Porcine circovirus type 2 (PCV2) is a significant viral pathogen in pig populations which can cause a multi-systemic syndrome known as porcine circovirus-associated diseases (PCVAD). This syndrome is associated with high economic loss due to decrease in production.
This study aimed to assess PCV2 infection using histopathology, immunohistochemistry (IHC) and quantitative polymerase chain reaction (qPCR) on tissues (mediastinal lymph node, spleen, tonsil and lung) and serum samples collected from slaughtered pigs (N = 47) that were healthy (12/47), had mild or moderate (20/47) and severe (15/47) respiratory signs in the Philippines. Histopathology was performed on haematoxylin-eosin-stained sections, while a specific mouse monoclonal anti-PCV2 antibody (Ingenasa) was used for IHC. qPCR result of >106 copies/ml of serum was considered consistent with clinical disease.
The following typical characteristic lesions of PCV2 infection were observed in the lymph nodes of eight animals: lymphoid depletion (8/8) and granulomatous inflammation (1/8). Four from these eight pigs were negative for both IHC and qPCR. IHC revealed PCV2 antigen in eight pigs (8/47) in at least one of the tissues: lymph nodes (5), spleen (3), tonsils (4) and lungs (5). PCV2 antigen was observed in three lymph nodes with lymphoid depletion and one lymph node with depletion and granulomatous inflammation. One pig with lymphoid depletion was negative for qPCR but had PCV2 antigen in MLN, tonsil and lung; two pigs with lymphoid depletion had <106 copies/ml serum - one had PCV2 antigen in MLN and the other had it in spleen and one pig with lymphoid depletion and granulomatous inflammation had >106 copies/ml serum and had PCV2 antigen in all tissues. One pig showed >106 as well that did not show histopathology lesions but had PCV2 antigen in spleen and tonsil. Based on these findings, it is suggestive that PCV2 clinical disease is present in the Philippines. Additionally, more samples are currently analysed for further evaluation to see the correlation of the different detection methods used.