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.

Induced sero-conversion in heifers with a field strain of bovine pestivirus--a comparison of methods and doses.

Losses from pestivirus infection in a closed herd of cattle occurred over several years. In order to prevent further losses, controlled exposure of non-pregnant heifers to pestivirus from viraemic carrier animals was undertaken. Two initial experiments were conducted using either intra-nasal EDTA blood or field contact. Subsequently, other yearling heifers were inoculated with various dilutions of serum using subcutaneous, conjunctival and intra-nasal routes. Effective doses were determined. Neither inoculation nor contact infection produced any clinical illness. The highest dilutions of serum at which sero-conversion occurred were conjunctival, undiluted; intranasal, 10(-1) and subcutaneous 10(-5). With the subcutaneous route all heifers sero-converted at 10(-3). The results for the subcutaneous inoculations showed that the 50% infectious dose for cattle was not distinguishable from that determined in cell culture. Inoculation with a field strain of pestivirus in freeze-thawed serum has effectively and safely induced sero-conversion in heifers. Inoculation of all cattle at risk is considered necessary because no secondary transmission from inoculated heifers was observed.

Incidence, epidemiology and control of bovine pestivirus infections and disease in Australia and New Zealand.

Pestivirus infection of cattle is widespread and common in both Australia and New Zealand. The majority of adult animals, of the order of 60%, carry antibody. Associated disease is almost entirely that resulting from infection in utero. This includes death of the conceptus, at any stage from conception through pregnancy, or, in those which are born as persistently infected carriers, mucosal disease, most commonly in a chronic form. Little or no disease is recognised as a result of the post-natal infection of non-pregnant animals and these appear to be of little consequence as spreaders of infection. Transmission and enzootic maintenance depend primarily on the persistently infected carriers that are immunotolerant after early in utero infection and range clinically from normal, or nearly normal, to overtly mucosal diseased. The expulsion of an infected conceptus, and associated discharges, also provides an effective source of infection. There is generally little active control attempted. Vaccines are not available in Australia and are not widely used in New Zealand. However, interest in control is growing in those areas of the industry, especially in breeding by artificial insemination and embryo transfer, where it is perceived that the pathogenic impact of the virus may be amplified.

New concepts in the pathogenesis, diagnosis and control of diseases caused by the bovine viral diarrhea virus.

The new information on the pathogenesis and epidemiology of mucosal disease of cattle is reviewed. It is now known that clinical mucosal disease occurs only in cattle which were infected with a pestivirus in early gestation and were born with persistent viral infection and specific immunotolerance. These animals may be clinically normal at birth but may develop fatal mucosal disease, perhaps following superinfection with another pestivirus, usually between 6 and 24 months of age. They may also remain clinically normal indefinitely and breed successfully. The progeny from persistently infected females will similarly be persistently viremic, and maternal families of such animals may be established.Congenital defects may occur when infection of the fetus occurs in mid-gestation. Although fetuses may be infected in utero in late gestation, the infections do not persist, the fetuses develop antibodies, and they appear to suffer no ill-effects. Postnatal infection can result in subclinical disease (bovine viral diarrhea) with a normal immune response; the virus may also be responsible for enhanced susceptibility to other infections, diarrhea in newborn calves, and reproductive failure.Prevention of the economically important diseases caused by the virus is dependent upon the identification and elimination of persistently viremic animals, which are reservoirs of infection, and the vaccination of immunocompetent females at least three weeks before breeding. However, because of serotypic differences between strains, there is some doubt whether vaccination will reliably provide protection against the transplacental fetal infections that are important in the pathogenesis of this disease. There is no substantial evidence to warrant the vaccination of feedlot cattle.

Group-specific and type-specific gel diffusion precipitin tests for bluetongue virus serotype 20 and related viruses.

