Diagnostic Approach to Paratuberculosis in Sheep and Goats: Clinical Evaluation, Ultrasonography and Laboratory

Paratuberculosis (PTB) presents a diagnostic challenge in sheep and goats because clinical signs often develop long after infection and may vary considerably between affected animals. Progressive weight loss is a common finding, but the absence of consistent diarrhea, particularly in goats, can make early clinical recognition difficult. A systematic diagnostic approach that combines clinical evaluation with imaging and laboratory testing can improve the likelihood of identifying infected animals and support timely flock-level management decisions. 

Begin with Clinical Suspicion 

The diagnostic process starts with recognizing animals that fit the typical clinical profile. Adult sheep and goats, particularly those between two and four years of age, presenting with chronic weight loss, declining body condition, decreased appetite, or progressive debilitation should raise suspicion for PTB¹. 

Clinical examination should not rely solely on diarrhea as an indicator of disease. Many infected goats maintain normal fecal consistency even in advanced stages, making body condition, disease progression, and overall clinical status more reliable indicators for further investigation². 

The Role of Ultrasonography in Clinical Practice 

Abdominal ultrasonography provides valuable supportive information during the evaluation of suspected PTB cases. The technique can detect structural changes within the intestines and associated lymph nodes that may not be evident during physical examination. 

One of the most consistent ultrasonographic findings in affected goats is an overall increase in intestinal mucosal thickness. Depending on disease severity, this thickening may be classified as mild, moderate, or severe². 

Additional intestinal changes include corrugation and folding of the intestinal mucosa, which are best appreciated during longitudinal imaging. However, the most remarkable and clinically significant ultrasonographic finding is enlargement of the mesenteric lymph nodes. Enlarged lymph nodes typically demonstrate a hypoechoic cortex with a hyperechoic medulla, making them an important imaging feature when PTB is suspected². 

Other abnormalities that may be identified include increased hepatic brightness, intestinal edema, pulmonary consolidation, and pleural, peritoneal, or pericardial effusions. Although these findings are not specific for PTB, they may provide additional information regarding the extent of systemic involvement². 

Laboratory Tests for Confirmation 

Because clinical and ultrasonographic findings alone cannot confirm PTB, laboratory testing remains essential. 

Several diagnostic methods are available for detecting Mycobacterium avium subsp. paratuberculosis (MAP), including: 

• Fecal culture 

• Polymerase chain reaction (PCR) 

• Enzyme-linked immunosorbent assay (ELISA) 

• Microscopic examination using Ziehl–Neelsen staining 

Fecal culture is regarded as the gold standard for MAP detection¹. However, its practical application may be limited because infected animals can shed low numbers of organisms, and the organism requires considerable time to grow in culture^1,3. 

PCR offers a sensitive method for MAP detection, but its performance depends on both the stage of infection and the quantity and quality of DNA obtained from the sample^2,4,5. 

For routine monitoring and economic feasibility, ELISA is the most widely used laboratory test. Its practicality makes it suitable for herd-level surveillance and screening programs^1,6. 

Another useful laboratory technique is Ziehl–Neelsen staining of rectal scrapings, which enables visualization of acid-fast bacilli and provides additional diagnostic support². 

Practical Clinical Insights 

No single diagnostic method is sufficient for every suspected PTB case. Clinical findings should guide the decision to perform additional diagnostic testing, while ultrasonography can strengthen suspicion by identifying characteristic intestinal and mesenteric lymph node changes. 

Once PTB is suspected, combining imaging findings with laboratory confirmation provides a more reliable diagnostic approach than relying on any single test. Animals showing compatible clinical signs together with suggestive ultrasonographic abnormalities should undergo confirmatory testing using ELISA, PCR, fecal culture, or appropriate microscopic examination. This integrated approach supports earlier diagnosis, facilitates timely isolation of suspect animals, and contributes to more effective disease control within the flock. 

References 

1. 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/ 

2. 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 

3. Mathevon Y, Foucras G, Falguières R, Corbiere F. Estimation of the sensitivity and specificity of two serum ELISAs and one fecal qPCR for diagnosis of paratuberculosis in sub-clinically infected young-adult French sheep using latent class Bayesian modeling. BMC Veterinary Research. 2017 Aug 3;13(1):230. https://link.springer.com/content/pdf/10.1186/s12917-017-1145-x.pdf 

4. Al-Swailem A, Al-Dubaib MA, Abo El-Hassan DG, Tharwat M, Al-Yamani E, Shehata M, Hashad M, Mahmoud OM. Treatment of paratuberculosis in camels by rifampin and streptomycin. J. Camel Pract. Res. 2011 Dec 1;18:225-9. https://www.researchgate.net/profile/Mohamed-Tharwat-7/publication/287836463 

5. Keller SM, Stephan R, Kuenzler R, Meylan M, Wittenbrink MM. Comparison of fecal culture and F57 real-time polymerase chain reaction for the detection of Mycobacterium avium subspecies paratuberculosis in Swiss cattle herds with a history of paratuberculosis. Acta Veterinaria Scandinavica. 2014 Oct 10;56(1):68. https://link.springer.com/content/pdf/10.1186/s13028-014-0068-9.pdf 

6. Hemati Z, Meletis E, Derakhshandeh A, Haghkhah M, Kostoulas P, Singh SV, Chaubey KK, Gupta S. Application of Bayesian modeling for diagnostic assays of Mycobacterium avium subsp. paratuberculosis in sheep and goats flocks. BMC veterinary research. 2022 Jan 18;18(1):47. https://link.springer.com/content/pdf/10.1186/s12917-022-03141-7.pdf