DNAJC14-Independent Replication of the Atypical Porcine Pestivirus.

Atypical porcine pestiviruses (APPV; Pestivirus K) are a recently discovered, very divergent species of the genus Pestivirus within the family Flaviviridae. The presence of APPV in piglet-producing farms is associated with the occurrence of so-called "shaking piglets," suffering from mild to severe congenital tremor type A-II. Previous studies showed that the cellular protein DNAJC14 is an essential cofactor of the NS2 autoprotease of all classical pestiviruses. Consequently, genetically engineered DNAJC14 knockout cell lines were resistant to all tested noncytopathogenic (non-cp) pestiviruses. Surprisingly, we found that the non-cp APPV can replicate in these cells in the absence of DNAJC14, suggesting a divergent mechanism of polyprotein processing. A complete laboratory system for the study of APPV was established to learn more about the replication of this unusual virus. The inactivation of the APPV NS2 autoprotease using reverse genetics resulted in nonreplicative genomes. To further investigate whether a regulation of the NS2-3 cleavage is also existing in APPV, we constructed synthetic viral genomes with deletions and duplications leading to the NS2 independent release of mature NS3. As observed with other pestiviruses, the increase of mature NS3 resulted in elevated viral RNA replication levels and increased protein expression. Our data suggest that APPV exhibit a divergent mechanism for the regulation of the NS2 autoprotease activity most likely utilizing a different cellular protein for the adjustment of replication levels. IMPORTANCE DNAJC14 is an essential cofactor of the pestiviral NS2 autoprotease, limiting replication to tolerable levels as a prerequisite for the noncytopathogenic biotype of pestiviruses. Surprisingly, we found that the atypical porcine pestivirus (APPV) is able to replicate in the absence of DNAJC14. We further investigated the NS2-3 processing of APPV using a molecular clone, monoclonal antibodies, and DNAJC14 knockout cells. We identified two potential active site residues of the NS2 autoprotease and could demonstrate that the release of NS3 by the NS2 autoprotease is essential for APPV replication. Defective interfering genomes and viral genomes with duplicated NS3 sequences that produce mature NS3 independent of the NS2 autoprotease activity showed increased replication and antigen expression. It seems likely that an alternative cellular cofactor controls NS2-3 cleavage and thus replication of APPV. The replication-optimized synthetic APPV genomes might be suitable live vaccine candidates, whose establishment and testing warrant further research.

The Diverse Roles of microRNAs at the Host⁻Virus Interface.

MicroRNAs (miRNAs) are small, non-coding RNAs that regulate gene expression at the post-transcriptional level. Through this activity, they are implicated in almost every cellular process investigated to date. Hence, it is not surprising that miRNAs play diverse roles in regulation of viral infections and antiviral responses. Diverse families of DNA and RNA viruses have been shown to take advantage of cellular miRNAs or produce virally encoded miRNAs that alter host or viral gene expression. MiRNA-mediated changes in gene expression have been demonstrated to modulate viral replication, antiviral immune responses, viral latency, and pathogenesis. Interestingly, viruses mediate both canonical and non-canonical interactions with miRNAs to downregulate specific targets or to promote viral genome stability, translation, and/or RNA accumulation. In this review, we focus on recent findings elucidating several key mechanisms employed by diverse virus families, with a focus on miRNAs at the host⁻virus interface during herpesvirus, polyomavirus, retroviruses, pestivirus, and hepacivirus infections.

In vitro inhibition of the bovine viral diarrhoea virus by the essential oil of Ocimum basilicum (basil) and monoterpenes.

