Estimation of the sensitivity of four sampling methods for Mycoplasma hyopneumoniae detection in live pigs using a Bayesian approach.

Four sampling techniques for Mycoplasma hyopneumoniae detection, namely nasal swabbing, oral-pharyngeal brushing, tracheo-bronchial swabbing and tracheo-bronchial washing, were compared in naturally infected live pigs. In addition, a quantitative real-time PCR assay for M. hyopneumoniae quantification was validated with the same samples. 60 finishing pigs were randomly selected from a batch of contemporary pigs on a farm chronically affected by respiratory disorders. Each pig was submitted to nasal swabbing, oral-pharyngeal brushing, tracheo-bronchial swabbing and tracheo-bronchial washing. Nested-PCR and real-time PCR assays were performed on all samples. A Bayesian approach was used to analyze the nested-PCR results of the four sampling methods (i.e. positive or negative) to estimate the sensitivity and specificity of each method. M. hyopneumoniae was detected by nested-PCR in at least one sample from 70% of the pigs. The most sensitive sampling methods for detecting M. hyopneumoniae in live naturally infected pigs were tracheo-bronchial swabbing and tracheo-bronchial washing, as compared to oral-pharyngeal brushing and nasal swabbing. Swabbing the nasal cavities appeared to be the least sensitive method. Significantly higher amounts of M. hyopneumoniae DNA were found at the sites of tracheo-bronchial sampling than in the nasal cavities or at the oral-pharyngeal site (p<0.001). There was no difference between the tracheo-bronchial washing and the tracheo-bronchial swabbing results (p>0.05). Our study indicated that tracheo-bronchial swabbing associated with real-time PCR could be an accurate diagnostic tool for assessing infection dynamics in pig herds.