Retrospective Analyses of Porcine Circovirus Type 3 (PCV-3) in Switzerland

Abstract

Porcine circovirus 3 (PCV-3) has emerged as a significant pathogen affecting global swine populations, yet its epidemiology and clinical implications remain incompletely understood. This retrospective study aimed to investigate the prevalence and histopathological features of PCV-3 infection in pigs from Switzerland, focusing on archival cases of suckling and weaner piglets presenting with suggestive lesions. An in-house qPCR assay was developed for detecting PCV-3 in frozen and formalin-fixed paraffin-embedded tissues, enhancing the national diagnostic capabilities. Histopathological reassessment identified PCV-3 systemic disease (PCV-3-SD) compatible lesions in 19 (6%) of archival cases, with 47% testing positive by qPCR across various organs. Notably, vascular lesions predominated, particularly in mesenteric arteries, heart, and kidneys. The study confirms the presence of PCV-3 in Switzerland since at least 2020, marking the first documented cases within the Swiss swine population. Despite challenges in in situ hybridization validation due to prolonged formalin fixation, the findings indicate viral systemic dissemination. These results contribute to the understanding of PCV-3 epidemiology in Swiss pigs, emphasizing the need for continued surveillance and further research on its clinical implications and interaction with host factors. Our study underscores the utility and limitations of molecular techniques in confirming PCV-3 infections.

Keywords: PCV-3 systemic disease (PCV-3-SD); diagnostic; histopathology; in situ hybridization (ISH); porcine circovirus 3 (PCV-3); real-time quantitative polymerase chain reaction (qPCR); tissue microarray (TMA); vascular lesions.

Figure 1

Examples of histopathological cardiac and renal lesions associated with PCV-3-SD: (a) Severe lymphoplasmacytic (peri-)arteritis in an epicardial artery, H&E. Bar 250 µm; (b) Severe lymphoplasmacytic (peri-)arteritis in multiple arteries in the renal pelvis, H&E. Bar 500 µm. Insert: Mononuclear infiltration of the arterial wall.

Figure 2

Examples of histopathological lesions of the mesenteric vascular plexus associated with PCV-3-SD and periarteritis score: (a) Severe (++; ≥20% affected arteries) lymphoplasmacytic and histiocytic (peri-)arteritis in mesenteric arteries, H&E. Bar 500 µm. Insert: Mononuclear infiltration in tunica adventitia; (b) Mild (+; ≤20% affected arteries) lymphoplasmacytic and histiocytic (peri-)arteritis in mesenteric arteries, H&E. Bar 500 µm.

Figure 3

Comparative results of ISH on the mesenteric vascular plexus between a positive control case (a,c) and the selected archival case (b,d), hematoxylin counterstain: (a) Marked PCV-3-ISH-RNA-positive signal in multiple arteries. Bar 250 µm; (b) PCV-3-ISH-RNA no to weak signal. Bar 250 µm; (c) Marked PCV-3-ISH-RNA-positive signal (brown) in the arterial wall. Bar 50 µm; (d) PCV-3-ISH-RNA-weak-positive signal (arrow) in the vascular wall of an artery. Bar 100 µm.