The bovine viral diarrhoea virus (BVDV) is suggested as a model for antiviral studies of the hepatitis C virus (HCV). The antiviral activity of the essential oil of Ocimum basilicum and the monoterpenes camphor, thymol and 1,8-cineole against BVDV was investigated. The cytotoxicities of the compounds were measured by the MTT (3-(4.5-dimethylthiazol-2-yl)-2.5-diphenyltetrazolium bromide) test, and the antiviral activities were tested by the plaque reduction assay. The oil or compounds were added to the assay in three different time points: a) pre-treatment of the virus (virucidal assay); b) pre-treatment of the cells; or c) post-treatment of the cells (after virus inoculation). The percentage of plaques inhibition for each compound was determined based on the number of plaques in the viral control. The results were expressed by CC50 (50% cytotoxic concentration), IC50 (inhibitory concentration for 50% of plaques) and SI (selectivity index = CC50/IC50). Camphor (CC50 = 4420.12 µg mL(-1)) and 1,8-cineole (CC50 = 2996.10 µg mL(-1)) showed the lowest cytotoxicities and the best antiviral activities (camphor SI = 13.88 and 1,8-cineol SI = 9.05) in the virucidal assay. The higher activities achieved by the monoterpenes in the virucidal assay suggest that these compounds act directly on the viral particle.

N pro of Bungowannah virus exhibits the same antagonistic function in the IFN induction pathway than that of other classical pestiviruses.

Bungowannah virus is the most divergent atypical pestivirus that had been detected up to now, and does not fit into any of the four approved species: Bovine viral diarrhea virus type 1 (BVDV-1) and type 2 (BVDV-2), Classical swine fever virus (CSFV) and Border disease virus (BDV). However, the presence of N(pro) and E(rns) coding regions, which are unique to pestiviruses, provides clear evidence of a pestivirus. Nevertheless, the amino acid identity of Bungowannah virus N(pro) and BVDV-1 N(pro) (strain CP7) is only 51.5%. By using a BVDV-1 backbone, a novel chimeric construct was generated, in which the genomic region encoding the non-structural protein N(pro) was replaced by that of Bungowannah virus (CP7_N(pro)-Bungo). In vitro studies of CP7_N(pro)-Bungo revealed autonomous replication with the same efficacy as the BVDV backbone CP7 and infectious high-titer virus could be collected. In order to compare the ability of interferon (IFN) suppression, two reporter gene assays, specific for type-I IFN, were carried out. In virus-infected cells, no significant difference in blocking of IFN expression between the parental virus CP7, Bungowannah virus and the chimeric construct CP7_N(pro)-Bungo could be detected. In contrast, an N(pro) deletion mutant showed an impaired replication in bovine cells and a marked type-I IFN response. Taken together, our findings reveal the compatibility of non-structural protein N(pro) of atypical Bungowannah virus with a BVDV type 1 backbone and its characteristic feature as an inhibitor of type-I IFN induction with an inhibitor-activity comparable to other pestiviruses.

In vitro inhibition of the bovine viral diarrhoea virus by the essential oil of Ocimum basilicum (basil) and monoterpenes

The bovine viral diarrhoea virus (BVDV) is suggested as a model for antiviral studies of the hepatitis C virus (HCV). The antiviral activity of the essential oil of Ocimum basilicum and the monoterpenes camphor, thymol and 1,8-cineole against BVDV was investigated. The cytotoxicities of the compounds were measured by the MTT (3-(4.5-dimethylthiazol-2-yl)-2.5-diphenyltetrazolium bromide) test, and the antiviral activities were tested by the plaque reduction assay. The oil or compounds were added to the assay in three different time points: a) pre-treatment of the virus (virucidal assay); b) pre-treatment of the cells; or c) post-treatment of the cells (after virus inoculation). The percentage of plaques inhibition for each compound was determined based on the number of plaques in the viral control. The results were expressed by CC50 (50% cytotoxic concentration), IC50 (inhibitory concentration for 50% of plaques) and SI (selectivity index = CC50/IC50). Camphor (CC50 = 4420.12 µgmL-1) and 1,8-cineole (CC50 = 2996.10 µgmL-1) showed the lowest cytotoxicities and the best antiviral activities (camphor SI = 13.88 and 1,8-cineol SI = 9.05) in the virucidal assay. The higher activities achieved by the monoterpenes in the virucidal assay suggest that these compounds act directly on the viral particle.

