PATHOGENESIS OF PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS-INFECTION IN GNOTOBIOTIC PIGS

The pathogenesis of porcine reproductive and respiratory syndrome viru s (PRRSV) was determined in gnotobiotic pigs by studying the sequentia l development of microscopic lesions and sites of virus distribution a nd replication. Thirty-two pigs (three pigs/infected group and one pig /control group) were inoculated by nasal instillation of either PRRSV isolate ATCC VR-2332 (total dose 10(2.6) TCID50) or uninfected cell cu lture supernatant. Infected and control pigs were euthanized at 12 hou rs, and 1, 2, 3, 5, 7, 14, and 21 days postexposure (PE). Gnotobiotic pigs experimentally infected with PRRSV were viremic by 12 hours PE an d subsequently developed pneumonia, lymphadenopathy, vasculitis, myoca rditis, and encephalitis. Lung lesions developed by day 3 PE, persiste d through day 21 PE and were characterized by alveolar septa thickened by macrophages, alveolar proteinaceous and karyorrhectic debris, alve olar syncytial cells, and multifocal type II pneumocyte hypertrophy. L ymph node lesions varied in distribution and severity and were charact erized by germinal center hypertrophy and hyperplasia, lymphocyte necr osis, multiple cystic spaces, and polykaryocytes within the cystic spa ces. Heart lesions were a late feature of infection and all infected p igs had heart lesions on day 21 PE characterized by subendocardial, my ocardial, and perivascular foci of lymphocytes. Vasculitis also varied in distribution and severity and affected all sizes of vessels. Resul ts of this experiment indicate that PRRSV is a multisystem disease cha racterized initially by viremia with subsequent virus distribution and replication in multiple organs causing interstitial pneumonia, vascul itis, lymphadenopathy, myocarditis, and encephalitis.