Reproduction of mucosal disease with cytopathogenic bovine viral diarrhoea virus selected in vitro

Isolates of non-cytopathogenic bovine viral diarrhoea (BVD) virus from 18 persistently infected calves from one herd were compared by using monoclonal antibodies directed against the major viral glycoprotein gp53. All the isolates displayed an almost identical reaction pattern. Based on this antigenic analysis three cytopathogenic BVD and three non-cytopathogenic BVD viruses closely related to the non-cytopathogenic BVD herd isolate were selected. Six of the persistently infected calves were inoculated with a pool of the three closely related cytopathogenic BVD viruses and two with a pool of the three non-cytopathogenic BVD viruses. In addition three animals were infected with one closely related cytopathogenic BVD strain (Indiana) and two animals with the antigenetically different cytopathogenic BVD viral strain A1138/69. Regardless of the inoculation route all the animals superinfected with closely related cytopathogenic BVD viruses developed the characteristic lesions of mucosal disease within 14 days of infection. Animals which were inoculated with non-cytopathogenic BVD viruses which closely resembled the herd isolate, or with cytopathogenic BVD viruses which did not resemble the herd isolate did not develop any signs of disease. However, the latter group produced antibodies to the superinfecting virus.     

An experimental contribution to the study of the pathogenesis of bovine viral diarrhea virus infection.

This presentation summarizes the results of a study on the pathogenesis of bovine viral diarrhea (BVDV) infection. The cytopathic (CP) strain TVM-2 of BVDV induced in calves an overt clinical disease which is usually recorded as the acute primary BVDV infection observed under natural conditions. In contrast the non-cytopathic (NCP) strain New York-1 of BVDV did not cause any significant signs of disease. However, when the calves were immunosuppressed by treatment with dexamethasone (DMS) the biotype of BVDV involved did not seem to be as important as it appeared to be in an immunologically normal animal. This was shown in this study by the NCP BVDV which caused a fatal disease in calves treated with DMS. A mixed infection given to calves by injecting them with both CP and NCP BVDV, did not result in any particularly serious disease. So, the potential immunosuppressive activity of BVDV itself for the host has not been proven under the experimental procedures used in this experiment. Finally, a modified-live CP BVDV vaccine was unable to cause clinical disease when injected into calves that had been infected previously with strain New York-1 of BVDV.     

Characterization of protection against systemic infection and disease from experimental bovine viral diarrhea virus type 2 infection by use of a modified-live noncytopathic type 1 vaccine in calves

OBJECTIVE: To evaluate protection resulting from use of a modified-live noncytopathic bovine viral diarrhea virus (BVDV) type 1 vaccine against systemic infection and clinical disease in calves challenged with type 2 BVDV. ANIMALS: 10 calves, 5 to 7 months of age. PROCEDURES: Calves were allocated (n = 5/group) to be nonvaccinated or vaccinated SC on day 0 with BVDV 1 (WRL strain). Calves in both groups were challenged intranasally with BVDV type 2 isolate 890 on day 21. Rectal temperatures and clinical signs of disease were recorded daily, and total and differential WBC and platelet counts were performed. Histologic examinations and immunohistochemical analyses to detect lesions and distribution of viral antigens, respectively, were performed. RESULTS: After challenge exposure to BVDV type 2, nonvaccinated calves developed high rectal temperatures, increased respiratory rates, viremia, leukopenia, lymphopenia, and infection of the thymus. Vaccinated calves did not develop high rectal temperatures or clinical signs of respiratory tract disease. Vaccinated calves appeared to be protected against systemic replication of virus in that they did not develop leukopenia, lymphopenia, viremia, or infection of target organs, and infectious virus was not detected in peripheral blood mononuclear cells or the thymus. CONCLUSIONS AND CLINICAL RELEVANCE: The modified-live BVDV type 1 vaccine protected against systemic infection and disease after experimental challenge exposure with BVDV type 2. The vaccine protected calves against infection and viremia and prevented infection of target lymphoid cells.     

Bovine herpes virus expressing envelope protein (E2) of bovine viral diarrhea virus as a vaccine candidate.

The gene encoding the envelope protein (E2) of bovine viral diarrhea virus (BVDV) was expressed under the thymidine kinase (TK) promoter of Korean bovine herpesvirus 1 (BHV-1) isolate. Thymidine kinase negative (TK-) BHV-1 recombinants expressing E2 of BVDV were constructed and the expression of E2 was identified by immunofluorescence and Western blotting. Compared to wild type BHV-1, the recombinant BHV-1 had a delayed cytopathogenic effect in cells. The immunogenicity of the recombinant BHV-1 was examined in guinea pigs and cattle. Although an increase in body temperature was detected for a few days, the inoculated cattle returned to normal temperature with the development of neutralizing antibodies to BVDV.     

