An assessment of the duration of Mycoplasma hyopneumoniae infection in an experimentally infected population of pigs

Mycoplasma hyopneumoniae (M. hyopneumoniae) is the primary pathogen of enzootic pneumonia (EP), a highly prevalent respiratory disease that affects pigs worldwide. Previous studies have demonstrated that M. hyopneumoniae infection can be longer than 185 days; however, the total duration of infection has not been determined yet. Therefore, the objective of this study was to determine the duration of M. hyopneumoniae infection in asymptomatic carriers. To achieve our goal, 60 pigs were inoculated with M. hyopneumoniae strain 232 and the persistence of M. hyopneumoniae in the respiratory tract was assessed by detection of the bacterial DNA in bronchial swabs and the ability of the infected pigs to transmit the pathogen to sentinels. Infection of the inoculated animals was demonstrated by the detection of M. hyopneumoniae DNA in nasal swabs, seroconversion to the bacteria and the onset of dry coughing. Experimentally infected pigs shed M. hyopneumoniae prior to and after the cough was observed. M. hyopneumoniae DNA was detected in 100% of experimentally infected pigs at 94 days post infection (dpi), 61% at 214 dpi and 0% at 254 dpi. Experimentally infected pigs transmitted the bacteria to sentinels at 80 and 200 dpi. Results of this study have demonstrated that M. hyopneumoniae infected pigs can be incubatory as well as convalescent carriers of the pathogen and that convalescent carriers can remain infectious for up to 200 days. Total clearance of M. hyopneumoniae in the group was evidenced, demonstrating that duration of M. hyopneumoniae infection lasts less than 254 days.