Multilocus Short Sequence Repeat Analysis of Mycobacterium avium subsp. paratuberculosis Isolates from Dairy Herds in Northeastern United States of a Longitudinal Study Indicates Low Shedders are Truly Infected

摘要

The objectives of this study were to evaluate whether low shedders of Mycobacterium avium subsp. paratuberculosis (MAP) were pass-through animals or whether they were truly infected. We also evaluated whether these animals were possibly infected by the super-shedders. The MAP isolates were obtained from a longitudinal study that involved three different herds in the northeastern US. The shedding levels of animals at each culture-positive occasion were determined. Selected isolates were collected from all animals that were culture-positive at the same time super-shedders were present in the herds and from super-shedders. Using a multilocus short sequence repeat (MLSSR) approach we found 15 different strains from a total of 142 isolates analyzed. The results indicated herd-specific infections; a clonal infection in herd C with 89% of animals sharing the same strain, different strains in herds A and B. In herd C, 100% and in herd A, 17 to 70% of cows shed the same strain as that of contemporary super-shedders at a given collection date. About 82% of available tissue samples were culture-positive indicating a true infection. Taken together the results of MAP strain-typing and shedding levels, we conclude that at least 50% of low shedders have same strain as that of a contemporary super-shedder. The results of this study indicate that very few cows had characteristics of a possible pass-through animal; many more cows were actively infected. The sharing of same strain of low shedders with the contemporary super-shedders suggests that low shedders may be infected as adults by the super-shedders.