Effects in calves of mixed infections with bovine viral diarrhea virus and several other bovine viruses

The objective of this study was to verify whether a mixed infection in calves with bovine viral diarrhea virus (BVDV) and other bovine viruses, such as bovid herpesvirus-4 (BHV-4), parainfluenza-3 (PI-3) and infectious bovine rhinotracheitis (IBR) virus, would influence the pathogenesis of the BVDV infection sufficiently to result in the typical form of mucosal disease being produced.

Accordingly, two experiments were undertaken. In one experiment calves were first infected with BVDV and subsequently with BHV-4 and IBR virus, respectively. The second experiment consisted in a simultaneous infection of calves with BVDV and PI-3 virus or BVDV and IBR virus.

From the first experiment it seems that BVDV infection can be reactivated in calves by BHV-4 and IBR virus. Evidence of this is that BVDV, at least the cytopathic (CP) strain, was recovered from calves following superinfection. Moreover, following such superinfection the calves showed signs which could most likely be ascribed to the pathogenetic activity of BVDV. Superinfection, especially by IBR virus, created a more severe clinical response in calves that were initially infected with CP BVDV, than in those previously given the non-cytopathic (NCP) biotype of the virus. Simultaneous infection with PI-3 virus did not seem to modify to any significant extent the pathogenesis of the experimentally induced BVDV infection whereas a severe clinical response was observed in calves when simultaneous infection was made with BVDV and IBR virus.     

Comparison of type I and type II bovine viral diarrhea virus infection in swine.

Some isolates of type II bovine viral diarrhea virus (BVDV) are capable of causing severe clinical disease in cattle. Bovine viral diarrhea virus infection has been reported in pigs, but the ability of these more virulent isolates of type II BVDV to induce severe clinical disease in pigs is unknown. It was our objective to compare clinical, virologic, and pathologic findings between type I and type II BVDV infection in pigs. Noninfected control and BVDV-infected 2-month-old pigs were used. A noncytopathic type I and a noncytopathic type II BVDV isolate were chosen for evaluation in feeder age swine based upon preliminary in vitro and in vivo experiments. A dose titration study was performed using 4 groups of 4 pigs for each viral isolate. The groups were inoculated intranasally with either sham (control), 10(3), 10(5), or 10(7) TCID50 of virus. The pigs were examined daily and clinical findings were recorded. Antemortem and postmortem samples were collected for virus isolation. Neither the type I nor type II BVDV isolates resulted in clinical signs of disease in pigs. Bovine viral diarrhea virus was isolated from antemortem and postmortem samples from groups of pigs receiving the 10(5) and the 10(7) TCID50 dose of the type I BVDV isolate. In contrast, BVDV was only isolated from postmortem samples in the group of pigs receiving the 10(7) TCID50 dose of the type II BVDV isolate. Type I BVDV was able to establish infection in pigs at lower doses by intranasal instillation than type II BVDV. Infection of pigs with a type II isolate of BVDV known to cause severe disease in calves did not result in clinically apparent disease in pigs.     

Comparison by the neutralisation assay of pairs of non-cytopathogenic and cytopathogenic strains of bovine virus diarrhoea virus isolated from cases of mucosal disease

Neutralising antibody to non-cytopathogenic and cytopathogenic strains of bovine virus diarrhoea virus (BVDV) was assayed in a microtitre test in which cultures of calf testis cells were stained by the immunoperoxidase method to detect viral replication. Fourteen BVDV strains were compared in cross neutralisation tests with antisera prepared in gnotobiotic calves. Ten of the strains comprised five pairs of non-cytopathogenic and cytopathogenic BVDV. Each pair was isolated from an animal with mucosal disease. All five animals were from five separate outbreaks of the disease. Each pair of strains from the same outbreak was found to be antigenically indistinguishable. In contrast, when the coefficient of antigenic similarity was calculated 11 of 45 comparisons between the pairs and 46 of 91 comparisons between all 14 viruses gave R values that distinguished strains. The observations suggest that an antigenic spectrum within a single related group exists for BVDV strains, rather than distinct serotypes. The findings are also consistent with the suggestion that cytopathogenic strains from natural outbreaks of mucosal disease arise by mutation from non-cytopathogenic virus.     

