Proceedings of the 10th International Colloquium on Paratuberculosis

#159 Experimental infection in adult sheep and lambs with Mycobacterium avium subsp
paratuberculosis (Map) at two different doses
Laetitia Delgado, Maria Muñoz, Carlos Garcia-Pariente, Miguel Fuertes, Julio Benavides, Jorge Gonzalez, M
Carmen Ferreras, J Francisco Garcia-Marin, Valentin Perez,
Universidad de Leon, Spain
Objective: To establish <strong>the</strong> effect <strong>of</strong> age and doses <strong>of</strong> Map upon susceptibility to Johne´s disease in ovine.
Materials and Methods: Sixteen 1,5-month-old lambs out <strong>of</strong> 24 and 22 adult sheep (over two years old)
out <strong>of</strong> 28 were experimentally challenged orally and both divided into two groups infected: a) with a high dose
(1.1x1010 CFU), b) with a lower dose (1.1x103 CFU) <strong>of</strong> an ovine field strain <strong>of</strong> Map. The remaining animals
were used as unchallenged control groups.
Peripheral cellular and humoral immune responses were assessed as well as Map fecal shedding between
0 and 210 dpi. Sixteen challenged and five control animals were slaughtered at 120 dpi, and <strong>the</strong> remaining
at 210dpi. Histological and bacteriological studies were conducted in samples <strong>of</strong> intestine and related
lymphoid tissue (Peyer´s patches and lymph nodes). Animals were classified according to <strong>the</strong>ir lesions and
granulomas were counted in 3 tissue sections from each sample.
Results: No gross lesions were observed in any <strong>of</strong> <strong>the</strong> animals. Only <strong>the</strong> high dose-challenged groups
showed histological lesions associated with paratuberculosis (92.3% <strong>of</strong> <strong>the</strong> adult sheep and 100% <strong>of</strong> <strong>the</strong>
lambs). However, those consisted <strong>of</strong> few small demarcated focal granulomas restricted to <strong>the</strong> lymphoid tissue
(mostly Peyer´s patches) in <strong>the</strong> adults, whereas <strong>the</strong>se were more numerous, larger and spreading to <strong>the</strong>
lamina propia in <strong>the</strong> lambs. The tissue and faeces culture were positive in 5 high dose-challenged lambs. Cellular
immune responses appeared earlier in <strong>the</strong> adult sheep than in lambs.
Conclusions: Adult sheep can be infected, as seen by <strong>the</strong> development <strong>of</strong> characteristic lesions; however,
<strong>the</strong>y seem to be able to control <strong>the</strong> progression <strong>of</strong> <strong>the</strong> disease. The dose <strong>of</strong> Map plays an important role
in <strong>the</strong> establishment <strong>of</strong> <strong>the</strong> infection both in adult sheep and lambs.
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