Fecal shedding of Mycobacterium avium subsp. paratuberculosis by dairy cows

Between 1982 and 2000, fecal samples were obtained from 786 cows that were shedding Mycobacterium avium subsp. paratuberculosis (Map). These cows were resident on 93 Pennsylvania dairies (mean herd size, 64 milk cows) that had no or minimal previous testing for Map. Feces were cultured on four tubes of Herrold's egg yolk medium and the distribution of mean Map colony forming units (CFU) was evaluated. Most cows were light (< 10 CFU/tube, 51.4%) or high (> 50 CFU/tube, 30.8%) fecal shedders with fewer cows in the moderate category (10-50 CFU/tube). Of the 786 cows, 192 (24.4%) had colonies in only one of four tubes. In the multivariable negative binomial model, there were significant associations between mean CFU/tube and prevalence, herd size, and season and an interaction between herd size and season. The linear mixed model of continuous tube counts with a random herd effect yielded similar findings with associations with herd size as a continuous variable, season, and an interaction between categorized prevalence and continuous herd size. Variability in CFU/tube was greatest among cows in the same herd, intermediate for replicate tubes from the same cow, and smallest among cows in different herds. Reduction in the number of replicate tubes from four would have reduced the sensitivity of fecal culture for Map by approximately 6% (for three tubes) to 12% (for two tubes).     

Environmental contamination with Mycobacterium avium subsp. paratuberculosis in endemically infected dairy herds

Environmental contamination with Mycobacterium avium subsp. paratuberculosis (MAP) is thought to be one of the primary sources of infection for dairy cattle. The exact link between fecal shedding of MAP by individual cows and environmental contamination levels at the herd level was explored with a cross-sectional analysis of longitudinally collected samples on 3 dairy farms. Composite samples from multiple environmental sites in 3 commercial dairy herds in the Northeast US were cultured quarterly for MAP, providing 1131 samples (133 (11.8%) were culture-positive), and all adult animals in the herds were tested biannually by fecal culture (FC), for 6 years. Of the environmental sites sampled, manure storage areas and shared alleyways were most likely to be culture-positive. Environmental sample results were compared to FC results from either the concurrent or previous sampling date at both the herd and the pen level. At the herd level, a 1 log unit increase in average fecal shedding increased the odds of a positive non-pen environmental sample by a factor of 6 and increased the average amount of MAP in non-pen samples by 2.9 cfu/g. At the pen level, a 1 log unit increase in average fecal shedding in the pen increased the odds of a positive environment by a factor of 2.4 and the average amount of MAP was increased by 3.5 cfu/g. We were not able to model the relationship between non-pen environmental sample status and the distance between shedding animals and the sample's location, and neighboring pens did not significantly affect the results of the pen-level analysis. The amount of MAP in pen-level samples and the probability of a pen testing positive for MAP were both positively but non-significantly correlated with the number of animals in the pen shedding >30 cfu/g of MAP. At least 6 environmental samples met the criteria for the U.S. Voluntary Bovine Johne's Disease Control Program on 47 of the 72 sampling dates; of these, 19 of the 47 FC-positive sampling dates were positive by the 6-sample environmental testing method, resulting in a herd sensitivity of 0.40 (95% CI: 0.26-0.54). None of the 3 FC-negative sampling dates produced positive environmental samples. Although environmental sampling can be used as a tool in understanding the level of MAP infection in a herd or pen, it did not appear to be a sensitive diagnostic method for herd positivity in these low prevalence herds, and its use may require caution.     

Evaluation of microbial culture of pooled fecal samples for detection of Mycobacterium avium subsp paratuberculosis in large dairy herds

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 in California. 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.     