A long distance RT-PCR able to amplify the Pestivirus genome.

A method to amplify long genomic regions (up to approximately 12.3 kb) from pestiviruses in one RT-PCR is described. The difficulty in designing conserved Pestivirus primers for the amplification of genomes from highly divergent isolates simply by means of overlapping segments is demonstrated using new bioinformatic tools. An alternative procedure consisting of optimizing the length of the genomic cDNA fragments and their subsequent amplification by polymerase chain reaction (PCR) using a limited set of specific primers is described. The amplification of long DNA fragments from a variety of sources, including genomic, mitochondrial, and viral DNAs as well as cDNA produced by reverse transcription (RT) has been achieved using this methodology, known as long distance PCR. In the case of viruses, it is necessary to obtain viral particles from infected cells prior to RT procedures. This work provides improvements in four steps of long distance RT-PCR (L-RT-PCR): (i) preparation of a viral stock, (ii) preparation of template RNA, (iii) reverse transcription and (iv) amplification of the cDNA by LD-PCR. The usefulness of L-RT-PCR is discussed in the light of current knowledge on pestivirus diversity. The genomic sequence of Singer_Arg reference strain obtained using this method is presented and characterized.

Noncytopathogenic pestivirus strains generated by nonhomologous RNA recombination: alterations in the NS4A/NS4B coding region.

Several studies have demonstrated that cytopathogenic (cp) pestivirus strains evolve from noncytopathogenic (noncp) viruses by nonhomologous RNA recombination. In addition, two recent reports showed the rapid emergence of noncp Bovine viral diarrhea virus (BVDV) after a few cell culture passages of cp BVDV strains by homologous recombination between identical duplicated viral sequences. To allow the identification of recombination sites from noncp BVDV strains that evolve from cp viruses, we constructed the cp BVDV strains CP442 and CP552. Both harbor duplicated viral sequences of different origin flanking the cellular insertion Nedd8*; the latter is a prerequisite for their cytopathogenicity. In contrast to the previous studies, isolation of noncp strains was possible only after extensive cell culture passages of CP442 and CP552. Sequence analysis of 15 isolated noncp BVDVs confirmed that all recombinant strains lack at least most of Nedd8*. Interestingly, only one strain resulted from homologous recombination while the other 14 strains were generated by nonhomologous recombination. Accordingly, our data suggest that the extent of sequence identity between participating sequences influences both frequency and mode (homologous versus nonhomologous) of RNA recombination in pestiviruses. Further analyses of the noncp recombinant strains revealed that a duplication of 14 codons in the BVDV nonstructural protein 4B (NS4B) gene does not interfere with efficient viral replication. Moreover, an insertion of viral sequences between the NS4A and NS4B genes was well tolerated. These findings thus led to the identification of two genomic loci which appear to be suited for the insertion of heterologous sequences into the genomes of pestiviruses and related viruses.

Seroprevalence of pestivirus in four species of alpine wild ungulates in the High Valley of Susa, Italy.

Wildlife, once infected, can serve as a reservoir of infectious diseases that form a constant threat to domestic livestock. To make control and eradication programs successful in the long-term, presence of pestivirus in wildlife populations should be monitored. The goal of this study was to investigate seroprevalence of pestivirus in four alpine wild ungulates in the High Valley of Susa, north-west Italy. Species studied were: red deer (Cervus elaphus), roe deer (Capreolus capreolus), wild boar (Sus scrofa) and chamois (Rupicapra rupicapra). A further goal was using virus neutralisation tests (VNT) for four strains of pestivirus in chamois and wild boar. Three hundred and seventy-five serum samples collected during the hunting season of 1999 were tested for pestivirus specific antibodies. Positive sera of chamois and wild boar were subsequently tested in a VNT with four major subtypes of pestivirus, and virus isolation was performed. No antibodies were found in the 73 samples of roe deer, while 7 (12.5%), 8 (5.9%) and 28 (25.5%) of 56, 136 and 110 samples of wild boar, red deer and chamois were ELISA-positive, respectively. Different ranges of titers were found in the VNT and no pestivirus was isolated in the ELISA-positive wild boar and chamois samples. Several possibilities, which might explain the high seroprevalence in chamois are discussed. Pestivirus antibodies were found in three out of four large alpine ungulates in the High Valley of Susa. Seroprevalence was particularly high in chamois. Further investigation is needed to characterise the pestiviruses that circulate in these animals.

