Objective—To evaluate sensitivities at the herd level
of test strategies used in the Voluntary Johne's
Disease Herd Status Program (VJDHSP) and alternative
test strategies for detecting dairy cattle herds
infected with Mycobacterium paratuberculosis.
Design—Nonrandom cross-sectional study.
Sample Population—64 dairy herds from
Pennsylvania, Minnesota, Colorado, Ohio, and
Wisconsin. Fifty-six herds had at least 1 cow shedding
M paratuberculosis in feces; the other 8 herds
were free from paratuberculosis.
Procedure—For all adult cows in each herd, serum
samples were tested for antibodies to M paratuberculosis with
an ELISA, and fecal samples were submitted
for bacterial culture for M paratuberculosis. Sensitivities
at the herd level (probability of detecting infected herd)
of various testing strategies were then evaluated.
Results—Sensitivity at the herd level of the testing
strategy used in level 1 of the VJDHSP (use of the
ELISA to test samples from 30 cows followed by confirmatory
bacterial culture of feces from cows with
positive ELISA result) ranged from 33 to 84% for
infected herds, depending on percentage of cows in
the herd with positive bacterial culture results. If follow-
up bacterial culture was not used to confirm positive
ELISA results, sensitivity ranged from 70 to
93%, but probability of identifying uninfected herds
as infected was 89%.
Conclusions and Clinical Relevance—Results suggest
that the testing strategy used in the VJDHSP will
fail to identify as infected most dairy herds with a low
prevalence of paratuberculosis. A higher percentage
of infected herds was detected if follow-up bacterial
culture was not used, but this test strategy was associated
with a high probability of misclassifying uninfected
herds. (J Am Vet Med Assoc 2002;220: 1053–1057)