Characterization of the long-term immune response to vaccination against Mycobacterium avium subsp. paratuberculosis in Danish dairy cows

Vaccination of cattle against Mycobacterium avium subsp. paratuberculosis (MAP) provides partial protection by delayed shedding of MAP and reduced numbers of clinically affected animals. The duration of vaccine induced immune response is not known. The primary objective of this study was therefore to characterize the long-term effect of whole-cell based vaccination against MAP on the immune response. A secondary objective was to evaluate whether immunodiagnosis of MAP and Mycobacterium bovis infections is affected by MAP vaccination. Two studies were performed: (1) A retrospective longitudinal study including 895 vaccinated and 2526 non-vaccinated dairy cows in 9 Danish dairy herds aiming at characterizing the long-term antibody-response to vaccination; and (2) a cross-sectional study of responses in the IFN-γ assay carried out in 140 vaccinated animals in two herds to evaluate the effect of vaccination on the cell-mediated immune response and to evaluate a possible interference with the diagnosis of M. bovis infections. The results showed that 37% of samples from vaccinated animals and 5% of samples from non-vaccinated animals, respectively, were test positive in the milk antibody ELISA. The prevalence of antibody responses of the vaccinated animals was relatively constant from 2 to 6 years of age, but decreased in older animals. Among the 140 vaccinated animals 88% tested positive with the IFN-γ test to johnin PPD and 50% responded to PPDb with IFN-γ production above a similar cut-off. Although Denmark is free of M. bovis, two of the vaccinated animals responded with higher IFN-γ levels when cultured with PPDb compared to PPDa. In conclusion, immunization with whole-cell MAP vaccines elicits both humoral and cell-mediated immune reactions, which may interfere with surveillance and diagnosis of both MAP and M. bovis infections using currently available tests.     

Efficacy of monensin sodium for the reduction of fecal shedding of Mycobacterium avium subsp. paratuberculosis in infected dairy cattle

Reducing the quantity of Mycobacterium avium subsp. paratuberculosis (MAP) being shed by cows with Johne's disease should decrease the risk of spread of this disease to young stock. Previous work has suggested that monensin sodium decreases the pathologic lesions associated with Johne's disease, but the impact on shedding of viable MAP remains unknown. After serologic screening of 32 dairy herds in southwestern Ontario, 228 cows from 13 of these herds were enrolled into a randomized clinical trial. Fecal culture and PCR were used to identify 114 cows as potential fecal shedders, while another 114 cows were enrolled as ELISA negative, herd and parity matched controls. All cows were randomized to receive either a monensin controlled release capsule (CRC) or a placebo capsule. Serial fecal and blood samples were collected for fecal culture and serum ELISA testing over a 98-day period. On day 98 of the study, treatments were switched for all cows continuing in the trial. These remaining cows were followed for another 98 days with a similar sampling protocol. Mixed effect models were used to measure the impact of treatment on the number of colony forming units identified on fecal cultures over time. During the first 98 days of the study, cows treated with a monensin CRC were found to shed 3.4 cfu per tube less than placebo treated cows (P = 0.05). The serum ELISA S/P ratio was reduced by 1.39 units in cows given monensin (P = 0.06). However, treatment with monensin did not reduce the odds of testing positive on serology. Only the cows shedding MAP on day 0 were found to have a reduced odds of testing positive on fecal culture when treated with monensin (OR = 0.27; P = 0.03). Monensin sodium administered to infected animals at 335 mg/day marginally reduced fecal shedding of MAP in mature dairy cattle, but the biological significance of this reduction is unknown.     

Lack of evidence for fecal shedding of Mycobacterium avium subsp. paratuberculosis in calves born to fecal culture positive dams

The objective was to detect presence of calves excreting Mycobacterium avium subsp. paratuberculosis (MAP) in their feces as a consequence of being born to MAP fecal culture positive (vs. negative) dams. For each cow that was about to calf, approximately 10 g of feces was collected manually by the herdsmen from the rectum using a disposable plastic examination sleeve within 48–72 h prior to actual calving. Between 1 and 3 d of birth, herd personnel collected approximately 10 g of fecal samples followed by monthly visits to the farm at which time 10 g of fecal samples were again collected by study investigators from each calf at approximately 30, 60 and 90 d of age. Mycobacterium avium subsp. paratuberculosis was recovered from 8% (5/60) of the cows that gave birth to calves. However, MAP was not recovered from any of the fecal samples (0/240) collected from study calves. Findings of the present study suggest lack of evidence for fecal excretion of MAP in calves born to fecal culture positive (vs. negative) dams in a heavily infected herd.     

