DIFFERENCES IN THE PATHOLOGY OBSERVED AFTER THE EXPERIMENTAL INFECTION OF LAMBS WITH DIFFERENT STRAINS OF Mycobacterium avium subsp. paratuberculosis

VERNA ANDREA1, GARCÍA PARIENTE CARLOS1, GEIJO MARIVI2, ROMANO MARISA3, MORENO OSCAR1, MUÑOZ MARIA1, REYES LUIS1, PAOLICCHI FERNANDO4, GARCÍA MARIN JUAN FRANCISCO1, PÉREZ VALENTIN1.

Olsztyn- Poland

Workshop; 22th meeting of the european society of veterinary pathology. 6th Meeting of the european society of veterinary clinical pathology/ european college of veterinary clinical pathology and continuing education day; 2004

Introduction: Different strains of Mycobacterium avium subsp. paratuberculosis (Map) have been recognized according to the animal species, microbiological properties or, or recently, genetic heterogenecity. However, the pathogenicity of the strains and their ability to infect other animal species different from the original, are document. In this study, a histopathological method has been used to assess the pathology induced by different Map strains in an experimental infection in lambs. Materials and Methods: A total of thirty 1 month old lambs, divided in 6 groups, were orally challenged with the following Map strains: Two bovine strains, with different genetic patterns, A and E (groups 1 and 2); an ovine strain, directly purified from the intestinal mucosa of a clinical case (group 3); a bovine strain, directly purified from the intestinal mucosa of a clinical case (group 4) and the same strain grown in Herrold media (group 5). A 6th group was kept as uninfected control. Humoral and cellular peripheral immune responses as well as the presence of Map DNA in blood were evaluated along 5 months post infection. At this time, lambs were humanely killed for pathological examination, focused on the histological evaluation of intestinal lymphoid tissue. The presence of Map in tissues was assessed by Ziehl-Neelsen, immunohistochemistry and PCR from frozen and paraffin embedded samples. Results: All the strains were able to infect the lambs. Humoral and cellular immune responses were observed in all the groups, with different intensities. Map DNA was found in blood samples from lambs belonging to the five infected groups only at the beginning of the experiment. In all the bovine-infected lambs, lesions had a focal or multifocal character. They appeared mostly in the ileocaececal and jejunal lymph nodes and were formed by well defined granulomata with caseous necrosis. With or without mineralization neutrophils and a high proportion of giant cells. Severity of the lesion varied among groups. In group 3 (ovine strain), lesions were diffuse and appeared in the intestine and lymph nodes, characterized by a granulomatous infiltrate, without necrosis and scarce giant cells. Map or its DNA were detected in tissues from all the groups. Only in diffuse lesions lesions were in high amounts. PCR was more sensitive when performed from paraffin sections than frozen tissue. Conclusion: These results suggest that Map strains have an effect  on the pathological features of the infection. Bovine strains, in lambs, induced focal or multifocal lesions, mainly limited to the lymph nodes, whereas ovine caused more diffuse and severe grnulomatous changes