Antigenic differences between a field isolate and vaccine strains of bovine viral diarrhea virus

Preparation and field study of combined vaccine against Clostridium perfringens type A and bovine viral diarrhea virus in camels

Purpose

The key objective of this study was to formulate a local combined inactivated gel adjuvanted vaccine containing bovine viral diarrhea virus (BVDV)-1, BVDV-2 viruses and Clostridium perfringens type A toxoid. The study evaluated its ability to enhance protective active immune response in camels’ calves against these infectious pathogens under field conditions.

Materials and Methods

The local BVDV cytopathic strains and a local strain of toxigenic C. perfringens type A were used in vaccines formulation. Vaccines A and B were monovalent vaccines against C. perfringens and both strains of BVDVs, respectively. While the vaccine C was the combined vaccine used against the three agents. All vaccines were adjuvanted with Montanide gel. Sterility, safety, and potency tests were applied on the formulated vaccines. Virus neutralization and toxin anti-toxin neutralization tests were used to evaluate the immune responses.

Results

Both monovalent (vaccine A) and combined vaccines (vaccine C) showed a protective level (4.5 and 3 IU/mL, respectively) against C. perfringens from the 2nd-week post-vaccination. The titer declined to 3 and 2 IU/mL, respectively at the 5th-month post-vaccination. The titer against BVDV, the monovalent vaccine (vaccine B) reached the beak (1.95 IU/mL) at the 1st-month post-vaccination and lasted till 6th-month post-vaccination (0.92 and 0.94 IU/mL) for BVDV-1a and BVDV-2, respectively.

Conclusion

Vaccination of camels with the combined vaccine adjuvanted by Montanide gel containing C. perfringens type A toxoid and BVDV strains with 6-month intervals is recommended to protect camels safely and efficiently against such infections in the field.

Evaluation of multiple immune parameters after vaccination with modified live or killed bovine viral diarrhea virus vaccines

The development of immunity to vaccine antigen was examined using three prime/boost strategies and the progression of immune activities was evaluated over the course of 8 weeks. Calves were vaccinated and multiple immune parameters were evaluated using several methods to assess humoral or cellular immunity from the same samples in parallel. The three vaccination protocols used were a killed vaccine followed by a killed boost (killed/killed), MLV vaccine and boost (MLV/MLV), or a MLV vaccine and killed boost (MLV/killed). All the vaccines used included modified live IBR/PI3 viruses to make the bystander context as similar as possible. The Singer strain of BVDV was used as the source antigen in the killed vaccine, and the NADL strain of BVDV was used in the MLV vaccine. Controls received a vaccine containing only MLV IBR/PI3. The assessment panel measured SN titers, as well as lymphocyte proliferation, cytokine mRNA expression, intracellular cytokine production, and released IFN-gamma after in vitro stimulation with three strains of BVDV virus. MLV/MLV and MLV/killed groups developed significant SN titers to the type 1 BVDV virus strains, Singer and NADL, and low crossover titers were also seen to the type 2 strain, 890 over the evaluation period. These two groups showed significant proliferation in response to the NADL virus as compared to controls. Multiple immune assessments were conducted simultaneously to attempt to provide a broader, more in depth evaluation of immune response to these BVDV vaccination protocols. We observed that the correlation among most of the assays conducted were weak; the correlation between SN titers and cellular proliferation assays demonstrated a moderate correlation.

Proteção fetal frente a desafio com o vírus da Diarréia Viral Bovina (BVDV) em ovelhas imunizadas com duas amostras de vírus modificadas experimentalmente

