Isolation and properties of bovine parvovirus type 1 from Japanese calves

Stability and integrity of self-assembled bovine parvovirus virus‑like particles (BPV‑VLPs) of VP2 and combination of VP1VP2 assisted by baculovirus-insect cell expression: a potential logistical platform for vaccine deployment

BACKGROUND

Bovine parvovirus (BPV) is an autonomous DNA virus with a smaller molecular size and subtle differences in its structural proteins, unlike other animal parvoviruses. More importantly, this virus has the potential to produce visible to silent economic catastrophes in the livestock business, despite receiving very little attention. Parvoviral virus-like particles (VLPs) as vaccines and as logistical platforms for vaccine deployment are well studied. However, no single experimental report on the role of VP1 in the assembly and stability of BPV-VLPs is available. Furthermore, the self-assembly, integrity and stability of the VLPs of recombinant BPV VP2 in comparison to VP1 VP2 Cap proteins using any expression method has not been studied previously. In this study, we experimentally evaluated the self-assembling ability with which BPV virus-like particles (VLPs) could be synthesized from a single structural protein (VP2) and by integrating both VP2 and VP1 amino acid sequences.

METHODS

In silico and experimental cloning methods were carried out. His-tagged and without-His-tag VP2 and V1VP2-encoding amino acid sequences were cloned and inserted into pFastbacdual, and insect cell-generated recombinant protein was evaluated by SDS‒PAGE and western blot. Period of infectivity and expression level were determined by IFA. The integrity and stability of the BPV VLPs were evaluated by transmission electron microscopy. The secondary structure of the BPV VLPs from both VP2 and V1VP2 was analyzed by circular dichroism.

RESULTS

Our findings show that VP2 alone was equally expressed and purified into detectable proteins, and the stability at different temperatures and pH values was not appreciably different between the two kinds of VLPs. Furthermore, BPV-VP2 VLPs were praised for their greater purity and integrity than BPV-VP1VP2 VLPs, as indicated by SDS‒PAGE. Therefore, our research demonstrates that the function of VP1 has no bearing on the stability or integrity of BPV-VLPs.

CONCLUSIONS

In summary, incredible physiochemically stable BPV VP2-derived VLPs have been found to be promising candidates for the development of multivalent vaccines and immunodiagnostic kits against enteric viruses and to carry heterogeneous epitopes for various economically important livestock diseases.

Persistent viremia by a novel parvovirus in a slow loris (Nycticebus coucang) with diffuse histiocytic sarcoma

Cancer is one of the leading health concerns for human and animal health. Since the tumorigenesis process is not completely understood and it is known that some viruses can induce carcinogenesis, it is highly important to identify novel oncoviruses and extensively study underlying oncogenic mechanisms. Here, we investigated a case of diffuse histiocytic sarcoma in a 22 year old slow loris (Nycticebus coucang), using a broad spectrum virus discovery technique. A novel parvovirus was discovered and the phylogenetic analysis performed on its fully sequenced genome demonstrated that it represents the first member of a novel genus. The possible causative correlation between this virus and the malignancy was further investigated and 20 serum and 61 organ samples from 25 animals (N. coucang and N. pygmaeus) were screened for the novel virus but only samples collected from the originally infected animal were positive. The virus was present in all tested organs (intestine, liver, spleen, kidneys, and lungs) and in all banked serum samples collected up to 8 years before death. All attempts to identify a latent viral form (integrated or episomal) were unsuccessful and the increase of variation in the viral sequences during the years was consistent with absence of latency. Since it is well known that parvoviruses are dependent on cell division to successfully replicate, we hypothesized that the virus could have benefitted from the constantly dividing cancer cells and may not have been the cause of the histiocytic sarcoma. It is also possible to conjecture that the virus had a role in delaying the tumor progression and this report might bring new exciting opportunities in recognizing viruses to be used in cancer virotherapy.

Further studies on thermal resistance of bovine parvovirus against moist and dry heat

To supplement the results of thermal resistance of bovine parvovirus (Haden strain, BPV) published previously, we carried out assays at 60 degrees C (moist heat) to compare the thermal resistance of BPV with that of hepatitis B-virus (HBV). What we know about the resistance of HBV at a temperature of 60 degrees C is mainly based on data collected within the context of blood product pasteurization. The results suggest that at a temperature of 60 degrees C, BPV shows thermal resistance comparable to HBV. Thus, BPV--which is easier to handle--can be considered a good test virus to verify the efficacy of thermal disinfection techniques against HBV. BPV is very resistant against dry heat of 100 degrees C, the inactivation largely depending upon the residual moisture of the lyophilisate. Reducing the residual moisture from 2% to less than 1%, the exposure time has to be prolonged by ca. 2.5 times to achieve the same virucidal effect.

Properties of an Australian isolate of bovine parvovirus type 1

An Australian bovine parvovirus isolate (BPV 267) was found to haemagglutinate human, guinea-pig, rat and dog erythrocytes, out of a range of 16 species of erythrocyte tested. The haemagglutinating activity was generally found to be both pH and temperature dependent. The virus was found to replicate best in intestinal epithelium, macrophage and lung cells, out of 9 bovine cell types tested. Highest yields of virus were obtained by the use of selected cell strains at low-passage levels which were maintained near neutral pH under conditions of high rates of cell growth. Studies of the rates of thermal inactivation with time showed the virus to be relatively stable at 37 degrees C, 56 degrees C and 70 degrees C, the incorporation of serum proteins, 1 M MgCl2 and 2 M NaCl in the medium having no influence on stability at 56 degrees C. The virus was resistant to the action of CHCl3, ether and 1% trypsin, and its replication was inhibited by BUDR, this effect being reversed by thymidine. Actinomycin D was found to inhibit virus replication, but only when applied during the first 8 h post-infection. Density gradient studies showed infective virus to have a density of 1.41 g cm-3; haemagglutinating non-infective virus with defective morphology having a density of 1.31 g cm-3. In addition, a proportion of morphologically-complete haemagglutinating, but non-infective virus particles was found at a density of 1.36 g cm-3. The virus proved to have a mean diameter of 22 nm.

Studies on the replication of a bovine parvovirus

Optimal replication of a bovine parvovirus type 1 was found to occur when parasynchronous bovine embryonic lung cells were infected during the S phase of the cell cycle, just prior to maximum DNA synthesis. Viral antigen was first detected in the cytoplasm by immunofluorescence at 8 h post-infection, reaching a maximum at this location by 16 h and then disappearing. In the nucleus, antigen was first detected at 12 h, concurrent with early inclusion body formation and first detection of intracellular virus production. Intranuclear antigen then increased rapidly to a maximum at 20 h, as the inclusions progressively matured, large amounts of virus were produced within the cell, with some release to the environment. From 24 h, the nuclear inclusions became increasingly shrunken and basophilic as virus migrated to the cytoplasm and was progressively released to the exterior concurrent with cell degeneration and fragmentation. The majority of virus remained cell associated, even at 28 h post-inoculation. Two morphological types of early and late stage intranuclear inclusions were produced by the virus, these appearing to be a distinct feature of bovine strains. In other aspects, the replication of bovine parvovirus appeared similar to that of other members of the genus.

Replication of bovine coronavirus in cell line BEK-1 culture

Bovine coronavirus readily multiplied and induced marked cytopathic effect in BEK-1 cultures, thus providing a sensitive, practical assay system for viral infectivity and neutralizing antibody and a satisfactory source of the virus.