Effect of vaccination on the potentiation of porcine reproductive and respiratory syndrome virus (PRRSV)-induced pneumonia by Mycoplasma hyopneumoniae.

Porcine reproductive and respiratory syndrome virus (PRRSV) and Mycoplasma hyopneumoniae are frequently isolated pathogens from pigs with respiratory disease. A previous study conducted in our laboratory found that infection with M. hyopneumoniae increased the duration and severity of respiratory disease induced by PRRSV. The purpose of this experiment was to determine whether vaccination against M. hyopneumoniae and/or PRRSV decreased the enhancement of PRRSV-induced pneumonia. Both M. hyopneumoniae bacterin and PRRSV vaccine decreased the severity of clinical respiratory disease. Infection or vaccination with PRRSV appeared to decrease the efficacy of the M. hyopneumoniae bacterin. Vaccination with M. hyopneumoniae bacterin decreased the potentiation of PRRSV-induced pneumonia observed in the dual infected pigs. However, PRRSV vaccination in combination with M. hyopneumoniae bacterin eliminated this benefit and the amount of pneumonia induced by PRRSV increased. PRRSV vaccine alone did not decrease the potentiation of PRRSV pneumonia by M. hyopneumoniae.