Duas amostras do vírus da Diarréia Viral Bovina (BVDV) submetidas a múltiplas passagens em cultivo celular e exposição à radiação ultravioleta (UV) a cada passagem foram avaliadas como candidatos a vírus vacinais. As amostras foram testadas quanto à sua atenuação para bezerros e fetos ovinos, reatividade antigênica contra isolados de campo, e capacidade de induzir proteção fetal em ovelhas prenhes. Inoculação intramuscular (IM) dos vírus modificados em quatro bezerros produziu apenas uma elevação discreta e passageira da temperatura corporal, seguida de produção de altos títulos de anticorpos neutralizantes. O vírus não foi detectado em secreções nasais ou sangue nos dias seguintes à inoculação. Porém, a inoculação IM desses vírus em quatro ovelhas prenhes foi seguida de transmissão transplacentária e infecção em todos os fetos. Para os testes de proteção fetal, ovelhas prenhes previamente imunizadas com duas doses vacinais, foram inoculadas por via intranasal com amostras de BVDV-1 (SV-126.8, n=6) ou BVDV-2 (SV-260, n=5). No dia do desafio (134 dias após a segunda dose), todos os animais apresentavam altos títulos de anticorpos neutralizantes (256 a >4096) contra os vírus vacinais; além de títulos variados (8 a >4096) contra várias isolados brasileiros de BVDV-1 e BVDV-2. Quinze dias após o desafio, as ovelhas foram sacrificadas e os tecidos fetais foram examinados para a presença de vírus. Todos os fetos das ovelhas controle não-vacinadas apresentaram-se (n=4) positivos para os vírus utilizados no desafio. Em contraste, nenhum feto das ovelhas imunizadas (n=11) foi positivo para vírus, indicando que a resposta imunológica induzida pela vacinação com os vírus modificados foi capaz de prevenir a infecção fetal. Estes resultados indicam que é possível obter-se forte resposta imunológica e proteção fetal contra o BVDV com o uso de vacinas vivas modificadas.

Genetic typing of bovine viral diarrhea virus isolates from Argentina

Genetic typing of 29 Bovine Viral Diarrhea Virus (BVDV) isolates from Argentina was carried out by sequencing 245 nucleotides of the RT-PCR products of the 5'-UTR region. Sequence analysis shows that these Argentinean BVDV include types 1 and 2. The majority (26/29) of the isolates are type 1, which comprises subtypes 1a and 1b, together with an additional subgroup within subtype 1a. This subgroup is close to the South African subgroup Ic of 1a viruses, and to the deer pestivirus strain "Deer". The three type 2 BVDV were isolated from fetal tissues or serum during the 7-8 years before a clinical outbreak in Argentina had been reported. Only inactivated vaccines are used in bovines of the country, thus the analysed viruses are authentic field strains. The long term circulation of type 2 BVDV (situation similar to that of North America before the epidemic of 1993), and the existence of viral populations which differ from the reference strains commonly used in vaccine elaboration should be considered by manufacturers of diagnostic reagents and vaccines.

Application of single-strand conformation polymorphism to the study of bovine viral diarrhea virus isolates

Single-strand conformation polymorphism (SSCP) analysis of polymerase chain reaction (PCR) products is a genetic screening technique for rapid detection of nucleotide substitutions in PCR-amplified genomic DNA or cDNA. It is based on the observation that partially formamide-denatured double-stranded DNA migrates as 2 single-stranded DNA molecules when electrophoresed in nondenaturing polyacrylamide gels. The mobility depends on the 3-dimensional conformation of the strand under the conditions used. It is possible to discriminate between DNA strands differing in only 1 nucleotide. The method was applied to the analysis of Bovine Viral Diarrhea Virus (BVDV) isolates. Reference and Argentinian strains were assessed for variations in their 5' untranslated region (5'-UTR). The PCR products of the 5'-UTR ends were formamide denatured and compared by SSCP analysis in nondenaturing 15% polyacrylamide and 15% polyacrilamide-5% glycerol gels. The reference strains SD-1, Singer, and Oregon C24V had differences in electrophoretic patterns. Despite the high conservation among the 5'-UTR of pestiviruses, the method allowed discrimination among all 9 Argentinian isolates. The 5'-UTR of a fetal kidney-derived isolate (1R93) was PCR amplified and cloned in a plasmid vector; the SSCP analysis of 30 PCR products obtained by direct amplification over randomly selected clones produced 5 different banding patterns, indicating the existence of viral quasispecies. The results show that SSCP may be used to identify and differentiate among BVDV isolates.