Mycobacterium avium subsp. paratuberculosis from free-ranging deer and rabbits surrounding Minnesota dairy herds

The objectives of this study were to estimate the prevalence of Mycobacterium avium subsp. paratuberculosis (MAP) among deer and rabbits surrounding infected and noninfected Minnesota dairy farms using fecal culture, and to describe the frequency that farm management practices were used that could potentially lead to transmission of infection between these species. Fecal samples from cows and the cow environment were collected from 108 Minnesota dairy herds, and fecal pellets from free-ranging white-tailed deer and eastern cottontail rabbits were collected from locations surrounding 114 farms; all samples were tested using bacterial culture. In addition, a questionnaire was administered to 114 herd owners. Sixty-two percent of the dairy herds had at least 1 positive fecal pool or environmental sample. A total of 218 rabbit samples were collected from 90% of the herds, and 309 deer samples were collected from 47% of the herds. On 2 (4%) of the farms sampled, 1 deer fecal sample was MAP positive. Both farms had samples from the cow fecal pool and cow environment that were positive by culture. On 2 (2%) other farms, 1 rabbit fecal sample was positive by culture to MAP, with one of these farms having positive cow fecal pools and cow environmental samples. Pasture was used on 79% of the study farms as a grazing area for cattle, mainly for dry cows (75%) and bred or prebred heifers (87%). Of the 114 farms, 88 (77%) provided access to drylot for their cattle, mainly for milking cows (77/88; 88%) and bred heifers (87%). Of all study farms, 90 (79%) used some solid manure broadcasting on their crop fields. Of all 114 farms, the estimated probability of daily physical contact between cattle manure and deer or rabbits was 20% and 25%, respectively. Possible contact between cattle manure and deer or rabbits was estimated to occur primarily from March through December. The frequency of pasture or drylot use and manure spreading on crop fields may be important risk factors for transmission of MAP among dairy cattle, deer, and rabbits. Although the MAP prevalence among rabbits and deer is low, their role as MAP reservoirs should be considered.     

Herd characteristics and management practices associated with seroprevalence of Mycobacterium avium subsp paratuberculosis infection in dairy herds

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 > or = 0.25 were considered seropositive, and herds with > or = 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 < or = 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.     

Herd-level prevalence of Mycobacterium avium subsp. paratuberculosis infection in United States dairy herds in 2007

Testing of composite fecal (environmental) samples from high traffic areas in dairy herds has been shown to be a cost-effective and sensitive method for classification of herd status for Mycobacterium avium subsp. paratuberculosis (MAP). In the National Animal Health Monitoring System's (NAHMS) Dairy 2007 study, the apparent herd-level prevalence of MAP was 70.4% (369/524 had ≥1 culture-positive composite fecal samples out of 6 tested). Based on these data, the true herd-level prevalence (HP) of MAP infection was estimated using Bayesian methods adjusting for the herd sensitivity (HSe) and herd specificity (HSp) of the test method. The Bayesian prior for HSe of composite fecal cultures was based on data from the NAHMS Dairy 2002 study and the prior for HSp was based on expert opinion. The posterior median HP (base model) was 91.1% (95% probability interval, 81.6 to 99.3%) and estimates were most sensitive to the prior for HSe. The HP was higher than estimated from the NAHMS Dairy 1996 and 2002 studies but estimates are not directly comparable with those of prior NAHMS studies because of the different testing methods and criteria used for herd classification.     

Longitudinal study to investigate variation in results of repeated ELISA and culture of fecal samples for Mycobacterium avium subsp paratuberculosis in commercial dairy herds

