Dose-dependent interferon-gamma release in dairy calves experimentally infected with Mycobacterium avium subspecies paratuberculosis

Invited review: Improved control of Johne's disease in dairy cattle through advancements in diagnostics, testing, and management of young stock

Johne's disease (JD; paratuberculosis) control programs have been regionally implemented across the globe, but few have successfully eradicated the pathogen (Mycobacterium avium ssp. paratuberculosis; MAP) causing this disease. The limited success may partly be attributed to excluding young stock (calves and replacement heifers or bulls) from testing strategies aimed at identifying MAP-infected cattle. Young stock can shed MAP in feces and can have detectable MAP-specific antibodies in blood, as confirmed in experimentally and naturally infected cattle. Furthermore, MAP transmission causes new infections in young stock. Calves and heifers are often included in JD management strategies on dairy farms but excluded from conventional diagnostic tests due to a presumed lag between infection and detection of MAP shedding and MAP-specific serum antibodies. We summarize evidence of MAP shedding early in the course of infection and discuss promising diagnostics, testing and management strategies to support inclusion of young stock in JD control programs. Improvements in fecal PCR, interferon-gamma release assay (IGRA), and ELISA enable earlier detection of MAP and specific early immune responses. Studies on IGRA and ELISA have focused on evaluation of new antigens and optimal age of testing. New diagnostics have been developed, including phage-based tests to detect viable MAP, as well as gene expression patterns and metabolomics to detect MAP-infected young stock. In addition, refinements in testing and management of calves and heifers may enable reductions in MAP prevalence. We provide recommendations for dairy farmers, researchers, veterinarians, and other stakeholders that may improve JD control programs with an objective to control and potentially eradicate JD. Additionally, we have identified the most pressing gaps in knowledge that currently hamper inclusion of young stock in JD prevention and control programs. In summary, transmission among young stock may cause new MAP infections, and appropriate use of new diagnostic tests, testing and management strategies for young stock may improve the efficacy of JD control programs.

Lining the small intestine with mycobacteriophages protects from Mycobacterium avium subsp. paratuberculosis and eliminates fecal shedding

Johne's disease (JD), a chronic, infectious enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP), affects wild and domestic ruminants. There is no cure or effective prevention, and current vaccines have substantial limitations, leaving this disease widespread in all substantial dairy industries causing economic, and animal welfare implications. Mycobacteriophages (MPs) have been gaining interest in recent years and are proposed as a promising solution to curtailing MAP infection. Using a well-validated infection model, we have demonstrated the preventative potential of MPs to protect dairy calves against MAP infection. Calves were supplemented daily with a phage cocktail from birth till weaning at 2 m of age and inoculated with MAP at 2 wk of age. Infection status was measured for 4.5 mo through blood, fecal, and postmortem tissue samples. Our findings highlight the remarkable efficacy of orally administered MPs. Notably, fecal shedding of MAP was entirely eliminated within 10 wk, in contrast to the infected control group where shedding continued for the entirety of the trial period. Postmortem tissue culture analysis further supported the effectiveness of MPs, with only 1 out of 6 animals in the phage-treated group testing positive for MAP colonized tissues compared to 6 out of 6 animals in the infected control group. Additionally, plaque assay results demonstrated the ability of phages to persist within the intestinal tract. Collectively, these results underscore the potential of orally administered MP cocktails as a highly effective intervention strategy to combat JD in dairy calves and by extension in the dairy industry.

Evaluation of Mycobacterium avium subsp. paratuberculosis isocitrate lyase (IcL) and ABC transporter (BacA) knockout mutants as vaccine candidates

There has been little success in controlling Johne's disease, caused by Mycobacterium avium subsp. paratuberculosis, due to suboptimal diagnostics and the ineffectiveness of available vaccines. By knocking out BacA and IcL, genes required for MAP survival in dairy calves, two live-attenuated vaccine candidates were created. This study evaluated the host-specific attenuation of MAP IcL and BacA mutants in mouse and calf models, as well as the elicited immune responses. Deletion mutants were generated in MAP strain A1-157 through specialized transduction and found viable in vitro. First, the mutants' attenuation and elicited cytokine secretion were assessed in a mouse model, 3 weeks after intraperitoneal inoculation with MAP strains. Later, vaccine strains were assessed in a natural host infection model where calves received 10⁹CFU oral dose of MAP wild-type or mutant strains at 2 weeks old. Transcription levels of cytokines in PBMCs were evaluated at 12-, 14-, and 16-weeks post-inoculation (WPI) and MAP colonization in tissue was assessed at 4.5 months after inoculation. Whereas both vaccine candidates colonized mouse tissues similarly to wild-type strain, both failed to persist in calf tissues. In either mouse or calf models, gene deletion did not reduce immunogenicity. Instead, inoculation with ΔBacA induced a greater upregulation of proinflammatory cytokines than ΔIcL and wild-type in both models and a greater expansion of cytotoxic and memory T-cells than uninfected control in calves. ΔBacA and wild-type strains significantly increased secretion of IP-10, MIG, TNFα, and RANTES in mice serum compared to uninfected control. This agreed with upregulation of IL-12, IL-17, and TNFα in calves inoculated with ΔBacA at all time points. The ΔBacA also gave rise to greater populations of CD4+CD45RO+, and CD8+ cells than uninfected control calves at 16 WPI. Low survival rate of MAP in macrophages co-incubated with PBMCs isolated from the ΔBacA group indicated that these cell populations are capable of killing MAP. Overall, the immune response elicited by ΔBacA is stronger compared to ΔIcL and it is maintained over two different models and over time in calves. Further investigation is warranted to evaluate the BacA mutant's protection against MAP infection as a live attenuated vaccine candidate.

