Clinical and immunologic responses of vaccinated and unvaccinated calves to infection with a virulent type-II isolate of bovine viral diarrhea virus.

OBJECTIVE: To determine efficacy of a modified-live type-I isolate of bovine viral diarrhea virus (BVDV) vaccine in protecting calves from infection with a virulent type-II isolate, and to determine which type of immune response (i.e., humoral or cellular) correlates with protection. DESIGN: Prospective study. ANIMALS: 28 neonatal Holstein and Holstein-cross calves. PROCEDURE: Within 18 hours of birth, calves received maternal colostrum or were fed pooled colostrum. On days 7 to 10 after birth, calves were determined to be seropositive (n = 16) or seronegative (12) for antibodies to BVDV on the basis of ELISA and virus neutralization test results. Seropositive and seronegative 10- to 14-day-old calves were then given a combined vaccine that contained a modified-live type-I isolate of BVDV or a similar vaccine that lacked protection against bovine viral diarrhea. All calves were inoculated intranasally approximately 21 days after vaccination with a virulent type-II isolate of BVDV. Clinical and immunologic variables, including clinical scores, rectal temperatures, results of CBC with lymphocyte subset analysis, antibody responses, and cell-mediated immune responses, were monitored for 14 days after inoculation. RESULTS: Seronegative-unvaccinated calves developed severe disease and required euthanasia. Vaccination of seronegative calves with a modified-live type-I isolate had a disease-sparing effect as did passive transfer of colostral antibodies to BVDV. Clinical scores were not significantly different between seropositive-vaccinated and seropositive-unvaccinated calves after viral inoculation. CLINICAL IMPLICATIONS: A single dose of a modified-live type-I isolate of BVDV vaccine protects young calves from clinical signs of disease associated with type-II isolates.

Characterization of novel circovirus DNAs associated with wasting syndromes in pigs.

Porcine circovirus (PCV) was initially recognized as a contaminant of continuous pig kidney cell lines and was not thought to be pathogenic. Antibodies reactive to the cell culture isolate of PCV (PCV PK-15) are prevalent in the swine population worldwide. Recently, PCV PK-15-like antigen and nucleic acid were demonstrated in lesions associated with wasting syndromes in pigs in North America and Europe. Monoclonal antibodies raised to circoviruses isolated from pigs with wasting syndromes highlighted differences between these circoviruses and the PCV PK-15 cell culture isolate. This has led to speculation that a new pathogenic PCV may have emerged in the swine populations of several countries. We report the cloning and characterization of novel circovirus DNAs purified from virus isolates made from tissues of North American and European pigs with wasting syndromes. These North American and European circoviruses form a closely related group at the nucleotide sequence level (> 96% intra-group nucleotide sequence identity) but exhibit < 80% nucleotide sequence identity with the PCV PK-15 cell culture isolate. This report provides evidence for a new type of possibly pathogenic PCV. We propose that these new circoviruses should be referred to as PCV2 as opposed to the original PK-15 cell culture isolate, which should be referred to as PCV1.

Effects of perinatal vaccination on humoral and cellular immune responses in cows and young calves.

OBJECTIVE: To examine the effects of perinatal vaccination on cellular and humoral responses in cows and on passive transfer of antibodies and cells to calves, and to assess the role of maternal antibodies in vaccination responses of neonatal calves. DESIGN: Prospective randomized control trial. ANIMALS: 52 beef cows and their calves. PROCEDURES: Assigned cows were vaccinated twice during the last month of gestation. Assigned calves were vaccinated at day 10 after birth. Antibody concentrations and cellular responses to bovine respiratory syncytial virus (BRSV) and bovine herpesvirus type 1 (BHV-1) were measured in blood and colostrum of cows and in blood of calves. Calves were assessed for passive transfer of lymphocytes. RESULTS: At parturition, serum antibody concentrations to BRSV as well as BHV-1- and BRSV-specific blastogenic responses were significantly higher in vaccinated cows. After birth, calves from vaccinated cows had significantly higher concentrations of BRSV-specific serum antibodies, but not BHV-1 specific antibodies. Calves did not develop delayed-type hypersensitivity responses to BRSV. At weaning, lymphocytes from neonatally vaccinated calves had significantly higher values for virus-specific proliferation than did lymphocytes from unvaccinated calves; however, significant differences were not detected between groups after vaccination at weaning. CLINICAL IMPLICATIONS: Administration of modified-live viral vaccines can boost systemic humoral and cellular responses to BRSV and BHV-1 in cows. Neonatal calves can be immunologically primed by vaccination with modified-live virus vaccines. Virus-specific memory cells persist in most calves until weaning.

Bovine respiratory syncytial virus-specific immune responses in calves after inoculation with commercially available vaccines.

