Detection Rates of Porcine Reproductive and Respiratory Syndrome Virus, Porcine Circovirus Type 2, and Swine Influenza Virus in Porcine Proliferative and Necrotizing Pneumonia

Abstract

A retrospective study on pig lung tissues from 60 cases of proliferative and necrotizing pneumonia (PNP) was performed to determine the presence of porcine reproductive and respiratory syndrome virus (PRRSV), swine influenza virus (SIV), and porcine circovirus type 2 (PCV2) in these lesions. Cases selected included 30 cases diagnosed between 1988 and 1992 and 30 cases diagnosed between 1997 and 2001. In each group of 30 cases, 10 were from suckling piglets, whereas the other 20 were from postweaned animals representing either nursery or grower-finisher pigs. Immunohistochemistry using a monoclonal antibody to influenza virus type A was used to determine the presence of SIV, and in situ hybridization was used for the detection of PRRSV and PCV2 nucleic acids. PRRSV was detected in 55 of the 60 cases examined (92%), PCV2 in 25 cases (42%), and SIV in only 1 case (2%). In 30 cases (50%), PRRSV was the only virus detected, whereas in 25 other cases (42%), a combination of PRRSV and PCV2 could be detected in the lungs with PNP lesions. PCV2 could not be detected in the lungs of suckling pigs with PNP. All PCV2-positive cases were found in postweaned pigs and were always in combination with PRRSV. In this latter age group, PCV2 was detected in 63% of the cases (25/40). Data from our study indicate that SIV is rarely identified in PNP and that PCV2 infection is not essential for the development of PNP lesions. The results of the present study demonstrate that PRRSV is consistently and predominantly associated with PNP and should be considered the key etiologic agent for the condition.

Immunohistochemical Detection of Aetiological Agents of Proliferative and Necrotizing Pneumonia in Italian Pigs

“…The results of the present study therefore suggest that the major aetiological agents of PNP in Italian pigs are PRRSV and PCV2, as previously documented in Canadian (Drolet et al, 2003) and European (Pesch et al, 2000;Grau-Roma and Segale´s, 2007) studies. However, the results of our investigation are more aligned with those of the Canadian study, in which PRRSV infection was more consistently demonstrated, rather than the European study that suggested a dominant role for PCV2 infection in PNP.…”

“…This finding is not dissimilar to those of other investigations. Grau-Roma and Segale´s (2007) detected no agents in eight out of 74 cases (10.8%) and Drolet et al (2003) described four out of 60 samples (7%) as negative for all agents for which they tested. The relatively higher percentage of negative samples in the present study probably reflects the smaller number of agents investigated.…”

“…On gross necropsy examination, PNP is characterized by consolidation and red-brown to grey discolouration of the lungs, with lesions generally localized to the cranial and middle lobes and the cranioventral portions of the caudal lobes (Morin et al, 1990). Microscopical examination reveals aggregation of necrotic cells and granular debris within the alveolar spaces together with hyperplasia and hypertrophy of type II pneumocytes (Morin et al, 1990;Larochelle et al, 1994;Drolet et al, 2003;Segale´s et al, 2004). Additionally, there is interstitial pneumonia of varying severity, with or without necrotizing bronchiolitis and/ or bronchopneumonia.…”

“…Larochelle et al (1994) attributed PNP to porcine reproductive and respiratory syndrome virus (PRRSV), demonstrating the presence of the virus in 28 out of 38 pneumonic lungs. Subsequent Canadian (Drolet et al, 2003) and European studies (Pesch et al, 2000;Grau-Roma and Segale´s, 2007) have reported the frequent concurrence of PRRSV and porcine circovirus type 2 (PCV2) in lungs with PNP. The Canadian study commonly demonstrated PRRSV infection in PNP, with concurrent PRRSV and PCV2 in 42% of cases; however, PRRSV was never the sole aetiological agent recovered.…”

“…In addition to PRRSV and PCV2, SIV (Pesch et al, 2000;Drolet et al, 2003;Grau-Roma and Segale´s, 2007) and ADV (Grau-Roma and Segale´s, 2007) are suspected to be aetiological agents for PNP. ADV is considered to be a causal agent of necrotizing pulmonary lesions in pigs in Spain (Segale´s et al, 1997;Grau-Roma and Segale´s, 2007), although in those studies only one of 74 pigs with PNP had ADV identified in pulmonary tissue and that animal was coinfected with PCV2 (Grau-Roma and Segale´s, 2007).…”