Serological diagnosis of goose circovirus infections

TaqMan-probe-based multiplex real-time RT-qPCR for simultaneous detection of GoAstV, GPV, and GoCV

Goose astrovirus (GoAstV), goose parvovirus (GPV), and goose circovirus (GoCV) infections have similar symptoms, such as severe diarrhea, and cause serious economic losses to the goose industry globally. Therefore, it is necessary to develop a rapid and accurate method for the differential diagnosis of the 3 viruses. In this study, a TaqMan probe-based multiplex reverse transcription-qualitative polymerase chain reaction (RT-qPCR) method was established and optimized for simultaneous detection of the three viruses. Three pairs of specific primers and probes were designed considering the conserved sequences of ORF2, VP3, and Rep of GoAstV, GPV, and GoCV, respectively. Singleplex real-time RT-qPCR detected a minimum of 10 copies of these genes, while multiplex real-time RT-qPCR detected a minimum of 100 copies. The correlation coefficients exceeded 0.99, and the amplification efficiency was 80 to 100%. The assay had high sensitivity, specificity, and repeatability. In 85 tissue samples, GoAstV and GPV were the main pathogens and demonstrated co-infection. This assay provides a rapid, efficient, specific, and sensitive tool for the detection of GoAstV, GPV, and GoCV. This can facilitate disease management and epidemiological surveillance.

Correlation between goose circovirus and goose parvovirus with gosling feather loss disease and goose broke feather disease in southern Taiwan

BACKGROUND

Goslings in several Taiwanese farms experienced gosling feather loss disease (GFL) at 21-35 days and goose broke feather disease (GBF) at 42-60 days. The prevalence ranges from a few birds to 500 cases per field. It is estimated that about 12,000 geese have been infected, the morbidity is 70-80% and the mortality is 20-30%.

OBJECTIVES

This study aims to investigate the pathogens that cause GFL and GBF. Focus on the study of the correlation between goose circovirus (GoCV) and goose parvovirus (GPV) with the goose feather loss in southern Taiwan. Furthermore, a phylogenetic tree was established to align the differences between southern and northern Taiwan and compare with virus strains from China and Europe.

METHODS

Samples were collected from animal hospitals. Molecular and microscopy diagnostics were used to examine 92 geese. Specific quantitative polymerase chain reaction (Q-PCR) assays are performed to evaluate GPV and GoCV viral loads and simultaneously evaluated the feather loss conditions in geese with the scoring method.

RESULTS

High prevalence of GoCV and GPV infection in geese showing signs of GFL and GBF. Inclusion body was detected in the feather follicles and Lieberkühn crypt epithelial cells. The Q-PCR showed the high correlation between feather loss and viruses during 3rd-5th week. However, the infection was not detected using the same test in 60 healthy geese.

CONCLUSIONS

Thus, GFL and GBF appear to be significantly closely related to GoCV and GPV. The geese feathers showed increasing recovery after being quarantined and disinfected.

Assembly of pigeon circovirus-like particles using baculovirus expression system

Pigeon circovirus (PiCV) is able to infect racing and meat pigeons of all ages and is a key factor that triggers young pigeon disease syndrome (YPDS). PiCV vaccine research has been impeded because PiCV cannot be grown or propagated in cell cultures. Virus-like particles (VLPs), which can be generated by a wide range of expression systems, have been shown to have outstanding immunogenicity and constitute promising vaccines against a wide range of pathogens. Cap protein, which contains neutralizing antibody epitopes, is the only capsid protein of PiCV. In this study, the baculovirus expression system was utilized to express the PiCV Cap protein, which was self-assembled into VLPs with a spherical morphology and diameters of 15-18 nm. Specific antibodies against the Cap protein were induced after BALB/c mice immunized intramuscularly (i.m.) with VLPs combined with adjuvant. Based on these findings, PiCV VLPs may be a promising candidate vaccine against PiCV.

Recombinant expression of beak and feather disease virus capsid protein and assembly of virus-like particles in Nicotiana benthamiana

BACKGROUND

Beak and feather disease virus (BFDV) is an important disease causing agent affecting psittacines. BFDV is highly infectious and can present as acute, chronic or subclinical disease. The virus causes immunodeficiency and is often associated with secondary infections. No commercial vaccine is available and yields of recombinant BFDV capsid protein (CP) expressed in insect cells and bacteria are yet to be seen as commercially viable, although both systems produced BFDV CP that could successfully assemble into virus-like particles (VLPs). Plants as expression systems are increasingly becoming favourable for the production of region-specific and niche market products. The aim of this study was to investigate the formation and potential for purification of BFDV VLPs in Nicotiana benthamiana.

