Clinical Recognition of Paratuberculosis in Sheep and Goats

Paratuberculosis (PTB), also known as Johne's disease, is a chronic contagious granulomatous disease caused by Mycobacterium avium subsp. paratuberculosis (MAP). In sheep and goats, the disease can remain undetected for long periods before clinical signs become apparent, allowing infected animals to contribute to disease transmission within the flock. Besides its impact on animal health, PTB is associated with reduced productivity and substantial economic losses, making timely clinical recognition an important component of herd health management^1,2,3. 

Understanding Disease Development 

Infection typically occurs early in life, with young animals under six months of age being particularly susceptible. MAP is primarily transmitted through the fecal–oral route via contaminated feed, water, bedding, and soiled udders. Newborn lambs and kids may also become infected through contaminated milk and colostrum from infected dams⁴. 

Following ingestion, MAP invades the gastrointestinal mucosa and multiplies within subepithelial macrophages. As the organism persists, granulomatous lesions gradually develop within the intestinal tissues, accompanied by a predominantly cell-mediated immune response. In more advanced stages, release of the organism from macrophages stimulates a stronger humoral antibody response, reflecting disease progression⁴. 

Although infection often occurs during the first week of life, clinical disease usually becomes evident much later. Most affected sheep and goats develop recognizable clinical signs between two and four years of age. Stressful events, particularly parturition, may precipitate the appearance of clinical disease in previously subclinical animals^2,4. 

Recognizing Clinical Signs in Practice 

Progressive weight loss remains the hallmark clinical feature of PTB in both sheep and goats. Affected animals gradually lose body condition despite management interventions, and decreased appetite is frequently observed. Changes in fecal consistency may occur but should not be considered a consistent diagnostic feature⁴. 

An important practical point is that diarrhea is considerably less reliable in small ruminants than in cattle. Many infected goats present with normal feces despite advanced disease. In one clinical series involving 54 goats with PTB, 29 animals had no diarrhea at presentation, while only four exhibited chronic watery diarrhea⁵. Likewise, diarrhea or soft feces may be present in only about 20% of affected animals during the final stages of infection⁴. 

As disease progresses, animals become increasingly emaciated and may develop anorexia, rough hair coat, depression, dehydration, anemia, fragile skin, and submandibular edema^4,6. In severely affected cases, sheep and goats may present in lateral recumbency, reflecting advanced systemic compromise. 

Body condition scoring can provide valuable clinical support during examination. Affected animals have been reported to have an average body condition score of 1.4 ± 0.5 compared with 3.7 ± 0.3 in healthy animals⁴. 

Hematobiochemical Findings That Support Clinical Assessment 

Although laboratory abnormalities are not diagnostic on their own, they can strengthen clinical suspicion when interpreted alongside history and physical examination. 

Reported hematological findings in goats include: 

• Neutropenia 

• Leukocytosis 

• Erythrocytosis 

• Increased hematocrit percentage 

• Increased hemoglobin concentration 

• Increased mean corpuscular hemoglobin and mean corpuscular volume 

Serum biochemical abnormalities include hypocalcemia, hypoalbuminemia, hypomagnesemia, increased creatine kinase activity, and, in clinically affected sheep, hypoproteinemia and intermandibular edema⁴. 

Practical Clinical Insights 

For field veterinarians, PTB should remain an important differential diagnosis whenever adult sheep or goats exhibit chronic weight loss, declining body condition, and progressive debilitation, even in the absence of diarrhea. Relying solely on fecal consistency may delay recognition of infected animals, particularly in goats where diarrhea is frequently absent. 

Evaluating age, disease progression, body condition, and supportive hematobiochemical changes together provides a stronger clinical foundation for identifying animals that require further diagnostic investigation. Early recognition not only facilitates timely confirmation but also supports flock-level management decisions aimed at reducing ongoing transmission. 

References 

1. Tharwat M, Ali H, Alkheraif AA. Clinical insights on paratuberculosis in Arabian camels (Camelus dromedarius): a review. Open Veterinary Journal. 2025 Jan 31;15(1):8. https://pmc.ncbi.nlm.nih.gov/articles/PMC11910307/ 

2. Idris SM, Eltom KH, Okuni JB, Ojok L, Elmagzoub WA, El Wahed AA, Eltayeb E, Gameel AA. Paratuberculosis: the hidden killer of small ruminants. Animals. 2021 Dec 21;12(1):12. https://www.mdpi.com/2076-2615/12/1/12 

3. Jiménez-Martín, D., García-Bocanegra, I., Risalde, M.A., Fernández-Molera, V., Jiménez-Ruiz, S., Isla, J. and Cano-Terriza, D. 2022. Epidemiology of paratuberculosis in sheep and goats in southern Spain. Prev. Vet. Med. 202, 105637. https://www.sciencedirect.com/science/article/pii/S0167587722000708 

4. 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/ 

5. 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 

6. Bauman CA, Jones-Bitton A, Menzies P, Toft N, Jansen J, Kelton D. Prevalence of paratuberculosis in the dairy goat and dairy sheep industries in Ontario, Canada. The Canadian veterinary journal. 2016 Feb;57(2):169. https://pmc.ncbi.nlm.nih.gov/articles/PMC4712996/pdf/cvj_02_169.pdf