Objective—To estimate herd-level sensitivity (HSe),
specificity (HSp), and predictive values for a positive
(HPVP) and negative (HPVN) test result for several
testing scenarios for detection of tuberculosis in cattle
by use of simulation modeling.
Sample Population—Empirical distributions of all
herds (15,468) and herds in a 10-county area (1,016) in
Procedures—5 test scenarios were simulated: scenario
1, serial interpretation of the caudal fold tuberculin
(CFT) test and comparative cervical test (CCT);
scenario 2, serial interpretation of the CFT test and
CCT, microbial culture for mycobacteria, and polymerase
chain reaction assay; scenario 3, same as scenario
2 but specificity was fixed at 1.0; and scenario 4,
sensitivity was 0.9 (scenario 4a) or 0.95 (scenario 4b),
and specificity was fixed at 1.0.
Results—Estimates for HSe were reasonably high,
ranging between 0.712 and 0.840. Estimates for HSp
were low when specificity was not fixed at 1.0.
Estimates of HPVP were low for scenarios 1 and 2
(0.042 and 0.143, respectively) but increased to 1.0
when specificity was fixed at 1.0. The HPVN remained
high for all 5 scenarios, ranging between 0.995 and
0.997. As herd size increased, HSe increased and HSp
and HPVP decreased. However, fixing specificity at
1.0 had only minor effects on HSp and HPVN, but HSe
was low when the herd size was small.
Conclusions and Clinical Relevance—Tests used
for detecting cattle herds infected with tuberculosis
work well on a herd basis. Herds with < approximately
100 cattle should be tested more frequently or for
a longer duration than larger herds to ensure that
these small herds are free of tuberculosis. (Am J Vet
Objective—To identify major environmental and farm
management factors associated with the occurrence
of tuberculosis (TB) on cattle farms in northeastern
Sample Population—17 cattle farms with infected
cattle and 51 control farms.
Procedure—Each case farm (laboratory confirmed
diagnosis of Mycobacterium bovis infection) was
matched with 2 to 4 control farms (negative whole-herd
test results within previous 12 months) on the basis of
type of farm (dairy or beef) and location. Cattle farm
data were collected from in-person interviews and
mailed questionnaires. Wildlife TB data were gathered
through state wildlife surveillance. Environmental data
were gathered from a satellite image-based geographic
information system. Multivariable conditional logistic
regression for matched analysis was performed.
Results—Major factors associated with increased
farm risk of TB were higher TB prevalence among wild
deer and cattle farms in the area, herd size, and ponds
or creeks in cattle housing areas. Factors associated
with reduced farm risk of TB were greater amounts of
natural open lands in the surrounding area and reducing
deer access to cattle housing areas by housing cattle
in barns, barnyards, or feedlots and use of electrified
wire or barbed wire for livestock fencing.
Conclusions and Clinical Relevance—Results suggest
that certain environmental and management factors
may be associated with risk of TB on cattle
farms. (J Am Vet Med Assoc 2002;221:837–842)
Objective—To determine prevalence of tuberculosis
caused by infection with Mycobacterium bovis in
cervids on privately owned ranches in northeastern
Animals—Cervids on 96 privately owned ranches.
Procedures—A combination of slaughter and skin
tuberculin testing was used to collect data. Infection
with M bovis was confirmed by use of standard
necropsy and bacteriologic culture techniques.
Results—Cervids with tuberculosis were detected
on 1 of the 96 ranches. The apparent prevalence of
tuberculosis in cervids from the 96 ranches was 1.1
cases/100 cervids (21 cases/1,867 cervids tested).
For the ranch with infected cervids, prevalence of
infection with M bovis was 12.1 cases/100 cervids
(21 cases/174 cervids tested). No obvious gross
lesions were seen in 8 of 21 white-tailed deer and 1
coyote with culture-confirmed M bovis infection.
Conclusions and Clinical Relevance—The lack of
visible lesions in a substantial proportion of infected
animals should be taken into consideration in studies
involving detection and prevalence of tuberculosis. (J
Am Vet Med Assoc 2002;220:656–659)
Objective—To determine the distribution of lesions
and extent of tissues infected with Mycobacterium
bovis in a captive population of white-tailed deer.
Animals—116 captive white-tailed deer.
Procedure—Deer were euthanatized, and postmortem
examinations were performed. Tissues with
gross lesions suggestive of tuberculosis were collected
for microscopic analysis and bacteriologic culture.
Tissues from the head, thorax, and abdomen of deer
with no gross lesions were pooled for bacteriologic
culture. Tonsillar, nasal, oral, and rectal swab specimens,
fecal samples, and samples of hay and pelleted
feed, soil around feeding sites, and water from 2 natural
ponds were collected for bacteriologic culture.
Results—Mycobacterium bovis was isolated from 14
of 116 (12%) deer; however, only 9 of 14 had lesions
consistent with tuberculosis. Most commonly affected
tissues included the medial retropharyngeal lymph
node and lung. Five of 14 tuberculous deer had no
gross lesions; however, M bovis was isolated from
pooled tissue specimens from the heads of each of
these deer. Bacteriologic culture of tonsillar swab specimens
from 2 of the infected deer yielded M bovis.
Mean (± SEM) age of tuberculous deer was 2.5 ± 0.3
years (range, 0.5 to 6 years). Mycobacterium bovis was
not isolated from feed, soil, water, or fecal samples.
