Cell-free and cell-associated viremia in pigs after oronasal infection with Aujeszky's disease virus.

Nine pigs were examined for the presence of viremia during the first week after oronasal inoculation of 10(8.0) TCID50 Aujeszky's disease virus (ADV). Blood was taken at 1, 2, 3, 5 and 7 days post inoculation (PI) and the presence of cell-free ADV in plasma and of ADV-infected mononuclear cells was examined by titration and by cocultivation with permissive cells, respectively. The mononuclear cells of 6 of the 9 pigs, collected at 3 and 5 days PI were further separated into subpopulations of enriched monocytes and enriched lymphocytes. Both subpopulations were cocultivated. Nasal secretions were collected from 4 of the 9 pigs for the determination of virus titers and interferon concentrations. Both infected mononuclear cells and cell-free ADV were demonstrated in 5 pigs, infected mononuclear cells only were found in 2 pigs, and neither cell-associated or cell-free ADV were detected in 2 pigs. Two of the 7 viremic animals were positive on one single day, 3 on 2 days, 1 on 3 days and 1 on 4 days. The number of infected cells was approximately 5 times higher in monocytes than in lymphocytes. The highest virus titers were present in those nasal fluids with the lowest alpha-interferon concentration. A correlation between the titer of locally produced ADV in the nose and the presence of a viremia was not found. In conclusion, we can state that a viremia regularly occurs under both cell-free and cell-associated form after an oronasal inoculation of ADV and that monocytes are the most susceptible mononuclear cells.