Bovine viral diarrhoea virus genotype 1 can be separated into at least eleven genetic groups

Genetic and antigenic typing of border disease virus isolates in sheep from the Iberian Peninsula

A selection of 10 pestiviruses isolated from sheep from the Iberian Peninsula from 2001 to 2004 was characterised at the molecular level. The 5' untranslated region (5'-UTR) and N(pro)-coding gene were amplified by the reverse transcription-polymerase chain reaction (RT-PCR) and sequenced directly from purified products. All isolates were also typed antigenically with a panel of monoclonal antibodies (mAbs) raised against representative isolates of the four recognised pestivirus species. The genetic typing placed all the isolates in a new tentative type 4 of border disease virus (BDV), which was closely related to a pestivirus recently found in Pyrenean chamois (Rupicapra pyrenaica pyrenaica). Overall, the genotyping indicated a relatively wide diversity of the BDV type 4, which was best defined on the basis of N(pro) sequences. Antigenically, the isolates were recognised by two pan-pestivirus specific anti-NS3 mAbs, but only by some of the anti-glycoprotein specific mAbs raised against BDV, indicating partial antigenic overlap with other BDV isolates.

Numerical taxonomy of the genus Pestivirus based on palindromic nucleotide substitutions in the 5' untranslated region

The palindromic nucleotide substitutions (PNS) at the three variable loci (V1, V2 and V3) in the 5' untranslated region (UTR) of Pestivirus RNA have been considered for taxonomical segregation of species, through the evaluation of 430 genomic sequences. On the basis of qualitative and quantitative secondary structure characteristics, six species have been identified: Bovine viral diarrhea virus 1 (BVDV-1), Bovine viral diarrhea virus 2 (BVDV-2), Classical swine fever virus (CSFV), Border disease virus (BDV), the tentative species Giraffe and a new proposed taxon named Pronghorn. The first step was qualitative and consisted in the characterization of the different positions of the three stems and loops in the 5' UTR sequences of all the strains under consideration belonging to the genus. Secondary structure sequences showing divergent base-pair combinations have been aligned for comparison. Palindromic positions have been characterized according to changes in nucleotide base-pairs identifying low-variable positions (LVP) including base-pairs present in less than 80% of the genus. The second step was quantitative, allowing the identification of genomic groups by clustering the base-pair combinations according to LVP. Relatedness among types was evaluated to identify homogeneous groups. Cross comparisons between types within the genus have been evaluated by computing the divergence percentage thus clarifying borderline and multirelated sequences.

A scoring system for risk assessment of the introduction and spread of bovine viral diarrhoea virus in dairy herds in Northern Italy

To support a voluntary disease control program, this study aimed to develop an integrated scoring system for the risk assessment of bovine viral diarrhoea virus (BVDV) infection in dairy herds in Northern Italy. Sixty-two dairy herds were classified according to their BVDV serological status. Farmers were interviewed using a questionnaire on potential BVDV risk factors. Scores were used to define risk levels for factors related to (1) BVDV introduction (through livestock trade, attendance of animals at shows/exhibitions and grazing common pasture), (2) within-herd spread of BVDV and (3) the results of initial serological testing. The calculated odds ratios were significant for all categories, except for livestock trade. The application of the screening test, the questionnaire and the related risk assessment showed this to be a practical approach to predicting BVDV herd status.

Evidence for positive selection on the E2 gene of bovine viral diarrhoea virus type 1

Despite the growing interest in the molecular epidemiology of pestivirus, there have been few attempts to determine which regions of the pestivirus genome are subject to positive selection, although this may be a key indicator of the nature of the interaction between host and virus. By using likelihood-based methods for phylogenetic inference, the positive selection pressure of BVDV-1 E2 gene were assessed and a site-by-site analysis of the dN/dS ratio was performed, to identify specific codons undergoing diversifying positive selection. The overall omega was 0.20, indicating that most sites were subject to strong purifying selection and five positively selected sites (886, 888, 905, 944, and 946) were identified. It is surprising to find that all the potential positively selected sites fall within the C-terminal of E2, and out of the N-terminal of E2 which is thought to be surface-exposed and therefore prime targets for host antibody response. In conclusion, these results suggest that selection favoring avoidance of antibody recognition has not been a major factor in the history of BVDV-1. Further analysis is necessary to see if amino acid substitutions in the BVDV-1 positively selected sites can lead to change of host tropism or\and escape from epitope-specific CD8 T-cell response.

Bovine viral diarrhoea virus (BVDV) diversity and vaccination. A review

BVDV is associated with a range of economically important clinical diseases including reproductive disorders and acute fatal haemorrhagic disease in cattle industry. Vaccination is still the most important control strategy for controlling BVDV infections in many countries of the world. The existence of great genetic and antigenic diversity of BVDV isolates is very important concern for BVDV vaccine development and protective efficacy of current vaccines. In this review, the protective efficacies of the selected examples of BVDV vaccines with regard to BVDV diversity and the novel marker vaccine development studies are discussed.

Genetic characterization of Brazilian bovine viral diarrhea virus isolates by partial nucleotide sequencing of the 5'-UTR region

Nineteen isolates of bovine viral diarrhea virus (BVDV) from Brazil were genetically characterized through partial nucleotide sequencing and analysis of the 5'UTR region. The isolates were grouped as BVDV-1 (11/19), BVDV-2 (6/19) or "atypical" pestivirus (2/19). Among the BVDV-1, eight isolates were classified as subgenotype BVDV-1a, whereas most (4 out of 6) BVDV-2 belonged to subgenotype 2b. Two isolates from aborted fetuses were not classified into any genetic group, being considered atypical BVDVs. Genetic diversity among Brazilian BVDV isolates may be responsible for vaccination and diag-nostic failure and therefore may influence the control strategies for BVDV infection in the country.

