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Title: Molecular Epidemiology of Mycobacterium avium subsp. paratuberculosis in a Longitudinal Study of Three Dairy Herds

Author
item PRADHAN, ABANI - Cornell University
item MITCHELL, REBECCA - Cornell University
item KRAMER, AAGJE - Utrecht University
item ZURAKOWSKI, MICHAEL - Cornell University
item FYOCK, TERRY - University Of Pennsylvania
item WHITLOCK, ROBERT - University Of Pennsylvania
item SMITH, JULIE - University Of Vermont
item HOVINGH, ERNEST - Pennsylvania State University
item Van Kessel, Jo Ann
item Karns, Jeffrey
item SCHUKKEN, YNTE - Cornell University

Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2010
Publication Date: 3/1/2011
Citation: Pradhan, A., Mitchell, R., Kramer, A., Zurakowski, M., Fyock, T., Whitlock, R., Smith, J., Hovingh, E., Van Kessel, J.S., Karns, J.S., Schukken, Y. 2011. Molecular Epidemiology of Mycobacterium avium subsp. paratuberculosis in a Longitudinal Study of Three Dairy Herds. Journal of Clinical Microbiology. 49(3):893-901.

Interpretive Summary: Johne’s disease is a chronic, progressive, infectious intestinal disease of cattle and is caused by infection with the bacterium, Mycobacterium avium subsp. paratuberculosis (MAP). A large number of US dairy herds are infected with MAP and the dairy industry incurs large economic losses as a result of Johne’s disease. MAP infection is characterized by a very long incubation period and identification of animals that are infected is very difficult. Previous work has indicated that some cows that have tested positive for MAP in their feces are not truly infected, rather are simply shedding MAP cells that they ingested (passive shedding). Additionally, ‘super shedder’ cows have been identified that shed billions of MAP cells in their feces. These super-shedder cows have the potential for contaminating much of the dairy farm environment. The objective of this study was to evaluate whether cows that were low shedders of MAP were passive shedding animals or whether they were truly infected with MAP. We also evaluated whether these MAP-infected animals could have been infected as adults by contemporary high-shedding animals (super-shedders). The MAP isolates were obtained from a longitudinal study of three dairy herds in the northeastern United States. Isolates were selected from fecal samples and tissues at slaughter from all animals that were culture-positive at the same time that super-shedders were present in the herds. Shedding levels of animals at each culture-positive occasion were determined. Using a multilocus short sequence repeat technique, a method to determine the relatedness between strains, we found 15 different strains of MAP from a total of 142 isolates analyzed. Results indicated herd-specific infection patterns; a clonal infection in herd C with 89% of animals sharing the same strain, whereas herds A and B showed several different strains infecting the animals at the same time. Tissues from 81% of cows with at least one positive fecal culture (other than super-shedders) were culture-positive indicating a true MAP infection rather than passive shedding. The results of MAP strain typing and observed shedding levels showed that at least 50% of low shedders had the same strain as that of a contemporary super-shedder. Results of this study suggest that in a dairy herd more of the low-shedding cows are truly infected with MAP versus passively shedding MAP. The sharing of strains between low shedders and the contemporary super-shedders suggests that low shedders may have been infected as adults by super-shedders. Due to the long incubation times of this organism, it was previously believed that adult infection was highly unlikely. Successful control strategies for Johne’s disease require a good understanding of the epidemiology of the disease. The results of this study will be helpful in the development of effective management protocols.

Technical Abstract: The objective of this study was to evaluate whether cows that were low shedders of Mycobacterium avium subsp. paratuberculosis (MAP) were passive shedding animals or whether they were truly infected with MAP. We also evaluated whether these MAP-infected animals could have been infected as adults by contemporary high-shedding animals (super-shedders). The MAP isolates were obtained from a longitudinal study of three dairy herds in the northeastern United States. Isolates were selected from fecal samples and tissues at slaughter from all animals that were culture-positive at the same time that super-shedders were present in the herds. Shedding levels (MAP cfu/g) of animals at each culture-positive occasion were determined. Using a multilocus short sequence repeat technique, we found 15 different strains of MAP from a total of 142 isolates analyzed. Results indicated herd-specific infection patterns; a clonal infection in herd C with 89% of animals sharing the same strain, whereas herds A and B showed several different strains infecting the animals at the same time. Tissues from 81% of cows with at least one positive fecal culture (other than super-shedders) were culture-positive indicating a true MAP infection. The results of MAP strain typing and observed shedding levels showed that at least 50% of low shedders have the same strain as that of a contemporary super-shedder. Results of this study suggest that in a dairy herd more of the low-shedding cows are truly infected with MAP versus passively shedding MAP. The sharing of strains between low shedders and the contemporary super-shedders suggests that low shedders may have been infected as adults by super-shedders.