Effect of vaccination on dual infection with Mycoplasma hyopneumoniae and PRRSVE.L. Thackera, P.G. Halburb and B.J. Thackerb
a Veterinary Medical Research Institute, Iowa State University, 1802 Elwood Drive, Ames, IA 50010, USA
b Veterinary Diagnostics and Production Animal Medicine, Veterinary Clinical Center, Iowa State University, Ames, IA 50010, USA
Abstract - Porcine respiratory disease complex (PRDC) has become an economically significant respiratory disorder for pork producers. This complex, characterized by slow growth, decreased feed efficiency, lethargy, anorexia, fever, cough and dyspnea is especially common in grow-finish pigs at around 18 to 20 weeks of age. Diagnostic laboratories have isolated a number of pathogens from cases of PRDC. Of these pathogens, porcine reproductive and respiratory syndrome virus (PRRSV), Mycoplasma hyopneumoniae and swine influenza (SIV) are most frequently isolated. Vaccines against M. hyopneumoniae and PRRSV are commonly used as aids in controlling swine respiratory disease. Recently, our laboratory found that infection of pigs 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 observed in our previous study. One hundred eighteen pigs received either a mycoplasma bacterin at 3 and 5 weeks of age and/or a modified-live PRRSV vaccine at 4 weeks of age or no vaccine. Schering-Plough's M+Pac (M. hyopneumoniae bacterin) and BI/NOBL Laboratories's RespPRRS (modified live PRRSV vaccine) were used in this trial. The pigs were challenged with M. hyopneumoniae and/or PRRSV two weeks following the second M. hyopneumoniae vaccination. Necropsies were performed at 10 and 38 days post infection (DPI). Severity of clinical respiratory disease induced by PRRSV was decreased in pigs vaccinated against either M. hyopneumoniae and/or PRRSV. Vaccination with RespPRRSV resulted in the greatest decrease in clinical signs, but did not eliminate clinical disease. Vaccination against M. hyopneumoniae caused a slight, but significant decrease in PRRSV-induced clinical disease in dual infected pigs. At 10 DPI, pigs challenged with both PRRSV and M. hyopneumoniae had a greater percentage of lung affected by M. hyopneumoniae than pigs which received only M. hyopneumoniae. PRRSV-induced lesions were equivalent in all groups which received PRRSV, independent of vaccination status. Macroscopic lesions at 38 DPI confirmed our earlier findings of potentiation of PRRSV-induced pneumonia by M. hyopneumoniae infection. The percentage of pneumonia induced by M. hyopneumoniae at 38 DPI was equivalent in all groups with no differences observed in vaccinated groups. At 38 DPI the percentage of PRRSV-induced pneumonia in the groups challenged only with PRRSV and the group vaccinated with the M. hyopneumoniae bacterin and receiving both pathogens was significantly less than all other dual infected groups. The groups which received PRRSV vaccine and were challenged with both PRRSV and M. hyopneumoniae were equivalent in severity to the non-vaccinated group. Based on these findings, vaccination with either M. hyopneumoniae bacterin or PRRSV vaccine decreased the severity of clinical respiratory disease, but did not eliminate clinical disease. Interestingly, it appears that PRRSV infection increases the severity of M. hyopneumoniae-induced pneumonia early in the course of the disease (10 DPI). However, by 38 DPI, there was no difference in the severity of mycoplasmal lung lesions between groups. The presence of PRRSV, whether from vaccine or challenge, appeared to decrease the efficacy of the M. hyopneumoniae bacterin against mycoplasmal pneumonia. However, administration of M. hyopneumoniae vaccine alone significantly decreased the potentiation of PRRSV-induced pneumonia observed in the dual infected pigs. PRRSV vaccine administration in addition to M. hyopneumoniae vaccination resulted in a loss of this benefit and the percentage of pneumonia induced by PRRSV increased. PRRSV vaccine alone did not decrease the potentiation of PRRSV pneumonia by M. hyopneumoniae.
Corresponding author: E.L. Thacker Tel.: (1) (515) 294 5097; fax: (1) (515) 294 1401; email: email@example.com
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