Objective—To investigate herd characteristics and management practices associated with a high seroprevalence of Mycobacterium avium subsp paratuberculosis (MAP) in dairy herds in central California.
Sample Population—60 randomly selected cows from each of 21 dairy herds.
Procedures—Sera of selected cows were tested for antibodies against MAP by use of an ELISA test kit. Cows with a test sample-to-positive control sample (S:P) ratio of ≥ 0.25 were considered seropositive, and herds with ≥ 4% seropositive cows were considered high-seroprevalence herds. Data on herd characteristics and management practices were collected via interviews with owners. Bayesian logistic regression was used to model the predictive probability of a herd having a high seroprevalence on the basis of various herd characteristics and management practices.
Results—9 of 21 (43%) herds were classified as high-seroprevalence herds. Five variables (history of previous signs of paratuberculosis in the herd, herd size, exposing cattle to water from manure storage lagoons, feeding unsalable milk to calves, and exposing heifers ≤ 6 months old to manure of adult cows) were included in the predictive model on the basis of statistical and biological considerations. In large herds, the predictive probability of a high seroprevalence of MAP infection decreased from 0.74 to 0.39 when management changed from poor to good practices. In small herds, a similar decrease from 0.64 to 0.29 was predicted.
Conclusions and Clinical Relevance—The seroprevalence of MAP infection in California dairies may be reduced by improvements in herd management practices.
Objective—To investigate the epidemiologic and financial impacts of targeted sampling of subpopulations of cows, compared with random sampling of all cows, for classification of dairy herd infection status for paratuberculosis.
Animals—All cows from 4 infected herds with a low-to-moderate prevalence of paratuberculosis and from 1 noninfected herd in California.
Procedure—The infection status of each cow was classified on the basis of results of an ELISA or combined ELISA and fecal culture results. Thirteen sampling schemes designed to randomly sample cows on the basis of lactation number, stage of lactation, and milk production were evaluated. Sampling without replacement was used to obtain a probability of herd detection of paratuberculosis for each evaluated sampling method and for simulated sample sizes between 30 and 150 cows. Marginal cost-effectiveness analysis was used to determine the cost increase relative to the increase in detection probability.
Results—Sampling cows in the third or higher lactation and ≥200 days into lactation yielded the highest detection probability in most instances, resulting in a detection probability that was 1.4 to 2.5 times that obtained by sampling 30 cows in the second or higher lactation. Costs of testing via the alternative method with a 95% detection probability were approximately $300 lower in a high-prevalence herd (31%) and $800 lower in a low-prevalence herd (9%), compared with use of the reference method.
Conclusions and Clinical Relevance—Detection of herds with paratuberculosis could be improved, and costs of testing substantially reduced by sampling targeted groups of cows.
Objective—To evaluate associations between Mycobacterium avium subsp paratuberculosis (MAP) and caudal fold tuberculin (CFT) test results in cattle.
Design—Longitudinal and cross-sectional evaluations.
Animals—1 California (approx 3,600 cows) and 3 Colorado (approx 640, 1,190, and 1,480 cows) dairy herds considered free of Mycobacterium bovis infection.
Procedures—In the California herd, the association between CFT response and MAP status was determined with ELISA and mycobacterial culture of feces within 1 year before and after CFT testing. The association between CFT and MAP status in all herds was modeled with mixed-effects logistic regression.
Results—In the California herd, significantly higher odds of being classified as suspect by CFT were found for cows with results of MAP ELISA negative before and positive after CFT testing (OR, 5.6) and cows positive before and after CFT testing (OR, 8.1). Higher odds were found for cows positive for mycobacterial culture of feces before and negative for culture after CFT testing (OR, 4.6) and cows negative for mycobacterial culture of feces before and positive for culture after CFT testing (OR, 13.2). All herds had higher odds of being classified as suspect by CFT testing for cows with positive results for ELISA (OR, 2.9) or mycobacterial culture of feces (OR, 5.0), compared with cows with negative results of the same tests.
Conclusions and Clinical Relevance—A strong association was found between positive MAP test results and being classified as a suspect by CFT testing. Within-herd MAP prevalence may affect specificity of CFT testing for tuberculosis in cattle.
Objective—To determine susceptibility of cattle to
infection with Ehrlichia equi and the agent of human
granulocytic ehrlichiosis (HGE).
Design—Experimental disease and prevalence survey.
