Viral culturing and attenuation
Lineage 1 PRRSV strain SD was continuously passaged in Marc-145 cells
using Dulbecco’s modified Eagle’s medium (DMEM) supplemented with 2%
foetal bovine serum and incubated at 37°C with 5% CO2.
The virus was harvested once the virus-infected Marc-145 cells showed
~80% cytopathic effect (CPE). The titres of the
wild-type strains SD and HLJWK108-1711 and NADC30-like PRRSV SD at
different passages were measured by seeding Marc-145 cells into 96-well
cell culture plates 2 d before infection. The 50% tissue culture
infective dose (TCID50) was calculated according to the
Reed-Muench method. The 125th passage of PRRSV strain
SD was harvested and designated lineage 1 PRRSV strain SD-R, which was
characterized and evaluated in the present study.