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Experimental infection model for Johne's disease in sheep
D J Begg1, R O'brien, C G Mackintosh
1Department of Microbiology and Immunology, University of Otago, P. O. Box 56, Dunedin, New Zealand.
Abstract:
Johne's disease in ruminants results in chronic enteritis caused by the pathogenic bacterium Mycobacterium avium subsp. paratuberculosis. This study examined two M. avium subsp. paratuberculosis strains (JD3 and W), using different doses and routes of infection, to establish the optimal time postchallenge when predictable levels of infection, gut lesions, and clinical disease occur in a large proportion of sheep. While a small proportion (25%) of sheep challenged with a low-passage-number laboratory culture of M. avium subsp. paratuberculosis (strain W) became infected, no infection was found in animals exposed to a high-passage-number culture isolate of strain W. In contrast, a primary tissue homogenate of M. avium subsp. paratuberculosis (JD3) resulted in high (90%) infection rates and gut histopathology following oral or intratonsillar challenge. The optimal conditions necessary to produce Johne's disease involve oral inoculation of 3-month-old lambs with four doses of 5 x 10(8) CFU of M. avium subsp. paratuberculosis isolated directly from the gut lymphatic tissues of clinically affected sheep. This resulted in consistent gut histopathology at 9 months and the onset of clinical disease by 11 months postchallenge.
Insights
Researchers identified optimal conditions for inducing Johne
Area of Science:
- Veterinary Microbiology
- Ruminant Pathology
Background:
- Johne's disease causes chronic enteritis in ruminants.
- It is caused by Mycobacterium avium subsp. paratuberculosis (MAP).
Purpose of the Study:
- To determine optimal conditions for inducing Johne's disease in sheep.
- To establish predictable infection levels, gut lesions, and clinical signs post-challenge.
Main Methods:
- Two MAP strains (JD3 and W) were tested with varying doses and routes.
- Sheep were orally or intratonsillar challenged with different MAP preparations.
- Infection rates, gut histopathology, and clinical signs were monitored.
Main Results:
- A primary tissue homogenate of MAP strain JD3 yielded high infection rates (90%).
- Oral inoculation of 3-month-old lambs with four doses (5 x 10^8 CFU) of JD3 was optimal.
- Consistent gut histopathology occurred at 9 months, with clinical disease by 11 months post-challenge.
Conclusions:
- Oral challenge with a specific MAP isolate and dosage effectively models Johne's disease in sheep.
- This model allows for predictable study of disease progression and intervention strategies.