A universal heterologous internal control system for duplex real-time RT-PCR assays used in a detection system for pestiviruses

A heterologous in vitro transcript based on a specific primer-probe HEX system was generated as a universal internal control (IC) to improve virus-specific real-time reverse-transcriptase PCR (RT-PCR) assays. By using a set of different primers, several PCR fragments of desired sizes of an in vitro transcript of the enhanced green fluorescent protein (EGFP) gene were generated, and the fragments were detected using a HEX-labelled probe. For long-term storage of the in vitro transcript a special RNA-safe buffer (RSB) was developed. Freezing and thawing of the IC diluted in RSB did not result in any substantial loss of detectable IC copy numbers. The new IC system was used for the first time in a duplex real-time RT-PCR assay for the detection of pestivirus-derived RNA, in particular from bovine viral diarrhea virus (BVDV). Primers and TaqMan probes for the 'panpesti' assay were selected by analysing the consensus sequence of the 5' non-translated region (5' NTR) of more than 600 different pestiviruses. Finally, the optimised primer probe combination showed an analytical sensitivity of less than 10 copies/reaction. In the duplex set-up, the analytical sensitivity of the validated real-time RT-PCR was identical to the sensitivity of the single assay without IC, and the diagnostic sensitivity of the duplex assay was equal or higher if compared to virus isolation.

Genetic variability of bovine viral diarrhoea virus subtypes at 3'-nontranslated region

Ten isolates belonging to different BVDV-1 subtypes and three BVDV-2 isolates were studied in 3'-nontranslated region (3'-NTR) by sequencing of PCR products and comparative computer-assisted nucleotide sequence analysis. The alignment of nucleotide sequences revealed that all BVDV-1 isolates except BVDV-1a isolates represented by NADL strain were characterised with a deletion of 38 nucleotides in the variable region located after the stop codon. For all BVDV-1 subtypes, a constant region at the end of viral genome was highly conserved. The variable and constant regions with no significant insertions or deletions were also identified in BVDV-2 isolates. The poly AT reach region was situated at different locations in both pestiviruses.

Sequencing and comparative analysis of a pig bovine viral diarrhea virus genome

In present study, we report the first complete genomic sequence of pig bovine viral diarrhea (BVD) virus, that of strain ZM-95, which is 12,220 nucleotides long and contains short 5' and 3' non-coding regions and one open reading frame encoding a large polyprotein with 28 potential N-glycosylation sites (Asn-X-Ser or Asn-X-Thr). Within the non-structural protein encoding region, no foreign nucleotide insertions was found as those usually observed for cytopathogenic BVDV-1, but close to the 3'-terminal of the capsid protein (1119-1124bp) it contains a short insertion of a six nucleotide sequence (CTCACA). Three hypervariable regions were identified in the polyprotein-encoding region, with one of them comprising a sequence motif encoding a unique five amino acid peptide HYKKK in glycoprotein E2 gene. The genomic comparison and phylogenetic analyses showed that ZM-95 should be classified into BVDV-1, but was genetically divergent from other pestiviruses sequenced to date since its highest genetic similarity was only 76.6% (with SD-1), therefore, placed as a novel subgroup of BVDV-1.

Pestiviruses in wild animals

Pestiviruses are not strictly host-species specific and can infect not only domestic but also wild animals. The most important pestivirus, CSFV, infects domestic pigs and wild boars, which may cause a major problem for successful CSFV eradication programmes. Mainly BVDV specific antibodies have been reported in captive and free-living animals. Virus has been isolated from some of these animal species, but since BVDV can contaminate cell cultures and foetal calf serum, early reports of BVDV isolation have to be considered with caution. Genetic typing of early pestivirus isolates from wild species revealed that the majority were BVDV-1. Of the pestiviruses identified so far three species (CSFV, BVDV-1, giraffe pestivirus) and three genotypes (BDV-2, BDV-4, pronghorn) appear to circulate in wildlife animal populations. The potential for pestiviruses to spread between farm animals and free-living animals is discussed as are epidemiological and technical problems, and the future direction of research.

Bovine viral diarrhoea virus (BVDV) subgenotypes in diagnostic laboratory accessions: distribution of BVDV1a, 1b, and 2a subgenotypes

The prevalence of bovine viral diarrhoea virus (BVDV) biotypes and subgenotypes was determined from 131 BVDV positive samples from a diagnostic laboratory. The majority of the isolates were from Oklahoma; however, other states including Kansas, Texas, and Arkansas were represented. These BVDV samples were from submissions of 76 live animals and 55 necropsy samples. There were 131 BVDV samples represented by 117 noncytopathic (NCP), 11 cytopathic (CP) and 3 cases with mixed NCP and CP biotypes. The NCP isolates were more common (P < 0.05) than the CP and NCP/CP combination. The BVDV samples were segregated into three subgenotypes by differential PCR and sequencing of a viral genomic region, 5'-untranslated region (5'-UTR). There were more BVDV1b subgenotypes 60/131 (45.8%) than BVDV1a, 37/131 (28.2%) or BVDV2a, 34/131 (26.0%) (P < 0.05). The organ system involvement included the major categories such as respiratory, digestive, mixed/multiple organs, abortions, and persistent infections (PI). All three BVDV subgenotypes were found in persistently infected (PI) cattle and respiratory diseases, both major requests for BVDV diagnosis. Only one of the 131 viruses was genetically similar to the strains present in U.S. vaccines.

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.

