks. Birds in the affected flock were found to show growth retardation and beak atrophy with tongue protrusions. Morbidity ranged between 15% and 40% (in one flock), while the mortality rate was 4-6%. Co-infection with duck circovirus, a known immunosuppressive agent, was observed in 85.7% of ducks. The complete coding regions of four isolates were sequenced and submitted to GenBank. The phylogenetic analysis revealed a close relationship of Polish viral sequences with the Chinese nGPV. Genomic sequence alignments showed 98.57-99.28% identity with the nGPV sequences obtained in China, and 96.42% identity with the classical GPV (cGPV; Derzsy's disease). The rate of amino acid mutations in comparison to cGPV and Chinese nGPV was higher in the Rep protein than in the Vp1 protein. To our knowledge, this is the first report of nGPV infection in Pekin ducks in Poland and Europe. It should be emphasized that monitoring and sequencing of waterfowl parvoviruses is important for tracking the viral genetic changes that enable adaptation to new species of waterbirds.

Detection of Novel Goose Parvovirus Disease Associated with Short Beak and Dwarfism Syndrome in Commercial Ducks

Simple Summary

Duck short beak and dwarfism syndrome is an emerging infectious disease caused by a novel goose parvovirus that has been detected in Europe and China since 1974. Low performance, slow growth and deaths of young ducklings were the main characteristics of the disease. To the best of our knowledge, such syndrome has not been recorded in Egypt, but since 2019, it was observed in some mule and pekin duck farms that resulted in drastic economic losses for waterfowl producers. Identification of the causative agent through viral and molecular detection of the causative virus was the aim of this study. Also, gene sequence of one of three viral protein genes which are responsible for the virulence was accomplished. The causative virus was isolated on primary cell culture, with partial gene sequence of viral VP1 gene that indicated the viral clustering with Chinese novel goose parvoviruses that may help in new vaccine manufacturing and development of a more sensitive diagnostic assay. Future studies to evaluate potential protection of an available market vaccine against the novel virus will be useful.

Abstract

Derzsy’s disease causes disastrous losses in domestic waterfowl farms. A genetically variant strain of Muscovy duck parvovirus (MDPV) and goose parvovirus (GPV) was named novel goose parvovirus (NGPV), which causes characteristic syndrome in young ducklings. The syndrome was clinically characterized by deformity in beaks and retarded growth, called short beaks and dwarfism syndrome (SBDS). Ten mule and pekin duck farms were investigated for parvovirus in three Egyptian provinces. Despite low recorded mortality rate (20%), morbidity rate was high (70%), but the economic losses were remarkable as a result of retarded growth and low performance. Isolation of NGPV was successful on primary cell culture of embryonated duck liver cells with a clear cytopathic effect. Partial gene sequence of the VP1 gene showed high amino acids identity among isolated strains and close identity with Chinese strains of NGPV, and low identity with classic GPV and MDPV strains. To the best of our knowledge, this can be considered the first record of NGPV infections in Egypt.

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.

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.

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.

Duckling short beak and dwarfism syndrome virus infection activates host innate immune response involving both DNA and RNA sensors

Duckling short beak and dwarfism syndrome virus (SBDSV), a newly identified goose parvovirus, causes devastating disease in domestic waterfowl and considerable economic losses to Chinese waterfowl industry. The molecular pathogenesis of SBDSV infection, nature and dynamics of host immune responses against SBDSV infection remained elusive. In this study, we systematically explored the relative mRNA expression profiles of major innate immune-related genes in SBDSV infected duck embryo fibroblasts. We found that SBDSV infection effectively activated host innate immune responses and resulted in significant up-regulation of IFN-β and several vital IFN-stimulated genes (ISGs). These up-regulation responses were mainly attributed to viral genomic DNA and dsRNA replication intermediates. Importantly, the expression of cGAS was significantly induced, whereas the expression of other DNA receptors including DDX41, STING, ZBP1, LSM14A and LRRFIP1 have no significant change. Furthermore, SBDSV infection also activates the up-regulation of TLR3 and inhibited the expression of TLR2 and TLR4; however, no effect was observed on the expression of TLR1, TLR5, TLR7, TLR15 and TLR21. Intriguingly, SBDSV infection significantly up-regulated the expression of RNA sensors such as MDA5 and LGP2, and resulted in a delayed but significant up-regulation of RIG-I gene. Taken together, these data indicate that host multiple sensors including DNA sensor (cGAS) and RNA sensors (TLR3, MDA5 and LGP2) are involved in recognizing a variety of different pathogen associated molecular patterns (PAMPs) including viral genomic ssDNA and dsRNA replication intermediates, which trigger an effective antiviral innate immune response.

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.

Pathological lesions in the immune organs of ducklings following experimental infection with goose parvovirus

Goose parvovirus (GPV) is the etiological agent of Derzsy's disease, with a natural reservoir consisting only of geese and Muscovy ducks. However, the pathological changes in the immune organs of ducklings experimentally infected with GPV remain unknown. In this study, 2-day-old Cherry Valley ducklings were intramuscularly injected with GPV. Immune organs (e.g., thymus, bursa of Fabricius, spleen, Harderian gland, cecal tonsil, bone marrow, and peripheral blood lymphocytes [PBLs]) were collected 1, 3, 5, 7, 10, and 14 days post-infection (dpi). Pathological lesions were assessed by histology and the viral load was concurrently assessed using quantitative real-time polymerase chain reaction. GPV antigen was detected via immunofluorescence staining and immunohistochemistry. No clinical symptoms or death were observed in the infected ducklings from 1 to 14 dpi; however, lesions with different degrees of hemorrhage and hyperemia were observed in the thymus, spleen and Harderian gland. Lymphocyte necrosis was identified in the thymus and spleen. In the immune organs, the highest viral loads were found in the spleen at 7 dpi, followed by the bone marrow, PBLs, and cecal tonsil at 3 dpi, and the bursa, Harderian gland, and thymus at 1 dpi. GPV antigen was primarily expressed in the cecal tonsil, spleen, and Harderian gland at 5 dpi, as well as in the PBLs and bone marrow at 3 dpi. Our findings indicate widespread GPV replication and dissemination in the immune organs of Cherry Valley ducklings.

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.

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.

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.