Effects of low (modified-live virus vaccine) and high (VR-2385)-virulence strains of porcine reproductive and respiratory syndrome virus on pulmonaryclearance of copper particles in pigs

Seventy-five 3-week-old, crossbred pigs from a herd free of porcine reprodu ctive and respiratory syndrome virus (PRSSV) were randomly assigned to thre e groups: uninfected controls, pigs inoculated intranasally with RespPRRS/R epro(TM) modified-live virus vaccine (RespPRRS), and pigs inoculated intran asally with a high-virulence strain of PRRSV (VR-2385). Pigs were intraveno usly infused with 3% copper phthalocyanine tetrasulfonic acid (0.2 ml/kg) i n normal saline 30 minutes before necropsy, which was performed 3, 7, 10, 1 4, or 28 days postinoculation (DPI) with PRRSV. There were no differences i n serum copper concentration in samples collected at 0, 15, or 30 minutes a fter infusion. Copper concentrations in the lungs of VR-2385-inoculated pig s were significantly lower than levels in the lungs of control and RespPRRS -inoculated pigs at 7, 10, and 14 DPI (P < 0.05). The greatest difference b etween the groups was observed at 10 DPI. Liver and spleen copper concentra tions were slightly, but not significantly, higher in both PRRSV-infected g roups. The percentage of lung affected by grossly visible pneumonia ranged from 0 to 5.6% in the RespPRRS-inoculated group and from 15.2 to 46.4% in t he VR-2385-inoculated group, with lesions peaking at 7 and 10 DPI, respecti vely. PRRSV antigen was demonstrated in both pulmonary alveolar macrophages (PAMs) and pulmonary intravascular macrophages (PIMs) by immunohistochemic al methods. Copper particles were demonstrated in the PIMs by light microsc opy. PRRSV was isolated from bronchoalveolar lavage fluid of VR-2385-infect ed pigs from 3 to 28 DPI and from RespPRRS-inoculated pigs from 7 to 28 DPI . No PRRSV, PRRSV antibodies, or PRRSV-induced pneumonia was detected in th e control group. These results suggest chat 1) PRRSV has a detrimental effe ct on the: uptake of copper particles by PIMs, 2) the severity of PRRSV-ind uced damage to PIMs differs among strains, and 3) demonstration of PRRSV-in duced decreased pulmonary clearance supports the hypothesis that PRRSV infe ction may make pigs more susceptible to bacterial septicemia.