Diagnosis and typing of bovine leukaemia virus using a PCR-RFLP test on DNA extracted from somatic cells in milk

The aim of this study was to assess the suitability of using DNA isolated from milk somatic cells for the diagnosis and molecular typing of bovine leukaemia virus (BLV). A total of 40 bulk milk samples were analysed and thirty three of them resulted seropositive to BLV after being evaluated using an indirect ELISA test. A PCR test confirmed the presence of the virus in all 33 seropositive samples whereas in the remaining seronegative samples it was not possible to detect a specific band for the virus. A RFLP analysis identified 2 out of the 3 known subgroups of BLV genetic variants. Individual analysis carried out in the PCR positive herd confirmed the presence of more than one genetic variant within this herd, suggesting that there is a possibility of re-infection occurring with another virus strain. This report is the first to describe the application of a PCR-RFLP test for the detection and molecular typing of BLV directly from milk samples. The simplicity of collecting bulk milk samples makes the described technique a convenient way for a quick diagnosis of the virus, which can also be used to study the molecular epidemiology and distribution of BLV infection in a specific area or even at national scale.