Pestivirus is a common contaminant in maedi-visna and caprine arthritis-encephalitis virus stocks.

Eight different laboratory stocks of maedi-visna or caprine arthritis-encephalitis virus were examined for the presence of pestiviruses by a fixed-cell immunoperoxidase assay with polyclonal and monoclonal antibodies. All of the viral stocks examined were found to contain noncytopathic pestivirus contaminants. The panel of monoclonal antibodies could not type the isolates as being more related to bovine virus diarrhea virus or border disease virus. However, the results did indicate that all isolates were not the same, except for two from the same laboratory where the source of pestivirus contamination may have been common.

Effects of bovine respiratory disease viruses and isoprinosine on bovine leukocyte function in vitro.

Peripheral blood mononuclear cells obtained from 4- to 6-month-old-calves were inoculated in vitro with bovine herpesvirus-1, parainfluenza-3, or bovine virus diarrhea viruses. No increase in infectious virus progeny was observed; however, the viruses were detected in the cells for at least 96 h post-infection without any significant reduction in cell viability. The three viruses, either alone or in combination, suppressed phytohemagglutinin-induced proliferation of the mononuclear cells. The greatest suppression was observed in cultures inoculated with bovine virus diarrhea virus. Addition of isoprinosine partially restored this viral-induced suppression of proliferative response, and the efficiency of reversal was greater in bovine virus diarrhea virus-infected cells. Interleukin-2 activity was higher in cultures of virus-infected mononuclear cells than in cultures of non-infected cells.

A rapid, quantitative assay for titration of bovine virus diarrhoea-mucosal disease virus.

An end point dilution microtitration assay is described that can be used for the titration of both cytopathic and non-cytopathic isolates of bovine virus diarrhoea-mucosal disease virus. Indirect immunofluorescence is used to detect infected MDBK cells in the wells of Terasaki plates. The virus titre is derived from the number of uninfected wells, using the Poisson distribution. The assay is simple, fast and economical. Titres of cytopathic virus determined by the microtitration assay and standard plaque assay are equivalent.

Comparison of five cell lines for the propagation of bovine viral diarrhea and infectious bovine rhinotracheitis viruses.

A comparative study was carried out to determine the susceptibility of 5 different cell types to bovine viral diarrhea (BVD) and infectious bovine rhinotracheitis (IBR) viruses. The cell systems used were swine testicle (ST), mink lung (ML), bovine turbinate (BT), porcine kidney (PK15) and equine dermal (ED) cells. For BVD virus, the titers obtained on day 8 post-infection were 10(1.13), 10(3.25), 10(4.13), 10(0.00) and 10(0.00), in ST, ML, BT, PK15 and ED cells, respectively. For the IBR virus, the titers obtained were 10(2.63), 10(8.5), 10(8.38), 10(3.00), and 10(4.63) in ST, ML, BT, PK15 and ED cells, respectively. This indicates, therefore, that BT and ML cells are optimal for the propagation of both BVD and IBR viruses and that ST, PK15, and ED cells are not very sensitive to these viruses.

A technique to obviate the risk of inadvertent infection of cell cultures with bovine viral diarrhoea virus.