OBJECTIVE: To determine sources and amounts of variation in a kinetics ELISA (KELA) and results of culture of fecal samples for Mycobacterium avium subsp paratuberculosis (MAP) in repeated tests of individual cows. ANIMALS: 112 cows on 6 commercial dairy farms in New York. PROCEDURE: A nonrandom longitudinal study was conducted from January 2001 to March 2002. A KELA was performed monthly, and MAP culture was performed bimonthly. Cow- and herd-level data were collected. The KELA and culture results were analyzed by use of models that corrected for clustering within herds and repeated measures on cows. RESULTS: Cows of second or higher lactation had increased KELA values, compared with values for first-lactation cows. Cows had lowest KELA values during the first 15 days in milk; KELA values increased until 60 days in milk and then stabilized. Moderate and heavy shedders had significantly higher KELA values than culture-negative cows, and KELA values of shedders progressively increased over time. On average, the KELA value was significantly increased 132 days after a cow was first detected to be a moderate shedder and 236 days after a cow was first detected to be a low shedder. CONCLUSIONS AND CLINICAL RELEVANCE: Analysis suggests that KELA results vary on a cow-level on the basis of lactation number and stage of lactation. High KELA values indicate heavy fecal shedding, but the KELA is not useful in identifying low and moderate shedders that can require up to 236 days to have a significant increase in KELA value.     

Impact of imperfect Mycobacterium avium subsp. paratuberculosis vaccines in dairy herds: A mathematical modeling approach

The objective of this study was to investigate the potential impacts of imperfect Mycobacterium avium subsp. paratuberculosis (MAP) vaccines on the dynamics of MAP infection in US dairy herds using a mathematical modeling approach. Vaccine-based control programs have been implemented to reduce the prevalence of MAP infection in some dairy herds; however, MAP vaccines are imperfect. Vaccines can provide partial protection for susceptible calves, reduce the infectiousness of animals shedding MAP, lengthen the latent period of infected animals, slow the progression from low shedding to high shedding in infectious animals, and reduce clinical disease. To quantitatively study the impacts of imperfect MAP vaccines, we developed a deterministic multi-group vaccination model and performed global sensitivity analyses. Our results explain why MAP vaccination might have a beneficial, negligible, or detrimental effect in the reduction of prevalence and show that vaccines that are beneficial to individual animals may not be useful for a herd-level control plan. The study suggests that high efficacy vaccines that are aimed at reducing the susceptibility of the host are the most effective in controlling MAP transmission. This work indicates that MAP vaccination should be integrated into a comprehensive control program that includes test-and-cull intervention and improved calf rearing management.     

Prevalence of antibodies against Mycobacterium avium subsp paratuberculosis among beef cow-calf herds

OBJECTIVE: To estimate the prevalence of Mycobacterium avium subsp paratuberculosis infection among cows on beef operations in the United States. DESIGN: Cross-sectional seroprevalence study. Sample Population-A convenience sample of 380 herds in 21 states. PROCEDURES: Serum samples were obtained from 10,371 cows and tested for antibodies to M avium subsp paratuberculosis with a commercial ELISA. Producers were interviewed to collect data on herd management practices. RESULTS: 30 (7.9%) herds had 1 or more animals for which results of the ELISA were positive; 40 (0.4%) of the individual cow samples yielded positive results. None of the herd management practices studied were found to be associated with whether any animals in the herd would be positive for antibodies to M avium subsp paratuberculosis. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the prevalence of antibodies to M avium subsp paratuberculosis among beef cows in the United States is low. Herds with seropositive animals were widely distributed geographically.     

Evaluation of cost-effectiveness of targeted sampling methods for detection of Mycobacterium avium subsp paratuberculosis infection in dairy herds

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 > or = 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 dollar 300 lower in a high-prevalence herd (31%) and dollar 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.     

Different Mycobacterium avium subsp. paratuberculosis MIRU-VNTR patterns coexist within cattle herds

A better understanding of the biodiversity of Mycobacterium avium subsp. paratuberculosis (MAP) offers more insight in the epidemiology of paratuberculosis and therefore may contribute to the control of the disease. The aim of this study was to investigate the genetic diversity in bovine MAP isolates using PCR-based methods detecting genetic elements called Variable-Number Tandem Repeats (VNTRs) and Mycobacterial Interspersed Repetitive Units (MIRUs) to determine if multiple MAP strains can coexist on farms with endemic MAP infection. For 52 temporal isolates originating from infected cattle from 32 commercial dairy herds with known trading history, MIRU-VNTR analysis was applied at 10 loci of which six showed variation. Within the group of 52 isolates, 17 different MIRU-VNTR patterns were detected. One MIRU-VNTR pattern was found in 29 isolates, one pattern in four isolates, one pattern in three isolates, two times one MIRU-VNTR pattern was found occurring in two isolates, and 12 patterns were found only once. Eleven herds provided multiple isolates. In five herds a single MIRU-VNTR pattern was detected among multiple isolates whereas in six herds more than one pattern was found. This study confirms that between dairy farms as well as within dairy farms, infected animals shed MAP with different MIRU-VNTR patterns. Analysis of trading history and age within herds indicated that cows born within the same birth cohort can be infected with MAP strains exhibiting variations in the number of MIRU-VNTR repeats. These data indicate that such multiple genotypes of MAP can coexist within one herd.     