Co-existence of genetically and antigenically diverse bovine viral diarrhoea viruses in an endemic situation

Bovine viral diarrhoea virus (BVDV) is an important cattle pathogen that causes acute or persistent infections. These are associated with immunotolerance to the viral strain persisting in animals that became infected early in their intrauterine development. To this date, the epidemiology of BVD in Switzerland runs virtually undisturbed by control measures such as restrictions on animal traffic or vaccination. Here, we analysed the viral genetics of 169 Swiss isolates and carried out crossed serum neutralisation tests to assess the antigenic spectrum of BVDV strains present in the cattle population. Besides confirming the presence of BVDV type 1 subgroups b, e, h and k, a single "orphan" BVDV-1 virus was detected that does not belong to any known BVDV-1 subgroup. No BVDV type 2 viruses were detected, suggesting that they are rare or not present in the cattle population. Antigenic comparison revealed significant differences between the different subgroups, with anti-1k immune serum having up to tenfold lower neutralising activity against 1b, 1e and 1h subgroup viruses, which however may still suffice to protect 1k-immune animals against superinfection by viruses of those other subgroups. Serum from routinely vaccinated animals revealed generally low titres but good cross-neutralisation. A geographic information system revealed that the viruses of the different subgroups are distributed in an apparently randomised fashion in the cattle population. This geographic distribution pattern may reflect peculiarities of the management practice in the Swiss cattle industry that, especially through annual transhumance of up to 25% of the entire population in the alpine region, tend to optimise the spread of BVDV.     

Cytopathogenicity markers in the genome of Hungarian cytopathic isolates of bovine viral diarrhoea virus

Since genetic recombination is a major factor in the evolution of the cytopathogenic (cp) bovine viral diarrhoea virus (BVDV) biotypes, in this study the cytopathogenicity markers were investigated in the genomes of two cp BVDV strains recently isolated from mucosal disease (MD) cases in Hungary. In the genome of strain H4956, a Jiv-like insertion was found similar to those described in reference strain NADL and in other BVDV 1, BVDV 2 and border disease virus (BDV) strains. The 133 amino acid Jiv-like sequence is inserted at nucleotide position 4984 (amino acid position 1533), 9 nucleotides upstream of that of strain NADL. The insertion showed 96% amino acid sequence identity with the cellular Jiv protein. In the genome of cp BVDV strain H115/PCR, an ubiquitin-containing duplication was found. The duplicated sequence started at nucleotide position 7978 (amino acid 2531) in the NS4B gene. The duplication contained a complete ubiquitin monomer of 76 amino acids and the complete NS3 gene starting at nucleotide position 5153 (amino acid 1589), which corresponds to the first N-terminal amino acid of NS3. The duplication was located further downstream of the known ubiquitin-containing genomic regions of cp BVDV strains, and it consisted of the shortest inserted nucleotide sequence. The insertions and duplication of strains H4956 and H115/PCR further confirmed that recombinations occurring at positions A and B are the most common mechanisms leading to the development of BVDV cytopathogenicity.     

Comparison of the pneumopathogenicity of two strains of bovine viral diarrhea virus

The pneumopathogenicity in calves of 2 strains of bovine viral diarrhea (BVD) virus, isolate 2724 (a noncytopathogenic virus) and isolate 72 (a cytopathogenic virus), was compared. All calves were inoculated endobronchially, using fiberoptic bronchoscopy. Two calves were given Pasteurella haemolytica, 2 calves were given the noncytopathogenic BVD virus, and 2 calves were given cytopathogenic BVD virus. Five calves were inoculated sequentially with BVD virus and, 5 days later, with P haemolytica. Two of these calves were inoculated with the noncytopathogenic BVD virus and the other 3 with the cytopathogenic strain. Both BVD virus strains caused marked respiratory tract disease in the calves sequentially inoculated with P haemolytica and also impaired pulmonary clearance of P haemolytica. However, the effect of the cytopathogenic strain was more severe than the noncytopathogenic strain, indicating that strains of BVD virus may vary in their pneumopathogenicity for calves.     

