Diagnosis of Paratuberculosis

Current and Emerging Diagnostic Approaches to Bacterial Diseases of Ruminants

The diagnostic approaches and methods to detect bacterial pathogens in ruminants are discussed, with a focus on cattle. Conventional diagnostic methods using culture, isolation, and characterization are being replaced or supplemented with new methods. These include molecular diagnostics such as real-time polymerase chain reaction and whole-genome sequencing. In addition, methods such as matrix-assisted laser desorption ionization-time-of-flight mass spectrometry enable rapid identification and enhanced pathogen characterization. These emerging diagnostic tools can greatly enhance the ability to detect and characterize pathogens, but performance and interpretation vary greatly across sample and pathogen types, disease syndromes, assay performance, and other factors.

Evaluation of Single Nucleotide Polymorphisms (SNPs) Associated with Genetic Resistance to Bovine Paratuberculosis in Marchigiana Beef Cattle, an Italian Native Breed

Mycobacterium avium ssp. paratuberculosis (MAP) is the causative agent of paratuberculosis (PTB), a widespread chronic enteritis of ruminants. The progression of the infection depends on the containment action of innate and cell-mediated immunity (CMI), and it is related to environmental and genetic factors. In particular, PTB susceptibility seems to be associated with specific genes coding for immune regulators involved in the cell-mediated response during the infection. The aim of this preliminary study was to verify, in Italian beef cattle, an association between MAP infectious status and the presence of single nucleotide polymorphisms (SNPs) in candidate genes. To the best of our knowledge, this is the first investigation conducted on a native beef cattle breed, known as Marchigiana, reared in Central Italy. The present research, based on a longitudinal study, aimed to identify and correlate phenotypic and genetic profiles characteristic of the subjects potentially able to contrast or contain PTB. In a MAP-infected herd, ELISA, IFN-γ tests, qPCR, and cultures were performed at a follow-up, occurring within a period ranging from three to six years, to evaluate the individual state of infection. Animals testing positive for at least one test were considered infected. DNA samples of 112 bovines, with known MAP statuses, were analyzed to verify an association with SNPs in the genes encoding gamma-interferon (BoIFNG), interleukin receptor 10 (IL10RA), interleukin receptor 12 (IL12RB2), and toll-like receptors (TLR1, TLR2, TLR4). Regarding statistical analysis, the differences among target genes and pairs of alleles in the analyzed groups of animals, were evaluated at a significance level of p < 0.05. For IL10RA and for IL12RB2 genes, relevant differences in genotypic frequencies among the considered cattle groups were observed. For all candidate genes studied in this investigation, SNP genotypes already associated with PTB resistance were found more frequently in our population, suggesting potential resistance traits in the Marchigiana breed.

Characterization of early immune responses elicited by live and inactivated vaccines against Johne's disease in goats

Mycobacterium avium subspecies paratuberculosis (M. paratuberculosis) is the causative agent of Johne's disease, a chronic debilitating condition affecting ruminants causing significant economic losses to the dairy industry. Available inactivated vaccines are not effective in controlling the disease and vaccinated animals can continue to infect newly born calves. Recently, we have shown that a live-attenuated vaccine candidate (pgsN) is protective in goats and calves following challenge with virulent strains of M. paratuberculosis. To decipher the dynamics of the immune responses elicited by both live-attenuated and inactivated vaccines, we analyzed key immunological parameters of goats immunized through different routes when a marker-less pgsN vaccine was used. Within a few weeks, the inactivated vaccine triggered the formation of granulomas both at the site of inoculation and in regional lymph nodes, that increased in size over time and persisted until the end of the experiment. In contrast, granulomas induced by the pgsN vaccine were small and subsided during the study. Interestingly, in this vaccine group, histology demonstrated an initial abundance of intra-histiocytic mycobacterial bacilli at the site of inoculation, with recruitment of very minimal T lymphocytes to poorly organized granulomas. Over time, granulomas became more organized, with recruitment of greater numbers of T and B lymphocytes, which coincided with a lack of mycobacteria. For the inactivated vaccine group, mycobacterial bacilli were identified extracellularly within the center of caseating granulomas, with relatively equal proportions of B- and T-lymphocytes maintained across both early and late times. Despite the differences in granuloma-specific lymphocyte recruitment, markers for cell-mediated immunity (e.g., IFN-γ release) were robust in both injected pgsN and inactivated vaccine groups. In contrast, the intranasal live-attenuated vaccine did not elicit any reaction at site of inoculation, nor cell-mediated immune responses. Finally, 80% of animals in the inactivated vaccine group significantly reacted to purified protein derivatives from M. bovis, while reactivity was detected in only 20% of animals receiving pgsN vaccine, suggesting a higher level of cross reactivity for bovine tuberculosis when inactivated vaccine is used. Overall, these results depict the cellular recruitment strategies driving immune responses elicited by both live-attenuated and inactivated vaccines that target Johne's disease.