Conclusions and Clinical Relevance—Examination of
hunter-killed white-tailed deer for tuberculosis commonly
includes only the lymph nodes of the head.
Results of such examinations may underestimate disease
prevalence by as much as 57%. Such discrepancy
should be considered when estimating disease prevalence.
(J Am Vet Med Assoc 2000;216:1921–1924)
Objective—To determine whether cats exposed at a
residence were infected with Mycobacterium bovis,
whether the tuberculin skin test can identify cats
infected with M bovis, and whether an ELISA could
identify tuberculosis-infected cats.
Animals—20 domestic cats exposed to a cat with
laboratory-confirmed disseminated M bovis infection.
Procedure—Cats were administered a tuberculin
skin test and monitored for 72 hours. Blood and fecal
samples were collected. Cats were then euthanatized,
and postmortem examinations were performed.
Tissues were examined grossly and histologically
for signs of mycobacteriosis. Pooled tissue
samples and fecal samples were submitted for
mycobacterial culture. Blood samples were examined
for evidence of tuberculosis by use of a comparative
Results—4 cats had positive responses for the
ELISA, and 2 cats had suspicious responses. All
tuberculin skin tests yielded negative results. No
gross or histologic lesions of tuberculosis were
detected in any tissues, and mycobacteria were not
isolated from tissues or feces obtained from the 20
Conclusions and Clinical Relevance—All cats that
had positive or suspicious responses for the ELISA
were offspring of the cat with tuberculosis. Evidence
of tuberculosis was not seen in other cats at the residence,
the owner, or the attending veterinarian. The
most likely source of tuberculosis for the infected cat
was through the consumption of M bovis-infected
wildlife carcasses or offal. Because M bovis is endemic
in wildlife in northeastern Michigan, there is a risk
of exposure to tuberculosis in companion animals,
their owners, and attending veterinarians. (Am J Vet
Objective—To determine whether cattle testing positive
for Mycobacterium avium subsp paratuberculosisas
determined by microbial culture of feces or antibody
ELISA were more likely to have false-positive
responses on the caudal fold tuberculin (CFT) test or
interferon-γ (IFN-γ) assay for Mycobacterium bovis
than cattle testing negative for M paratuberculosis.
Animals—1,043 cattle from 10 herds in Michigan.
Procedure—Feces and blood samples for plasma
were collected from cattle ≥ 24 months old on the day
the CFT test was read. Fecal samples were submitted
for microbial culture for M paratuberculosis. Plasma
samples were tested for antibody against M paratuberculosis,
and IFN-γ after stimulation with purified
protein derivative tuberculin from M bovis or M avium.
Results—Of 1,043 cattle, 180 (17.3%) had positive CFT
test results (suspects) and 8 (0.8%) had positive IFN-γ
assay results after stimulation with purified protein
derivative tuberculin from M bovis. Forty-five (4.3%) and
115 (11.0%) cattle tested positive for M paratuberculosis
as determined by microbial culture of feces and antibody
ELISA, respectively. Cattle with positive responses
for M paratuberculosis appeared to have an
increased likelihood of false-positive results on the CFT
test, although this association was not significant.
Conclusions and Clinical Relevance—No significant
association was detected among cattle testing positive
for M paratuberculosis as determined by microbial
culture of feces and antibody ELISA and positive
CFT test and IFN-γ assay results for M bovis. (J Am
Vet Med Assoc 2005;226:429–435)
OBJECTIVE To describe use of whole-genome sequencing (WGS) and evaluate the apparent sensitivity and specificity of antemortem tuberculosis tests during investigation of an unusual outbreak of Mycobacterium bovis infection in a Michigan dairy herd.
PROCEDURES All cattle in the index dairy herd were screened for bTB with the caudal fold test (CFT), and cattle ≥ 6 months old were also screened with a γ-interferon (γIFN) assay. The index herd was depopulated along with all barn cats and a dog that were fed unpasteurized milk from the herd. Select isolates from M bovis–infected animals from the index herd and other bTB-affected herds underwent WGS. Wildlife around all affected premises was examined for bTB.
RESULTS No evidence of bTB was found in any wildlife examined. Within the index herd, 53 of 451 (11.8%) cattle and 12 of 21 (57%) cats were confirmed to be infected with M bovis. Prevalence of M bovis–infected cattle was greatest among 4- to 7-month-old calves (16/49 [33%]) followed by adult cows (36/203 [18%]). The apparent sensitivity and specificity were 86.8% and 92.7% for the CFT and 80.4% and 96.5% for the γIFN assay when results for those tests were interpreted separately and 96.1% and 91.7% when results were interpreted in parallel. Results of WGS revealed that M bovis–infected barn cats and cattle from the index herd and 6 beef operations were infected with the same strain of M bovis. Of the 6 bTB-affected beef operations identified during the investigation, 3 were linked to the index herd only by WGS results; there was no record of movement of livestock or waste milk from the index herd to those operations.
CONCLUSIONS AND CLINICAL RELEVANCE Whole-genome sequencing enhanced the epidemiological investigation and should be used in all disease investigations. Performing the CFT and γIFN assay in parallel improved the antemortem ability to detect M bovis–infected animals. Contact with M bovis–infected cattle and contaminated milk were major risk factors for transmission of bTB within and between herds of this outbreak.