Estimated within-herd prevalence (WHP) of Mycobacterium avium subsp. paratuberculosis in a sample of Minnesota dairy herds using bacterial culture of pooled fecal samples

The objective of this study was to describe the estimated within-herd prevalence (WHP) of Mycobacterium avium subsp. paratuberculosis (Map) in a sample of infected dairy herds in Minnesota (N = 66) using test results from bacterial culture of pooled fecal samples. Fecal samples were collected from up to 100 cows in each herd and were tested using bacterial culture in pools of 5 cows based on age order. The mean herd size was 222 (44 to 1500) milking cows; the cows were predominantly Holstein. Using a frequentist approach, the within-herd mean individual fecal prevalence was 10% [95% confidence interval (CI) = 4% to 16%] assuming 70% test sensitivity and 99.5% test specificity. Using Bayesian methods, the estimated true within-herd individual cow prevalence was 14% (95% CI = 7% to 27%). Within-herd prevalence was higher in larger dairy herds than in herds with fewer cows. As Map is the causative agent of Johne's disease (JD), the results of this study could contribute to the success of a nationwide control program for this disease.     

Evaluation of environmental fecal culture for Mycobacterium avium subspecies paratuberculosis detection in dairy herds and association with apparent within-herd prevalence

This study evaluated test characteristics of environmental culture (EC) for the detection of Mycobacterium avium subspecies paratuberculosis (MAP) in 32 herds over a 2-year period. Individual fecal samples were collected every 6 mo and environmental samples every 3 mo. Individual fecal culture was performed on samples from positive pools. Samples were cultured in broth, with confirmatory polymerase chain reaction performed on positive fecal samples. Repeated measures were accounted for using GEE logistic models. Relative to a MAP herd-status based on all pooled fecal culture results collected during the study, sensitivity of a set of 6 EC-samples collected from prescribed locations within the herd environment (EC-6) was 71% [95% confidence interval (CI): 49% to 86%] and specificity was 99% (95% CI: 95% to 100%). Sensitivity of EC increased as apparent within-herd fecal culture prevalence (aWHP) increased. The estimated aWHP increased as the proportion of positive EC-samples within an EC-6 set increased. Environmental culture is an acceptable tool for herd diagnosis of MAP in low-prevalence herds.     

The association between Mycobacterium avium subsp. paratuberculosis fecal shedding or clinical Johne's disease and lactation performance on two Minnesota, USA dairy farms

Lactation performance of cows infected with Mycobacterium avium subsp. paratuberculosis (Map) was previously studied using only serum ELISA as a diagnostic method. This study evaluated on two dairy farms in Minnesota, USA the lactation performance (measures of health, production, reproduction, and survival) of cows shedding Map in feces before calving and of cows culled with clinical signs consistent with Johne's disease (JD) during the subsequent lactation. Fecal samples were collected from 1052 cows within 21 day before calving and tested for Map with bacterial culture. Producers’ observed signs of clinical disease (milk fever, retained placenta, metritis, ketosis, displaced abomasum, lameness, mastitis, pneumonia, and JD) and production and reproduction data were recorded for each cow. The association between fecal shedding or clinical JD and lactation performance was evaluated. Logistic regression was used to evaluate the association with any clinical and subclinical diseases as the outcome. General linear model was used to evaluate the association with milk production, and survival analysis techniques were used to evaluate the association with days in the study before culling and days from calving to conception. In 84 cows (8% of 1052 cows) fecal samples were positive for Map (46% light, 26% moderate, and 28% heavy shedders). In multivariable analysis, light, moderate, and heavy fecal shedding cows produced on average 537, 1403, and 1534 kg, respectively, less milk per lactation and 1.4, 5.2, and 7.5 kg, respectively, less milk per day than fecal negative cows. Fecal culture positive cows were less likely to be bred and conceive. In the multivariable analysis the 56 cows culled with presumed JD produced approximately 1500 kg/lactation or 5 kg/day less than all other cows. The negative economic impact implied by decreased lactation performance in cows shedding Map or with clinical JD may motivate producers to implement programs to control Map infection and subsequent JD.     