Detection of Low MAP Shedder Prevalence in Large Free-Stall Dairy Herds by Repeated Testing of Environmental Samples and Pooled Milk Samples

Simple Summary

Paratuberculosis is a disease which affects ruminants worldwide. Many countries have implemented certification and monitoring systems to control the disease, particularly in dairy herds. Monitoring herds certified as paratuberculosis non-suspect is an important component of paratuberculosis herd certification programs. The challenge is to detect the introduction or reintroduction of the infectious agent as early as possible with reasonable efforts but high certainty. In our study, we evaluated different low-cost testing schemes in herds where the share of infected animals was low, resulting in a low within-herd prevalence of animals shedding the bacteria that causes paratuberculosis in their feces. The test methods used were repeated pooled milk samples and fecal samples from the barn environment. Our study showed that numerous repetitions of different samples are necessary to monitor such herds with sufficiently high certainty. In the case of herds with a very low prevalence, our study showed that a combination of different sampling approaches is required.

Abstract

An easy-to-use and affordable surveillance system is crucial for paratuberculosis control. The use of environmental samples and milk pools has been proven to be effective for the detection of Mycobacterium avium subsp. paratuberculosis (MAP)-infected herds, but not for monitoring dairy herds certified as MAP non-suspect. We aimed to evaluate methods for the repeated testing of large dairy herds with a very low prevalence of MAP shedders, using different sets of environmental samples or pooled milk samples, collected monthly over a period of one year in 36 herds with known MAP shedder prevalence. Environmental samples were analyzed by bacterial culture and fecal PCR, and pools of 25 and 50 individual milk samples were analyzed by ELISA for MAP-specific antibodies. We estimated the cumulative sensitivity and specificity for up to twelve sampling events by adapting a Bayesian latent class model and taking into account the between- and within-test correlation. Our study revealed that at least seven repeated samplings of feces from the barn environment are necessary to achieve a sensitivity of 95% in herds with a within-herd shedder prevalence of at least 2%. The detection of herds with a prevalence of less than 2% is more challenging and, in addition to numerous repetitions, requires a combination of different samples.

Detection of Mycobacterium avium Subspecies paratuberculosis (MAP) Microorganisms Using Antigenic MAP Cell Envelope Proteins

