Simultaneous Porcine Circovirus Type 2 and Mycoplasma hyopneumoniae Co-inoculation does not Potentiate Disease in Conventional Pigs

The aim of this study was to assess the effect of simultaneous experimental inoculation of porcine circovirus type 2 (PCV2; intranasal delivery) and Mycoplasma hyopneumoniae (Mhyo; transtracheal delivery) into conventional, seropositive 6-week-old piglets. Thirty-six male piglets were assigned randomly to four groups: control (n = 6), PCV2 (n = 6), Mhyo (n = 12) and PCV2 + Mhyo (n = 12). Blood samples and faecal and nasal swabs were collected at 0, 7, 14 and 21 days post inoculation (dpi). No significant clinical signs attributable to PCV2 infection were observed during the experiment. Coughing was recorded in three pigs from the Mhyo group and six from the PCV2 + Mhyo group. No significant differences in mean body weight and rectal temperature were observed between the groups. Mild microscopical lesions similar to those reported for post-weaning multisystemic wasting syndrome were observed in two PCV2 pigs and in one PCV2 + Mhyo animal. Mhyo-compatible lung lesions were observed in 21/24 pigs inoculated with Mhyo (10 from the Mhyo group and 11 from the PCV2 + Mhyo group). PCV2 was detected by in-situ hybridization in 3/12 PCV2 and in 4/12 PCV2 + Mhyo animals. No significant differences in PCV2 load (serum and nasal and faecal swabs), duration of viraemia or antibody titre were detected between PCV2-inoculated groups. No significant differences in Mhyo load in nasal swabs, percentage of Mhyo-seropositive pigs and mean lung score was detected between Mhyo-inoculated groups. Under the conditions of the present study, concurrent inoculation of PCV2 and Mhyo did not result in potentiation of clinical signs and lesions attributed to either infection.