Culture of strategically pooled bovine fecal samples as a method to screen herds for paratuberculosis.

Fecal samples from 733 cows in 11 dairy herds with a low prevalence of paratuberculosis were cultured for the presence of Mycobacterium avium subsp. paratuberculosis both individually and after combining (pooling) in groups of 5. The culture procedure was the modified Jorgensen method, which uses NaOH and oxalic acid for decontamination and modified Lowenstein-Jensen agar slants for cultivation. Pooling was performed by mixing fecal samples from 5 animals ordered by age, herein referred to as strategic pooling. Culture of individual fecal samples detected M. a. paratuberculosis infections in 43 of the 733 cows and 7 of 11 infected herds (herd sensitivity = 64%). Culture of pooled fecal samples detected M. a. paratuberculosis in 28 of 151 pooled samples representing 8 of the infected 11 herds (herd sensitivity = 73%). Feces of the 43 culture-positive cows was included in 32 pools: of these 32 pools, 26 were culture positive and 6 were culture negative. In addition to the 26 positive pools containing feces from cows that were found culture positive on individual fecal samples, another 2 pools were culture positive, although comprised of feces from cows with negative results after culture of individual fecal samples. From the total of 45 infected cows that were found (43 by individual fecal culture and an additional 2 by pooled fecal culture), individual fecal culture detected 43 of these 45 (96%), while pooled fecal culture detected 39 (87%). Culture of strategically pooled fecal samples using the modified Jorgensen method was equivalent in herd sensitivity to the culture of individual fecal samples and is significantly less expensive.     

Evaluation of four commercial serum ELISAs for detection of Mycobacterium avium subsp. paratuberculosis infection in dairy cows

During the first 3 months of 2006, a study was performed on four dairy cattle herds with a history of clinical paratuberculosis, to evaluate different enzyme-linked immunosorbent assays (ELISAs). Serum samples obtained from 326 animals were analysed using four ELISAs to detect antibodies to Mycobacterium avium subsp. paratuberculosis (MAP). Kappa (kappa) concordance coefficients in pairwise comparisons of the ELISA outcomes ranged up to 0.22 (linear kappa) and 0.25 (quadratic kappa). When the borderline positives obtained were considered as negatives, kappa values remained low (kappa up to 0.19). Having performed the serological tests, faecal samples were then obtained from 55 animals (including all animals testing positive in two or more ELISAs) from the same herds. Faecal culture and faecal polymerase chain reaction (PCR) for the detection of MAP were negative in all cases. The results indicate that neither the currently available serum ELISAs nor faecal culture and PCR are effective for the early detection of MAP in dairy cattle.     

Identification of Mycobacterium avium ssp. paratuberculosis infected dairy herds by environmental sampling

In herds with known prevalence (P) use of environmental sampling (ES) to detect Mycobacterium avium ssp. paratuberculosis (MAP) infected cattle herds was proofed in relation to P. In 31 MAP-infected free stall dairy herds and 15 non-infected herds P was defined by annually repeated whole herd testing by fecal culture (34 877 individual samples). Eight infected herds had a very low (> 0-2%), 14 a low (> 2-5%), four a medium (> 5-10%), and five a high P (> 10%). A mean number of nine environmental samples per herd were collected from the floor of lactating cows, milking, calving and sick cow areas and the crossover to the calf area. After twelve weeks cultivation on HEYM-medium with and without mycobactin positive samples were further characterized by PCR. All non-infected herds (100%) showed negative and 22 (71%) of the infected herds positive results in ES. Nine infected herds with negative ES results had a low P (0.04-4,04%). Proportion of positive ES depended on P and on sampling areas with 53.3% positive results in lactating cow areas and 45.2% in milking areas. For P > 5%, ES in these two areas caused a positive herd status; herds with P < 5% required sampling in the other areas too. The ES method has a herd sensitivity of 87% for dairy herds with P > 2% and provides an efficient tool to determine MAP infection status or herd prevalence.     

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.     

