Study of caprine paratuberculosis detected during official bovine tuberculosis eradication program in slaughterhouses of the Canary Islands.

Abstract

Paratuberculosis (PTB), also known as Johne’s disease (JD), is an infectious disease caused by Mycobacterium avium subsp. paratuberculosis (MAP), which primarily affects ruminants. The lesions it produces in infected animals result in decreased carcass weight, milk production, and income for affected farms due to culling. In this retrospective study, 529 cases were retrieved from the histopathology archive, corresponding to goats sampled at slaughterhouses in the Canary Islands, which were culled as part of the Programa Nacional de Erradicación de Tuberculosis Bovina (PNETB) during the period 2005-2019. After applying inclusion and exclusion criteria, 310 cases were selected for analysis. The absolute and relative frequencies of the comparative intradermal tuberculin test (CIT-test), origin and geographical distribution of the cases, and the gross and microscopic lesions compatible with PTB were described. Lesions were classified using qualitative methods, and statistical analyses were performed with IBM SPSS 29 software. Most cases originated from Gran Canaria, which were distributed across 71.4% (15/21) of its municipalities. Of all animals analyzed, 83.5% tested positive, 12.9% negative, and 3.5% doubtful on the CIT-test. Gross and microscopic lesions were identified in the mesenteric lymph node (MSLN) and/or ileocecal valve (ICV) in 21.9% and 32.3% cases, respectively. According to microscopic grading, grade IV lesions predominated in the MSLN, while the most frequently observed lesions in the ICV were mild in severity and multifocal in distribution. The agreement between gross and microscopic diagnoses, assessed using the Kappa statistic, ranged from slight to poor. The geographic distribution of the cases analyzed in most municipalities of Gran Canaria contributes to evidence that the disease is endemic in the region. The high percentage of animals that tested positive for the CIT-test and those without lesions reflects the test’s low sensitivity and cross-reactions with other mycobacateria. Finally, the agreement between gross and microscopic diagnoses of MSLN and/or ICV lesions was poor, highlighting the need to incorporate histopathological examination as a routine for the diagnosis of PTB.