Microbiological assessment of sheep lymph nodes with lymphadenitis found duringpost-mortemexamination of slaughtered sheep: implications for veterinary-sanitary meat control

Background Microbiological examination of lesions found in slaughtered animals during meat inspection is an important part of public health protection as such lesions may be due to zoonotic agents that can be transmitted by meat. Examination of inflamed lymph nodes also plays a particular important role, as lymphadenitis may reflect a more widespread infection. Such lesions in sheep are mainly caused by pyogenic bacteria but also mycobacteria are occasionally found. Meat inspection data from 2017 to 2018 from southern Poland, especially from the Malopolska region, indicate that purulent or caseous lymphadenitis involving the mediastinal and tracheobronchial lymph nodes (MTLNs) is a common finding. The primary aim of the current study was to determine the aetiology of these lesions. Furthermore, it was investigated how presence of lesions was correlated with age and grazing strategy of affected sheep. Results Post-mortemexamination revealed purulent or caseous lymphadenitis in the MTLNs of 49 out of 284 animals (17.3%). Subsequent microbiological examination revealed the presence ofCorynebacterium pseudotuberculosis(34.7%),Streptococcus dysgalactiaesubsp.equisimilis(34.7%),Staphylococcus aureus(8.2%),Enterococcusspp. (2.0%),Trueperella pyogenes(2.0%), and beta-haemolytic strains ofEscherichia coli(2.0%).Mycobacteriumspp. andRhodococcus equiwere not detected. In older sheep, the probability of the presence of purulent or caseous lymphadenitis was higher than in younger, and the risk was increasing by 1.5% with each month of life. Sheep grazing locally had 4.5-times greater risk of having purulent or caseous lymphadenitis than individuals summer grazing in the mountains. Conclusion The most common aetiological agents of purulent or caseous lymphadenitis in the MTLNs of sheep in the Malopolska region wereC. pseudotuberculosisandS. dysgalactiaesubsp.equisimilis. Particular attention duringpost-mortemexamination should be paid to the carcasses of older sheep and sheep grazing on permanent pastures, as they seem more prone to develop purulent or caseous lymphadenitis.