Comparison of postmortem airway swabs and lung tissue for detection of common porcine respiratory pathogens by bacterial culture and polymerase chain reaction assays

Abstract

Objective: To compare pathogen detection from tracheobronchial swabs with lung tissue in diagnostic submissions from pigs with reported respiratory disease. Materials and methods: Individual lung samples (n = 153) from 133 laboratory submissions were included in this study. Inclusion criteria were a lung sample where the tracheal bifurcation or major bronchus was readily identifiable and a clinical report of respiratory disease symptoms. Sterile, nylon-locked swabs were used to sample the largest available airway before the lung tissue was routinely processed for diagnostic testing. Swabs were placed in Amies transport medium and tested in blinded parallel with the lung tissue by bacterial culture and polymerase chain reaction (PCR) for common swine respiratory pathogens. Results: there was excellent agreement between PCR detection from lung and bronchial swab samples for porcine reproductive and respiratory syndrome virus, influenza A virus, Mycoplasma hyopneumoniae, and porcine circovirus 2 (kappa > 0.8, all assays). Agreement between bacterial culture from lung and swabs was substantial for Pasteurella multocida and Salmonella spp. And fair for Streptococcus suis. Lung tissue was culture positive more offen than swabs for Haemophilus parasuis and Actinobacillus spp.; however, in these cases, PCR for the respective pathogen was 100% positive on swab samples regardless of culture status of the swab. Implications: Tracheobronchial swabs are a single, uniform sample that can be easily collected at postmortem and transported to the laboratory for detection of swine respiratory pathogens by culture and PCR. Such swabs may serve as a rapid screening tool for unexpected mortalities in a population.