Proceedings of the 10th International Colloquium on Paratuberculosis

In <strong>the</strong> presence <strong>of</strong> super-shedders in herds, 57.1, 16.7, 20.0, and 70.0% <strong>of</strong> animals o<strong>the</strong>r
than identified as super-shedders shed <strong>the</strong> same strain as that <strong>of</strong> contemporary super-shedders
on farm A. Although this scenario did not occur on farm B, 100% <strong>of</strong> culture-positive animals on
farm C o<strong>the</strong>r than identified as super-shedders shed <strong>the</strong> same strain as that <strong>of</strong> contemporary
super-shedders during first, third, and fourth visits to <strong>the</strong> farm. For <strong>the</strong> available tissue data,
tissues from about 82% <strong>of</strong> cows o<strong>the</strong>r than super-shedders were culture-positive for MAP,
indicating a true infection. For low shedders in three herds, about 65% <strong>of</strong> animals for fecals and
56% for fecal and tissues, shared only <strong>the</strong> same strain as super-shedders. On farm C, animals
491, 493, and 495 were purchased from o<strong>the</strong>r sources; animal 491 was truly infected, which
may be a case <strong>of</strong> adult infection. In few occasions we found multiple strains in different samples
during <strong>the</strong>ir life time in some animals. It was indicated that while it is reasonable to speculate
that coinfection with multiple genotypes is possible, it was recognized that this may be rare
event (Harris et al., 2006).
To conclude, taken toge<strong>the</strong>r <strong>the</strong> results <strong>of</strong> MAP strains and observed shedding levels, at
least 50% <strong>of</strong> low shedders have <strong>the</strong> same strain as that <strong>of</strong> contemporary super-shedders. The
results <strong>of</strong> this study indicate that very few cows had characteristics <strong>of</strong> a possible pass-through
animal; many more cows were truly infected. Sharing <strong>of</strong> <strong>the</strong> same strain <strong>of</strong> low shedders with
<strong>the</strong> contemporary super-shedders suggests that low shedders may be infected as adults by <strong>the</strong>
super-shedders. The use <strong>of</strong> SSR strain-typing combined with observed shedding levels
provided a unique opportunity to get a better insight into herd infection dynamics <strong>of</strong> MAP.
ACKNOWLEDGEMENTS
This project was supported in part by <strong>the</strong> USDA-Agricultural Research Service (Agreements.
58-1265-3-155, 58-1265-3-156, 58-1265-3-158, 58-1265-4-020, and 58-1265-8-064) for <strong>the</strong>
Regional Dairy Quality Management Alliance (RDQMA) and <strong>the</strong> Johne’s Disease Integrated
Program (JDIP, USDA contract 45105). We acknowledge JDIP for providing scholarship award
(USDA-CSREES-NRA Award No 2008-55620-18710) to attend and present this study at 10 th
<strong>International</strong> <strong>Colloquium</strong> on Paratuberculosis (ICP) meeting at Minneapolis, MN, USA.
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