Use of long-term vaccination with a killed vaccine to prevent fecal shedding of Mycobacterium avium subsp paratuberculosis in dairy herds

OBJECTIVES: To determine whether vaccination with a killed vaccine prevents fecal shedding of Mycobacterium avium subsp paratuberculosis, to compare effectiveness of a culture and cull program in vaccinated and nonvaccinated herds, and to compare paratuberculosis-related preventive management in vaccinated and nonvaccinated herds. SAMPLE POPULATION: 58 commercial Dutch dairy herds. DESIGN: Cross-sectional study (study A) in vaccinated (n = 25) and nonvaccinated (29) herds of dairy cows. Longitudinal study (study B) in vaccinated (n = 2) and nonvaccinated (2) herds of dairy cows. PROCEDURE: In study A, fecal samples were obtained from adult cows in herds with and without a history of vaccination with a killed vaccine. Management measures were evaluated. In study B, fecal samples were obtained 4 times at 6-month intervals from cows older than 6 months. Cows that had positive test results were removed from the herd directly after the outcome of the culture. RESULTS: In study A, differences were not detected among the 25 herds that were vaccinated; culture results were positive for M avium subsp paratuberculosis in 4.4% of herds. In 29 herds that had not been vaccinated, culture results were positive in 6.7%. In study B, the percentage of positive results on culture decreased from 10.9% and 5.7% to 3.5% and 0%, respectively in the 2 vaccinated herds. In the 2 nonvaccinated herds, percentages decreased from 6.1% and 16.5% to 0% and 2.3%, respectively. Management practices were different between herds that were vaccinated and herds that were not; owners of herds that were not vaccinated followed more preventive management procedures and practiced less feeding of raw milk to calves. CONCLUSIONS AND CLINICAL RELEVANCE: Vaccination of calves with a killed vaccine does not prevent transmission of M avium subsp paratuberculosis; therefore, hygienic practices remain essential in herd management.     

Seroprevalence of Mycobacterium avium subsp paratuberculosis infection among dairy cows in Colorado and herd-level risk factors for seropositivity

OBJECTIVE: To estimate seroprevalence of Mycobacterium avium subsp paratuberculosis (MAP) infection among adult dairy cows in Colorado and determine herd-level factors associated with the risk that individual cows would be seropositive. DESIGN: Cross-sectional observational study. ANIMALS: 10,280 adult (> or = 2 years old) dairy cows in 15 herds in Colorado. PROCEDURE: Serum samples were tested with a commercial ELISA. A herd was considered to be infected with MAP if results of mycobacterial culture of > or = 1 individual cow fecal sample were positive or if > or = 1 culled cow had histologic evidence of MAP infection. RESULTS: 424 of the 10,280 (4.12%) cows were seropositive. Within-herd prevalence of seropositive cows ranged from 0% to 7.82% (mean, 2.6%). Infection was confirmed in 11 dairies. Cows in herds that had imported > or = 8% of their current herd size annually during the preceding 5 years were 3.28 times as likely to be seropositive as were cows in herds that imported < 8%. Cows in herds with > or = 600 lactating cows were 3.12 times as likely to be seropositive as were cows in herds with < 600 lactating cows. Cows in herds with a history of clinical signs of MAP infection were 2.27 times as likely to be seropositive as were cows in herds without clinical signs. CONCLUSIONS AND CLINICAL RELEVANCE: Annual importation rate, herd size, and whether cows in the herd had clinical signs typical of MAP infection were associated with the risk that individual cows would be seropositive for MAP infection.     

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.     

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.     

Comparison of fecal culture and F57 real-time polymerase chain reaction for the detection of Mycobacterium avium subspecies paratuberculosis in Swiss cattle herds with a history of paratuberculosis

Background

Bovine paratuberculosis is an incurable chronic granulomatous enteritis caused by Mycobacterium avium subspecies paratuberculosis (MAP). The prevalence of MAP in the Swiss cattle population is hard to estimate, since only a few cases of clinical paratuberculosis are reported to the Swiss Federal Food Safety and Veterinary Office each year.Fecal samples from 1,339 cattle (855 animals from 12 dairy herds, 484 animals from 11 suckling cow herds, all herds with a history of sporadic paratuberculosis) were investigated by culture and real-time polymerase chain reaction (PCR) for shedding of MAP.

Results

By culture, MAP was detected in 62 of 445 fecal pools (13.9%), whereas PCR detected MAP in 9 of 445 pools (2.0%). All 186 samples of the 62 culture-positive pools were reanalyzed individually. By culture, MAP was grown from 59 individual samples (31.7%), whereas PCR detected MAP in 12 individual samples (6.5%), all of which came from animals showing symptoms of paratuberculosis during the study. Overall, MAP was detected in 10 out of 12 dairy herds (83.3%) and in 8 out of 11 suckling cow herds (72.7%).

