Efficient control of Johne's disease is dependent on
early detection and removal of Mycobacterium
avium subsp. paratuberculosis(MAP) infected
cows to prevent spreading of the disease and associated economic
losses to the cattle industry. Testing schemes optimized for cost
and ease of implementation are often based on screening of milk
samples and ELISA methodology rather than the use of blood serum
samples with ELISA. The goal of this study was to determine the
diagnostic performance of the PARACHEK® Mycobacterium paratuberculosis
antibody test kit (Prionics AG, Schlieren, Switzerland)
using milk and blood serum samples compared to the culture results
of feces for MAP bacteria. For this purpose milk, blood serum and
fecal samples were collected from 531 dairy cows in the
Netherlands. These cows derived from 10 dairy herds. Eight herds
had a recent history of paratuberculosis and two farms had a
confirmed status of freedom of paratuberculosis infection based on
their participation in a Dutch herd-certification program (1).
Serum samples were collected from all 531 cows and stored at
-20°C until analyzed. Milk samples were obtained from
lactating cows (n=483) and stored at -20°C until further use.
Fecal samples (n=531) were obtained directly from the rectum of the
cows. The feces samples were decontaminated (3) and subsequently
cultured in the TREK ESP para-JEM Culture System II (TREK
Diagnostic Systems, Cleveland, Ohio, USA). All samples detected by
the system and all samples not yet detected by the system at the
conclusion of the experiment (49 days) were further investigated
via Ziehl Neelsen staining and PCR methodologies (2). Milk and
serum samples were analyzed using the indirect enzyme immunoassay
PARACHEK® to detect antibodies
against MAP. The manufacturer has two different protocols for milk
and blood serum samples using the same kit. The samples were
analyzed according to the manufacturer's
instructions.
The
results showed that in total 4.0% of the cows (21 out of 531) were
culture positive. The sensitivity of the
PARACHEK® with regard to
culture positive cows was 52.4% (11/21) in serum and 57.9% (11/19)
in milk samples. The specificity was 98.6% (503/510) and 98.9%
(445/450), respectively. None of the cows from certified
MAP-negative herds were determined as positive with the
PARACHEK® either with serum or
with milk samples. This suggests that false positive determinations
from herds with a recent history of paratuberculosis may in fact
indicate truly infected cows. These cows are possibly only negative
in culture analysis due to intermittent or low mycobacterial
shedding in feces, i.e. levels which are below the detection limit
of the culture method.
The agreement between the
results from milk and serum samples was excellent with a proportion
of agreement of 0.98 and a weighted kappa value of 0.843.
In
conclusion, the results of this study indicate that surveillance of
cattle herds with the PARACHEK® using either serum or
milk is an efficient, cost effective and reliable method to detect
paratuberculosis in infected herds. In combination with good farm
management, this test can contribute substantially to the reduction
in prevalence of Johne's disease in cattle herds.
-
Benedictus, G., J. Verhoeff, Y. H. Schukken, and J. W. Hesselink.
2000. Dutch paratuberculosis programme history, principles and
development. Vet Microbiol 77:399-413.
-
Kalis,
C. H., J. W. Hesselink, H. W. Barkema, and M. T. Collins. 2000.
Culture of strategically pooled bovine fecal samples as a method to
screen herds for paratuberculosis. J Vet Diagn Invest
12:547-51.
3.
Stabel, J. R. 1997. An improved method for cultivation of
Mycobacterium paratuberculosis from bovine fecal samples and
comparison to threeother methods. J Vet Diagn Invest 9:375-80.