Cell envelope proteins from Mycobacterium avium subspecies paratuberculosis (MAP) that are antigenically distinct from closely related mycobacterial species are potentially useful for Johne's Disease (JD) diagnosis. We evaluated the potential of ELISAs, based on six antigenically distinct recombinant MAP cell envelope proteins (SdhA, FadE25_2, FadE3_2, Mkl, DesA2, and hypothetical protein MAP1233) as well as an extract of MAP total cell envelope proteins, to detect antibodies against MAP in the sera of infected cattle. The sensitivity (Se) and specificity (Sp) of an ELISA based on MAP total cell envelope proteins, when analyzing 153 bovine serum samples, was 75 and 96%, respectively. Analysis of the same samples, using a commercial serum ELISA resulted in a Se of 56% and Sp of 99%. Results of ELISA analysis using plates coated with recombinant cell envelope proteins ranged from a highest Se of 94% and a lowest Sp of 79% for Sdh A to a lowest Se of 67% and a highest Sp of 95% for hypothetical protein MAP1233. Using polyclonal antibodies to MAP total cell envelope proteins, immunohistochemical analysis of intestinal and lymph node tissues from JD-positive cattle detected MAP organisms whereas antibodies to recombinant proteins did not. Finally, polyclonal antibodies to MAP total cell envelope protein and to recombinant SdhA, FadE25_2, and DesA2 proteins immunomagnetically separated MAP microorganisms spiked in PBS. These results suggest that antigenically distinct MAP cell envelope proteins and antibodies to these proteins may have potential to detect MAP infection in dairy cattle.

Short communication: Occurrence and differentiation of Mycobacterium avium ssp. paratuberculosis (MAP) strains from milk of cows from herd with low prevalence of MAP

Mycobacterium avium ssp. paratuberculosis (MAP) is an important pathogen responsible for the chronic progressive granulomatous enteritis known as paratuberculosis. None of the detection methods of MAP infection based on isolation of the bacterium is 100% sensitive or specific. In this article, we describe the comparison of 2 MAP detection methods: direct isolation of genetic material and culture, in individual and pooled milk samples. The genetic types of MAP detected in the samples were also identified. The study was performed in a herd of 321 cows; apparent herd seroprevalence was 3.43%. Seven of 11 individual milk samples from seropositive cows were positive by culture (and confirmed by PCR), whereas all 11 were positive by direct PCR. Of the 62 milk pools from seronegative animals, 15 were positive by culture (and confirmed by PCR) and 13 were positive by direct PCR. Using multiplex PCR and PCR-restriction enzyme analysis (PCR-REA) methods, C (cattle) and S (sheep)-types of mycobacteria were identified. Most of the genetic material tested belonged to C-type. Detection of the MAP type occurring in an infected herd can help track the source of infection. We suggest using genetic material isolated directly from pooled milk samples for quick diagnosis, identification of MAP type, and tracking of infection, without the need to sequence the entire genome.

Effects of freezing on ability to detect Mycobacterium avium subsp. paratuberculosis from bovine tissues following culture

Mycobacterium avium subsp. paratuberculosis (MAP) is the bacterium that causes Johne's disease in cattle. Although infected cattle can be identified by examining fecal, blood, or milk samples, the gold standard is identification of MAP in tissue samples postmortem. Although tissue samples are commonly frozen, the ability to detect MAP in frozen-thawed tissue samples has apparently not been reported. We therefore determined the ability to detect MAP in tissue samples following freezing. Tissue samples were collected from calves that were either inoculated (IN) 3 mo prior, or contact-exposed (CE) for 3 mo. Following autopsy, tissues were immediately processed for culture, followed by DNA extraction and detection by qPCR. Samples were categorized as positive or negative based on the cycle threshold (Ct) value. The remaining unprocessed tissue samples were frozen at -80°C. After 18 mo, 50 tissue samples designated MAP-positive were thawed and processed for detection of MAP. Four (8%) samples were qPCR-negative, and Ct values of the remaining 46 samples were higher after freezing. Given the small numerical change in Ct values for MAP-positive samples after 18 mo of frozen storage, freezing and thawing may have had some deleterious effects on MAP detection in tissues. Although the decrease in ability to detect MAP-positive samples was minor for IN calves, there may be a greater effect for CE calves that should be considered when freezing tissue samples.

