Detection of porcine reproductive and respiratory syndrome virus, porcine circovirus type 2, swine influenza virus and Aujeszky's disease virus in cases of porcine proliferative and necrotizing pneumonia (PNP) in Spain

Proliferative and necrotizing pneumonia (PNP) is a severe form of interstitial pneumonia characterised by hypertrophy and proliferation of pneumocytes type 2 and presence of necrotic cells within alveoli lumen. Many viral agents have been linked to PNP aetiology, with especial emphasis on porcine reproductive and respiratory syndrome virus (PRRSV). To gain knowledge on PNP causality, a retrospective study on 74 PNP cases from postweaning pigs from Spain was carried out. Coupled with histopathological examinations, the presence of porcine circovirus type 2 (PCV2) by in situ hybridization (ISH), and PRRSV, swine influenza virus (SIV) and Aujeszky's disease virus (ADV) by immunohistochemical (IHC) methods, were investigated. PCV2 was the most prevalent viral agent in PNP cases (85.1%) followed by PRRSV (44.6%); 39.1% of PNP cases showed PCV2 as the solely detected agent, while only 4.1% had PRRSV as the unique pathogen. SIV and ADV were very sporadically detected in PNP cases, and always in co-infection with PCV2. Therefore, present data indicate that PCV2 is the most important aetiological agent in PNP cases from Spain and that PRRSV is not essential for the development of PNP. Taking into account the presented results and available literature, we suggest that PCV2 is possibly the main contributor to PNP cases in Europe while PRRSV could play a similar role in North America.