METHODS

The BFDV CP was transiently expressed in N. benthamiana using an Agrobacterium-mediated system and plant expression vectors that included a bean yellow dwarf virus (BeYDV)-based replicating DNA vector. Plant-produced BFDV CP was detected using immunoblotting. VLPs were purified using sucrose cushion and CsCl density gradient centrifugation and visualised using transmission electron microscopy.

RESULTS

In this study we demonstrate that the BFDV CP can be successfully expressed in N. benthamiana, albeit at relatively low yield. Using a purification strategy based on centrifugation we demonstrated that the expressed CP can self-assemble into VLPs that can be detected using electron microscopy. These plant-produced BFDV VLPs resemble those produced in established recombinant expression systems and infectious virions. It is possible that the VLPs are spontaneously incorporating amplicon DNA produced from the replicating BeYDV plant vector.

CONCLUSIONS

This is the first report of plant-made full-length BFDV CP assembling into VLPs. The putative pseudovirions could be used to further the efficacy of vaccines against BFDV.

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.

Xenogenic rolling-circle replication of a synthetic beak and feather disease virus genomic clone in 293TT mammalian cells and Nicotiana benthamiana

The preparation of infectious beak and feather disease circovirus virions (BFDV) has until now relied on the extraction of virus from whole tissue of deceased or euthanized parrots known to be infected with the virus. Extraction from diseased tissue is necessary, as the virus has yet to be grown in vitro using tissue-cultured cells from any source. While infectious DNA clones have been synthesized for porcine and duck circoviruses, and both replicate in host cells and result in active viral infection in animals, this has not been shown for BFDV. The aim of this study was to prepare an infectious BFDV genomic clone that could be used as challenge material in birds for vaccine testing. A putatively infectious BFDV genomic clone was designed and tested in mammalian cell culture, and in the plant Nicotiana benthamiana in the presence of plant-specific ssDNA geminivirus replication components. Replication was assessed using rolling-circle amplification, qPCR, replication-deficient clones and rescue plasmids. We showed that a synthetic partially dimeric BFDV genomic clone self-replicated when transfected into 293TT mammalian cells, and was also replicated in N. benthamiana in the presence of geminivirus replication elements. This is the first report of a BFDV genome replicating in any cell system, and the first report of a circovirus replicating with the aid of a geminivirus in a plant. Both of these developments could open up possibilities for making reagents and vaccines for BFDV, testing vaccine efficacy and investigating viral replication using rationally designed artificial genomes.

Evidence of a deep viral host switch event with beak and feather disease virus infection in rainbow bee-eaters (Merops ornatus)

Since the characterization of psittacine beak and feather disease (PBFD) in 1984, a wide range of avian circoviruses have been discovered with varying pathogenic effects amongst a diverse range of avian hosts. Until recently these circovirus species were thought to be restricted to within avian Orders such as the Psittaciformes for beak and feather disease virus (BFDV) and Columbiformes for pigeon circovirus with little evidence of cross-family transmission or replication. We report evidence of a naturally occurring novel host switch event with self-limiting BFDV infection in a group of rainbow bee-eaters (Merops ornatus) a species of Coraciiformes unrelated to parrots and not previously known to be susceptible to any avian circovirus. The outbreak highlights important and unexpected aspects of disease emergence and host-switching pertinent to other situations when viruses might cross species boundaries as well as the potential of avian circoviruses to infect disparate host species.

Pathological observations of an experimental infection of geese with goose circovirus

There is so far no report describing the pathogenicity of goose circovirus (GoCV) following experimental infection. We report here an experimental inoculation of 21-day-old geese with a GoCV polymerase chain reaction (PCR)-positive sample of bursa of Fabricius (BF) homogenate, and the results of clinicopathological changes. Forty geese were randomly assigned to two groups: the inoculated group (n=30) receiving tissue homogenate and the uninoculated group (n=10) receiving a placebo (physiological saline). Tissue samples were collected for histopathological examination and GoCV detection. The main clinical signs in the GoCV-inoculated geese included diarrhoea at 17 to 30 days post inoculation, marked differences of growth rate and feather disorders in three of the geese. Viraemia was detected by PCR only at 14 days post inoculation. The BF, thymus, spleen, duodenum and liver of some inoculated geese were also PCR-positive. Real-time PCR showed that there was relatively more viral load in the BF. Histological examination revealed lymphocytic depletion and histiocytosis in the BF and inflammation characterized by lymphatic infiltration in the lung, liver and kidney. Immunohistochemistry applied to PCR-positive samples showed that in only three BF samples was GoCV antigen detected in lymphocytes in both the cortex and medulla. In situ apoptosis detection of all BF samples indicated that GoCV inoculation was associated with an increase in bursal lymphocytic apoptotic events.