A one-step multiplex real-time RT-PCR for detection and typing of bovine viral diarrhea viruses

A one-step multiplex real-time reverse transcriptase-polymerase chain reaction (RT-PCR) using SmartCycler technology and TaqMan probes was developed for detection and typing of bovine viral diarrhea viruses (BVDV). Common primers and type-specific (BVDV1 and BVDV2) TaqMan probes were designed in the 5'-untranslated region of the viral genome. The real-time assay was able to detect 10-100 TCID50 of virus, with correlation coefficient (r2) values of 0.998 and 0.999 for BVDV1 and BVDV2, respectively. The assay accurately typed 54 BVDV strains and field isolates and specificity of the TaqMan probes was further demonstrated by the lack of reactivity with the closely related Pestiviruses, classical swine fever virus and border disease virus. The assay was also shown to have high reproducibility. When the assay was compared with virus isolation for bovine serum samples, there was full agreement between the tests. Thus, the one-step real-time RT-PCR assay appears to be a rapid, sensitive, and specific test for detection and typing of BVDV.

Phylogenetic analysis of Portuguese bovine viral diarrhoea virus

Bovine viral diarrhoea virus (BVDV) infections are an important cause of morbidity and mortality worldwide in dairy and beef cattle. To date, little is know about BVDV genotypes circulating in Portugal. For this purpose, a fragment within the 5'-untranslated region (5'-UTR) from 34 Portuguese field strains of BVDV was amplified by RT-PCR, cloned and sequenced. A maximum-likelihood phylogenetic analysis revealed that most of viruses, originated from cattle from different regions of the country, belong to BVDV type 1 (BVDV-1), genotypes 1b (n = 19), 1a (n = 6), 1d (n = 3) and 1e (n = 3); whereas three viruses clustered in BVDV type 2 (BVDV-2). The results from this study demonstrate that BVDV-lb is the most prevalent genotype and also shows the presence of BVDV-2 in Portugal.

Genetic heterogeneity of pestiviruses of ruminants in Switzerland

We have genetically analyzed ruminant pestiviruses. All >150 bovine viral diarrhea (BVD) viruses isolated from cattle in Switzerland belonged to genotype 1, with subgenogroups e, h, k and b found in decreasing frequency. To date, representatives of subgenogroup k have been detected in Switzerland only. Despite serological evidence of Border disease in sheep, only few Border disease viruses have been isolated, all of which belong to the novel group 3. Serological evidence suggested that pestivirus infections may occur also in wild ruminants in Switzerland but no isolates are available for analysis. In addition, we describe two pestiviruses, one a cell culture contaminant and the other isolated from a buffalo, that cluster with a recently proposed novel pestivirus species.

Practical significance of heterogeneity among BVDV strains: Impact of biotype and genotype on U.S. control programs

In the early 1990s research groups in North America noted that a newly recognized severe acute form of bovine viral diarrhea virus infection, referred to as hemorrhagic syndrome or severe acute BVDV (SA BVDV), was associated with a genetically distinct subgroup of BVDV strains. This new subgroup was named BVDV genotype 2 or BVDV2. All BVDV strains previously characterized in the literature belonged to a separate genotype, BVDV1. However, not all strains identified as BVDV2 were associated with severe acute infections. If I did this deletion, I did not mean to do it. I think it was already here, though. I see there are some other big edits that I did not do; fine. Hollis subsequent surveys of BVDV strains isolated from clinical submissions to diagnostic laboratories and contaminated fetal calf serum suggested that the ratio of BVDV2 to BVDV1 strains in the U.S. approached 50%. Further, while antigenic cross reactivity is seen between BVDV1 and BVDV2 strains, a log or more difference is typically observed in titers against viruses from different genotypes. These observations prompted vaccine manufacturers in North America to produce vaccines against BVDV that contained antigens from both BVDV1 and BVDV2 strains. Under experimental conditions, these new vaccines offered improved protection against type 2 strains, however field data are still insufficient to assess their efficacy in practice. The BVDV genotypes may also be segregated into subgenotypes. Two subgenotypes of both BVDV1 (BVDV1a and BVDV1b) and BVDV2 (BVDV2a and BVDV2b) have been reported in North American. BVDV2a predominates with BVDV2b isolation a rare event. In contrast, BVDV1a and BVDV1b are both commonly isolated. Antigenic differences observed between strains from the BVDV1a and BVDV1b subgenotypes have led to the suggestion that protection may be improved by inclusion of strains from both BVDV1a and BVDV1b in vaccines in addition to BVDV2. The cost to benefit ratio of this proposal is currently a matter of debate.

Molecular epidemiology of bovine viral diarrhoea during the final phase of the Swedish BVD-eradication programme

The Swedish BVD-eradication programme has been successfully running since 1993 and is now in its final phase. Nevertheless, new infections are occasionally being detected. In this paper we describe the first results of a programme where we apply a molecular-epidemiological approach to trace sources and routes of BVDV infection, and that we expect will speed up the final phase of the BVD-programme and help to reach total eradication.

Control of BVDV-infection on common grassland--the key for successful BVDV-eradication in Lower Austria

A bovine viral diarrhea/mucosal disease (BVD/MD) control and eradication program was introduced in Lower Austria in 1996, according to the Swedish model. At present 9800 out of 17,000 herds are part of this program. An important risk factor for BVDV-transmission under local conditions is communal grazing. Approximately 3-4% of livestock share common pastures, in which susceptible pregnant cattle may be mixed with unrecognised persistently infected (PI) animals. Rules and regulations were defined to allow only herds free from BVDV-infection on to common grassland. At the moment, 5067 herds are certified free from BVDV. The percentage of BVDV-free herds in regions with intensive pasture utilisation is higher (57.3%) than in the other regions (43.0%) of Lower Austria. With a reliable system for identification of PI-animals and a high certainty of prevention of PI-animals on common grassland, the main transmission of BVDV infection can be stopped, even if the animals are derived from infected herds and transiently infected animals cannot be excluded.