Experimental infection of calves with two strains of bovine virus diarrhoea virus: virus recovery and clinical reactions

Fifteen calves were inoculated with a mixture of two strains of bovine virus diarrhoea virus (BVDV), the cytopathogenic NADL strain which had been passaged over 20 times n vitro, and the non-cytopathogenic FCS strain, passaged only once after isolation from fetal calf serum. In a second experiment, seven calves received the NADL strain, and eight the FCS strain. The clinical and virological results of the two experiments were compared. In dual infections, the NADL strain interfered with the replication of the FCS strain resulting in less severe disease than the FCS strain alone. The FCS-BVDV was recovered from nasopharyngeal swabs and buffy coat cells whereas the NADL-BVDV was recovered only from nasopharyngeal swabs. The cytopathogenicity of the two strains did not change after passage in vivo. The differences observed are discussed in relation to cultural history and cytopathogenicity.     

Characterization of protection from systemic infection and disease by use of a modified-live noncytopathic bovine viral diarrhea virus type 1 vaccine in experimentally infected calves

OBJECTIVE: To evaluate protection against systemic infection and clinical disease provided by use of a modified-live noncytopathic bovine viral diarrhea virus (BVDV) type 1 vaccine in calves challenged with NY-1 BVDV. ANIMALS: 10 calves, 5 to 7 months of age. PROCEDURES: Calves were allocated (n = 5/group) to be nonvaccinated or vaccinated SC on day 0 with BVDV type 1 (WRL strain). Calves in both groups were challenged intranasally with NY-1 BVDV on day 21. Calves' rectal temperatures and clinical signs of disease were recorded daily, total and differential WBC and platelet counts were performed, and serum neutralizing antibody titers against NY-1 BVDV were determined. Histologic examinations and immunohistochemical analyses to detect gross lesions and distribution of viral antigens, respectively, were performed. RESULTS: After challenge exposure to NY-1 BVDV, nonvaccinated calves developed high rectal temperatures, increased respiratory rates, viremia, leukopenia, lymphopenia, and infection of the thymus. Vaccinated calves did not develop high rectal temperatures or clinical signs of respiratory tract disease. Vaccinated calves appeared to be protected against systemic replication of virus in that they did not develop leukopenia, lymphopenia, viremia, or infection of target organs, and infectious virus was not detected in peripheral blood mononuclear cells or the thymus. CONCLUSIONS AND CLINICAL RELEVANCE: The modified-live BVDV vaccine protected calves against systemic infection and disease after experimental challenge exposure with NY-1 BVDV. The vaccine protected calves against infection and viremia and prevented infection of target lymphoid cells.     

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.     

Distribution of viral antigen and tissue lesions in persistent and acute infection with the homologous strain of noncytopathic bovine viral diarrhea virus.

Viral distribution and lesions were compared between calves born with persistent infection (PI) and calves acutely infected with the same bovine viral diarrhea virus (BVDV) isolate. Two PI calves from 1 dairy herd were necropsied. The PI viruses from these calves were isolated, characterized by sequencing, and found to be identical. This virus strain, designated BVDV2-RS886, was characterized as a noncytopathic (ncp) type 2 BVDV. To establish acute infections, BVDV2-RS886 was used to inoculate clinically healthy, seronegative calves which were 3 weeks to 3 months old. Nine calves received 10(6)-10(7) tissue culture infective dose of BVDV2-RS886 intranasally. Four additional age-matched animals served as noninfected controls. Infected calves were necropsied at 3, 6, 9, or 13 days postinoculation (dpi). Viral antigen was detected by immunohistochemistry in frozen sections, and lesions were evaluated in hematoxylin eosin-stained paraplast sections. In the PI calves, a wide distribution of viral antigen was found in all tissues and was not associated with lesions. In the acutely infected calves, viral antigen was widespread in lymphoid tissues at 6 dpi but had been mostly eliminated at 9 and 13 dpi. Depletion of lymphoid tissues was seen at 6, 9, and 13 dpi and repopulation at 9 and 13 dpi. In 1 of the calves at 13 dpi, severe arteritis was present in lymph nodes and myocardium. This comparison shows that an ncp BVDV strain that causes no lesions in PI animals is able to induce marked depletion of lymphoid tissues in calves with acute infection. Therefore, the failure to eliminate PI cattle from a herd causes problems not only in pregnant cattle but may also affect other age groups.     

