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Liver biopsy histopathology for diagnosis of Johne's disease in sheep
S L Smith1, P R Wilson2, M G Collett2
1Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand s.l.smith@massey.ac.nz.
Abstract:
Sheep with Johne's disease develop epithelioid macrophage microgranulomas, specific to Mycobacterium avium subsp. paratuberculosis (Map) infection, in the terminal ileum, mesenteric lymph nodes, and organs distant to the alimentary tract such as the liver. The objectives of this study were to determine whether liver pathology was present in ewes affected by Map and whether liver cores provide adequate tissue for this potential diagnostic marker. One hundred and twenty-six adult, low body condition ewes were euthanized, necropsied, and underwent simulated liver biopsy. Ileal lesions typical of Map were found in 60 ewes. Hepatic epithelioid microgranulomas were observed in all ewes with Type 3b (n = 40) and 82% (n = 11) with Type 3c ileal lesions. None were found in ewes unaffected by Map or with Type 1, 2, or 3a ileal lesions. Liver biopsy core samples provided adequate tissue for histopathology with a sensitivity and specificity of 96% (95% confidence interval [CI], 0.87-0.99) and 100% (95% CI, 0.95-1), respectively for detection of types 3b and 3c ileal lesions.
Insights
Johne's disease in sheep, caused by Mycobacterium avium subsp. paratuberculosis (Map), leads to liver microgranulomas. Liver biopsies are a sensitive and specific diagnostic tool for detecting Map infection in affected ewes.
Area of Science:
- Veterinary Pathology
- Sheep Infectious Diseases
Background:
- Johne's disease, caused by Mycobacterium avium subsp. paratuberculosis (Map), is characterized by epithelioid macrophage microgranulomas in sheep.
- Lesions are typically found in the terminal ileum and mesenteric lymph nodes, but also in distant organs like the liver.
Purpose of the Study:
- To investigate the presence of liver pathology in ewes infected with Map.
- To evaluate the efficacy of liver biopsy as a diagnostic method for Map infection.
Main Methods:
- Necropsy and simulated liver biopsy of 126 adult ewes with low body condition.
- Histopathological examination of ileal and liver tissues.
- Assessment of liver biopsy sensitivity and specificity for detecting Map-associated lesions.
Main Results:
- Hepatic epithelioid microgranulomas were present in ewes with advanced ileal lesions (Type 3b and 3c).
- No liver lesions were observed in Map-unaffected ewes or those with early ileal lesions (Type 1, 2, 3a).
- Liver biopsy demonstrated high sensitivity (96%) and specificity (100%) for detecting Types 3b and 3c ileal lesions.
Conclusions:
- Liver microgranulomas are a reliable indicator of advanced Johne's disease in sheep.
- Liver biopsy is a valuable and accurate diagnostic tool for identifying Map infection in ewes.
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