The role of co-infections in M. hyopneumoniae outbreaks among heavy fattening pigs: a field study.

Little is known about how co-infections and genotype dynamics affect Mycoplasma hyopneumoniae infection in fattening pigs. This study was aimed at assessing the role of co-infections in M. hyopneumoniae outbreaks, their influence on the presence of M. hyopneumoniae genotypes and their impact on consequent lung lesions. Tracheobronchial swabs (TBS) from 300 finishers were collected from 10 farms at the onset of enzootic pneumonia outbreaks and 1 month later, sampling of 3 groups per farm: Group A showed clinical signs first, Group B was housed near Group A, and Group C was located in a different building. Pigs' lungs were scored at the slaughterhouse. TBS were tested for the main pathogens involved in respiratory diseases, and samples positive for M. hyopneumoniae were genotyped by multiple-locus variable-number tandem repeat analysis (MLVA). Pigs in Group A showed the highest prevalence and load of M. hyopneumoniae. A positive association was detected between M. hyopneumoniae and Mycoplasma hyorhinis, whereas Actinobacillus pleuropneumoniae was more frequent when the M. hyopneumoniae load was higher. Nevertheless, co-infection had no effect on lung lesion scores. The presence of multiple MLVA types (mixed infections) increased in time only in pigs from Group C and was positively associated with porcine reproductive and respiratory syndrome virus infection. Lung lesions were more severe in pigs with at least one TBS positive for M. hyopneumoniae and in pigs with a history of mixed infections. The central role of M. hyopneumoniae and relevance of mixed infections suggest that increased biosecurity might be beneficial for lung lesion sequelae.