RÉSUMÉ
Enzootic haematuria and urinary bladder cancer in cattle are associated with feeding on bracken fern and bovine papillomavirus (BPV) infection. An increased rate of chromosomal aberrations in peripheral blood lymphocytes from chronically affected haematuric cows raised in bracken fern pastures has been reported, suggesting the presence of BPV in the peripheral blood of afflicted animals. The purpose of the present investigation was to examine the role of peripheral blood as a potential BPV-transmitting agent and search for clastogenic effects in experimentally infected animals kept on a bracken fern-free diet. Healthy cows were inoculated with blood samples of haematuric animals every two weeks for 18 months. Recipient cows, their offspring, donor animals and a control group were kept on a bracken fern-free diet throughout the experiment. Clinical and molecular analyses for detection of BPV infection were carried out periodically in all groups. Short-term lymphocyte cultures were performed to assess chromosomal aberration levels. The donor cows, the recipient cows and their offspring presented increased levels of chromosomal aberrations. BPV-2 DNA was identified by Southern blotting, PCR and cycle-sequencing of PCR products in peripheral blood of donor and recipient animals and in the progeny of recipient animals. Data support both the concept that BPV can be transmitted through blood and the hypothesis that infection with the virus causes the clastogenic alterations observed in the present experimental model. The presence of BPV-2 DNA and chromosomal alterations in peripheral blood of offspring at the moment of birth is evidence for vertical transmission of BPV.