Comparison of three DNA extraction methods for molecular confirmation of Mycobacterium avium subspecies paratuberculosis from the VersaTrek™ liquid cultures of bovine fecal samples

We evaluated three DNA extraction methods for confirmation of Mycobacterium avium subspecies paratuberculosis from liquid cultures of bovine feces. Use of DNA Extract All Reagents Kit™ resulted in efficient extraction of amplifiable DNA from higher proportion (96.29%) of known positive samples compared to Chelex-100 resin (25.92%) and polyethylene glycol (0%).

Pathogenesis, Molecular Genetics, and Genomics of Mycobacterium avium subsp. paratuberculosis, the Etiologic Agent of Johne's Disease

Mycobacterium avium subsp. paratuberculosis (MAP) is the etiologic agent of Johne's disease in ruminants causing chronic diarrhea, malnutrition, and muscular wasting. Neonates and young animals are infected primarily by the fecal-oral route. MAP attaches to, translocates via the intestinal mucosa, and is phagocytosed by macrophages. The ensuing host cellular immune response leads to granulomatous enteritis characterized by a thick and corrugated intestinal wall. We review various tissue culture systems, ileal loops, and mice, goats, and cattle used to study MAP pathogenesis. MAP can be detected in clinical samples by microscopy, culturing, PCR, and an enzyme-linked immunosorbent assay. There are commercial vaccines that reduce clinical disease and shedding, unfortunately, their efficacies are limited and may not engender long-term protective immunity. Moreover, the potential linkage with Crohn's disease and other human diseases makes MAP a concern as a zoonotic pathogen. Potential therapies with anti-mycobacterial agents are also discussed. The completion of the MAP K-10 genome sequence has greatly improved our understanding of MAP pathogenesis. The analysis of this sequence has identified a wide range of gene functions involved in virulence, lipid metabolism, transcriptional regulation, and main metabolic pathways. We also review the transposons utilized to generate random transposon mutant libraries and the recent advances in the post-genomic era. This includes the generation and characterization of allelic exchange mutants, transcriptomic analysis, transposon mutant banks analysis, new efforts to generate comprehensive mutant libraries, and the application of transposon site hybridization mutagenesis and transposon sequencing for global analysis of the MAP genome. Further analysis of candidate vaccine strains development is also provided with critical discussions on their benefits and shortcomings, and strategies to develop a highly efficacious live-attenuated vaccine capable of differentiating infected from vaccinated animals.

Fecal shedding and tissue infections demonstrate transmission of Mycobacterium avium subsp. paratuberculosis in group-housed dairy calves

Current Johne’s disease control programs primarily focus on decreasing transmission of Mycobacterium avium subsp. paratuberculosis (MAP) from infectious adult cows to susceptible calves. However, potential transmission between calves is largely overlooked. The objective was to determine the extent of MAP infection in calves contact-exposed to infectious penmates. Thirty-two newborn Holstein–Friesian calves were grouped into 7 experimental groups of 4, consisting of 2 inoculated (IN) calves, and 2 contact-exposed (CE) calves, and 1 control pen with 4 non-exposed calves. Calves were group housed for 3 months, with fecal samples were collected 3 times per week, blood and environmental samples weekly, and tissue samples at the end of the trial. The IN calves exited the trial after 3 months of group housing, whereas CE calves were individually housed for an additional 3 months before euthanasia. Control calves were group-housed for the entire trial. All CE and IN calves had MAP-positive fecal samples during the period of group housing; however, fecal shedding had ceased at time of individual housing. All IN calves had MAP-positive tissue samples at necropsy, and 7 (50%) of the CE had positive tissue samples. None of the calves had a humoral immune response, whereas INF-γ responses were detected in all IN calves and 5 (36%) CE calves. In conclusion, new MAP infections occurred due to exposure of infectious penmates to contact calves. Therefore, calf-to-calf transmission is a potential route of uncontrolled transmission on cattle farms.

