In the present study, small intestines and associated mesenteric lymph nodes of 400 apparently healthy cattle slaughtered at ELFORA export abattoir were examined for gross pathological lesions of paratuberculosis. Gross pathological lesions suggestive of paratuberculosis gross lesion were used for estimation of the prevalence of paratuberculosis in these cattle. The gross pathological lesions of paratuberculosis were furthered processed by histopathological examination for confirmation of the lesions. Based on the type and amount of cellular infiltrations, the microscopic lesions were classified into four grades of (I-IV).
Based on gross post mortem examination of tissue samples in the present abattoir study, the prevalence of gross lesions resembling paratuberculosis recorded in the present study was in line with the results reported by the study conducted earlier [27]. However, the prevalence of gross lesions resembling paratuberculosis found in this study is lower than those reported previously in other countries [5, 14], while it was higher than finding reported by other authors [28, 29]. The difference in the prevalence of paratuberculosis gross lesions could be due to the difference in the origin or type of production system, age of the host, immune status and breed of the animals that are slaughtered in the abattoir.
Macroscopically, a variety of gross lesions that were normally associated with paratuberculosis were observed in the small intestinal ileum. In the present study thickening and corrugations of the intestinal ileum were obvious in cattle especially in the last portion of the small intestinal ileum particularly at the ileoceacal junction. In highly developed cases there is diffuse thickening along with transverse and longitudinal corrugations of the intestinal wall making irregular folds [30, 31, 32, 33]. Congested, edematous, enlarged and corded mesenteric lymph nodes around the ileum and ileoceacal junctions were evident, which is in agreement with the reports made by others [5, 33].
The histopathological confirmation of the gross lesions compatible with paratuberculosis recorded in the present study is comparable with the findings of a study [33], while it was higher than those reported by others [28, 5 29, 34]. However, out of the 45 animals having gross lesions that are normally associated with JD only 8 (17.9%) animals were only having microscopic lesions but many gross lesions were not have microscopic lesions. Microscopic examination of those samples with characteristic gross lesions but no histological JD lesions showed that they had different proliferative enteropathies and vascular disturbances like hyperaemia, haemorrhages and oedema. Thus, gross examination should be followed by histological examinations which may be confirmed by other tests. Care should be taken to avoid making conclusive diagnosis of JD based on gross lesions as is usually done in some epidemiological abattoir studies.
Microscopically, the thickness and corrugations occurred as a result of cellular infiltrations in the mucosa and lamina propria as reported earlier [30, 35]. The histopathological findings such as infiltration of the mucosa and lamina propria with lymphocytes, macrophages, replacement of the crypt with inflammatory cells, Peyer’s patches proliferation and extending towards the mucosa and the presence of multinucleated giant cells in the present study had a close resemblance to those observed in small ruminants and cattle by other authors [36, 37, 38, 26, 5, 32, 33, 14]. The mesenteric lymph nodes were enlarged, edematous and congested with diffuse infiltration of mononuclear cells is in agreement with the findings of [26, 5, 14].
The grade III lesion found in 2 cattle had diffuse infiltration of epithelioid cells, macrophages and multinucleated giant cells in the last portion of the small intestinal ileum and their associated lymph nodes together with the presence of AFB. The grade III lesions described in this case and the number of acid fast staining bacteria within the macrophages corresponds most closely to those of the multibacillary form of paratuberculosis which is in agreement with the earlier reports [39, 40, 41, 38, 42, 5]. This form of paratuberculosis is thought to be the result of weak cellular immune response and strong humeral responses, which is common during the last stage of the disease [43].
Grade II lesions had the same pathological pattern of grade III, except that the severity of the lesions were moderate with few epithelioid cells, but there were more lymphocyte infiltrations. While the grade I lesions had less cellular infiltrations which was consisted more of lymphocytes and some scattered macrophages. Similar to previous studies, infiltration of few epithelioid cells among numerous lymphocytes in grade II lesions marked the lesions in preclinical stage of paratuberculosis [41, 36]. Previous studies on experimental and natural cases of paratuberculosis in sheep and goat have indicated preponderance of lymphoid cells to epithelioid cells in the early paucibacillary cases, in which bacteria could not generally demonstrated [41, 44, 36, 45]. Diffuse lymphocytic infiltrations has been reported in the early stages of other mycobacterial infections and correlated with strong cell-mediated immune responses mediated by different subpopulation of lymphocytes such as helper, cytotoxic and suppressor cell [46, 47, 38, 48].