Low temperature and dust favour in vitro survival of Mycoplasma hyopneumoniae: time to revisit indirect transmission in pig housing.

Porcine enzootic pneumonia (EP) caused by Mycoplasma hyopneumoniae adversely affects pig welfare and is associated with major economic losses in the pig industry worldwide. Transmission is predominantly by direct contact, but the role of indirect transmission remains poorly understood. This study examined survival of six M. hyopneumoniae isolates dried onto five different surfaces encountered in pig units and exposed to temperatures of 4, 25 and 37°C for up to 12 days. Survival of the organisms was determined by recovering the organism from the surface material and culturing in Friis broth. Data were analysed by logistic regression to identify factors influencing survival of M. hyopneumoniae. Maximum survival was 8 days for all isolates on at least one surface (except stainless steel) at 4°C and was limited to 2 days at 25 and 37°C. Overall, dust and polypropylene copolymer supported M. hyopneumoniae survival the longest when compared with other surface materials. In conclusion, we have demonstrated that M. hyopneumoniae can survive outside the host for at least 8 days.

SIGNIFICANCE AND IMPACT OF THE STUDY: Understanding the transmission of Mycoplasma hyopneumoniae and optimizing biosecurity practices are keys to reducing the use of antimicrobial agents to control this pathogen. Direct transmission of the pathogen between pigs is the main route of spread and its lack of cell wall may compromise its resilience outside the host. The results from our study show that M. hyopneumoniae can survive for up to several days on dry surfaces and therefore may have the potential to infect pigs by indirect transmission. Factors influencing the survival of M. hyopneumoniae outside the host are further elucidated.