Conclusions

There is a serious clinically inapparent MAP reservoir in the Swiss cattle population. PCR cannot replace culture to identify individual MAP shedders but is suitable to identify MAP-infected herds, given that the amount of MAP shed in feces is increasing in diseased animals or in animals in the phase of transition to clinical disease.     

Effects of infectious young stock on results of certification, surveillance and control programmes for paratuberculosis in dairy herds

In many epidemiological models for paratuberculosis, it is assumed that infected young stock (<2 years of age) do not shed Mycobacterium avium subsp. paratuberculosis (MAP) before adulthood. If this assumption were true, the effective separation of young stock from adult cattle (≥ 2 years) would largely prevent postnatal infections, provided that uninfected adult cattle are highly resistant to infection. However, this assumption is in contrast with observed faecal shedding of MAP in young stock. Consequently, this assumption may have resulted in an underestimation of the effects of MAP transmission in herds participating in certification-, surveillance-, and control programmes for paratuberculosis. Therefore, the aim of the present study was to evaluate the long-term effects of transmission of MAP amongst young stock on key output parameters of certification-, surveillance-, and control programmes for paratuberculosis in simulated closed dairy herds. Closed Dutch dairy herds participating in a paratuberculosis programme were simulated with a stochastic model, JohneSSim. Various test schemes, preventive management measures, distributions of age at onset of faecal shedding and rates of effective contacts between young stock were simulated. The results indicate that transmission of MAP amongst young stock has no relevant effects on the animal-level prevalence and milk quality of herds that are certified in a paratuberculosis programme. However, transmission of MAP amongst young stock increased the economic losses due to paratuberculosis and costs of participation in a programme. Moreover, it substantially decreased the beneficial effect of the separation of young stock from adult cattle on the probability of being certified. However, even in the presence of transmission of MAP amongst young stock, preventive management measures to separate young stock from adult cattle remain important.     

Bayesian analysis to validate a commercial ELISA to detect paratuberculosis in dairy herds of southern Chile

In Chile, Mycobacterium avium subsp. paratuberculosis (Map) has been isolated on several occasions and clinical cases have been reported. Nevertheless, diagnostic tests have not yet been validated for this agent in the Chilean setting. The objective of the study was to validate a commercial ELISA to detect Map shedding dairy cows in management conditions, prevalence and stages of infection existing in Southern Chile, utilising different statistical approaches. Blood and faeces were collected from 1333 lactating cows in 27 dairy herds (both large commercial and smallholder dairy farms) between September 2003 and August 2004. Within the herds up to a maximum of 100 dairy cows were selected based on age (>or=3 years old) and, if present, clinical signs of a Map infection. In herds with less than 100 cows, all cows >or=3 years old were sampled. Blood samples were tested using a commercial ELISA kit (IDEXX Laboratories, Inc.). Faecal samples were cultured on Herrold's Egg Yolk Medium (HEYM). Latent class models (i.e. maximum likelihood (ML) methods and Bayesian inference) were used to determine the validity of the ELISA. Map was cultured from 54 (4.1%) cows and 10 (37.0%) herds, which were all large, commercial dairy herds. As a result of empty cells in the cross-tabulations, the ML model provided the same results as the validation with faecal culture as the gold-standard. In the Bayesian model, the Se and Sp of the ELISA were estimated to be 26% (95% CI: 18-35%) and 98.5% (95% CI: 97.4-99.4%), respectively. For faecal culture, the Se was 54% (95% CI: 46-62%) and the Sp was 100% (95% CI: 99.9-100%). Interestingly, the prevalence in the smallholder dairy farms was estimated to be 8% even though there were no faecal culture positive cows detected in those herds. There was no significant correlation between the two tests. The advantage of Bayesian inference is that the Se and Sp of both tests are obtained in one model relative to the (latent) true disease status, the model can handle small datasets and empty cells and the estimates can be corrected for the correlation between tests when the tests are not conditionally independent. Therefore, Bayesian analysis was the preferred method for Map that lacks a gold-standard and usually has low cow-level prevalence.     

