Variations in the pathological response of lambs experimentally infected with different Map strains

VERNA A, GARCÍA-PARIENTE C, MORENO O, REYES LE, BENAVIDES J, PAOLICCHI F1, ROMANO MI2, GARCÍA MARÍN JF, PÉREZ V

Copenhaguen. Denmark

Congreso; 8th International Colloquium on Paratuberculosis.; 2005

Infection by Mycobacterium avium subsp. paratuberculosis (Map) causes a granulomatous inflammatory response in the intestine and associated lymph nodes. Differences in the pathological features (organs affected or inflammatory infiltrate) have been observed between species and individuals. The host immune responses or the role of different Map strains have been suggested as possible explanations. A total of 30 lambs, 1 month-old, divided in 6 groups, were challenged with several strains of Map: groups 1 and 2, with two bovine strains showing different genetic pattern (A and E); groups 3 and 4, with a bovine strain, directly purified from the intestinal mucosa of a clinical case, or the same strain grown in culture media, respectively; group 5, an ovine strain, directly purified from the intestinal mucosa of a clinical case; group 6 was kept as control. Peripheral immune responses were assessed from 0 to 150 days-postinfection (dpi), when lambs were humanely killed. Pathological and bacteriological studies were performed in tissues from the intestine and lymph nodes. Lesional type and the inflammatory infiltrate were examined. Number of granulomas per section and area occupied by lesion in the lymph nodes were counted, as indicators of pathogenicity. All the lambs infected by bovine Map strains, regardless the type, showed a common lesional pattern, characterised by focal lesions, located mainly in the mesenteric lymph nodes, the presence of fibrous tissue, and occasionally necrosis, in the granulomas and the existence of numerous giant cells. Differences in lesion severity were seen among groups: lambs from groups 1 and 2 had the highest number of granulomas and lymph node area affected. In animals from group 5, lesions were more severe and appeared mainly in the intestinal lymphoid tissue. Necrosis, fibrosis or giant cells were never detected. Map was isolated from tissues from all the groups and showed the same pattern than the inoculum. The type of Map strain influences the pathological response of the infected lambs.