Growth kinetics of an Indian isolate of highly pathogenic porcine reproductive and respiratory syndrome virus in MARC-145 cells.

The aim of the present study was to understand the replication kinetics of an Indian isolate of highly pathogenic porcine reproductive and respiratory syndrome (PRRS) virus (Ind-297221) in MARC-145 cells infected at different multiplicity of infection (MOI) of 1.0, 0.1, 0.01 and 0.001. PRRSV titre in the infected cell fraction and the culture supernatant harvested at different intervals (12, 36, 48, 72, 96 and 120 h) post infection (hpi) was estimated by immunoperoxidase monolayer assay. Viral RNA copy numbers were quantified by TaqMan RT-PCR. PRRS virus could be detected first in intracellular fraction at 12 hpi in cells infected at 1.0 MOI, whereas in the extracellular fraction, earliest detection was at 36 hpi. Highest PRRSV titre of 1.3 × 10(5.0) TCID(50)/mL was achieved in 0.01 and 0.001 MOI groups at 96 hpi. Infection with 0.01 MOI resulted in the maintenance of maximum titre up to 120 hpi. The maximum viral copy numbers observed was 3.15 × 10(7.0) in 0.1 MOI group at 120 hpi in culture medium. The results of the study showed that MARC-145 cells infected with Indian PRRSV at 0.01 MOI and harvested in 96-120 hpi was found to be optimum for obtaining maximum virus yield and hence can be used for bulk propagation of the virus.