Cross-infection studies of normal calves infected with homologous pairs of non-cytopathic and cytopathic bovine viral diarrhoea virus (BVDV) showed significant differences in both humoral and cellmediated immune responses against either biotype over a period of 5 months. Serological assays after primary intranasal inoculation showed striking significant (P 0n05) differences between biotypes. Neutralizing titres were detected earlier and were much higher with the non-cytopathic strain than with the homologous cytopathic strain. Significant biotype-specific differences were also observed in the lymphocyte proliferative responses of cattle following in vitro stimulation by non-cytopathic/ cytopathic BVDV and the non-structural p80 protein (NS3). The secondary immune response seems to be largely influenced by the biotype used for the primary inoculation and only to a lesser extent by the biotype inoculated for the second time after an

Abstract. Recently a commercial real-time reverse transcription polymerase chain reaction (RT-PCR) kit has been marketed for the detection of Bovine respiratory syncytial virus (BRSV). However, diagnostic interpretation of the results of this kit requires its comparison to commonly used methods. Therefore, the objective of this study was to evaluate the performance of this kit in comparison with the conventional direct fluorescent antibody test (FAT). Twenty BRSV strains and 14 heterologous bovine viruses were used to check the kit's sensitivity and specificity. The efficiency and detection limit of the kit were determined by testing dilution series of a BRSV strain. In conclusion, the kit evaluated in this study was sensitive, specific, and had a low threshold of detection. Furthermore, the use of this kit instead of FAT allows an improvement of the sensitivity for the detection of BRSV in clinical samples.

The relationship between the two biotypes of bovine viral diarrhoea virus (BVDV) and the biological responses they induce was studied in 3-to 6-month-old calves inoculated intranasally with a homologous pair of non-cytopathic and cytopathic strains. Marked differences in virological and serological events occurred following exposure to a specific BVDV strain. The non-cytopathic biotype was frequently recovered from nasal secretions and blood cells during the first 28 days post-inoculation whereas the cytopathic counterpart was detected infrequently in nasopharyngeal swabs only. There was no correlation of the recovery of infectious virus in vivo with the biotype-specific neutralizing humoral immune response. Furthermore, seroconversion did not correlate with resistance to reinfection as judged by the transient viraemia and/or shedding of virus observed in a challenge experiment. Bovine viral diarrhoea virus (BVDV) belongs to the genusPestivirus in the family Flaviviridae (Wengler, 1991). The strains of BVDV are grouped into two biotypes, non-cytopathic (ncp) and cytopathic (cp), according to their behaviour in cell culture (Baker, 1987) and the rearrangements in the non-structural NS23\NS3 coding gene (reviewed in Meyers & Thiel, 1996). The ncp biotype is commonly isolated from cases of acute infection and is invariably present in animals born persistently

Seventeen four- to five-week-old calves that were not shedding bovine respiratory syncytial virus (BRSV) were vaccinated intranasally against the disease and sampled by nasal swabbing on 16 different days for up to 20 days after vaccination. BRSV vaccine virus was detected in 15 of the 17 calves. Five of the calves were PCR positive on only one swab, eight were PCR positive on two to five swabs and two were PCR positive on more than five swabs. Twelve of the calves were positive only before day 14 and three were positive after day 14. The nasal shedding of BRSV vaccine virus was very variable.