Immune reactions in cattle after immunization with a Mycobacterium paratuberculosis vaccine and implications for the diagnosis of M. paratuberculosisand M. bovis infections

After immunization of four carves with a live modified Mycobacterium paratu berculosis vaccine the course of the humoral and cell-mediated immune react ions was studied during a 2-year clinical investigation. Furthermore, the p ossibility of shedding of the vaccine strain and the influence of the vacci nation on the tuberculin skin test was determined. In addition to standard procedures recently developed diagnostic methods (antibody enzyme-linked im munosorbent assay, interferon-gamma test, polymerase chain reaction) were u sed. A cell-mediated immune reaction, reflected in an increased, specifical ly induced, interferon-gamma production developed much earlier (1-2 weeks p ost-immunization) than humoral immunity (8-16 weeks post-gamma immunization ). While the increase in antibody titres was transient, declining to extrem ely low levels 48-60 weeks post-immunization, cell-mediated immunity remain ed detectable until the end of the investigation. Spread of the vaccine str ain into the body and shedding were never detected during the whole course of the study except for one colon site in one calf. As late as 2 years afte r vaccine application positive or doubtful skin reactions against M. bovis purified protein derivative were measured, reflecting possible interference of the immunization with the diagnosis of bovine tuberculosis. At the end of the investigation, a positive cell-mediated immune reaction was also det ected in the control animal although clinical, pathological and bacteriolog ical examinations gave no indication for a mycobacterial infection.