Detection of M. hyopneumoniae infections in live pigs is difficult for the producer, the field veterinarian and the diagnostician. This study was designed and performed with the objective to compare various samples types and diagnostic assays for their sensitivity to detect pigs infected with M. hyopneumoniae during the first 4 weeks after experimental infection. All testing and comparisons was performed in a side-by-side fashion. Twenty three 8-week old M. hyopneumoniae free pigs were employed in this investigation. Two pigs were housed in an experimental room and served as non-infected controls. A group of 21 pigs were divided into three experimental rooms (7 pigs per room), were intra-tracheally inoculated with a strain of M. hyopneumoniae of moderate virulence, and were sampled a total of 7 times during 4 weeks, being 0, 2, 5, 9, 14, 21 and 28 days after inoculation. Blood samples, nasal swabs, laryngeal swabs, trachea-bronchial lavages and oral fluids were collected every time pigs were sampled. Bronchial swabs and lung lavages were collected at the last day of sample collection, after euthanasia. Also, lung lesions were blindly scored in all pigs after euthanasia. Control pigs remained negative to M. hyopneumoniae throughout the study. Genetic material from M. hyopneumoniae was detected in various percentages of the experimentally infected pigs on days 5, 9, 14, 21 and 28 after experimental infection by means of nasal swabs, laryngeal swabs and trachea-bronchial lavages. M. hyopneumoniae was detected in oral fluids obtained from 2 of the 3 rooms housing infected pigs at 9 and 28 days after infection. Commercial ELISA assays detected experimentally infected pigs at days 21 and 28 after infection. The sensitivity of the various commercial ELISA assays to detect M. hyopneumoniae antibodies used in this investigation was similar. IgM was detected in experimentally infected pigs at 9, 14 and 21 days after infection. IgA was detected in trachea-bronchial lavages at 28 days after infection, but was not detected in oral fluids at any sampling point. M. hyopneumoniae specific proteins in serum were only observed in a small proportion of pigs at 28 days after infection. In summary, the results of this study suggest that the combination of PCR testing in laryngeal swabs was the most sensitive tool for M. hyopneumoniae detection in live pigs during the first 4 weeks after infection, followed by tracheo-bronchial lavages, nasal swabs and oral fluids.
Contact information: Dr. Maria Pieters – [email protected]