Contact transmission of bovine leukemia virus under insect-free conditions.

Experiments on contact transmission of bovine leukemia virus (BLV) were performed in insect-free isolated pens. Three and five calves, respectively, were kept in each of two pens. One and two of them, respectively, were inoculated with BLV. In these three experimentally infected calves, cell-free viremia was detected between 4 and 12 days after the inoculation. It disappeared after the development of virus-neutralizing antibodies. BLV, however, could be continuously recovered from the peripheral blood lymphocytes thereafter. During the experimental period one of five uninoculated calves showed seroconversion for antibodies to BLV 89 days after the beginning of the experiment. The other four remained negative for BLV infection for 12 months.