Myeloid to Erythroid (M: E) ratio in the evaluation of bone marrow cytology of Porcine Circovirus type 2 affected pigs

Abstract

Porcine circovirus associated diseases (PCVAD) caused by porcine circovirus type-2 (PCV-2) are emerging viral diseases with unfavourable effects on animal health and swine economy. We have a lot of information regarding the changes in the lymphoid organs and spleen in PCV-2 infected pigs whereas the reason for anaemic changes in the carcasses and the pathological effects of PCV-2 in bone marrow are still not well studied. Hence, an extensive study to identify the changes in myeloid and erythroid cells of bone marrow in PCV-2 infected pigs was carried out. Myeloid and erythroid series of cells were counted and analysed from the freshly collected bone marrow cytological smears from the PCV-2 suspected samples. Later, PCV-2 infection was confirmed by polymerase chain reaction (PCR) and characteristic histopathological findings. The PCR yielded an amplicon of ~ 481 bp product and those positive cases were selected for determining the Myeloid to Erythroid ratio (M : E ratio). However, values did not significantly differ in any of the cellular components between PCV-2 positive animals and PCV-2 negative animals which indicated that the bone marrow was not the specific target organ for PCV-2 viral infections. However, increased lympho-histiocytic and plasmacytic infiltration was noticed in both lymphoid and non-lymphoid organs. These characteristic features of PCV-2 infection could be considered as a major reason for increased proliferation of myeloid cells.