DIFFERENCES IN SUSCEPTIBILITY OF DUROC, HAMPSHIRE, AND MEISHAN PIGS TO INFECTION WITH A HIGH VIRULENCE STRAIN (VR2385) OF PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS (PRRSV)

The objective of this research was to determine if there is genetic in fluence on the resistance or susceptibility to PRRSV-induced disease a nd lesions. Pigs of three breeds from two or three litters per ere ran domly assigned to treatment or control groups. Treatment consisted of inoculation with a well characterized, high virulence strain (VR2385) oi PRRSV. Duroc, Hampshire, and Meishan pigs were weaned at 9-10 days of age and inoculated with PRRSV at 22-38 days of age. Animals were ho used and cared for according to approved animal use and care standards . Pigs were inoculated intranasally with 5 ml of cell culture media co ntaining 10(5.8) S TCID50 of PRRSV VR2385. Controls were mock-infected . Clinical disease scores and rectal temperatures were recorded daily. Macroscopic lesion scores were estimated at necropsy at 10 days post inoculation. All organ systems were examined microscopically in a blin ded fashion. Serum antibody response was measured by an indirect immun ofluorescence assay. Hampshire pigs had significantly more severe macr oscopic lung lesion scores (43.0 +/- 3.7) than Duroc (29.43 +/- 3.3) o r Meishan (25.0 +/- 3.5) plgs. Meishan pigs had significantly less PRR SV antigen detected in the lungs. Significantly more Meishan plgs had myocarditis and encephalitis. Duroc plgs had significantly lower norma lized serum antibody titres to PRRSV. Differences in severity and dist ribution of PRRSV-induced lesions, and in normalized serum antibody re sponse to PRRSV may be in part influenced by pig genetic factors. The ability to select animals which are less susceptible to the devastatin g consequences of PRRSV infection would be of tremendous value to the swine industry.