Comparative pathogenicity of three Korean and one Lelystad type 1 porcine reproductive and respiratory syndrome virus (pan-European subtype 1) isolates in experimentally infected pigs.

The aim of this study was to compare the pathogenicity of three type 1 porcine reproductive and respiratory syndrome virus (PRRSV) isolates that originated from Korean herds with varying severity of respiratory disease with one Lelystad virus. An experimental infection model was used to study virus distribution, sites of viral replication, viraemia, gross and microscopical lesions and the humoural immune response. Each virus isolate was given intranasally to 3-week-old pigs. Differences were found in the severity of gross and microscopical pulmonary lesions and the distribution of virus-labelled cells in lung and lymph nodes (LNs). The gross and microscopical pulmonary lesion scores were significantly greater in pigs inoculated with the SNUVR100744 isolate. The distribution of PRRSV-labelled cells within tissues and organs was similar for the different virus isolates; however, significantly more PRRSV-positive cells were detected in the lung and LNs of pigs inoculated with the SNUVR100744 isolate than were detected in the same tissues of pigs inoculated with Lelystad virus. The results of the present study demonstrate that type 1 PRRSV isolates differ in their ability to induce viral replication in tissues and induce interstitial pneumonia in pigs.