Using antigens prepared from cell cultures infected by bluetongue (BLU) virus type 20 (BLU-20), and sera from cattle which had recovered from experimental infection by that virus, two distinct precipitin reactions were demonstrated by immunodiffusion. Two distinct gel diffusion precipitin tests were developed based on these reactions. The antigen of one was common to BLU-20 and two other Australian BLU isolates, CSIRO 154 (BLU-21) and CSIRO 156 (BLU-1). It was therefore concluded to be a group-specific test. The antigen of the second appeared to be unique to BLU-20. The test based on this antigen correlated well with the virus neutralization test for BLU-20 and it was therefore concluded to be type-specific. Similar methods applied to a virus of the Palyam (PAL) group demonstrated two precipitin reactions of similar broad (group) and narrow (type) specificity.

The occurrence of antibody to bluetongue virus in New South Wales. II. Coastal region and age distribution surveys.

Three surveys of cattle for bluetongue (BLU) antibody were conducted over the years 1978-1980 in coastal areas of New South Wales. In each survey the samples were identified by age. The prevalence of BLU-group antibody, demonstrated in a gel diffusion precipitin test, was highest in the north and decreased progressively to the south. Antibody prevalence increased with age. However, according to variations in prevalence by age and region, it was concluded that the activity of relevant viruses was highly variable between years and was geographically discontinuous. Evidence is presented that much of the antibody found, especially in animals less than 4 years old, failed to persist from one year to another. Factors likely to contribute to more persistent reactions in older animals are discussed. Neutralizing antibodies to bluetongue virus serotypes 1 and 21 were demonstrated and prevalence of these was associated with location and age, as was that of group-specific antibody.

The occurrence of antibody to bluetongue virus in New South Wales. I. Statewide surveys of cattle and sheep.

Two State-wide surveys were carried out in 1978 to detect bluetongue (BLU) virus antibody in cattle and sheep sera in New South Wales (NSW). The first survey showed that BLU group antibody in cattle 18-24 months old was confined to the coastal regions (east of the Great Dividing Range) and the Hunter Valley. However, in the second survey, of cattle more than 5 years old, reactors were much more widely distributed over the north-eastern third of the State and into the western division with prevalences up to 85% in some areas. In contrast, very few reactors were detected in sheep in either survey (less than 1% of the sheep sera tested). In a retrospective study of stored cattle sera, BLU group reactors were detected in the north-east of the State in each year examined since 1968, the earliest year in which samples were available from that region. Areas to the south and west were free of antibody from 1966 until the summer of 1973, but subsequently reactors were common. Examination of selected area for type-specific antibody indicated that infection of cattle with two of the three Australian BLU serotypes which were known at the time, BLU-1 and BLU-21, had occurred in NSW. No antibody to BLU-20, the original Australian isolate, was detected. A close association was observed between strong group antibody reactions and type-specific neutralizing activity against BLU-1 and BLU-21. Both were largely confined to that area of the State in which a high (75% or more) prevalence of group antibody was recognised in the older animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Bluetongue and related viruses in New South Wales: isolations from, and serological tests on samples from sentinel cattle.

Sentinel cattle at a number of localities in northern and central coastal New South Wales were sampled over the summer and autumn seasons of the years 1979, 1980 and 1981. A total of 118 orbiviruses were isolated; 99 were of the Palyam group, 15 were of the epizootic haemorrhagic disease (EHD) of deer group, and 4 of the bluetongue group. The Palyam group viruses were identified by serotype as 68 Bunyip Creek, 23 CSIRO Village, 7 D'Aguilar and one was not typed. The EHD viruses were identified as 13 type 5 and 2 type 6. All 4 bluetongue viruses were type 21. There was also convincing serological evidence that bluetongue type 1 infection occurred in 1980. Antibody to the bluetongue group, as demonstrated in a gel diffusion precipitin test, was often transient. It appeared to be mostly cross-reactive with, and induced by, other orbivirus infections, particularly those of the EHD group. Viruses of the Palyam group also seemed to be implicated in some circumstances. Where infections by viruses of the bluetongue group were demonstrated, the precipitating antibody responses to a bluetongue group antigen were not noticeably stronger than many which followed EHD virus infection. The results generally confirm previous conclusions, deduced from serological surveys, regarding the frequency of orbivirus infections, the presence of bluetongue viruses, and the transient nature of many bluetongue group antibody reactions.

