Distribution of proviral DNA of bovine leukaemia virus in blood and different tissues in asymptomatically infected cattle.

Introduction: Bovine leukaemia virus (BLV) is the aetiological agent of enzootic bovine leukosis. The aim of the study was to ascertain the ability of qPCR to detect proviral BLV DNA in various tissues from slaughtered cattle when BLV was suspected but serological testing was not possible. Material and Methods: Three types of tissues were collected during sanitary slaughtering of 22 cattle naturally infected with BLV: spleen, lymph node and muscle. The proviral load (PVL) was estimated in this tissue by a real-time quantitative PCR (qPCR) for BLV based on the pol gene. To measure provirus copy number per 106 cells, the bovine histone H3 family 3A gene was also amplified by qPCR. Results: The PVL was the highest in the spleen and ranged there from 1 to 59,188 copies/106 cells, with four cases in which no proviral DNA was detected. In the lymph nodes the PVL ranged from 2 to 6,888 copies/106 cells, with seven cases in which no copies were detected. The lowest PVL was recorded in DNA from muscle samples and ranged from 1 to 119 copies/106 cells; no BLV was detected in 6 out of 22 samples. Conclusion: The BLV qPCR is a suitable tool for the detection of proviral BLV DNA in various tissues when infection is suspected and no blood or other fluids are available for serological examination.