Pathological Findings in Young and Adult Sheep Following Experimental Infection With 2 Different Doses of Mycobacterium avium Subspecies paratuberculosis

Abstract

Mycobacterium avium subsp paratuberculosis (Map) is assumed to infect young ruminants; however, little is known concerning the possibility of adult animals becoming infected. An experimental infection was conducted to establish the effect of age and doses of Map on susceptibility to paratuberculosis in sheep. Sixteen of twenty-four 1.5-month-old Churra lambs and 23 of 30 adult ewes (from 2-11 years old) were orally challenged with an ovine field strain of Map. Thirteen ewes and 8 lambs were infected with a high dose (HD) and 10 adult sheep and 8 lambs with a low dose (LD) of Map. The remaining animals were unchallenged controls. Animals were euthanized at 110 to 120 and 210 to 220 days postinfection. Histological, bacteriological, and nested polymerase chain reaction (PCR) studies were conducted in samples of intestine and related lymphoid tissue (Peyer patches, lymph nodes). Animals were classified according to their lesions. The number of granulomas was counted in 3 tissue sections from each sample. Only the HD groups showed lesions associated with paratuberculosis (92.3% of ewes and 100% of lambs). Adults had lesions characterized by few small demarcated focal granulomas restricted to the lymphoid tissue, whereas granulomas were more numerous and larger, appearing in the lamina propria unrelated to lymphoid tissue, in the lambs. Only HD-infected lambs were positive to culture, whereas nested PCR also detected positive HD ewes and some LD animals. These results suggest that adult sheep can become infected by Map, as seen by the development of lesions, but they are focal and restricted to the lymphoid tissue.

Experimental infection of lambs with C and S-type strains of Mycobacterium avium subspecies paratuberculosis: immunological and pathological findings

“…Thus, from our results, it can be hypothesized that infection induced by C-type strains could have reached its highest development around 150 dpi, but infected lambs were able to mount a more efficient and specialized immunologic response that would have caused a regression of the lesions. A similar mechanism has been proposed to occur in adult ewes or cows infected with Map showing a higher resistance to infection [27,28,33]. It might have been interesting to have followed these animals over a more uniform and longer timescale such as culling every two months after infection for a longer period.…”

“…Some of the lambs infected with C-type strains, at 150 dpi showed diffuse lesions affecting wide areas of intestinal mucosa not associated with the lymphoid tissue, which has been regarded as related to more advanced stages of Map infection [4-6,23,28,29]. According to the pathological findings at 390 dpi, lesions induced by C strains in sheep showed an evolution towards resolution, with a marked decrease in their severity, characterized by lower numbers of smaller, well-encapsulated and fibrotic granulomas.…”

“…The sections were incubated with a specific rabbit anti- Map serum at a dilution of 1/9000, as described elsewhere [28]. …”

“…All the lesions consistent with Map infection observed in the digestive tract were classified following the guidelines previously proposed [5,28] for paratuberculosis lesions in the ovine species, according to the presence and location of granulomas in the different intestinal lymphoid tissue compartments.…”

Macrophage Subsets Within Granulomatous Intestinal Lesions in Bovine Paratuberculosis

“…6,11,18 This study has shown that macrophages present in the granulomatous infiltrates show different immunohistochemical expression of the markers examined, as seen by the differences in the H-scores for several of these markers, depending on the lesion type. These differences can probably play different roles in their development.…”