Interaction between Mycoplasma hyopneumoniae and swine influenza virus

An experimental respiratory model Was used to investigate the interaction b etween Mycoplasma hyopneumoniae and swine influenza virus (SIV) in the indu ction of pneumonia in susceptible swine. Previous studies demonstrated that M. hyopneumoniae, which produces a chronic bronchopneumonia in swine, pote ntiates a viral pneumonia induced by the porcine reproductive and respirato ry syndrome virus (PRRSV). In this study, pigs were inoculated with M. hyop neumoniae 21 days prior to inoculation with SIV. Clinical disease as charac terized by the severity of cough and fever was evaluated daily. Percentages of lung tissue with visual lesions and microscopic lesions were assessed u pon necropsy at 3, 7, 14, and 21 days following SIV inoculation, Clinical o bservations revealed that pigs infected with both SN and M. hyopneumoniae c oughed significantly more than pigs inoculated with a single agent. Macrosc opic pneumonia on necropsy at days 3 and 7 was greatest in both SIV-infecte d groups, with minimal levels of pneumonia in the M. hyopneumoniae-only-inf ected pigs, At 14 days post-SIV inoculation, pneumonia was significantly mo re severe in pigs infected with both pathogens. However, by 21 days postino culation, the level of pneumonia in the dual-infected pigs was similar to t hat of the M. hyopneumoniae-only-infected group, and the pneumonia in the p igs inoculated with only SIV was nearly resolved. Microscopically, there wa s no apparent increase in the severity of pneumonia in pigs infected with b oth agents compared to that of single-agent-challenged pigs, The results of this study found that while pigs infected with both agents exhibited more severe clinical disease, the relationship between the two pathogens lacked the profound potentiation found with dual infection with M. hyopneumoniae a nd PRRSV. These findings demonstrate that the relationship between mycoplas mas and viruses varies with the individual agent.