Genetic diversity of BVDV: consequences for classification and molecular epidemiology

Genetic typing of bovine viral diarrhoea virus (BVDV) is important for the precise classification of viruses as well as for the development of molecular epidemiology. BVDV isolates were usually typed based on comparison of genomic sequences from the 5'-untranslated region (5'-UTR), N(pro) and E2 region. Recently we have identified 11 genetic groups (subgenotypes) of BVDV-1. Our further experiments confirmed a new subgenotype, BVDV-1k, isolated from cattle in Switzerland. BVDV isolates from India were typed as BVDV-1b whereas BVDV-1c is a predominant subgenotype in Australia. The results of genetic typing of BVDV indicate that distribution of subgenotypes has no relationship to the geographic origin of viral isolates.

Genetic diversity of bovine viral diarrhoea viruses (BVDV) in Denmark during a 10-year eradication period

A 243 base-pair fragment of the 5'- untranslated region (5'-UTR) of bovine viral diarrhoea virus (BVDV) was RT-PCR amplified from tissue samples (after one passage) or from plasma collected from Danish cattle in 1962 (1), 1993 (7), or in 2002-03 (28) when BVD was almost extinct as a result of a 6-year eradication programme. The PCR products were sequenced and phylogenetically analysed. All 36 samples were BVDV species 1 (BVDV-1), 29 sequences belonged to the BVDV 1d subtype, 6 to the BVDV 1b subtype, and one sequence to the BVDV 1e subtype. While all samples from 1993 and 1962 were of 1d subtype, the samples collected in 2002-2003 belonged to 1d (22 samples), 1b (5 samples) and 1e (1 sample) subtypes. In five herds, materials from two animals were obtained for PCR analysis. In four of five herds the sequences of the two viruses were identical, but in one herd the obtained sequences belonged to two different subtypes. Routine analysis detected 11 PI calves older than 2 months of age. For early detection of infected calves it is recommended that antigen ELISA be replaced by PCR detection. Here we present the first sequence analysis of Danish BVDV strains.

Variation in immunogenicity of ruminant pestiviruses as determined by the neutralisation assay

Immunogenicity in naive three-month-old Friesian bull calves of nine ruminant pestiviruses, three each of type 1 bovine virus diarrhoea virus (BVDV), type 2 BVDV and border disease virus (BDV) was directly compared in reciprocal cross-neutralisation tests using sera obtained eight weeks after intranasal and intravenous inoculation with live virus. Cytopathic (CP) type 1 BVDV strain C86, non-cytopathic (NCP) type 2 BVDV strain 890 and NCP BDV strain V2536/2 were found to elicit significantly broad cross-neutralising antibodies against viruses in other species whereas other virus strains in all three species produced a much more pronounced homologous and/or species specific response. Results are clearly relevant in the selection of strains for vaccines against diseases caused by these successful, economically important ubiquitous viruses.

Characterization of a novel pestivirus originating from a pronghorn antelope

A unique pestivirus, isolated from a pronghorn antelope (Antilocopra americana), was characterized. Serum neutralization studies suggested that this virus was antigenically related to pestiviruses. Genomic characteristics, unique to pestiviruses, indicated that this virus belongs to the Pestivirus genus. These characteristics included the organization of the 5' untranslated region (5'-UTR), the presence and length of a viral Npro coding region, conservation of cysteine residues in Npro, conservation of predicted amino acid sequences flanking the cleavage sites between viral polypeptides Npro and C and between C and Erns and conservation of predicted hydrophobicity plots of Npro protein. While this data indicated the virus belongs to the Pestivirus genus, phylogenetic analysis in 5'-UTR, Npro and E2 regions suggested that it is the most divergent of the pestiviruses identified to date. This conclusion was also supported by the amino acid identity in coding regions. The corresponding values were much lower for the comparison of pronghorn pestivirus to other pestivirus genotypes than only between previous recognized genotypes. These results suggest the virus isolated from pronghorn antelope represents a new pestivirus genotype. It also represents the only pestivirus genotype first isolated from New World wildlife.

Genetic analysis of bovine viral diarrhoea viruses from Australia

Eighty-nine bovine viral diarrhoea viruses (BVDV) from Australia have been genetically typed by sequencing of the 5' untranslated region (5'-UTR) and for selected isolates the N(pro) region of the viral genome. Phylogenetic reconstructions indicated that all of the samples examined clustered within the BVDV type 1 genotype. Of the 11 previously described genetic groups of BVDV-1, 87 of the samples examined in this study clustered with the BVDV-1c, while two samples clustered with the BVDV-1a. Based on these analyses there appears to be limited genetic variation within the Australian BVDV field isolates. In addition, the phylogenetic reconstructions indicate that the clustering of Australian BVDV in the phylogenetic trees is not a result of geographic isolation.

Homologous recombination in bovine pestiviruses. Phylogenetic and statistic evidence

Bovine pestiviruses (Bovine Viral Diarrea Virus 1 (BVDV 1) and Bovine Viral Diarrea Virus 2 (BVDV 2)) belong to the genus Pestivirus (Flaviviridae), which is composed of positive stranded RNA viruses causing significant economic losses world-wide. We used phylogenetic and bootstrap analyses to systematically scan alignments of previously sequenced genomes in order to explore further the evolutionary mechanisms responsible for variation in the virus. Previously published data suggested that homologous crossover might be one of the mechanisms responsible for the genomic rearrangements observed in cytopathic (cp) strains of bovine pestiviruses. Nevertheless, homologous recombination involves not just homologous crossovers, but also replacement of a homologous region of the acceptor RNA. Furthermore, cytopathic strains represent dead paths in evolution, since they are isolated exclusively from the fatal cases of mucosal disease. Herein, we report evidence of homologous inter-genotype recombination in the genome of a non-cytopathic (ncp) strain of Bovine Viral Diarrea Virus 1, the type species of the genus Pestivirus. We also show that intra-genotype homologous recombination might be a common phenomenon in both species of Pestivirus. This evidence demonstrates that homologous recombination contribute to the diversification of bovine pestiviruses in nature. Implications for virus evolution, taxonomy and phylogenetics are discussed.

