Leukogenic properties of purified BLV and possible routes of its transmission with blood cells present in milk.

The results of five years studies on the possibility of experimental induction of bovine leukemia with purified BLV and different BLV-containing materials demonstrated that inoculation of calves with purified BLV (structures of 1.14-1.17 g/ml density in 20-60% sucrose gradient) can induce oncornavirus infection and bovine leukemia. From 41 experimentally infected calves 9 showed evidence of bovine leukemia. 5 of these 9 animals were from a group of 22 calves inoculated with purified BLV. Diagnosis of bovine leukemia in these 9 animals was established by hematologic (3 animals) and histologic method (6 animals). BLV was isolated from leukocytes of all of them. It was shown also that before the development of bovine leukemia the development of oncornavirus infection takes place. But only a small part of the animals with oncornavirus infection and presence of antibodies became ill with typical forms of hemoblastosis. The investigation of the role of milk and blood cells in milk in bovine leukemia transmission was also carried out. The presence was demonstrated of oncornavirus structures antigenically identical with BLV in milk and reproduction of these structures in blood cells being present in milk. These results, and also the induction of bovine leukemia, in cattle by rearing with raw milk from cattle with leukemia, allow us to suppose the possible routes of bovine leukemia transmission in nature.