A study was designed to determine if inactivated bovine respiratory syncytial virus (BRSV) vaccines induce the same types of antibody and cellular responses as does a modified-live BRSV vaccine. Ninety mixed-breed, 5- to 6-month-old beef calves were randomly assigned to 1 of 6 groups with 15 animals/group. Calves in 5 of the groups were inoculated on days 0 and 14 with 1 of 4 inactivated virus vaccines or with a modified-live virus vaccine. The remaining 15 calves were maintained as unvaccinated controls. Immune responses were measured on days 0 and 24, by means of ELISA, virus neutralization assay, blocking ELISA for the BRSV fusion (F) protein, immunoblotting, and lymphocyte blastogenesis assay. All vaccines induced production of antibodies that recognized the F protein; however, the ratio of neutralizing antibody titer to change in BRSV-specific IgG antibody concentration (as determined by use of ELISA) was lower for calves that received an inactivated virus vaccine than for calves that received the modified-live virus vaccine. All of the vaccines induced lymphocyte proliferative responses to BRSV. Results suggest that commercially employed inactivation processes can alter functionally important epitopes on BRSV envelope glycoproteins, leading to production of predominantly nonneutralizing antibodies in immunized cattle.

Prevalence of antibodies to infectious bovine rhinotracheitis, parainfluenza 3, bovine respiratory syncytial, and bovine viral diarrhea viruses in cattle in Saskatchewan and Alberta.

A total of 1745 healthy cattle from 295 farms in Saskatchewan and Alberta was tested by ELISA for antibodies to four viruses. Antibodies to infectious bovine rhinotracheitis (IBR) virus were found in 37.8% of sera (59.5% of properties), to parainfluenza 3 (PI3) virus in 93.9% of sera (99.7% of properties), to bovine respiratory syncytial (BRS) virus in 78.5% of sera (86.6% of properties), and to bovine viral diarrhea (BVD) virus in 40.6% of sera (66.7% of properties)The prevalence of PI3 viral antibodies among Saskatchewan cattle was not affected by district of origin, breed, sex, age, or vaccination practices, though BRS viral antibodies appeared less frequent in young, male, and unvaccinated animals. Antibodies to IBR and BVD viruses were less prevalent in the Prince Albert/Tisdale districts and in young, male, and unvaccinated animals, but were more common in Holstein cattle. Antibodies to IBR virus appeared less frequent in Herefords. Antibodies were more prevalent in cattle which had been vaccinated against IBR, BRS, and BVD virus infections.The relatively small number of cattle sampled from Alberta had a similar prevalence of antibodies to PI3 and BRS viruses to that seen in cattle in Saskatchewan, though IBR and BVD prevalence rates were lower.

An enzyme-linked immunosorbent assay (ELISA) for antibodies to bovine viral diarrhea virus.

A single dilution enzyme-linked immunosorbent assay (ELISA) was developed to detect antibodies to bovine viral diarrhea (BVD) virus in cattle sera. Viral antigen (NADL strain) was grown in a pig kidney cell line (PK15), and after removal of nuclear debris, was purified by ultracentrifugation through a potassium tartrate cushion. Antigen grown in embryonic bovine tracheal epithelial cells was also satisfactory. The test used a high salt buffer to minimize nonspecific reactivity, polyethylene glycol to enhance the reaction, and Protein G as the labelling agent. Comparative testing with the virus neutralization test (VNT) showed the ELISA results to have a high level of correlation with the VNT titers (r = 0.83). In vaccinated animals the ELISA detected antibodies earlier than the VNT. All animals sampled from a BVD-free herd were negative for BVD antibody. The single dilution test showed close agreement (r = 0.84) with ELISA values obtained using a serial dilution technique, and also proved to have a high level of reproducibility. The test procedures were relatively easy to carry out, and were economic in their use of materials.

Viruses and virus-like particles detected during examination of feces from calves and piglets with diarrhea.

A total of 763 fecal or intestinal samples from diarrheic calves and piglets were examined for viral content by immunofluorescence, electron microscopy or cell culture. Routine fluorescent antibody and cultural tests detected rotavirus (n=126), coronavirus (n=80) and bovine viral diarrhea virus (n=13). Electron microscopy detected rotaviruses (n=24) and coronaviruses (n=17) not identified by standard fluorescent antibody tests. Other viruses detected by electron microscopy included Breda virus-like particles (n=49), astroviruses (n=1), caliciviruses (n=1), rhabdoviruses (n=1), parvoviruses (n=2), enteroviruses (n=3), togavirus-like particles (n=2), and "chained" particles (n=5). Mixtures of several of the viruses were detected in a number of fecal samples.The survey emphasized the value of electron microscopy as a broad-spectrum diagnostic tool.