An evaluation of a modified interferon-gamma assay for the detection of paratuberculosis in dairy herds

Whole blood samples were obtained from multiple dairy herds in Pennsylvannia and in Wisconsin which were previously determined to be infected with Mycobacterium paratuberculosis (MpS) (Johne's disease) by fecal culture. Blood samples were shipped overnight to the National Animal Disease Center (NADC) in Ames, IA for processing and interferon-gamma (IFN-gamma) analysis. Blood samples were incubated alone (non-stimulated) or with concanavalin A (ConA), a T-cell mitogen used as a positive control in the assay, for 18h. In addition, samples were incubated with M. avium purified protein derivative (AvPPD), M. bovis purified protein derivative (BoPPD), or a whole cell sonicate of M. paratuberculosis for 18h to elicit antigen-specific IFN-gamma production. After incubation, plasma was harvested and analyzed for IFN-gamma by ELISA. Values for IFN-gamma for non-stimulated blood samples (background) were consistently low for animals in all herds evaluated. In contrast, ConA stimulation of blood samples evoked a significant secretion of IFN-gamma regardless of infection status or fecal culture results for individual cows, indicating that immune cells were still viable after overnight shipment and capable of responding to stimulation. Antigen-specific IFN-gamma results were positively correlated with infection status as determined by previous fecal shedding and/or current fecal shedding of M. paratuberculosis. Accuracy of the IFN-gamma assay for correctly predicting infection status of individual cows in the herds with low levels of infection ranged from 50 to 75% when used as a single test. Combined use of the IFN-gamma test and a commercial ELISA antibody test accurately predicted infection status of 73% of cows from a dairy herd with a high level of M. paratuberculosis infection and 90% from a well-characterized group of dairy cows at the NADC. These results indicate that the antigen-specific IFN-gamma assay is a very sensitive diagnostic tool for detection of subclinical paratuberculosis in cattle and may be useful on an individual animal basis to remove infected animals from the 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.     

Bacteriological investigations about paratuberculosis in dairy herds in Switzerland

In Switzerland clinical bovine paratuberculosis is registered sporadically with on average seven outbreaks per year. Our present studies are aimed to investigate the prevalence of Mycobacterium avium ssp. paratuberculosis (MAP)-infections in the Swiss cattle population and, therefore methods to culture MAP from bovine feces as well as a commercially available ELISA to detect MAP-specific antibodies are evaluated by using fecal samples and blood sera from herds with cases of clinical paratuberculosis. A series of molecular methods i.e. PCR-coupled RFLP analysis of the IS1311-insertion element of M. avium, PCR-coupled RFLP-analysis of the mycobacterial rpoB-gene, and DNA analysis of the mycobacterial 16S rRNA gene are used to identify mycobacterial isolates grown from bovine feces. Up to now, MAP was detected by culture in 12 of 155 (7.7%) animals from herds with paratuberculosis. A rather striking result is the finding of atypical mycobacteria in feces of 75 cattle (48.3%). Among these isolates, M. avium ssp. avium, M. thermoresistibile, and M. hassiacum/M. buckleii have been identified so far.     

Herd-level prevalence of Mycobacterium avium subspecies paratuberculosis by bulk-tank milk PCR in Fars province (southern Iran) dairy herds

A cross-sectional study was conducted from March to August 2006 in dairy herds in Fars province, southern Iran to determine the herd-level prevalence of Mycobacterium avium subspecies paratuberculosis (MAP) infection. Bulk-tank milk samples were collected from 110 dairy herds in the 3 districts (Shiraz, Marvdasht and Sepidan) of the province. Among study populations, 12 herds (11%, 95%CI: 5-17%) were positive for MAP infection based on IS900 nested PCR. The prevalence of positive milk samples in the three districts of Fars province was different ranging from 8.6% to 23% which was not statistically significant (P=0.19). It is recommended to conduct further epidemiologic studies to determine cow-level prevalence and risk factors for infection, and to evaluate the economic consequences of the MAP infection in the region.     

Seroprevalence of antibodies against bovine leukemia virus, bovine viral diarrhea virus, Mycobacterium avium subspecies paratuberculosis, and Neospora caninum in dairy cattle in Saskatchewan

Blood was drawn from 1530 dairy cows in 51 herds. For antibodies against bovine leukemia virus, Mycobacterium avium subspecies paratuberculosis, and Neospora caninum, 37.4%, 2.7%, and 5.6% of cows were test positive, respectively, while 29.2% of herds had unvaccinated animals with > or = 1:64 for bovine viral diarrhea virus.     

