Fig. 5.
The cloned virus retains in vivo markers of virulence and is genetically stable. Three groups of pigs (four pigs per group) were sham-inoculated or inoculated with either vParental or vFL12 at TCID50/ml of 105.2 and 104.8, respectively. (A) Temperatures were recorded daily from 2 days before inoculation to 16 dpi. Average temperatures from four different animals in each group are shown. (B) Serum samples were collected at 4, 7, 14, and 22 dpi and virus titers were determined and expressed as TCID50/ml. Values represent average titers from four animals. (C) Serum antibody titers were determined with the Idexx ELISA kit. Values represent average titers from four animals. Dashed line at 0.4 S/P ratio designates threshold value above which titers are considered positive for anti-PRRSV antibodies. Error bars in panels A, B, and C represent standard deviation. (D) Serum from 14 dpi, recovered from inoculated animals, was used to distinguish between vFL12 and vParental by examining for the presence of the BsrGI genetic tag (left panel). Viral RNA extracted from sera was amplified by RT-PCR and the products were digested with BsrGI. Similar analysis (lane 7) was performed with virus in serum from a sentinel pig at 8 days postcohabitation with pigs infected with vFL12 (right panel). Gel image is inverted. Error bars represent standard deviation.