Comparative effectiveness of different biological specimens for PRRSv detection in naturally infected fattening pigs.

One of the most critical aspects of PRRS outbreak control in swine herds is the reliable virus detection in both newly introduced animals and replacement gilts. In present study we compared the effectiveness of different biological specimens which - alone or in combination - allow to detect PRRSv carrier animals by mean of Reverse Transcriptase nested PCR (RT-nPCR). Five different matrices (serum, nasal swab, oral fluid, tracheobronchial swab and bronchoalveolar lavage fluid - BALF), known to be effective for PRRSv detection, were included in diagnostic efficacy comparison. Thirty-five pigs newly introduced into a fattening unit of a PRRS chronically affected farm were randomly selected to be submitted to serial sampling of each of the matrices above described, during the first three months of fattening period. A Bayesian approach was used to analyze the RT-nPCR results (i.e., positive or negative) of each sampling method and their respective sensitivity was estimated. PRRSv was detected by RT-nPCR in at least one matrix from 58% to 100% of the pigs. Tracheobronchial swabbing, as well as the combination of tracheobronchial swabbing plus bronchoalveolar washing, or tracheobronchial swabbing plus serum sampling were proved to be the most sensitive sampling methods to detect PRRSv in naturally infected live pigs. This study enlightens as the tracheobronchial swabbing associated with RT-nPCR could be the most recommended diagnostic tool for assessing infection dynamics in pig herds.