A novel pestivirus associated with deaths in Pyrenean chamois (Rupicapra pyrenaica pyrenaica)

During investigations into recent population decreases in Pyrenean chamois (Rupicapra pyrenaica pyrenaica) 21 animals found dead or dying were necropsied. Immunohistochemistry revealed the presence of a pestivirus in organs from two of the 21 chamois. From one of these animals a pestivirus was isolated from the spleen, skin and serum. The virus had better growth in ovine than in bovine cells and was neutralized most effectively by an anti-border disease virus (BDV) reference antiserum. Using panpestivirus and genotype-specific primers selected from 5'-untranslated region (UTR) of the pestivirus genome, BDV RNA was demonstrated by RT-PCR. Comparison of the chamois sequences from 5'-UTR, entire N(pro) and E2 gene coding regions with those of other pestivirus genotypes revealed that this virus did not fall into any of the pestivirus genotypes identified so far. Results of phylogenetic analysis suggested that the chamois pestivirus was closely related to BDV and it was typed as BDV-4 genotype.

Genetic and antigenic characterization of an atypical pestivirus isolate, a putative member of a novel pestivirus species

The genus Pestivirus within the family Flaviviridae currently consists of four different main species: Classical swine fever virus, Bovine viral diarrhea virus types 1 and 2 and Border disease virus. A fifth tentative species is represented by an isolate from a giraffe. In this study, a completely new pestivirus, isolated from a batch of fetal calf serum that was collected in Brazil, is described. It is proposed that the isolate D32/00_'HoBi' may constitute a novel sixth pestivirus species, because it is genetically, as well as antigenically, markedly different from all other pestiviruses. Based on the entire N(pro)- and E2-encoding sequences, identities of <70 % to all other pestivirus species were determined. Similarly, cross-neutralization and binding studies using antisera and mAbs revealed marked antigenic differences between D32/00_'HoBi' and all other pestiviruses.

Origination and consequences of bovine viral diarrhea virus diversity

The potential consequences of BVDV genetic and antigenic diversity are far ranging. The complexity of clinical presentations associated with BVDV likely arises from factors encoded by the virus genome. More importantly,prevention and control of BVDV may be complicated by diagnostic and immunization failure resulting from virus diversity. Evolutionary pressures will continue to drive further diversity, making control of BVDV challenging. Current and the potential for future BVDV strain diversity should be considered when designing BVDV control programs both at the individual farm and national herd level.

Laboratory diagnosis of bovine viral diarrhea virus infections

The past 20 years have witnessed dramatic improvements in laboratory methods for diagnosing bovine viral diarrhea virus(BVDV) infections. However, improvements in diagnostic technology have not necessarily led to improved diagnosis of BVDV at the individual animal or herd level. This article reviews BVDV laboratory diagnostic methods in the context of their rational application for improved detection of BVDV in the field.

Genetic typing of bovine viral diarrhoea virus: most Slovenian isolates are of genotypes 1d and 1f

A selection of 43 bovine viral diarrhoea viruses isolated from mainly persistently infected cattle on 23 Slovenian farms between 1997 and 2001 were characterised genetically. Viral RNA was extracted from infected cell cultures, reverse transcribed and amplified by PCR with primers targeting the 5'-UTR and the N(pro) gene, followed by direct sequencing of purified PCR products obtained for both genomic regions. The N(pro) sequences provided the best genetic resolution, and gave also higher statistical support for phylogenetic classification of the viruses. Thirty-eight of the Slovenian isolates were of genetic subtypes 1d and 1f, four were 1b, and one subtype 1g. No BVDV type 2 viruses were found. This genetic prevalence matched those previously reported for neighbouring countries, as opposed to findings reported for more distant European countries, e.g. France, Spain and the UK. From eight cattle herds several virus isolates were analysed; with one exception all isolates from each herd were of the same genetic group. Extended sequencing of the N(pro) and part of the C gene of virus isolates with identical 5'-UTR sequences allowed differentiation between isolates obtained at different times from one herd.

Phylogenetic analysis of bovine viral diarrhea viruses using five different genetic regions

Phylogenetic analysis of the five different regions (5' non-coding region (5'NCR), N(pro), E2, NS3 and NS5B-3'NCR) of 48 Japanese and reported bovine viral diarrhea virus (BVDV) genomes was performed. Japanese BVDVs were segregated into BVDV1 subdivided into six subgroups and BVDV2. One isolate, So CP/75, isolated in 1975 and previously proposed as subgroup 1e according to its 5'NCR sequence, was quite unique and formed an independent lineage in the tree of any region. Another isolate, 190CP, obtained from an experimental mucosal disease case was classified as subgroup 1e, defined by Becher et al. in the 5'NCR, N(pro) and E2 regions, whereas it was classified as subgroup 1a in the NS5B-3'NCR region. The genomic sequences of the American isolates ILLC and ILLNC obtained from the GenBank database were assigned into subgroup 1b in the 5'NCR, N(pro), E2 and NS5B-3'NCR regions, whereas they were assigned into subgroup 1a in the NS3 region, suggesting that recombination between the virus strains classified into different subgroups had occurred in an animal. These findings suggest that phylogenetic analysis of several genetic regions is useful for the further characterization of field BVDV isolates.

