Objective—To compare cytokine secretion patterns
of peripheral blood mononuclear cells (PBMC) from
healthy cows and cows subclinically and clinically
infected with Mycobacterium paratuberculosis.
Animals—5 noninfected cows, 6 cows with subclinical
paratuberculosis, and 4 cows with clinical paratuberculosis.
Procedure—PBMC were isolated, and concentrations
or activities of secreted interleukin (IL)-1, IL-2, IL-
6, tumor necrosis factor (TNF), and interferon−γ
(IFN-γ) were measured after in vitro stimulation of
cells with concanavalin A (ConA), lipopolysaccharide
(LPS), or a whole-cell sonicate of M paratuberculosis
(MpS). Proliferative responses of PBMC were also
determined after stimulation with ConA, phytohemagglutinin,
pokeweed mitogen (PWM), or MpS.
Results—After stimulation with ConA, cells from subclinically
infected cows secreted significantly more,
and cells from clinically infected cows secreted significantly
less, IFN-γ, compared with cells from control
cows. Cells from cows with subclinical paratuberculosis
produced significantly more TNF and IFN-γ in
response to MpS than cells from the other 2 groups.
Stimulation of PBMC from subclinically infected cows
with ConA or MpS resulted in significantly higher proliferative
responses, compared with cells from control
and clinically infected cows. In contrast, clinically
infected cows had significantly higher proliferative
responses to PWM than cells from the other 2
Conclusions and Clinical Relevance—A decrease in
T-cell responses to mitogens or MpS was observed in
cows clinically infected with M paratuberculosis, compared
with subclinically infected cows, suggesting
that activated T cells may delay the progression of
paratuberculosis. (Am J Vet Res 2000;61:754–760)
Objective—To estimate the risk of subclinical Mycobacterium avium subsp paratuberculosis (MAP) infection in cows that ingested MAP DNA–positive raw colostrum as calves, compared with risk in cows that ingested MAP DNA–negative raw colostrum as calves.
Animals—205 calves born in 12 commercial dairy herds.
Procedures—Each calf was separated from its dam within 30 to 60 minutes after birth and fed raw colostrum. For each calf, samples of the colostrum fed were collected and tested for the presence of MAP DNA by use of a nested PCR assay for the target gene ISMAP02. Calves fed colostrum positive or negative for MAP DNA were classified into exposed (n = 69) and unexposed (136) groups, respectively. Each calf was tested for MAP infection at 30, 42, and 54 months of age by use of a serum ELISA and bacterial culture of feces. Weibull hazard regression models were used to evaluate the association between exposure to MAP DNA–positive colostrum and time to testing positive for MAP infection.
Results—Hazard of MAP infection was not different between groups (exposed vs unexposed) when serum ELISA, bacterial culture of feces, or both diagnostic tests (parallel interpretation) were positive.
Conclusions and Clinical Relevance—Heifer calves fed MAP DNA–positive colostrum were at no greater risk of MAP infection, compared with heifer calves fed MAP DNA–negative colostrum. This result contradicts findings from other studies and should be interpreted with caution.
Objective—To evaluate sensitivity and specificity of a
new ELISA for antibodies against Mycobacterium
avium subsp paratuberculosis.
Design—Cross-sectional observational survey.
Sample Population—Serum samples from 590 cattle
that were infected with M avium subsp paratuberculosis
and 723 cattle that were not infected.
Procedure—Serum samples were tested by use of
an ELISA for antibodies against M avium subsp
Results—Sensitivity of the test varied from 15.4 to
88.1%, depending on the clinical stage and bacterial
shedding status of the cattle.
Conclusions and Clinical Relevance—Results
obtained with use of the new ELISA agreed favorably
with those of a previous ELISA. Practitioners must be
aware of variability in the sensitivity of the test, which
depends on the clinical and shedding status of the
cattle, because this may affect interpretation of test
results. (J Am Vet Med Assoc 2001;218:1163–1166)