Application of antibodies to recombinant heat shock protein 70 in immunohistochemical diagnosis of mycobacterium avium subspecies paratuberculosis in tissues of naturally infected cattle

Background

Detection of Mycobacterium avium subspecies paratuberculosis (MAP) infection is key to the control of Johne’s disease. Immunohistochemistry is one of the methods of detection of MAP infection in tissues. However, unavailability of commercial antibodies that can detect the organism is a limiting factor for the use of immunohistochemistry. This study was aimed at developing an immunohistochemistry method to diagnose MAP in infected tissues using antibodies against MAP recombinant heat shock protein 70kd.

Results

MAP Heat shock protein 70 gene was amplified and cloned into an expression vector, Champion pET-SUMO, then expressed in E coli, purified and used to produce polyclonal rabbit antibodies against the Heat shock protein. Immunohistochemistry was performed in 35 MAP infected tissues with anti-HSP70 polyclonal antibodies. All 35 MAP infected tissues were positive for MAP within macrophages, epithelioid cells and giant cells either in clumps or singly as individual bacilli. No positive staining was seen in the three uninfected normal tissues and in MAP infected tissues where primary antibodies were substituted with PBS or pre-immune serum from the same rabbit.

Conclusion

Anti-HSP70 produced in this study offers an opportunity for improved diagnosis, screening of MAP in animal tissues and in studies on the pathogenesis of MAP

Electronic supplementary material

The online version of this article (doi:10.1186/s13620-017-0088-7) contains supplementary material, which is available to authorized users.

Mycobacterium avium ssp. paratuberculosis detection in animals, food, water and other sources or vehicles of human exposure: A scoping review of the existing evidence

Mycobacterium avium ssp. paratuberculosis is the etiologic agent of Johne's disease in ruminants and is hypothesized to be an infectious cause of Crohn's disease, as well as some other human diseases. Due to key knowledge gaps, the potential public health impact of M. paratuberculosis is unknown. This scoping review aims to identify and characterised the evidence on potential sources and vehicles of M. paratuberculosis exposure for humans to better understand how exposure is likely to occur. Evidence from 255 primary research papers is summarized; most examined the prevalence or concentration of M. paratuberculosis in animals (farmed domestic, pets and wildlife) (n=148), food for human consumption (62) (milk, dairy, meat, infant formula) or water (drinking and recreational) and the environment (farm, pasture and areas affected by runoff water) (20). The majority of this research has been published since 2000 (Figure- abstract). Nine case-control studies examining risk factors for Crohn's disease highlighted significant associations with the consumption of processed meats and cheese, while direct contact with ruminants, high risk occupations (farmer, veterinarian), milk consumption and water source were factors not associated with the disease and/or M. paratuberculosis exposure status. Molecular epidemiology studies demonstrated strain-sharing between species. Produce and seafood were the only previously suggested sources of human exposure for which there was no supporting evidence identified in this scoping review. The results of this review indicate that ruminant populations from around the globe are infected with M. paratuberculosis and many non-ruminant species have also been found to carry or be infected with M. paratuberculosis. Several potential sources for human exposure to M. paratuberculosis were identified; however there remain important gaps in quantitative information on the prevalence and concentration of M. paratuberculosis in contaminated sources of exposure. This information is critical to understanding the risk of exposure, opportunities for risk mitigation interventions and modelling exposures to distill the importance of various sources of human exposure to M. paratuberculosis including direct contact with animals and the environment as well as consumption of contaminated foods and water. Results of this study may be used to prioritize future research and to support evidence-informed decision-making on the M. paratuberculosis issue.

Implications of PCR and ELISA results on the routes of bulk-tank contamination with Mycobacterium avium ssp. paratuberculosis