Humoral and T cell-mediated immune responses to bivalent killed bovine viral diarrhea virus vaccine in beef cattle

The objective of this research project was to evaluate the antibody and cell-mediated immune responses to a multivalent vaccine containing killed bovine viral diarrhea virus (BVDV) types 1 and 2. Twenty castrated male crossbred beef cattle (350-420kg body weight) seronegative to BVDV were randomly divided into two groups of 10 each. Group 1 served as negative mock-vaccinated control. Group 2 was vaccinated subcutaneously twice, 3 weeks apart, with modified live bovine herpesvirus 1, parainfluenza 3 virus and bovine respiratory syncytial virus diluted in diluent containing killed BVDV type 1 (strain 5960) and type 2 (strain 53637) in an adjuvant containing Quil A, Amphigen, and cholesterol. Serum samples were collected from all cattle at days -21, 0, and days 21, 28, 35, 56 and 70 post-vaccination. Standard serum virus neutralization tests were performed with BVDV type 1 (strain 5960) and type 2 (strain 125C). Anticoagulated blood samples were collected at day 0, and days 28, 35, 56 and 70 post-vaccination. Peripheral blood mononuclear cells (PBMCs) were isolated, stimulated with live BVDV type 1 (strain TGAN) and type 2 (strain 890) and cultured in vitro for 4 days. Supernatants of cultured cells were collected and saved for interferon gamma (IFNgamma) indirect enzyme-linked immunosorbent assay (ELISA). Four-color flow cytometry was performed to stain and identify cultured PBMC for three T cell surface markers (CD4, CD8, and gammadelta TCR) and to detect the activation marker CD25 (alpha chain of IL-2 receptor) expression. The net increase in %CD25+ cells (Delta%CD25+) of each T cell subset of individual cattle was calculated. The results of all post-vaccination weeks of each animal were plotted and the areas under the curve of each T cell subset were statistically analyzed and compared between groups. The mean area under the curve of the Delta%CD25+ data for days 0-70 of all subsets, except CD4-CD8+gammadelta TCR- (cytotoxic) T cell subset of both BVDV types 1 and 2 stimulated cells, of the vaccinated group were significantly higher than the control group (P<0.05). IFNgamma production by PBMC from the vaccinated group showed significantly higher results (P<0.05) than the control group in the BVDV types 1 and 2 stimulated cells for at least some time points after vaccination. The vaccinated group also had significantly (P<0.0001) higher neutralizing antibody titers than the control group from day 28 onward.     

Platelet aggregation responses and virus isolation from platelets in calves experimentally infected with type I or type II bovine viral diarrhea virus.

Altered platelet function has been reported in calves experimentally infected with type II bovine viral diarrhea virus (BVDV). The purpose of the present study was to further evaluate the ability of BVDV isolates to alter platelet function and to examine for the presence of a virus-platelet interaction during BVDV infection. Colostrum-deprived Holstein calves were obtained immediately after birth, housed in isolation, and assigned to 1 of 4 groups (1 control and 3 treatment groups). Control calves (n = 4) were sham inoculated, while calves in the infected groups (n = 4 for each group) were inoculated by intranasal instillation with 10(7) TCID50 of either BVDV 890 (type II), BVDV 7937 (type II), or BVDV TGAN (type I). Whole blood was collected prior to inoculation (day 0) and on days 4, 6, 8, 10, and 12 after inoculation for platelet function testing by optical aggregometry by using adenosine diphosphate and platelet activating factor. The maximum percentage aggregation and the slope of the aggregation curve decreased over time in BVDV-infected calves; however, statistically significant differences (Freidman repeated measures ANOVA on ranks, P < 0.05) were only observed in calves infected with the type II BVDV isolates. Bovine viral diarrhea virus was not isolated from control calves, but was isolated from all calves infected with both type II BVDV isolates from days 4 through 12 after inoculation. In calves infected with type I BVDV, virus was isolated from 1 of 4 calves on days 4 and 12 after inoculation and from all calves on days 6 and 8 after inoculation. Altered platelet function was observed in calves infected with both type II BVDV isolates, but was not observed in calves infected with type I BVDV. Altered platelet function may be important as a difference in virulence between type I and type II BVDV infection.     

Prevention of persistent infection in calves by vaccination of dams with noncytopathic type-1 modified-live bovine viral diarrhea virus prior to breeding

