Epidemiological associations between Mycoplasma hyopneumoniae and Actinobacillus pleuropneumoniae antibody titers and lung lesions in Prince Edward Island swine herds

The frequencies of anteroventral (AV) lung lesions and pleuritis were determined and serological surveys for M. pleuropneumoniae (MH) and A. pleuropneumoniae (AP) were conducted on a minimum of 25 slaughter pigs from each of 18 randomly sampled Prince Edward Island farms (producing over 1000 market pigs per year). The data were analysed to evaluate the potential role of these 2 agents as risk factors for the 2 conditions, using crude and multivariable techniques, as well as individual and herd data. Anteroventral lung lesions were present in 50.5% of the pigs at slaughter, and pleuritis in 15.4%. Least squares multivariable regression was used to analyse the simultaneous ability of MH, AP and MH/AP interaction to predict the herd prevalence of AV lung lesions. Only MH was associated with AV lung lesions. In spite of a statistically significant association, MH accounted for only 53% of the herd variation in prevalence of lung lesions. Some herds maintained very low levels of lung lesions despite moderate (up to 30%) prevalence of MH. Discrepancies between the analytical techniques suggested that herd-level factors play an important role in the development of lung lesions. Pleuritis did not appear to be associated with either of the agents studied..