Mycobacterium avium ssp. paratuberculosis (MAP), the etiologic agent of Johne's disease in dairy cattle, may enter the bulk tank via environmental contamination or direct excretion into milk. Traditionally, diagnostics to identify MAP in milk target either MAP antibodies (by ELISA) or the organism itself (by culture or PCR). High ELISA titers may be directly associated with excretion of MAP into milk but only indirectly linked to environmental contamination of the bulk tank. Patterns of bulk-milk ELISA and bulk-milk PCR results could therefore provide insight into the routes of contamination and level of infection or environmental burden. Coupled with questionnaire responses pertaining to management, the results of these diagnostic tests could reveal correlations with herd characteristics or on-farm practices that distinguish herds with high and low environmental bulk-tank MAP contamination. A questionnaire on hygiene, management, and Johne's specific parameters was administered to 292 dairy farms in New York, Oregon, and Wisconsin. Bulk-tank samples were collected from each farm for evaluation by real-time PCR and ELISA. Before DNA extraction and testing of the unknown samples, bulk-milk template preparation was optimized with respect to parameters such as MAP fractionation patterns and lysis. Two regression models were developed to explore the relationships among bulk-tank PCR, ELISA, environmental predictors, and herd characteristics. First, ELISA optical density (OD) was designated as the outcome in a linear regression model. Second, the log odds of being PCR positive in the bulk tank were modeled using binary logistic regression with penalized maximum likelihood. The proportion of PCR-positive bulk tanks was highest for New York and for organic farms, providing a clue as to the geographical patterns of MAP-positive bulk-tank samples and relationship to production type. Bulk-milk PCR positivity was also higher for large relative to small herds. The models revealed that bulk-milk PCR result could predict ELISA OD, with PCR-positive results corresponding to high bulk-milk ELISA titers. Similarly, ELISA was a predictor of PCR result, although the association was stronger for organic farms. Despite agreement between high bulk-milk ELISA titers and positive PCR results, a large proportion of high ELISA farms had PCR-negative bulk tanks, suggesting that farms are able to maintain satisfactory hygiene and management despite a presence of MAP in these herds.

Mycobacterium avium Subspecies paratuberculosis and Bovine Leukemia Virus Seroprevalence and Associated Risk Factors in Commercial Dairy and Beef Cattle in Northern and Northeastern China

Mycobacterium avium subspecies paratuberculosis (MAP) and bovine leukemia virus (BLV) are important pathogens, commonly responsible for economical loss to cattle farms all over the world, yet their epidemiology in commercial dairy and beef cattle in China is still unknown. Thus, from September 2013 to December 2014, a large-scale seroprevalence study was conducted to determine the seroprevalence and identify herd-level risk factors associated with MAP and BLV infection. The source sample was 3674 cattle from 113 herds in northern and northeastern China. Antibodies against MAP and BLV were detected using ELISA tests. At animal-level, the seroprevalence of antibodies against MAP and BLV was 11.79% (433/3674) and 18.29% (672/3674), respectively. At herd-level, the seroprevalence of antibodies against MAP and BLV was 20.35% and 21.24% (24/113), respectively. Herd size was identified to be associated with MAP infection while herd size and presence of cattle introduced from other farms were significantly associated with BLV infection. Further research is needed to confirm these findings and improve the knowledge of the epidemiology of these two pathogens in these regions and elsewhere in China.

Sensitivity and specificity of repeated test results from a commercial milk enzyme-linked immunosorbent assay for detection of Mycobacterium avium subspecies paratuberculosis in dairy cattle

OBJECTIVE

To investigate the sensitivity and specificity of results of initial and repeated milk ELISAs (at 6- or 12-month intervals) to detect cows that were shedding Mycobacterium avium subsp paratuberculosis (ie, were infectious) and to evaluate factors influencing the probability that the results of a repeated milk ELISA would be positive for an infectious cow if the results of the initial milk ELISA were negative.

DESIGN

Prospective cohort study.

ANIMALS

3,145 dairy cows from 32 herds.

PROCEDURES

Herds from the 3 Maritime provinces in Canada (Prince Edward Island, New Brunswick, and Nova Scotia), participating in a Dairy Herd Improvement program, and that had undergone a prior Mycobacterium avium subsp paratuberculosis awareness project were selected for the study. Sample collection occurred between April 2009 and March 2011 with milk and fecal samples collected from all lactating cows in study herds every 6 months. Herds completing < 3 herd visits with collection of individual cow fecal or milk samples, within this sampling timeframe, were excluded from analyses. Fecal samples were cultured in liquid medium and a cow was defined as infectious if ≥ 1 sample was culture positive (reference test). A milk ELISA (index test) was completed with a commercial kit, following manufacturer's instructions.

