Investigations of the Australian bovine lentivirus

The bovine lentiviruses (BL), Bovine immunodeficiency virus (BIV) and Jembrana disease virus (JDV) are two relatively unknown lentiviruses that produce remarkably different disease syndromes. BIV typically causes a mild and transient lymphocytosis with associated lymphadenopathy in Bos taurus cattle with some suggested mild immune suppression. JDV, on the other hand, is an acutely pathogenic lentivirus causing marked leucopoenia with associated lymphadenopathy and splenomegaly and has an experimental mortality rate of approximately 20%. Recombinant antigens of both bovine lentivirus including the immunodominant viral proteins, capsid (CA or p26) and transmembrane (TM or p42) envelope proteins were developed using a glutathione-s-transferase fusion protein expressed m a heterologous Escherichia coli expression system. The recombinant proteins were recognised by antisera from experimentally infected animals of the respective viruses but also showed significant cross-reactivity. The recombinant proteins were used as antigens to develop western immunoblot and ELISA serological assays to identify cattle with antibody to bovine lentivirus with high specificity and sensitivity. An antigenically-related bovine lentivirus was identified in Australian cattle including the states of Queensland, South Australia and Western Austnilia. Sera from random cattle provided by the local agricultural department (AgWA) showed reactivity to BIV and JDV CA antigens with only slight reactivity to TM proteins. Interestingly, serum samples varied in specificity for the BIV or JDV antigens indicating exposure to antigenically variable viruses. Of the 690 Dairy cattle in Western Australia surveyed, approximately 16% by western immunoblot (WIB) and 4% by ELISA were found to have been exposed to an antigenically-related bovine lentivirus. A high percentage (74% by ELISA and 61% by WIB) of WA dairy properties were also found to have at least one animal with bovine lentivirus antibody. Subsequent investigation concluded that bovine lentivirus infection is endemic to Australian cattle herds. Several herds in Queensland, South Australia and Western Australia with a history of immune suppressive disorders of unknown aetiology were also investigated for the seroprevalence of bovine lentivirus. There was high level of correlation of bovine lentivirus antigen reactivity and the presence of the immune suppressive disease in IX these problem herds. However, the role of bovine lentivirus infection in the cause of the condition was unclear but unlikely to be the cause of such diseases. A PCR assay was developed that could identify .bovine lentiviruses. Many sets of published PCR primers for the identification of BIV were examined for specificity and sensitivity. Specific primer sets that could identify both of the known bovine lentiviruses and also differentiate between JDV and BIV were determined. The sensitivity of the PCR assay was adequate but showed high specificity to the target. Attempts to further investigate the Australian bovine lentivirus by in vitro culture and nucleotide sequencing from antibody-positive cattle were unsuccessful. There was an indication that a very low number of lymphocytes contain bovine lentivirus genetic material and most probably contains a divergent nucleotide sequence to that known for the US isolate. In addition, co-culture of peripheral blood mononuclear cells from antibody-positive animals with primary foetal bovine lung cells did not show any significant evidence of BIV replication. For these reasons, it concluded that the PCR assay for BIV based upon US isolates was not applicable to the Australian bovine lentivirus, possibly due to low specificity and sensitivity. Experimental infection with blood from seropositive cattle commonly caused a mild transient lymphocytosis and mild lymphadenopathy but had no association with apparent clinical disease. Individual animals responded differently to experimental infection ranging from a marked persistent lymphocytosis to a mild and transient lymphocytosis. As a direct result of this research, there is an increased understanding of the extent of bovine lentivirus infection in Australia and a possible association with immune suppressive disorders present. This study has produced information about the Australian bovine lentivirus that will be the foundation of bovine lentivirus research to determine the effect it may have on the cattle industry in Australia and Indonesia. This study has been valuable for the reagents developed that will be used for the specific surveillance of JDV in Indonesia and vaccination for JDV in Indonesian cattle