Semiliki forest virus vector carrying the bovine viral diarrhea virus NS3 (p80) cDNA induced immune responses in mice and expressed BVDV protein in mammalian cells

Bovine viral diarrhea virus (BVDV) is a primary pathogen responsible for bovine enteric, respiratory and reproductive failure. A genetic region is encoding the p80 (NS3) of BVDV as the most conserved protein among Pestiviruses. BVDV infection in cattle induces NS3 specific lymphocyte proliferation and humoral responses. To generate a DNA vaccine against BVDV, the gene for BVDV-NADL NS3 was cloned into an eukaryotic expression vector of Semiliki Forest virus (pSFV-1). Quadriceps muscles of BALB/c mice were injected with recombinant DNA generated statistically significant cytotoxic T-lymphocyte activity (CTL) and cell mediated immune (CMI) responses against cytopathic and noncytopathic BVDV. Whereas, the BVDV-NS3 did not generate neutralizing antibodies against BVDVin mice. pSFV-1-NS3 DNA was subjected to in vitro transcription into mRNA. The mRNA was transfected into baby hamster kidney cells (BHK-21) and Madin-Darby bovine kidney cells (MDBK). The recombinant cells were used in the detection of DNA antigen responses by immunological assays. This report establishes the ability of BVDV-NS3 DNA inoculation to induce a strong cellular immune responses in mice.

Application of recombinant bovine viral diarrhea virus proteins in the diagnosis of bovine viral diarrhea infection in cattle

The National Animal Disease Laboratory (NADL) vaccine strain of bovine viral diarrhea virus (BVDV) genes for gp48 and p80 were expressed in Escherichia coli. The BVDV-NADL gene for gp62 was integrated into a baculovirus genome for expression in Spodoptera frugiperda (Sf-9) insect ovarian cells. The antigenicity of baculovirus expressed BVDV protein was detected by anti-BVDV specific antibodies in an enzyme-linked immunosorbent assay (ELISA), indirect immunofluorescent assay (IFA) and radio-immunoprecipitation (RIP). The recombinant proteins isolated from bacteria showed antigenic properties when analyzed by ELISA and immunoblotting using BVDV antibodies. The recombinant proteins were then used in ELISA or IFA to detect BVDV infection by testing 54 independent bovine serum samples. The baculovirus-expressed BVDV protein was used as an ELISA and IFA antigen, and the bacteria-expressed proteins were used as ELISA antigens. BVDV-NADL-infected Madin-Darby bovine kidney (MDBK) cell monolayers served as a control antigen. Statistical analysis showed a high degree of correlation between the reactivity of recombinants and natural antigens in ELISA using bovine sera. The results of ELISA or IFA proved there is a high degree of correlation with the virus neutralization. In the comparative ELISA assays, the insect-cell-mediated expression revealed greater specificity and sensitivity than the bacterial expression or the natural BVDV antigens produced by cell cultures.

Neutralizing antibodies to type 1 and 2 bovine viral diarrhea viruses: detection by inhibition of viral cytopathology and infectivity by immunoperoxidase assay

Neutralizing antibodies to type 1 and 2 bovine viral diarrhea virus (BVDV) strains were measured by a microtiter virus neutralization test (MVNT) in cell culture. Antibodies (neutralizing) were detected by inhibition of viral infectivity, by the absence of viral cytopathology for cytopathic strains, or by immunoperoxidase staining for noncytopathic strains. The immunoperoxidase-stained monolayers could be detected without the aid of light microscopy. Twenty BVDV strains were used as challenge viruses in the in vitro MVNT, including 14 type 1 and 6 type 2 strains. Representative noncytopathic and cytopathic strains of both types were used. Positive control serum samples available for diagnostic testing contained both type 1 and type 2 BVDV antibodies. There did not appear to be major differences in antibody titers among the respective type strains, regardless of biotype (cytopathic or noncytopathic). In a study with sera from calves receiving a modified live virus or inactivated BVDV vaccine, the calves receiving type 1 strains responded with higher antibody titers to type 1 strains than to type 2 strains.