Hematological and immunological parameters of 4 1/2-month old pigs infected with PRRS virus.

4 1/2-month old SPF pigs were experimentally infected with PRRS virus. Blood samples were collected with regular intervals up to day 35 post inoculation (PI). Serum was used for PRRS virus isolation and antibody detection and stabilized blood for total leucocyte counts, differential counts and characterization of lymphocyte subpopulations by flow cytometry analysis using monoclonal antibodies specific for porcine CD2, CD4 and CD8. After an initial viremic period of 1-7 days duration for individual pigs, PRRS virus was intermittently detected in pigs up to day 18 PI. All pigs had developed antibodies against PRRS virus by day 14 PI. Total blood leucocyte counts and lymphocyte counts were significantly decreased for a few days shortly after infection, but had returned to pre-infection levels on day 8-10 PI. A major change in the distribution of lymphocyte subpopulations was observed on day 3 PI, where the percentages of CD2+, CD4+ and CD8+ cells were significantly decreased. However, the percentages of these lymphocyte subsets quickly returned to approximately pre-infection values. The observed changes of the parameters examined do not indicate long-term systemic immunosuppression of the infected pigs.