Johne's Disease
Johne's disease, also known as paratuberculosis, is a chronic infection that affects the intestines of ruminant animals, including sheep. It is caused by the bacterium Mycobacterium avium subspecies paratuberculosis (MAP). This disease is widespread and often goes undiagnosed, leading to significant productivity losses in affected flocks.
Symptoms and Diagnosis 🩺
Symptoms
Sheep with Johne's disease typically show signs of chronic weight loss and poor body condition despite having a good appetite. Unlike cattle, sheep do not usually exhibit diarrhea. Other symptoms include:
- Emaciation
- Poor quality wool and open fleece
- Sunken sublumbar fossae due to reduced rumen fill
- In extreme cases, submandibular edema (bottle jaw)
- Low birth weights in lambs born to infected ewes
Infected sheep often appear bright and alert but fail to gain condition. The disease progresses slowly, and clinical signs may not appear until the sheep are older.
Diagnosis
Diagnosing Johne's disease can be challenging. There is no single test that can detect all stages of the disease. Common diagnostic methods include:
- Post-mortem examination: Thickened intestines, enlarged lymph nodes, and orange pigmentation of the gut can indicate Johne's disease.
- Histological samples: Confirm the presence of the disease.
- Serological tests: Such as ELISA, though they have a high false-negative rate.
- Faecal culture: Useful but time-consuming and often contaminated.
Sub-clinically infected sheep are difficult to diagnose and can test negative even when infected.
Treatment 💊
Unfortunately, there is no recognized treatment for Johne's disease in sheep. Affected animals should be euthanized to prevent further spread of the disease. Antibiotic therapy is generally ineffective and not recommended.
Prevention 🛡️
Preventing Infection
Preventing Johne's disease involves several strategies:
- Early culling: Cull affected animals and their offspring to limit the spread of the disease.
- Screening: Conduct annual screenings of older, thin ewes using pooled faecal samples after weaning.
- Vaccination: Vaccination programs have shown encouraging results in reducing disease prevalence. The Gudair vaccine, for example, has been effective in reducing mortality and delaying the onset of the disease.
- Environmental management: Since the bacteria can survive in the environment for long periods, maintaining good hygiene and minimizing faecal contamination of feed and water sources is crucial.
Conclusion
Johne's disease is a significant concern for sheep farmers due to its impact on productivity and the difficulty in diagnosing and treating the disease. By implementing preventive measures and working closely with your veterinarian, you can help manage and reduce the prevalence of Johne's disease in your flock.