RESULTS

For a 6-month test interval, sensitivities of the milk ELISA to detect infectious cows were 22.0% and 32.6% for initial and combined initial and repeated tests (parallel interpretation), respectively. Specificity of the initial ELISA was 99.6% and was 99.2% for combined tests. For a 12-month test interval, sensitivities of the milk ELISA to detect infectious cows were 25.6% and 45.3% for initial and combined initial and repeated tests (parallel interpretation), respectively. Specificity of the initial ELISA was 99.6% and was 98.9% for combined tests. In infectious cows, magnitude of the initial negative ELISA result was a positive predictor for a positive repeated ELISA result.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of a repeated milk ELISA improved detection of Mycobacterium avium subsp paratuberculosis infectious cows, with minimal loss of specificity. A 12-month test interval provided a greater increase in sensitivity, relative to an initial test, than did a 6-month interval. Infectious cows with an initial negative milk ELISA result close to the cutoff for a positive test were more likely to have positive results on a repeated ELISA. Repeated testing improved detection of infectious cows and reduced risk of misclassification compared with a single ELISA result.

Susceptibility to and diagnosis of Mycobacterium avium subspecies paratuberculosis infection in dairy calves: A review

The primary objectives of paratuberculosis control programs are reducing exposure of calves to Mycobacterium avium subspecies paratuberculosis (MAP), reducing herd infection pressure and regular testing of cattle >36 months of age. Although control programs based on these principles have reduced prevalence of MAP infection in dairy herds, they have generally not eliminated the infection. Recent infection trial(s) have yielded new knowledge regarding diagnostic testing and age- and dose-dependent susceptibility to MAP infection. Calves up to 1 year of age are still susceptible to MAP infection; therefore, control programs should refrain from referring to specific ages with respect to susceptibility and prevention of new infections. Notwithstanding, lesions were more severe when calves were inoculated at 2 weeks versus 1 year of age. Furthermore, a high inoculation dose resulted in more pronounced lesions than a low inoculation dose, especially in young calves. Consequently, keeping infection pressure low should decrease the incidence of new MAP infections and severity of JD in cattle that do acquire the infection. It was also evident that early diagnosis of MAP infection was possible and could improve efficacy of control programs. Although its use will still need to be validated in the field, a combination of antibody ELISA and fecal culture in young stock, in addition to testing cattle >36 months of age when screening a herd for paratuberculosis, was expected to improve detection of dairy cattle infected with MAP. Although calves were inoculated using a standardized method in a controlled environment, there were substantial differences among calves with regards to immune response, shedding and pathology. Therefore, we inferred there were genetic differences in susceptibility. Important insights were derived from experimental infection trials. Therefore, it was expected that these could improve paratuberculosis control programs by reducing severity and incidence of JD by lowering infection pressure on-farm, and reducing exposure of young calves and older cattle. Furthermore, an earlier diagnosis could be achieved by combining ELISA and fecal shedding in young stock, in addition to testing cattle >36 months of age.

Development and evaluation of a novel multicopy-element-targeting triplex PCR for detection of Mycobacterium avium subsp. paratuberculosis in feces

