Growth characteristics of the novel goose parvovirus SD15 strain in vitro

Novel goose parvovirus in naturally infected ducks suffering from locomotor disorders: Molecular Detection, Histopathological examination, Immunohistochemical signals, and Full genome sequencing

AbstractIn this study, we investigated the pathological effect of novel goose parvovirus (NGPV) infection on the skeletal muscle, brain, and intestine of naturally affected ducks suffering from locomotor dysfunction as a new approach for deeper understanding of such clinical form. For this purpose, a total of 97 diseased ducks, representing 24 flocks of different duck breeds (14-75 days old), were clinically examined. 72 tissue pools of intestine, brain, and skeletal muscle samples were submitted for molecular identification. Typical clinical signs among the examined ducks suggested the parvovirus infection. Regarding postmortem examination, all examined ducks showed muscle emaciation (100%) either accompanied by congestion (34%) or paleness (66%). Slight congestion, either in the brain (82.5%) or intestine (75.25%), was predominantly detected. Based on molecular identification, the intestine had the highest percentage of positive detection (91.7%), followed by the skeletal muscle (70.8%), and the brain (20.8%). The main histopathological alterations were myofiber atrophy and degeneration, marked enteritis accompanied by lymphocytic infiltration in the lamina propria and submucosa, while the affected brains showed vasculitis, diffuse gliosis, and Purkinje cell degeneration in the cerebellum. Next generation sequencing further confirmed the presence of a variant strain of goose parvovirus (vGPV) that is globally known as NGPV and closely related to Chinese NGPV isolates. Using immunohistochemistry, the NGPV antigen was positively detected in the muscle fibres, enterocytes, and Purkinje cells in the cerebellum. These findings provided proof of the involvement of virus replication in the locomotor disorders linked to NGPV infection in ducks.

Expression of VP2 protein of novel goose parvovirus in baculovirus and evaluation of its immune effect

Short-beak and dwarfism syndrome (SBDS) is a new disease caused by a genetic variant of goose parvovirus in ducks that results in enormous economic losses for the waterfowl industry. Currently, there is no commercial vaccine for this disease, so it is urgent to develop a safer and more effective vaccine to prevent this disease. In this study, we optimized the production conditions to enhance the expression of the recombinant VP2 protein and identified the optimal conditions for subsequent large-scale expression. Furthermore, the protein underwent purification via nickel column affinity chromatography, followed by concentration using ultrafiltration tube. Subsequently, it was observed by transmission electron microscopy (TEM) that the NGPV recombinant VP2 protein assembled into virus-like particles (VLPs) resembling those of the original virus. Finally, the ISA 78-VG adjuvant was mixed with the NGPV-VP2 VLPs to be prepared as a subunit vaccine. Furthermore, both agar gel precipitation test (AGP) and serum neutralization test demonstrated that NGPV VLP subunit vaccine could induce the increase of NGPV antibody in breeding ducks. The ducklings were also challenged with the NGPV, and the results showed that the maternal antibody level could provide sufficient protection to the ducklings. These results indicated that the use of the NGPV VLP subunit vaccine based on the baculovirus expression system could facilitate the large-scale development of a reliable vaccine in the future.

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.

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.

The First Nonmammalian Pegivirus Demonstrates Efficient In Vitro Replication and High Lymphotropism

Members of the Pegivirus genus, family Flaviviridae, widely infect humans and other mammals, including nonhuman primates, bats, horses, pigs, and rodents, but are not associated with disease. Here, we report a new, genetically distinct pegivirus in goose (Anser cygnoides), the first identified in a nonmammalian host species. Goose pegivirus (GPgV) can be propagated in goslings, embryonated goose eggs, and primary goose embryo fibroblasts, and is thus the first pegivirus that can be efficiently cultured in vitro Experimental infection of GPgV in goslings via intravenous injection revealed robust replication and high lymphotropism. Analysis of the tissue tropism of GPgV revealed that the spleen and thymus were the organs bearing the highest viral loads. Importantly, GPgV could promote clinical manifestations of goose parvovirus infection, including reduced weight gain and 7% mortality. This finding contrasts with the lack of pathogenicity that is characteristic of previously reported pegiviruses.IMPORTANCE Members of the Pegivirus genus, family Flaviviridae, widely infect humans and other mammals, but are described as causing persistent infection and lacking pathogenicity. The efficiency of in vitro replication systems for pegivirus is poor, thus limiting investigation into viral replication steps. Because of that, the pathogenesis, cellular tropism, route of transmission, biology, and epidemiology of pegiviruses remain largely uncovered. Here, we report a phylogenetically distinct goose pegivirus (GPgV) that should be classified as a new species. GPgV proliferated in cell culture in a species- and cell-type-specific manner. Animal experiments show GPgV lymphotropism and promote goose parvovirus clinical manifestations. This study provides the first cell culture model for pegivirus, opening new possibilities for studies of pegivirus molecular biology. More importantly, our findings stand in contrast to the lack of identified pathogenicity of previously reported pegiviruses, which sheds lights on the pathobiology of pegivirus.

Meta-Transcriptomic Discovery of a Divergent Circovirus and a Chaphamaparvovirus in Captive Reptiles with Proliferative Respiratory Syndrome

Viral pathogens are being increasingly described in association with mass morbidity and mortality events in reptiles. However, our knowledge of reptile viruses remains limited. Herein, we describe the meta-transcriptomic investigation of a mass morbidity and mortality event in a colony of central bearded dragons (Pogona vitticeps) in 2014. Severe, extensive proliferation of the respiratory epithelium was consistently found in affected dragons. Similar proliferative lung lesions were identified in bearded dragons from the same colony in 2020 in association with increased intermittent mortality. Total RNA sequencing identified two divergent DNA viruses: a reptile-infecting circovirus, denoted bearded dragon circovirus (BDCV), and the first exogeneous reptilian chaphamaparvovirus—bearded dragon chaphamaparvovirus (BDchPV). Phylogenetic analysis revealed that BDCV was most closely related to bat-associated circoviruses, exhibiting 70% amino acid sequence identity in the Replicase (Rep) protein. In contrast, in the nonstructural (NS) protein, the newly discovered BDchPV showed approximately 31%–35% identity to parvoviruses obtained from tilapia fish and crocodiles in China. Subsequent specific PCR assays revealed BDCV and BDchPV in both diseased and apparently normal captive reptiles, although only BDCV was found in those animals with proliferative pulmonary lesions and respiratory disease. This study expands our understanding of viral diversity in captive reptiles.