Bovine viral diarrhea virus 1 is classified into different subgenotypes depending on the analyzed region within the viral genome

Phylogenetic analyses of bovine viral diarrhea virus (BVDV) were performed based on the nucleotide sequences of the 5' untranslated region (5'-UTR) and E2-coding gene. Thirty-six BVDV detected from naturally infected cattle in the northern region of Japan were divided into three genotypes, BVDV1a, BVDV1b and BVDV2, in a 5'-UTR phylogenetic tree. In a phylogenetic tree constructed from the E2-coding gene, BVDV1c was identified and the viruses classified in BVDV1c were included in BVDV1a in the 5'-UTR phylogenetic tree. Moreover, BVDV1a and BVDV1b in the E2-phylogenetic tree clustered closer together than in the 5'-UTR tree. These results suggested that phylogenetic analysis of the E2 gene was more useful for identification of subgenotypes within BVDV1.

Caracterização de amostras atenuadas do vírus da Diarréia Viral Bovina (BVDV) tipos 1 e 2 para uso em vacinas

Este artigo relata a caracterização de duas amostras citopáticas do vírus da Diarréia Viral Bovina (BVDV-1: IBSP-2; BVDV-2: SV-253) submetidas à atenuação por múltiplas passagens em cultivo celular e exposição à radiação ultravioleta. As amostras foram caracterizadas in vitro (tamanho e morfologia de placas, cinética de replicação e perfil antigênico) e in vivo (atenuação e resposta sorológica em bovinos). A caracterização in vitro de populações clonadas dos vírus obtidas nas diferentes passagens em cultivo celular (0, 1, 10, 20 e 30), demonstrou que o processo de atenuação não afetou negativamente as características antigênicas e fenotípicas das amostras. Não foram observadas alterações significativas no tamanho e morfologia de placas e na cinética de replicação. A reatividade com 48 anticorpos monoclonais demonstrou que o perfil antigênico não doi alterado durante as sucessivas passagens in vitro. A inoculação intramuscular dos clones de vírus obtidos na passagem 30 (IBSP-2: 10(7,3) DICC50; SV-253: 10(6,8) DICC50) em 12 novilhas soronegativas com idade média de 15 meses, não resultou em sinais clínicos, comprovando sua atenuação. Após a inoculação, o vírus foi detectado em leucócitos da maioria dos animais inoculados (10/12) entre os dias 3 e 6 pós-inoculação (pi) e em secreções nasais de três animais (dias 4, 7 e 8pi). No entanto, não ocorreu transmissão dos vírus vacinais aos três animais soronegativos mantidos como sentinelas. Todos os animais vacinados soroconverteram aos 14 dias pós-vacinação (dpv). Títulos moderados a altos de anticorpos neutralizantes foram detectados frente a 5 isolados brasileiros do BVDV-1 (títulos de 80 a > 1280) e quatro isolados do BVDV-2 (títulos de 20 a 640). Em geral, os títulos foram de magnitude superior frente a isolados brasileiros do BVDV-1. Aos 240dpv, os animais receberam uma segunda dose dos vírus vacinais (IBSP-2: 10(7,3) DICC50; SV-253: 10(6,8) DICC50). A revacinação induziu uma resposta secundária na maioria dos animais, resultando em um aumento dos títulos de anticorpos neutralizantes principalmente frente ao BVDV-2. Esses resultados são promissores no sentido da utilização dessas amostras na formulação de vacinas atenuadas para o controle da infecção pelo BVDV no Brasil.

Progress of control and prevention programs for bovine viral diarrhea virus in Europe

In Europe, nationwide BVD control programs based on the TC principle have been running for up to 10 years in the Nordic countries. The results have shown that BVD eradication by removal of PI animals without use of vaccines is effective and that today's diagnostic tests, when used by experienced diagnosticians, are suitable for this task. Furthermore, to avoid control programs becoming Sisyphean tasks, adherence to strict biosecurity guide-lines to minimize infection of susceptible herds is a crucial additional measure. Efficient organization of testing, with sufficient capacity of diagnostic laboratories, is also important to minimize the period of overlap when remaining infected and recently emerged naive herds coexist close to each other. Control programs based on voluntary participation are possible, but when approaching final clearance of a national herd, significant delays can easily be suffered if any herd owners are allowed not to clear their herds. The control schemes used in the Nordic countries were tailored to fit the structure of the cattle production in each country. If BVD control programs based on the same principles are to be set up for other bovine populations,it is important to recognize and take into account for differences in the epidemiology of BVD and in the structure of the animal production,including cattle density and husbandry practices. To ensure optimal performance of the diagnostic tests, the diversity of BVDV in the region to be tested should also be considered.

Genetic heterogeneity of bovine viral diarrhoea virus in Italy

The genetic characteristics, of 38 field isolates of bovine viral diarrhoea virus (BVDV) collected in 1999 from sick or healthy and persistently infected cattle of dairy farms situated in northern Italy, were investigated. A partial 5'-untranslated region (5'-UTR) sequence of each isolate was determined and a phylogenetic analysis was performed. All the isolates were classified as belonging to the BVDV-1 genotype and could be assigned to different BVDV-1 groups, namely BVDV-1b (n = 20), BVDV-1d (n = 6) and BVDV-1e (n = 10). Two remaining isolates could be classified as BVDV-1f and BVDV-1h, respectively. These results provided evidence for genetic heterogeneity of BVDV in Italy, and contribute to a better knowledge of the circulation of BVDV strains, and to their classification.

Genetic heterogeneity of bovine viral diarrhoea viruses from Spain

Forty-four bovine viral diarrhoea virus (BVDV) isolates collected from the north of Spain between 1989 and 2000 were characterised at the molecular level. For 24 of these isolates the entire N(pro) gene sequence was determined. Phylogenetic analysis revealed that 21 isolates belong to subgroup BVDV-1b, while two BVDV-1c isolates and one BVDV-1h isolate were found. Furthermore, 20 additional virus isolates were analysed by differential reverse transcription-polymerase chain reaction (RT-PCR) and classified as BVDV-1. The results from our study demonstrate that BVDV-1b is the most prevalent subgroup present in bovine dairy herds of Spain, while there is no evidence for the presence of BVDV-2.

