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Researchers of CReSA (Spain) have published a retrospective study suggesting that PCV2-lung disease is probably a negligible condition and porcine circovirus type 2 mainly contributes to porcine respiratory disease complex by means its systemic infection.
Porcine respiratory disease complex (PRDC) is the name used to describe a clinical presentation characterized by respiratory signs and poor growth in growing-finishing pigs. It is a multifactorial disease of mainly growing-finishing pigs with morbidity ranging from 10 to 40% and mortality varying from 2 to 20%.
The respiratory lesions in PRDC have a multifactorial aetiology, involving several potential viruses like porcine circovirus type 2 (PCV2). This virus has been mainly linked to PCV2-systemic disease (PCV2-SD). However, some reports have suggested that PCV2 can cause respiratory lesions in the absence of systemic lymphoid damage; this apparently different condition has been referred as PCV2-lung disease (PCV2-LD).
The present study analysed retrospectively the relation between PRDC and PCV2 infection from a pathological point of view. Of the 317 selected pigs suffering from PRDC and submitted for necropsy between 1998 and 2011, the most prevalent lesions were subacute interstitial pneumonia (27.7%) and the combination of subacute interstitial pneumonia plus catarrhal-purulent bronchopneumonia (28.4%). Two hundred and twenty-six pigs were positive for PCV2 by in situ hybridization (ISH). Among positive pigs for PCV2 ISH, 184 animals suffered from PCV2-SD. The rest of 42 PCV2 ISH positive pigs had no lymphoid lesions and low amount of viral nucleic acid in these tissues and, therefore, did not qualify for PCVD-SD; only 9 had concomitant PCV2 ISH positivity in the lung, also to a low amount.
In conclusion, all PRDC-PCV2 ISH positive cases had evidence of viral systemic infection. It is suggested that PCV2-LD is probably a negligible condition and PCV2 mainly contributes to porcine respiratory disease complex (PRDC) in relation to PCV2-SD occurrence.
Ticó G, Segalés J, Martínez J. The blurred border between porcine circovirus type 2-systemic disease and porcine respiratory disease complex. Vet Microbiol. 2013 May 3;163(3-4):242-7.
