IN-VIVO REPLICATION OF PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS IN SWINE ALVEOLAR MACROPHAGES AND CHANGE IN THE CELL-POPULATION IN BRONCHOALVEOLAR LAVAGE FLUID AFTER INFECTION

Replication of porcine reproductive and respiratory syndrome (PRRS) vi rus in swine alveolar macrophages (AM) and cell population in broncho- alveolar lavage fluid (BALF) obtained from PRRS virus-infected pigs we re investigated. BALF samples were periodically collected from 6 pigs infected with PRRS virus and 3 non-inoculated control pigs by means of fiber-optic bronchoscope between post-inoculation day (PID) 0 and 56. The mean ratio of macrophages in BALF collected from infected group w as 92.7 +/- 3.2% before inoculation and gradually decreased from PID 1 4. On the other hand, the ratio of lymphocytes was 4.8 +/- 3.2% before inoculation and increased from PID 21 and indicated 41.8 +/- 9.1% on PID 28. After that, they decreased gradually and that of macrophages c orrespondingly increased. The ratio of neutrophils maintained between 0.7% and 5.1%. The ratios of macrophages, lymphocytes and neutrophils collected from control group were almost stable through the examinatio n. Intracellular PRRS virus antigens in AM were detected from PID 2 by indirect immunofluorescence assay (IIFA). PRRS virus was first isolat ed from BALF samples collected from inoculated group between PID 2 and 49. From serum, virus was isolated between PID 2 and 21. Antibodies i n sera measured by IIFA to PRRS virus were first detected on PID 14 an d the antibody titer rose to 1:640 or 1:1,280. The results suggested t hat PRRS virus replicates in swine AM for a relatively long period.