Investigating porcine parvovirus 2 infection using in situ polymerases chain reaction

Porcine parvovirus 2 (PPV2) was detected in swine serum without showing any relation with a disease. The emergence of the virus seemed to be a unique event until other, genetically highly similar parvoviruses were identified in China while later in 2012 the presence of the virus was also described in Europe. Phylodynamic analysis indicated that PPV2 must have been around in Europe since 1920 in domestic and sylvatic hosts. It seems that PPV2 is widely distributed in pig populations and it is suspected to be involved in respiratory conditions of pigs, based on the frequent detection of the virus in lung samples

In order to investigate its possible implication in pathological conditions samples from 46 and 22 dead animals from two farms were examined – necropsied and checked for PPV2 and PCV2 by PCR; tissue embedded in paraffin block was submitted to H&E and Brown and Brenn staining, immunohistochemistry (IHC) to detect CD3, CD79α, swine leukocyte antigen class II DQ (SLAIIDQ), lysozyme, porcine reproductive and respiratory syndrome virus, swine influenza, Mycoplasma hyopneumoniae and in situ hybridization to detect ssDNA and dsDNA of PCV2. PPV2 positive samples were submitted to in situ PCR (IS-PCR) including double staining method to detect PPV2 and cell marker

We found that PPV2 increased intensity of bleedings in lymph nodes and was associated with the increased amount of PCV2 in lymph follicles and decreased replication of PCV2 in lymph follicles, cortex and around blood vessels, appeared to cause higher reduction of alveolar spaces as well as more inflamed cells in alveolar spaces. PPV2 was detected in lungs, lymph nodes, liver and spleen in 4 out of 22 animals of the second farm. Using IS-PCR moderate to severe infection of PPV2 was detected in three lungs. Extensive areas were infected and positive signals were mostly found in lymphocyteand macrophage-like cells in alveolar space. PPV2-positive lungs were associated with strong congestion, lymphocytic infiltration, reduction of alveolar spaces, and necrosis of ciliary epithelial. PPV2 infected cells did not express any of the studied markers or mainly but very poorly the SLAIIDQ antigen.

We found that the PPV2 was localized mostly in lymphocytes in lungs, lymph nodes and liver. Neither CD3 antigen nor lysozyme was expressed by these infected cells. In contrast low level of SLAIIDQ was expressed by infected cells suggesting that PPV2 may have a specific tropism for immature B lymphocytes and/or NK cells but possibly not T lymphocytes. We were able to conclude that PPV2 may contribute to the pathogenesis of pneumonia.

Disclosure of Interest: None Declared.