DETECTION OF CALVES PERSISTENTLY INFECTED WITH BOVINE PESTIVIRUS IN ASAMPLE OF DAIRY CALVES IN SOUTH-EASTERN QUEENSLAND

Objective To determine the proportion and incidence of calves persiste ntly infected with bovine pestivirus in calves (n = 1521) supplied to the Tick Fever Research Centre and to assess the test regime to detect calves persistently infected with bovine pestivirus, Design Calves, 1 to 6 weeks old, selected for use in the production of the tick fever vaccine were collected from 21 properties in 56 separate groups betwee n October 1990 and December 1996. Each group was examined for the pres ence of carves persistently infected with bovine pestivirus. Procedure Ail calves were routinely tested for antibody to bovine pestivirus an d bovine pestivirus antigen using a serum neutralisation test and an a ntigen-capture ELISA, respectively. Pooled lymphocyte samples from cal ves were also monitored for bovine pestivirus by inoculation of sheep, Whole herd testing was carried out in eight herds, using a serum neut ralisation test as a screen test followed by an antigen-capture ELISA of cattle with a serum neutralisation test titre of less than 32. Resu lts Fourteen of the 1521 calves tested (0.9%), were detected as persis tently infected and the incidence ranged from 0.0 to 3.0 % per year ov er 8 years, Persistently infected calves were found in 13 of the 59 gr oups and originated from 7 of the 21 herds used, In whole herd testing on the properties of origin, cattle persistently infected with bovine pestivirus were detected in four of the eight herds tested Conclusion s The proportion of carves persistently infected with bovine pestiviru s is similar to that in other countries and indicates that bovine pest ivirus could be a significant cause of economic loss in Australian cat tle herds. In detecting carves persistently infected with bovine pesti virus, the combination of sheep inoculation, paired antigen-capture EL ISA and serum neutralisation tests appeared to be highly sensitive and specific.