Pathological Findings of Paratuberculosis in Sheep and Goats: Gross and Histopathological Features

Paratuberculosis (PTB), or Johne's disease, is a chronic granulomatous disease that primarily affects the intestinal tract of sheep and goats. While clinical examination and laboratory testing are essential for diagnosis, postmortem and histopathological findings provide valuable confirmation and improve understanding of disease progression. Recognizing the characteristic lesions associated with PTB can help veterinarians strengthen diagnostic accuracy, particularly in chronic wasting cases where the diagnosis remains uncertain during life. 

Gross Pathological Findings in Sheep 

The intestinal tract is the primary site of pathological change in sheep affected by PTB. During necropsy, one of the most consistent findings is thickening of the intestinal wall, particularly near the ileocecal junction. The intestinal mucosa often appears folded and corrugated, reflecting the chronic inflammatory process within the bowel^1,2. 

Although lesions may extend to other intestinal segments, the terminal ileum generally exhibits more pronounced changes than the cecum or colon². Careful examination of this region during necropsy can therefore improve the likelihood of identifying characteristic lesions. 

Regional lymph nodes should also be evaluated thoroughly. Edematous enlargement of the ileocecal and mesenteric lymph nodes is commonly observed and serves as an important indicator of disease involvement³. 

Gross Pathological Findings in Goats 

Many pathological changes observed in goats resemble those seen in sheep, although some findings are particularly prominent. 

Enlargement of the mesenteric lymph nodes is one of the most characteristic necropsy findings. In addition, the walls of the small intestine become thickened, and the mucosal surface develops distinct folds and corrugations, consistent with chronic intestinal inflammation⁴. 

Other lesions may indicate more advanced systemic involvement. These include pleural and pericardial effusion, ascites, intestinal edema, pulmonary consolidation, and fatty liver⁴. While these findings are not exclusive to PTB, their presence alongside characteristic intestinal lesions can strengthen diagnostic suspicion during postmortem examination. 

Histopathological Features 

Microscopic examination provides further confirmation of PTB by demonstrating the characteristic inflammatory response within affected tissues. 

In sheep, histopathology typically reveals granulomatous enteritis accompanied by extensive cellular infiltration. The inflammatory infiltrate consists predominantly of lymphocytes, epithelioid cells, macrophages, and multinucleated giant cells. Acid-fast organisms are frequently identified within these lesions, supporting the diagnosis of MAP infection⁵. 

Additional microscopic changes may include hyperplasia of Peyer's patches, villous atrophy, and areas of tissue necrosis. Examination of enlarged lymph nodes commonly demonstrates infiltration by macrophages and epithelioid cells containing acid-fast MAP bacilli, with occasional caseous necrosis and giant cell formation³. 

In goats, histopathological changes vary with disease progression. During the early stages, inflammatory cell infiltration is primarily confined to the lamina propria and consists of plasma cells, lymphocytes, and macrophages. As the disease advances, macrophages and giant cells extend into the submucosa and muscle layers of the intestine. Acid-fast organisms may be present in large numbers within affected tissues, reflecting progressive infection¹. 

Practical Clinical Insights 

For practicing veterinarians, pathological examination remains an important component of PTB diagnosis, particularly when animals with chronic wasting disease die or are euthanized before a definitive diagnosis has been established. 

During necropsy, careful evaluation of the terminal ileum, ileocecal region, and mesenteric lymph nodes should form part of the routine examination in suspected cases. Thickened intestinal walls, corrugated mucosa, and enlarged regional lymph nodes are characteristic findings that warrant further laboratory investigation. 

Histopathology complements gross examination by confirming the presence of granulomatous inflammation and acid-fast organisms within intestinal and lymphoid tissues. When these pathological findings are interpreted alongside the animal's clinical history and laboratory results, they provide a strong foundation for confirming PTB and supporting appropriate flock-level disease management decisions. 

References 

1. Sikandar A, Cheema AH, Adil M, Younus M, Zaneb H, Tipu MZ, Masood S. Ovine paratuberculosis-A histopathological study from Pakistan. Journal of Animal and Plant Sciences. 2013 Jun 1;23(3):749-53. https://thejaps.org.pk/manuscript/2013-japs-312.pdf 

2. Tharwat M, Ali H, Alkheraif AA. Paratuberculosis in sheep and goats: Pathogenesis, diagnostic findings, and control strategies. Open Veterinary Journal. 2025 Jan 31;15(1):1. https://pmc.ncbi.nlm.nih.gov/articles/PMC11910304/ 

3. Coelho AC, Coelho AM, GarcÍA-Diez J, Pires MA, Pinto ML. Detection of Mycobacterium avium subsp. paratuberculosis by several diagnostics techniques in clinical suspected sheep. Journal of the Hellenic Veterinary Medical Society. 2017;68(2):167-74. https://ejournals.epublishing.ekt.gr/index.php/jhvms/article/download/15601/14055 

4. Tharwat, M., Al-Sobayil, F., Hashad, M. and Buczinski, S. 2012b. Transabdominal ultrasonographic findings in goats with paratuberculosis. Can. Vet. J. 53, 1063–1070. https://pmc.ncbi.nlm.nih.gov/articles/PMC3447308/pdf/cvj_10_1063.pdf 

5. Hamid MA, Mohammed GE, Bakheit AO, Saeed EM. Histopathological and RT-PCR detection of mycobacterium paratu https://iijls.com/currentissue/Histopathologically_RT_PCR_Detection_Paratuberculosis_Tissues.pdf