When bovine embryonic kidneys collected at the Gorgie Abattoir, Edinburgh were examined for evidence of infection with bovine viral diarrhoea virus (BVDV), 11 out of 26 kidneys were found to be positive. A technique that detected the presence of inadvertent BVDV in cell cultures consisted of processing and digesting the kidneys to produce cell suspensions, adding dimethyl sulphoxide and dispersing the suspensions in small aliquots that were stored frozen at - 114 degrees C. One aliquot was cultured and screened for BVDV by indirect immuno-fluorescence and interference tests. Bovine embryonic kidney cells so processed retained their viability and virus susceptibility for 15 to 18 months. Selected stocks of "clean" cells only are then used for vaccine production or diagnostic purposes. The cytopathic NADL strain of BVDV multiplied in naturally infected cell cultures but the titres attained were significantly lower than in "clean" cell cultures.

[Experiments to culture the bovine pestivirus in heterologous cell cultures]. / Opiti za kultivirane na govezhdiia pestivirus v kheterolozhni kletuchni kulturi.

Attempts were made to adapt a strain of the bovine pestivirus to cell cultures of swine kidney in a series of 15 passages. The adaptation of the virus was followed up through the production of a cytopathic effect, through comparative investigations, and by means of cytologic preparations. It was found that the cytopathic effect induced and the titer of the virus grew with increasing the number of the serial passages. Immunofluorescence and cytologic data showed the progressive development of the virus in cell cultures of swine kidney. It was also established that the time of incubation of the infected cultures to produce an overall cytopathic effect was shorter.

Susceptibility of various cell culture systems to bovine viral diarrhea virus.

A comparative study was carried out on the susceptibility of primary bovine embryo kidney (pBEK) cell cultures and those of three other cell culture systems, i.e., primary calf testicle (pCT) cells and two cell lines, one of which originated from bovine embryonic trachea (EBTr) and the other from buffalo lung (IMR-31), to bovine viral diarrhea (BVD) virus. The virus titers obtained in the three culture systems under study did not differ significantly from those of pBEK cells. Moreover, the growth curve study demonstrated thad the pCT cells, as well as the two cell lines, were similar to the pBEK cultures in their susceptibility to the virus. Accordingly, it appeared reasonable to conclude that pCT, EBTr and IMR-31 cell cultures possess the general requirements for use in studies on the BVD virus. However, inasmuch as the cytopathic effects (CPE) produced by the EBTr and the IMR-31 cell lines did not display any distinctive characteristics typical of BVD virus-induced CPE, it is recommended that the two cell lines not be used for isolation of the virus from specimen material.

[Cultivation of bovine pestivirus in organ culture]. / Kultivirane na govezhdiia pestivirus v organni kulturi.

Attempts were made to culture strains of the bovine pestivirus in organ cultures of tracheal rings. Contrary to other scientists the authors used roller organ cultures of calf tracheal rings. The development of the virus in the cultures was judged by its presence in the maintaining medium through ELISA or by titration in cell cultures of fetal calf kidney. It was found that the two strains tested could be replicated in organ cultures of calf trachea, the intensity of multiplication being strongest between the third and the sixth day as demonstrated by ELISA. It was also established that the various batches of tracheal tissue had varying susceptibility.

Experimental production of fatal mucosal disease in cattle.

Three outbreaks of mucosal disease were investigated. Careful examination of 47 cattle that were persistently viraemic with bovine virus diarrhoea virus (BVDV) revealed no clinical disease, no or low levels of BVDV antibody and only non-cytopathic virus in their blood. The four animals with mucosal disease all showed clinical disease and both cytopathic and non-cytopathic virus in their blood. Following post mortem examination, there were particularly high levels of cytopathic virus in gut tissue. A hypothesis for the induction of mucosal disease is suggested. It states that animals become persistently infected with non-cytopathic virus following in utero infection and when, in post natal life, they become superinfected with a cytopathic virus, then mucosal disease ensues. The experimental reproduction of mucosal disease in support of this hypothesis is described.