Calves shedding Mycobacterium avium subspecies paratuberculosis are common on infected dairy farms

Mycobacterium avium subspecies paratuberculosis (MAP) causes Johne’s disease, a chronic progressive enteritis. It is generally assumed that calves rarely shed MAP bacteria and that calf-to-calf transmission is of minor importance. The objectives were 1) to estimate the prevalence of MAP-shedding young stock in MAP-infected dairy herds, and identify predictors for test-positive young stock; and 2) to estimate proportions of MAP-contaminated young stock group housing pens and air spaces, and furthermore, identify predictors for test-positive pens. Fecal samples were collected from 2606 young stock on 18 MAP-infected dairy farms. Environmental fecal samples were collected from all group-housing pens and dust samples were collected from all barns. All individual samples were analysed using IS900 and F57 qPCR; fecal samples positive by either PCR and all environmental and dust samples were cultured. Overall, 8.1, 1.2 and 2.0% of cattle were positive on IS900 qPCR, F57 qPCR and bacterial culture, respectively. Young stock housed on farms with culture-positive environmental samples collected from adult cow housing and manure storage had higher odds of testing IS900 qPCR-positive than young stock housed on farms with only negative environmental samples. Furthermore, 14% of collected environmental samples, but no dust samples, were test-positive. Age of cattle in the pen was a significant predictor for environmental sample results. Young stock excreted MAP bacteria in their feces which provided strong evidence for calves as sources of within-herd transmission of MAP on dairy farms known to be infected with this organism.

Electronic supplementary material

The online version of this article (doi:10.1186/s13567-015-0192-1) contains supplementary material, which is available to authorized users.     

Cow-level evaluation of a kinetics ELISA with multiple cutoff values to detect fecal shedding of Mycobacterium avium subspecies paratuberculosis in New York State dairy cows

In control programs for Mycobacterium avium subsp. paratuberculosis (Map), the infection status of the cows in a herd is often obtained by testing (a sample of) the herd with an ELISA that may lack some sensitivity and specificity but that is fast and inexpensive. In New York State (NYS), an unabsorbed kinetics ELISA (KELA) has been used extensively for Map control. The objective of this study was to determine the relative sensitivity and specificity of the KELA for detection of fecal shedding of Map for the NYS dairy cow population, taking into account possible confounders such as different antigen batches and Map prevalence in a herd.

The data for the study consisted of all serum samples from NYS dairy cows with concurrent fecal culture results submitted to the NY Animal Health Diagnostic Laboratory (NYAHDL) between 1991 and 1996 (n = 10,562). The data represented cows with different levels of fecal shedding from herds with different within-herd Map prevalence, including herds that were whole herd fecal culture negative on repeated testing.

The cutoff values were based on the predictive value for fecal shedding obtained with a multiple logistic regression model that included variables for the three antigen batches and the Map prevalence in the herd. The KELA could not distinguish between non-shedders and low shedders (≤30 total colony forming units (TCFU)) and thus the predictive value of the KELA to detect moderate to heavy fecal shedders (>30 TCFU) was modeled. The three cutoff values of 65, 135 and 170 were based on low (<0.2), moderate (<0.80) and high (>0.95) probabilities for moderate to heavy fecal shedding. The sensitivity and specificity values relative to culture were 67% and 95.2%, 31% and 99.7%, and 11% and 99.9% for the three cutoff values, respectively. Cutoff values for the KELA decreased for herds with increasing within-herd Map prevalence. For the best positive predictive value of a KELA for moderate to heavy fecal shedding, the cutoff values should be determined based on the apparent within-herd prevalence in a herd.