PARATUBERCULOSIS

Paratuberculosis (Johne's disease) is a chronic, wasting, widespread m ycobacteriosis of ruminants. It involves extensive mycobacterial shedd ing, which accounts for the high contagiousness, and ends with a fatal enteritis. Decreases in weight, milk production, and fertility produc e severe economic loss. The DNA of the etiological agent (Mycobacteriu m paratuberculosis) has a base composition (66 to 67% G+C) within the range of that of mycobacteria (62 to 70% G+C), a size (44 X 10(6) to 4 .7 x 10(6) bp) larger than that of most pathogenic mycobacteria (2.0 X 10(6) to 4.2 x 10(6) bp), and a high relatedness (>90%) to Mycobacter ium avium DNA. However, the DNAs of the two organisms can be distingui shed by restriction fragment length polymorphism analysis M. paratuber culosis genes coding for a transposase, a cell wall-associated protein (P34), and two heat shock proteins have been clotted and sequenced Nu cleic acid probes (two of which are species specific) are used after P CR amplification, for M paratuberculosis identification in stools and milk. As in leprosy, with disease progression, cellular immune reactio ns decrease and humoral immune reactions increase. Cutaneous testing w ith sensitins, lymphocyte proliferation assays, and cytokine tests are used to monitor cellular immune reactions in paratuberculosis, but th ese tests lack specificity. Complement fixation, immunodiffusion, and enzymometric tests based on antibodies to M. paratuberculosis extracts , to mycobacterial antigen complex A36, to glycolipids, and to protein s help identify affected cattle but are not species specific. The carb oxyl-terminal portion of the 34-kDa cell wall-associated A36 protein ( P34) carries species-specific B-cell epitopes and is the basis for an enzyme-linked immunosorbent assay. Diagnostic tests for paratuberculos is are also used in Crohn's disease, a chronic human ileitis mimicking Johne's disease, in which isolates identified as M. paratuberculosis have been found.