The enteropathy called paratuberculosis (PTB), which mainly affects ruminants and has a worldwide distribution, is caused by Mycobacterium avium subsp. paratuberculosis. This disease significantly reduces the cost-effectiveness of ruminant farms, and therefore, reliable and rapid detection methods are needed to control the spread of the bacterium in livestock and in the environment. The aim of this study was to identify a specific and sensitive combination of DNA extraction and amplification to detect M. avium subsp. paratuberculosis in feces. Negative bovine fecal samples were inoculated with increasing concentrations of two different bacterial strains (field and reference) to compare the performance of four extraction and five amplification protocols. The best results were obtained using the JohnePrep and MagMax extraction kits combined with an in-house triplex real-time PCR designed to detect IS900, ISMap02 (an insertion sequence of M. avium subsp. paratuberculosis present in 6 copies per genome), and an internal amplification control DNA simultaneously. These combinations detected 10 M. avium subsp. paratuberculosis cells/g of spiked feces. The triplex PCR detected 1 fg of genomic DNA extracted from the reference strain K10. The performance of the robotized version of the MagMax extraction kit combined with the IS900 and ISMap02 PCR was further evaluated using 615 archival fecal samples from the first sampling of nine Friesian cattle herds included in a PTB control program and followed up for at least 4 years. The analysis of the results obtained in this survey demonstrated that the diagnostic method was highly specific and sensitive for the detection of M. avium subsp. paratuberculosis in fecal samples from cattle and a very valuable tool to be used in PTB control programs.

Associations between Mycobacterium avium subsp. paratuberculosis antibodies in bulk tank milk, season of sampling and protocols for managing infected cows

BACKGROUND

The objective of this study was to identify associations between the concentration of Mycobacterium avium subsp. paratuberculosis (MAP) antibodies in bulk milk and potential risk factors in herd management and herd characteristics, explaining high MAP antibody titers in milk. An extensive questionnaire was administered to 292 organic and conventional dairy farms from New York, Wisconsin and Oregon. Bulk milk samples were taken from each farm for MAP enzyme-linked immunosorbent assay (ELISA). A general linear model was constructed with MAP ELISA value as the outcome variable and the management factors and herd characteristics as independent variables, while at the same time controlling for the study design variables of state, herd size, and production system (organic or conventional). High bulk tank MAP ELISA value may be due to either a high prevalence of MAP in a herd with many cows contributing to the antibody titer or due to a few infected cows that produce large quantities of antibodies.

RESULTS

Results of the regression models indicated that bulk milk ELISA value was associated with season of sampling and the presence or absence of protocols for managing MAP-positive cows. The concentration of MAP antibodies in bulk milk varied seasonally with a peak in the summer and low concentrations in the winter months. When compared to farms that had never observed clinical Johne's disease, keeping MAP-positive cows or only culling them after a period of delay was associated with an increase in optical density.

CONCLUSIONS

The seasonal variation in MAP antibody titers, with a peak in the summer, may be due to a seasonal increase in MAP-bacterial load. Additionally, seasonal calving practices may contribute to seasonal fluctuations in MAP antibody titers in bulk tank milk. Keeping MAP-positive cows increases the antibody titer in bulk milk, likely due to direct antibody production in the infected cow and indirect triggering of antibody production in herdmates.

Paratuberculosis (Johne's disease) in cattle and other susceptible species

Paratuberculosis (Johne's disease) is a widespread and costly disease. This consensus statement will summarize recommendations regarding diagnosis, control, and treatment of Johne's disease in cattle and other species. Each section of recommendations is followed by a statement that subjectively characterizes the strength of the supporting evidence. The role played by Mycobacterium avium subsp. paratuberculosis (MAP) in the pathogenesis has been a matter of controversy for many years. This statement concludes with an assessment of the evidence in favor of MAP as a potential zoonotic pathogen.

Mycobacterium avium subspecies paratuberculosis: an insidious problem for the ruminant industry

Mycobacterium avium subspecies paratuberculosis is considered as one of the most serious problems affecting the world's ruminant industry due to its significant impact on the global economy and the controversial issue that it may be pathogenic for humans. M. avium subspecies paratuberculosis is the causative agent of Johne's disease in animals and might be implicated in cases of human Crohn's disease. We provide an insight into M. avium subspecies paratuberculosis from some bacteriological, clinical, and molecular epidemiological perspectives.