Investigating porcine parvovirus 3 infection using in situ polymerases chain reaction

Parvoviruses are small, non-enveloped icosahedral viruses ubiquitous in different animal species. Porcine parvovirus 3 (PPV3) or according to novel classification Ungulate tetraparvovirus 2 belongs to the Tetraparvovirus genus. PPV3 was found in tissues of healthy and sick pigs. The aim of this study was to detect PPV3, using two in situ methods that target nucleic acids, like in situ hybridization (ISH) and in situ polymerase chain reaction (IS-PCR) and to apply immunohistochemistry in order to detect host immune response or to determine expression of cell markers in infected cells.

To investigate its possible involvement in pathological conditions samples from 46 and 22 dead animals from two farms were examined – necropsied and checked for PPV3 including qRT-PCR to determined viral load 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, lysozyme, porcine reproductive and respiratory syndrome virus (PRRSV), swine influenza, Mycoplasma hyopneumoniae and ISH to detect PPV3, ssDNA and dsDNA of PCV2. PPV2 positive samples were submitted to in situ PCR including double staining method to detect PPV3 and cell markers.

Out of 46 lung and lymph node samples tested 10 were positive for the presence of PPV3. PPV3 level ranged between10²-10⁶ copies per gram of tissue. Reductions of lymphocytic depletion and of histiocytic infiltration were associated with PPV3 infection. Only one lung was positive by IS-PCR and was associated with moderate congestion, mixed inflammatory reaction, weak proliferation of alveolar walls. The alveolar spaces were filled with inflammatory cells were also affected by PRRSV. PPV3 was detected predominantly in bronchus, few areas with positive cells were observed in alveolar spaces in inflamed parts. Cells that expressed positive signal for PPV3 were mostly lymphocyte- and macrophage-like cells. Infected cells poorly expressed SLAIIDQ antigen, and not at all CD3 or lysozyme antigens.

We found that the PPV3 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 PPV3 may have a specific tropism for immature B lymphocytes and/or NK lymphocytes but possibly not T lymphocytes. Furthermore we were able to conclude that PPV3 may contribute to the pathogenesis of pneumonia

Disclosure of Interest: None Declared.