EVALUATION OF THE PATHOGENICITY OF SEVERAL STRAINS OF Mycobacterium avium subspecies paratuberculosis IN AN EXPERIMENTAL INFECTION OF LAMBS

A VERNA1, M MUÑOZ1, O MORENO1, C GARCÍA PARIENTE1, L E REYES1, M GEIJO2, M I ROMANO4, F PAOLICCHI3, J F GARCÍA MARÍN1, V PÉREZ1.

Casa das Artes de Vila Nova de Famalicao. Portugal

Congreso; 12th Annual Meeting of the portuguese Society of Animal pathology with 16th Annual Meeting of the Spanish Society of Veterinary pathology; 2004

Paratuberculosis or Johne´s desease is chronic granulomatous enteritis of ruminants caused by Mycobacterium avium subsp paratuberculosis (Map). Infected animals show a variety of lesions, with differences concerning its type and location, between ovine and bovine species. On the other hand, it is well known that different strains can be recognized in Map. according to the animal species and microbiological properties. Their existence has been confirmed by recent molecular techniques. However, the pathogenicity of the strains and their ability to infect other animal species different from the one which they  were isolated, it is not well documented. In this study, a method or the histopathological evaluation of lesions produced by Map infection has been used for assessing the sensitivity and pathogenicity of several strains of this bacteria, by means of an experimental infection carried out in lambs. A total of 30 animals, divided in 6 groups, were orally challenged with several strains of Map: group 1 & 2: two bovine strains with different genetic patterns (A and E): group 3 & 4 a bovine strain directly purified from the intestinal mucosa of a clinical case, and the same strain grown in culture media: group 5: an ovine strain, directly purified from the intestinal mucosa of a clinical case: group 6: control lambs. Throughout 5 months, humoral and cellular peripheral immune responses were evaluated as well as the existence of map DNA in blood by PCR. At 150 dpi, all the lambs were humanely killed and a pathological study was made, focused on the intestinal lymphoid tissue. The presence of Map in the tissues was assessed by Ziehl Neelsen, immunohistochemistry and PCR, either in paraffin-embedded or in frozen samples. All the strains were able to infect the lambs, but differences were observed in the lesions. The ovine strain caused diffuse and severe lesions formed by epithelioid  cells whereas bovine strains induced focal or multifocal lesions, composed of granulomas with a high proportion of giant cells and lymphocytes, although variations in the intensity were seen among groups. In the bovine groups, lymph nodes were the most affected organs whereas in group 5 lesions appeared in the intestine, mainly in jejunal  Peyer´s patches. Map or its DNA was detected intissues from all the groups what different sensitivity depending on the sample and technique used. In all the lambs a peripheral immune response was induced, with variations among groups. In a total of 13 lambs DNA from Map was identified in blood samples until 120 dpi. Its absence was associated with an increase in the cellular immune response. These results suggest that Map strains can have an effect on the pathological features of the infection