Detection of Mycobacterium avium subsp. paratuberculosis in intestinal and mammary tissues and in lymph nodes of sheep with different techniques and its relationship with enteric lesions

Paratuberculosis is a widespread disease of ruminants caused by Mycobacterium avium subspecies paratuberculosis (MAP). For long time the infection has been believed as confined to the intestine. Disseminated infection in ruminants with MAP has gained more interest in recent years. In this study the histological lesions, the distribution of MAP in intestinal and mammary tissues of seropositive sheep and the sensitivity of direct diagnostic tests are evaluated. Histopathological lesions were observed in the proximal jejunum, distal jejunum and ileum of 19 sheep. Types 3b and 3c lesions were observed. Sheep with subclinical infection had type 3c ileal lesions, while clinically infected animals had mainly type 3b ileal lesions (p < 0.05). Ziehl–Neelsen (ZN) staining was more sensitive for detecting acid-fast bacilli in type 3b intestinal lesions than in type 3c (p < 0.05). Immunohistochemistry (IHC) was more sensitive than ZN staining in detecting infected intestinal samples (p < 0.05). PCR was the most sensitive technique in detecting MAP in both intestinal and extra-intestinal samples (p < 0.05). MAP was mainly observed in mammary tissues of sheep with type 3b intestinal lesions, although these findings were not statistically significant (p > 0.05). The number of MAP in the intestine might influence the clinical course and the local histopathological lesions, but probably further factors contribute to the discrimination between local and general infection.