Increased reproductive losses in cattle infected with bovine pestivirus around the time of insemination.

Unmated heifers seronegative to bovine pestivirus were used to investigate the effects on conception and embryo-fetal survival of pestivirus infection around the time of artificial insemination. The reproductive performances of three groups were compared; the control group did not become infected during pregnancy, group 1 heifers were infected by contact with a persistently infected cow and calf four days after insemination and group 2 heifers were infected intranasally nine days before insemination. Conception rates and embryo-fetal survival were monitored by serial serum progesterone assays, transrectal ultrasonography and manual palpation of the uterus. The conception rates (determined 20 days after insemination) of 60 per cent (nine of 15) and 44 per cent (eight of 18) for groups 1 and 2 were lower than the 79 per cent (11 of 14) achieved by the control group. The group 1 heifers subsequently experienced significant embryo-fetal loss, resulting in a pregnancy rate (determined 77 days after insemination) of 33 per cent (five of 15), significantly lower than the control group's 79 per cent (11 of 14). The pregnancy rate of the group 2 heifers (39 per cent, seven of 18) was also significantly lower than that of the controls, largely as a result of the group's poor conception rate. All the heifers diagnosed pregnant 275 days after insemination were induced to calve. No persistently infected calves were born.

An antigen-capture ELISA detects pestivirus antigens in blood and tissues of immunotolerant carrier cattle.

An antigen-capture ELISA was developed for the detection of pestivirus-specific antigens in peripheral blood leucocytes (PBLs), blood clots and tissue samples of immunotolerant cattle persistently infected with virus. The ELISA demonstrated complete agreement with conventional virus isolation procedures undertaken on specimens from a total of 58 carrier animals and 360 uninfected animals. The technique is based on capturing antigen with a high-titred goat polyclonal antiserum and detecting the bound antigen with a combination of 3 broadly-reactive monoclonal antibodies. Increased sensitivity was obtained with the use of an avidin-biotin complex (ABC) amplification method. On average, ELISA optical densities (ODs) for PBL and blood clot samples derived from carrier animals were 1.53 and 0.95, respectively, while uninfected animals had corresponding values of less than 0.15 for all blood samples. Tissue samples from carrier cattle had OD values ranging from an average of 0.95 for liver to 1.77 for spleen, with negative values for all tissues again averaging less than 0.20. Signal-to-noise (S/N) ratios calculated from the ELISA OD readings for carrier cattle showed an average of 15.6 for blood samples and 16.4 for tissues. In contrast, all samples from negative cattle had S/N ratios less than 2.0. The antigen-capture ELISA has been validated on field samples and is suitable for routine diagnostic and certification testing.

Replication of bovine viral diarrhoea virus in the bovine reproductive tract and excretion of virus in semen during acute and chronic infections.

Five mature bulls were studied during an acute transient infection with bovine viral diarrhoea virus (BVDV). The bulls had been infected experimentally by the intranasal instillation of blood and serum from a cow which was a persistent carrier of the virus. Infection was confirmed by the demonstration of a low titred viraemia in four of the five animals and by the seroconversion of all five. Semen samples were collected from each bull on four occasions between seven and 14 days after infection. The virus was isolated from the semen of three of the five bulls and from nine of 12 batches of semen from them. In contrast to other studies of the infection of semen, BVDV was isolated with similar efficiency from raw, unprocessed semen and from diluted, extended semen. The titres of virus in the semen ranged from 5 to 75 TCID50/ml. The infection did not appear to affect the quality of the semen. Shedding of virus continued after the end of the period of viraemia and appeared to be a consequence of the replication of the virus in the reproductive tract and its subsequent excretion in the seminal fluid. Virological studies of the reproductive tracts of these bulls suggested that the most productive sites of virus replication were the seminal vesicles and the prostate gland. Concurrent studies in a persistently infected bull supported these findings.