In small ruminants, paratuberculosis has been demonstrated to be an spectral disease in which infected animals can show a variety of lesions, from focal, located exclusively in the intestinal lymphoid tissue to diffuse forms, either multibacillar or lymphocytic. This pathological forms have been shown as closely related to the immune responses. In cattle, diffuse lesions have been commonly described but not the rest of the forms. A total of 90 adult cattle, with or without clinical signs, from farms having clinical cases of paratuberculosis have been studied by histopathological methods. Samples were taken from the different parts of the gut and jejunal, ileal and ileo-caecal lymph nodes. In 84 of them, serological tests were performed, and in 36 cattle (-IFN was determined. Microbiological cultures were performed in 18 of the animals. Lesions were classified as follows: focal (small groups of macrophages mainly in the ileal and ileocaecal lymph nodes, n=35), multifocal (small granulomata in the intestinal mucosa, without modifying remarkably the histological architecture; n=7) and diffuse forms (extensive granulomatous infiltrates classified, according to the cellular types, in multibacillar, n=8; lymphocytic, n=2; and intermediate -sharing characteristics of both forms; n=8-). Mycobacteria were isolated in animals showing all the types of lesion. Positive serological responses were observed in all the cattle with multibacilar forms, and in high percentages of animals with intermediate or multifocal lesions; positive (-IFN responses were noted mainly in cattle with focal lesions, but also in animals with no lesions. In conclusion, a pathological spectrum was found in bovine natural paratuberculosis, but, in contrast to small ruminants, it is poorly defined, with large number of cattle with diffuse lesions not clearly identified between the classical two types. It is remarkable the importance of ileal lymph nodes in the location of focal lesions, instead of the intestinal lymphoid tissue, as in sheep. Correlation between pathological forms and immune responses has been also demonstrated in this work.
Supported by grants 1FD1997-224 and AGL2001-0309 (GAN) from MCYT.