Pathological Features and Genotyping of Mycobacterium avium sub spp. paratuberculosis (MAP) in Small Ruminants in...

Johne's disease, caused by Mycobacterium avium subsp. paratuberculosis (MAP), is endemic in Saudi Arabia and contributes to substantial production losses in small-ruminant herds. This study investigated MAP infection in 388 locally raised small ruminants (151 sheep and 237 goats) using IS900 real-time PCR (qPCR) on fecal samples and indirect ELISA on serum samples. Ziehl-Neelsen (ZN) staining and pathological assessment were applied as supportive tools in necropsied cases. Overall, qPCR detected MAP DNA in 135/388 animals (34.8%), with higher positivity in goats (100/237; 42.1%) than in sheep (35/151; 23.1%). ELISA detected MAP antibodies in 120/388 animals (30.9%), including 90/237 goats (37.9%) and 30/151 sheep (19.8%). Based on clinical examination (presence/absence of clinical signs), qPCR-positive animals were categorized as subclinical (n = 15; 10 goats and 5 sheep) or clinically progressed (n = 120; 90 goats and 30 sheep). Gross and histopathological findings were assessed in a necropsied subset (n = 20; 10 subclinical and 10 clinically progressed), revealing mild focal granulomatous enteritis with scant acid-fast bacilli in subclinical cases and diffuse lepromatous-type granulomatous lesions with abundant bacilli in clinically progressed animals. Genotyping and subtyping were performed on tissue-derived DNA from six necropsied cases using DMC, IS900, and F57 targets, and IS900 sequencing confirmed the circulation of both Type C/II and Type S/I MAP strains. Collectively, these findings demonstrate widespread MAP infection among small ruminants in Saudi Arabia, with higher detection rates and more pronounced pathology in goats, and highlight the genetic heterogeneity of circulating MAP strains.