Macropodid herpesviruses 1 and 2: two herpesviruses from Australian marsupials differentiated by restriction endonucleases, DNA composition and hybridization. Brief report.

The DNAs of a number of herpesviruses from Australian marsupials have been analyzed using restriction endonucleases, dot-blot hybridizations, and analytical ultracentrifugation in CsCl. The data clearly show the presence of 2 distinct viruses, designated macropodid herpesviruses 1 and 2.

Eperythrozoon ovis and copper poisoning as causes of jaundice in lamb carcases.

A total of 126 lamb carcases, of which 80 were jaundiced and 46 were grossly normal at routine meat inspection, were examined. Two specific diseases were demonstrated to be associated with jaundiced carcases. Eperythrozoon infection was demonstrated in 65% of jaundiced, and 12% of non-jaundiced carcases from jaundice-affected lots, but not in 5 normal carcases from unaffected killing lots. Copper poisoning was demonstrated in 2 of the jaundiced carcases. Infection with Eperythrozoon ovis was therefore the condition most commonly associated with, and presumably the major cause of jaundice in these lamb carcases. Copper poisoning was a less common cause of jaundice.

Evaluation of a gel diffusion precipitin test for porcine parvovirus.

The use of a gel diffusion precipitin (GDP) test for the detection of porcine parvovirus (PPV) infection in pigs is described. The close correlation between gel diffusion precipitin and haemagglutination inhibiting (HI) antibody titres indicates that, with careful standardisation, a high level of sensitivity can be achieved with the GDP test and that it is a simple and relatively inexpensive alternative to the more commonly used HI test. Experimental infection of 2 groups of pigs showed that GDP and HI antibody responses were closely correlated and that GDP antibodies to PPV persisted for at least 41 weeks after infection. In a commercial herd study, serological evidence of declining passive immunity and subsequent acquisition of active immunity was demonstrated by measuring the GDP and HI antibody titres in sequential serum samples of pigs from a known PPV endemic farm. The GDP test described was shown to be less sensitive than haemagglutination (HA) in the detection of viral antigen but was, nevertheless, considered useful as a simple screening test for the amounts of antigen usually present in PPV infected mummified foetuses.

Serological studies of Australian and Papua New Guinean cattle and Australian sheep for the presence of antibodies against bluetongue group viruses.

Following isolation of a virus (CSIRO19) from insects in Australia and its identification as bluetongue virus serotype 20 (BTV20), a nationwide survey of antibodies in cattle and sheep sera was undertaken. Initial studies using the serum neutralization (SN) test showed that the distribution of BTV20 antibodies in cattle was confined to the northern part of Australia. Group-reactive antibody tests (agar gel diffusion precipitin, AGDP, and complement-fixation, CF) showed group-reactive cattle sera south of the BTV20 zone (northern Australia), and southwards from Queensland to New South Wales. Very few group-reactive sheep sera (45 out of 16213) were found and these were of doubtful epidemiological significance. Some of these BTV group-reactive, BTV20-negative, sera were tested in SN tests against BTV1 to 17 and Ibaraki (IBA) virus. The results indicated that BTV1, or a closely related orbivirus, was active in cattle in Queensland, northern Western Australia, and New South Wales, and that antibody to BTV15 was present in some of the cattle sera in northern Western Australia and the Northern Territory. Antibody to IBA virus was present in some cattle sera in Queensland, northern Western Australia and New South Wales. SN antibody titres greater than or equal to 60 were also found to a number of other BTV serotypes in cattle sera in northern Western Australia and Queensland (principally, BTV2 and BTV7). Low level reactions were commonly observed against these and a number of other BTV serotypes, often in the same serum samples. Further, 22% of the group-reactive cattle sera did not react with any of the viruses in the SN tests. Such results were difficult to interpret in terms of known Australian BTV or BTV-related isolates.