The effects of Mycoplasma hyopneumoniae on porcine circovirus type 2 replication in vitro PK-15 cells

•We developed PCV2-Mhp co-infection model in vitro.•We examined PCV2 replication in vitro by co-infection with Mhp.•Mhp co-infection can elicit substantive enhancement of PCV2 replication in the model system.•PCV2 replication co-infected with Mhp was related to different factors of Mhp.

Porcine circovirus type 2 (PCV2) is the causative agent of postweaning multisystemic wasting syndrome (PMWS). Mycoplasma hyopneumoniae (Mhp) is a very well-known co-factor that potentially enhances PCV2 replication and thus the development of PMWS. However, co-infection with Mhp and PCV2 in vivo under different conditions can produce divergent clinical signs and lesions. In this study, PCV2 replication could be enhanced by subsequent co-inoculation with Mhp (PCV2 + Mhp) in a time and dose dependent method, but not by prior (Mhp + PCV2) or simultaneous (Mhp/PCV2) co-inoculation. Furthermore, different magnitudes of PCV2-infected cells, varying from 150% ± 14% to 351% ± 28%, were detected when co-infected with different Mhp strains. The relative percentage of PCV2-infected cells greatly decreased from 351% ± 28 to 141% ± 18 when the Mhp strain was treated with UV light for 12 h. These results offer the evidences to better understand the complex clinical syndromes in Mhp/PCV2 co-infection cases, and the occurrence of PMWS.