Bovine viral diarrhoea virus antigen in foetal calf serum batches and consequences of such contamination for vaccine production

A protocol to test foetal calf serum (FCS) for contamination with bovine viral diarrhoea virus (BVDV) is described. Following this protocol, which combines cell culture methods and detection of pestivirus RNA, seven batches of FCS were tested. Infectious BVDV was detected in four of those batches. One of the remaining batches contained a relatively high number of non-infectious BVDV particles. A sample of this batch was formulated with aluminium hydroxide and aluminium phosphate as adjuvant into an experimental vaccine preparation. This product was injected twice into BVDV seronegative cattle with a 4 week interval. Blood samples taken 4 weeks after the second application were negative for BVDV specific antibodies. Our data stress that detection of BVDV RNA is not sufficient for a complete risk assessment on FCS. Discrimination between infectious and non-infectious BVDV is essential. This can only be achieved by cell culture methods.

Expression of the genomic form of the bovine viral diarrhea virus E2 ORF in a bovine herpesvirus-1 vector

Bovine viral diarrhea virus (BVDV) is a ubiquitous pathogen of cattle with a world-wide distribution. Recently, the possibility of using recombinant virus vectors to immunize cattle against selected BVDV genes has gained widespread interest. Among the virus vectors tested, bovine herpesvirus-1 (BHV1) provides many unique advantages. However, results of recent studies have raised the possibility that the codon usage pattern required for optimal expression in a BHV1-infected cell may be incompatible with the codon usage pattern of BVDV. If true, use of BHV1 to express BVDV proteins would require construction of synthetic BVDV genes that have been modified to resemble the codon pattern of BHV1. To explore this possibility, we constructed a BHV1 recombinant containing the genomic form of the BVDV (NADL) E2 ORF and compared expression of the E2 protein with that of the endogenous BHV1 gD protein. We observed that E2 was expressed at a significant rate compared to that of the gD protein. We conclude that codon usage problems are unlikely to constitute a serious problem for expression of BVDV proteins in BHV1 vectors.

A hepadnavirus regulatory element enhances expression of a type 2 bovine viral diarrhea virus E2 protein from a bovine herpesvirus 1 vector

Recently, the possibility of using virus vectors to immunize cattle against selected bovine viral diarrhea virus (BVDV) genes has gained widespread interest. However, when we attempted to express the E2 protein from type 2 (890 strain) BVDV in a bovine herpesvirus 1 (BHV1) vector, we observed that expression was poor. This often happens when genes from a cytoplasmic virus are expressed in the cell nucleus. To counter this effect, we attempted to enhance expression by a strategy employed by viruses. RNAs of retroviruses and hepadnaviruses contain cis-acting elements that facilitate expression of RNAs that otherwise are degraded or retained within the nucleus. In Mason-Pfizer monkey virus, the required RNA sequence element is known as a constitutive transport element (CTE). A related element from woodchuck hepatitis virus is known as the woodchuck posttranscriptional regulatory element (WPRE). We tested the ability of the CTE, the WPRE, and introns to enhance expression of E2. All three elements stimulated expression of E2 from plasmids. The combination of the WPRE and an intron yielded the highest level of E2 expression in plasmids. However, when E2 was expressed from a BHV1 vector, the presence of an intron was inhibitory. In contrast, the WPRE was very efficient at stimulating E2 expression from a BHV1 vector. This result represents the first expression of a type 2 BVDV E2 protein from a mammalian virus vector and raises the possibility that the WPRE may provide a general method of enhancing foreign gene expression from BHV1 and other herpesvirus vectors.

A survey for BVDV antibodies in cattle farms in Slovakia and genetic typing of BVDV isolates from imported animals

A serological survey for bovine viral diarrhoea virus (BVDV) antibodies on a collection of 1295 serum samples obtained from 6-12 months old cattle originating from 45 farms in Slovakia was carried out. On 13 farms more than 90% of the examined animals were seropositive, on 14 farms 71-90% seroprevalence was observed, on 13 farms only 50-70% animals were found to be positive for BVDV antibodies, while the remaining 5 farms showed fewer than 50% seropositive animals. The average incidence of BVDV antibodies (around 70%) was similar as determined 30 years ago. Of 84 serum samples from seronegative animals originating from 14 farms in which 70-98% seropositivity was observed, six were positive in Ag-BVDV ELISA indicating persistently infected (PI) cattle. On a farm to which animals were imported from abroad, a BVD outbreak was observed. Of 110 animals tested, four were positive in Ag-ELISA indicating the presence of PI cattle on this farm. Genetic typing of two isolates from imported animals performed by RT-PCR (324/326 primers from 5'-UTR), sequencing of PCR products and computer-assisted phylogenetic analysis revealed that they belong to BVDV-1 h group.

Genetic and antigenic characterization of novel pestivirus genotypes: implications for classification

Currently, the genus Pestivirus comprises the four approved species Bovine viral diarrhea virus 1 (BVDV-1), BVDV-2, Classical swine fever virus (CSFV), and Border disease virus (BDV) and one tentative fifth species represented by a single strain (H138) isolated from a giraffe in Kenya more than 30 years ago. To further address the issue of heterogeneity of pestiviruses we have determined the entire N(pro) and E2 coding sequences for several new pestivirus isolates. Interestingly, phylogenetic analysis revealed that one pestivirus isolated in the 1990s in Africa is closely related to strain H138. Moreover, several novel pestiviruses isolated from sheep group together with the previously described strain V60 (Reindeer-1) isolated from a reindeer, whereas one ovine pestivirus strain (Gifhorn) significantly differs from all previously described pestiviruses, including BDV. We propose to term these mainly sheep-derived pestiviruses BDV-2 (V60-like isolates) and BDV-3 (Gifhorn); consequently, the "classical" BDV isolates should be termed BDV-1. As an additional criterion for segregation of pestiviruses, the antigenic relatedness of pestivirus isolates covering all observed major genotypes was studied by cross-neutralization assays. Analysis of the antigenic similarities indicated the presence of seven major antigenic groups corresponding to BVDV-1, BVDV-2, CSFV, BDV-1, BDV-2, BDV-3, and "giraffe". Taking into account the host origin, the lack of differences concerning the course of disease, and the results of our genetic and antigenic analyses, we suggest that BDV-1, BDV-2, and BDV-3 should be considered as major genotypes within the species BDV.