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.     

Effect of paratuberculosis on culling, milk production, and milk quality in dairy herds

OBJECTIVE: To determine the effect of paratuberculosis on culling, milk production, and milk quality in infected dairy herds. DESIGN: Cross-sectional study. ANIMALS: 689 lactating dairy cows in 9 herds. PROCEDURE: Milk, blood, and fecal samples were obtained from all cows. Fecal samples were evaluated via mycobacterial culture. Serum samples were tested with a commercially available ELISA for antibodies against Mycobacterium avium subsp paratuberculosis, and preserved milk samples were tested with an ELISA for antibodies against M paratuberculosis. Mixed effect and proportional hazards models were used to determine the effect of paratuberculosis on 305-day milk, fat, and protein production; somatic cell count linear score; and the risk of culling. RESULTS: Cows with positive results of bacteriologic culture of feces and milk ELISA produced less milk, fat, and protein, compared with herdmates with negative results. No difference in 305-day milk or fat production was detected in cows with positive results of serum ELISA, compared with seronegative cows. The 3 survival analyses revealed that cows with positive results of each test were at higher risk of being culled than cows with negative results. Paratuberculosis status, as determined by use of all 3 diagnostic tests, was not associated with milk somatic cell count linear score. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that for the 9 herds in this study, paratuberculosis significantly decreased milk production and cow longevity.     

Diagnosis of paratuberculosis by fecal culture and ELISA on milk and serum samples in two types of Chilean dairy goat herds.

Fecal culture has been the primary method used to diagnose paratuberculosis in goats. It is laborious, slow, and expensive. Validation of enzyme-linked immunosorbent assays (ELISAs) on milk samples could make paratuberculosis testing more widely available for goat farmers. The aim of this study was to determine the accuracy of serum and milk ELISAs for paratuberculosis, relative to fecal culture, in Chilean dairy goats. Eight dairy goat herds were selected. Feces, blood, and milk samples were collected from all female goats >2 years old. Fecal samples were cultured using Herrold egg yolk medium with mycobactin J and antibiotics. Serum and milk samples were tested using a commercial ELISA kit for Mycobacterium avium subsp. paratuberculosis antibody detection. A total of 383 goats were tested by ELISA and fecal culture. The sensitivity of ELISA on serum and milk relative to fecal culture was 74.3% (95% CI: 59.8-88.8) and 60% (95% CI: 43.8-76.2), respectively. The corresponding values for ELISA specificity based on the percentage of non- M. avium subsp. paratuberculosis-infected goats testing ELISA-negative were 98.6% (95% CI: 96.6-100) and 99.3% (95% CI: 97.9-100) on serum and milk, respectively. Proportions of positive results for serum and fecal samples were significantly different, whereas the proportions of positive results for milk and fecal samples were not significantly different. The milk ELISA had a moderate level of agreement with fecal culture results (Kappa = 0.57). The paratuberculosis ELISA on goat milk samples may be a cost-effective, accurate alternative to fecal culture.     

Paratuberculosis in cattle and free-living exotic deer.

Paratuberculosis was studied among dairy cows and exotic deer that shared grazing areas at Point Reyes National Seashore, California. Of the 10 dairy herds tested, 5 (50%) were infected with Mycobacterium paratuberculosis (based on results of fecal culture). Mycobacterium paratuberculosis was cultured from 9 (8.7%) of the 103 bovine fecal samples and from 4 (3.9%) of the 103 bovine rectal mucosa scapings tested. Of 89 fecal samples from 52 axis deer (Axis axis) and 37 fallow deer (Dama dama), 5 (9.6%) and 3 (8.1%), respectively, contained M paratuberculosis. Culture of intestinal necropsy samples from the same deer indicated that 3 (5.8%) of the axis deer and 2 (5.4%) of the fallow deer were infected with M paratuberculosis. The cows were tested for serum antibodies by the complement-fixation test and by radioimmunoassay. Of 95 sera tested by complement fixation, 15 (15.8%) were positive, as were 15 (14.7%) of 102 sera tested by radioimmunoassay. Culture results and serologic test results were compared on a herd basis.