OBJECTIVE: To determine the ability of a modified-live virus (MLV) bovine viral diarrhea virus (BVDV) type 1 (BVDV1) vaccine administered to heifers prior to breeding to stimulate protective immunity that would block transmission of virulent heterologous BVDV during gestation, thus preventing persistent infection of a fetus. ANIMAL: 40 crossbred Angus heifers that were 15 to 18 months old and seronegative for BVDV and 36 calves born to those heifers. PROCEDURE: Heifers were randomly assigned to control (n = 13) or vaccinated (27) groups. The control group was administered a multivalent vaccine where-in the BVDV component had been omitted. The vaccinated heifers were administered a single dose of vaccine (IM or SC) containing MLV BVDV1 (WRL strain). All vaccinated and control heifers were maintained in pastures and exposed to BVDV-negative bulls 21 days later. Thirty-five heifers were confirmed pregnant and were challenge exposed at 55 to 100 days of gestation by IV administration of virulent BVDV1 (7443 strain). RESULTS: All control heifers were viremic following challenge exposure, and calves born to control heifers were persistently infected with BVDV. Viremia was not detected in the vaccinated heifers, and 92% of calves born to vaccinated heifers were not persistently infected with BVDV. CONCLUSIONS AND CLINICAL RELEVANCE: These results document that vaccination with BVDV1 strain WRL protects fetuses from infection with heterologous virulent BVDV1.     

一株源于商品胎牛血清的BVDV-2型的分离鉴定及基因组序列分析

牛病毒性腹泻病毒（BVDV）是引起牛病毒性腹泻/黏膜病的重要病原,也是牛血清及其制品污染中的常见病原体。本研究从商品化胎牛血清中分离到一株致细胞病变（CP）型BVDV（GS2018株）,利用电镜观察、免疫荧光检测、分子鉴定、基因组测序及遗传进化分析对其进行鉴定。结果表明,GS2018株接种MDBK细胞后可见明显的细胞病变（CPE）,培养第4天病毒滴度达1×10^6.2·0.1 mL^-1。病毒粒子呈圆形,直径为50~60 nm,间接免疫荧光检测为阳性;其5'UTR扩增片段与BVDV-2相应序列高度相似,病毒基因组包含12 235个核苷酸（nt）。5'UTR、N^pro及E2基因系统进化分析发现,GS2018株与美国BVDV-2 USMARC-60764分离株核苷酸一致性达98%,证明其属于CP型BVDV-2a亚型。但GS2018株在NS2/3区无核酸片段插入,这与大多数CP型BVDV-2明显不同,说明BVDV致细胞病变可能涉及更复杂的机制。     

Development of a neutralising antibody response to an inoculated cytopathic strain of bovine virus diarrhoea virus

Fourteen clinically healthy cattle that were persistently infected with non-cytopathic bovine virus diarrhoea virus (BVDV) and three BVDV-free cattle were inoculated with one of three cytopathic BVDV strains. Mucosal disease developed in 12 of the viraemic cattle, resulting in a moribund condition 17 to 99 days after inoculation. Two of the viraemic cattle remained clinically healthy until the end of the experiment, 14 months after inoculation. The BVDV-free cattle did not develop clinical signs after inoculation. From each cow with mucosal disease a noncytopathic and a cytopathic BVDV strain were isolated from tissue specimens collected post mortem. All the cattle developed moderate to high levels of neutralising antibodies against the cytopathic BVDV strain with which they were inoculated. The antibodies from 10 of the 12 cattle with mucosal disease did not react with the cytopathic BVDV strains isolated post mortem, and antibodies from none of them reacted with the non-cytopathic BVDV isolates. Antibody responses to the inoculated BVDV strains developed earlier in the viraemic cattle than in the BVDV-free cattle.     

Comparative pathogenicity of selected bovine viral diarrhea virus isolates in gnotobiotic lambs

The infectivity and pathogenicity of selected bovine viral diarrhea virus (BVDV) isolates were determined in gnotobiotic, colostrum-deprived neonatal lambs. Five-day-old cesarean-derived gnotobiotic lambs were exposed to 1 of 10 BVDV isolates via aerosol suspension. These isolates were from tissues or secretions of calves or lambs affected with respiratory tract disease, weak neonatal calves, aborted bovine fetuses, or reference Singer or Draper BVDV. The pathogenicity of each isolate, relative to the others, was evaluated in lambs by measurement of the neutralizing antibody response, virus isolation from nasal secretions or tissues, and postmortem lesions. The BVDV isolates varied in their infectivity and pathogenicity. Singer, the cytopathic reference strain, was the most lymphotrophic isolate and stimulated the greatest neutralizing antibody response. Encephalitis was the most consistent lesion observed and was used as the final determinant of relative pathogenicity of the viruses. The most neuropathogenic isolates were the 2 viruses originating from lambs affected with respiratory tract disease, the 2 weak neonatal calf isolates, and 1 isolate from an aborted bovine fetus. The least pathogenic isolates were the 2 reference isolates, Draper and Singer; the 2 mucosal disease isolates; and 1 isolate originating from an aborted bovine fetus.