Animals—6 cattle, 2 horses, and 2,725 serum samples
from healthy cattle.
Procedure—2 cattle and 1 horse were inoculated
with E equi, 2 cattle and 1 horse were inoculated with
the HGE agent, and 2 cattle served as sham-inoculated
controls; inoculated animals were evaluated via
clinical, hematologic, serologic, and real-time polymerase
chain reaction tests. Prevalence of antibodies
against E equi in 2,725 healthy cattle was determined
by use of an indirect immunofluorescent technique.
Results—No abnormal clinical or hematologic findings
or inclusion bodies within granulocytes were
observed in the cattle after inoculation, and results of
all polymerase chain reaction tests were negative.
Seroconversion in inoculated cattle developed 10 to
12 days after inoculation (reciprocal titers, 160). Both
horses developed clinical signs of ehrlichiosis. Five of
2,725 (0.18%) cattle were seropositive for E equi,
with titers ranging from 20 to 80. All seropositive cattle
originated from the same tick-rich region in the
Sierra Nevada foothills.
Conclusions and Clinical Relevance—Results suggest
that cattle are not susceptible to infection with E
equi or the agent of HGE and that prevalence of exposure
to E equi in healthy cattle is low. Therefore, E
equi and the agent of HGE are likely of negligible
importance for cattle in North America. (J Am Vet Med
Objective—To evaluate sensitivity of microbial culture
of pooled fecal samples for detection of
Mycobacterium avium subsp paratuberculosis (MAP)
in large dairy herds and assess the use of the method
for estimation of MAP prevalence.
Animals—1,740 lactating cows from 29 dairy herds
Procedure—Serum from each cow was tested by
use of a commercial ELISA kit. Individual fecal samples
were cultured and used to create pooled fecal
samples (10 randomly selected fecal samples/pool; 6
pooled samples/herd). Sensitivity of MAP detection
was compared between Herrold's egg yolk (HEY) agar
and a new liquid culture method. Bayesian methods
were used to estimate true prevalence of MAP-infected
cows and herd sensitivity.
Results—Estimated sensitivity for pooled fecal
samples among all herds was 0.69 (25 culture-positive
pools/36 pools that were MAP positive).
Sensitivity increased as the number of culture-positive
samples in a pool increased. The HEY agar
method detected more infected cows than the liquid
culture method but had lower sensitivity for
pooled fecal samples. Prevalence of MAP-infected
cows was estimated to be 4% (95% probability
interval, 2% to 6%) on the basis of culture of
pooled fecal samples. Herd-level sensitivity estimate
ranged from 90% to 100% and was dependent
on prevalence in the population and the sensitivity
for culture of pooled fecal samples.
Conclusions and Clinical Relevance—Use of pooled
fecal samples from 10 cows was a cost-effective tool
for herd screening and may provide a good estimate
of the percentage of MAP-infected cows in dairy
herds with a low prevalence of MAP. (Am J Vet Res
Objective—To describe the epizootiological investigation of an outbreak of Q fever (Coxiella burnetii infection).
Animals—17 goat herds in Washington, Montana, and Oregon.
Procedures—In April 2011, an abortion storm at a commercial goat farm in Washington was determined to be caused by C burnetii. A joint epidemiological investigation by public health and veterinary professionals was subsequently performed to assess the extent of the outbreak by performing a trace-forward of goats sold from the index farm, to determine risk factors associated with infection, and to implement control measures. A herd management plan was developed to control the outbreak and reduce risk of human exposure. Quarantine and temporary holds preventing the sale or movement of goats allowed time for trace-forward investigation, education of farmers regarding disease risk, and testing to determine the scope of the outbreak.
Results—17 farms were affected; 21 human Q fever cases were identified. Bacterial shedding in feces, vaginal fluid, or milk was confirmed in 156 of 629 (25%) goats tested by PCR assay. Seroprevalence of antibodies against C burnetii in goats, determined by ELISA, was 12%. The risk for C burnetii infection in goats was highest among females, those on farms associated with human Q fever, and those on Washington farms. A protective effect was observed for goats at farms where the primary form of goat carcass disposal was burial.
Conclusions and Clinical Relevance—This outbreak illustrated the importance of a joint investigation for zoonotic pathogens and the need to expand and strengthen relationships between medical, public health, and veterinary partners. Heightened awareness and enhanced veterinary diagnostic capabilities for C burnetii are needed to identify and control outbreaks expediently.