Genetic diversity of ruminant pestiviruses from Spain

The genetic diversity of ruminant pestiviruses from Spain was investigated by sequencing analysis of the 5' non-coding region (5'NCR) from 10 ovine and 41 bovine samples collected along 4 years (1999-2002) from different farms. The 5'NCR amplicons generated by a one-tube RT-PCR using primers 324/326 were sequenced and phylogenetically analyzed. When compared with strains from GenBank database, Spanish viruses clustered into three genotypes: BVDV 1, BDV and CSFV. No BVDV 2 strains were identified. The 41 bovine samples were all BVDV 1 genotype, but they were further subdivided into subgroups 1b (35) and 1e (6). There was no apparent association between the genotype and clinical symptoms, or the geographic area of origin. However, subgroup 1e has been recently described for isolates from France and, interestingly, subgroup 1e viruses were collected from areas close to the French border. Nine of the ten ovine samples formed a tight cluster within BDV type but clearly differed from BDV subgroups A and B sustaining the need to define a new subgroup as BDV-C in which these ovine strains would be included. Finally, although further studies are needed, the grouping of an ovine sample with CSFV strains would be the first description of a CSFV genotype for ovine pestiviruses.

Genetic diversity of recent bovine viral diarrhoea viruses from the southeast of Austria (Styria)

To characterise the bovine virus diarrhoea virus (BVDV) isolates circulating in the southeastern region of Austria, namely in the province of Styria, 71 blood samples collected between 1998 and 2000 from persistently infected cattle in 62 herds were subjected to genetic typing. For this, 288bp fragments from the 5' untranslated region (5'-UTR) were amplified by polymerase chain reaction after reverse transcription (RT-PCR). The products were sequenced and used for phylogenetic analysis. Seventy virus isolates were typed as BVDV species 1 (BVDV-1). Only one isolate was typed as BVDV species 2 (BVDV-2), representing the first isolate of this pestivirus genotype found in Austria. In addition, phylogenetic analysis revealed that viruses belonging to five genetic groups within BVDV-1 are circulating in Styria. Most viruses (53) were found in group BVDV-1f, nine viruses in BVDV-1h, four viruses in BVDV-1b, three viruses in BVDV-1d and one virus in BVDV-1g. No virus was found in genetic group BVDV-1a, which is dominant in the UK and widely distributed in USA. Likewise, the BVDV isolates predominating in a neighbouring country, namely Germany, belonged to different genogroups than those circulating in Styria. We conclude that in a particular region and environment certain BVDV-1 genetic groups predominate. New groups, including BVDV-2, can be introduced, e.g. by trade of animals. The low incidence of BVDV-2 in Styria is in concert with the sporadic occurrence of these viruses in other regions of Europe.

Isolation of bovine viral diarrhea virus from an alpaca

A frozen, stillborn alpaca (Lama pacos) was submitted to the Minnesota Veterinary Diagnostic Laboratory for diagnostic purposes. No gross or histopathologic changes of any significance were seen. A pool of lung, liver, and brain tissues was positive for bovine viral diarrhea virus (BVDV) by reverse transcription-polymerase chain reaction. On inoculation in cell cultures, a noncytopathic BVDV (type 1b) was isolated. No evidence of BVDV was seen on immunohistochemical examination of tissues. This indicates the importance of using multiple tests for arriving at a diagnosis and appears to be the first report of BVDV isolation from alpaca.

Clinical and epidemiologic observations of bovine viral diarrhea virus in the northwestern United States

Retrospective analyses of cases from which bovine viral diarrhea virus (BVDV) was isolated from 1980 to 2000 were conducted. These cases originated from the northwestern US and included both beef and dairy cattle. The results indicated that there was a shift in diseases associated with BVDV infection and in the animal age at onset of disease. Comparative results from the 1980 data indicated a low fetal infection rate (<5%), followed by steady increases of clinical cases and peaking at 6 months (30%). By 2000, the shift of BVDV cases was noticeable and indicated a biphasic occurrence of disease. The first phase was fetal infections, which increased to >25%, followed by a second phase at 6 months (>35%). Phylogenetic analysis was conducted on selected isolates from the time period 1998-2000 (n = 54). There were representative viral isolates from the two genotypes (BVDV1 and BVDV2), as well as subgenotypes, BVDV1a and BVDV1b. The types were further correlated with the clinical manifestation, which were reported as mucosal disease, persistently infected (PI)-poor doer, and abortion-open cows. The results indicated that BVDV were distributed throughout the clinical spectrum of disease, with BVDV2 representing the greatest frequency of isolation, and the greatest association with abortion-open cows. When the BVDV genotypes and subgenotypes were categorized into early (<100 days gestation) versus late (>100 days gestation) fetal infections, there was an inverse relationship noted. It was observed that BVDV1a was associated least with early infection (14%) and most with late infections (86%). BVDV1b was intermediate, followed by BVDV2, which was associated more with early infections (45%) and less with late infections (55%) when compared with BVDV1a and BVDV1b.