Metabolomic Changes in Naturally MAP-Infected Holstein-Friesian Heifers Indicate Immunologically Related Biochemical Reprogramming

Johne’s disease, caused by Mycobacterium avium subsp. paratuberculosis (MAP), causes weight loss, diarrhoea, and reduced milk yields in clinically infected cattle. Asymptomatic, subclinically infected cattle shed MAP bacteria but are frequently not detected by diagnostic tests. Herein, we compare the metabolite profiles of sera from subclinically infected Holstein–Friesian heifers and antibody binding to selected MAP antigens. The study used biobanked serum samples from 10 naturally MAP-infected and 10 control heifers, sampled monthly from ~1 to 19 months of age. Sera were assessed using flow infusion electrospray–high-resolution mass spectrometry (FIE–HRMS) on a Q Exactive hybrid quadrupole–Orbitrap mass spectrometer for high-throughput, sensitive, non-targeted metabolite fingerprinting. Partial least-squares discriminant analyses (PLS-DA) and hierarchical cluster analysis (HCA) of the data discriminated between naturally MAP-infected and control heifers. In total, 33 metabolites that differentially accumulated in naturally MAP-infected heifers compared to controls were identified. Five were significantly elevated within MAP-infected heifers throughout the study, i.e., leukotriene B4, bicyclo prostaglandin E2 (bicyclo PGE2), itaconic acid, 2-hydroxyglutaric acid and N6-acetyl-L-lysine. These findings highlight the potential of metabolomics in the identification of novel MAP diagnostic markers and particular biochemical pathways, which may provide insights into the bovine immune response to MAP.

Inducing cellular immune responses with a marked Mycobacterium avium subsp. paratuberculosis strain in dairy calves

Mycobacterium avium subsp. paratuberculosis (MAP) is the etiological agent of Johne's disease, a chronic granulomatous enteritis with a high global prevalence in dairy cattle. This disease causes significant economic loss in the dairy industry and has been challenging to control, as current diagnostic assays are low in sensitivity and specificity, and previously developed vaccines do not prevent infection and face regulatory concerns due to interference with bovine tuberculosis diagnostics. To remediate this issue, positive and negative immune markers were created in a MAP strain as a step towards a vaccine capable of differentiating infected from vaccinated animals (DIVA). A gene coding for an immunogenic protein (MAP1693c) in the MAP genome was replaced with a library of epitope-tagged immunogenic genes (pepA) via a stable allelic exchange method. These markers were evaluated in a calf infection trial, where Holstein-Friesian dairy calves were inoculated at two weeks of age with either the marked strain or the parent strain, or remained uninfected controls. Cellular immune responses to the markers were measured using an interferon gamma release assay (IGRA). There were no MAP1693c marker-specific differences in cellular immune responses between infection groups. A scrambled version of the HA (human influenza hemagglutinin) epitope, but not the actual HA epitope, induced a significant IFN-γ response in marker-infected calves compared to WT-infected and uninfected groups at 4.5 months post-inoculation. This scrambled HA epitope thus holds potential as a diagnostic tool as part of a DIVA vaccine for Johne's disease.

Quantifying transmission of Mycobacterium avium subsp. paratuberculosis among group-housed dairy calves

Johne’s disease (JD) is a chronic enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP), with control primarily aimed at preventing new infections among calves. The aim of the current study was to quantify calf-to-calf transmission of MAP among penmates in an experimental trial. Newborn Holstein bull calves (n = 32) were allocated into pens of 4, with 2 inoculated (IN) calves and 2 calves that were contact exposed (CE). Calves were group-housed for 3 months, with frequent collection of fecal and blood samples and tissue collection after euthanasia. The basic reproduction ratio (R₀) was estimated using a final size (FS) model with a susceptible-infected model, based on INF-γ ELISA and tissue culture followed by qPCR. In addition, the transmission rate parameter (β) for new shedding events was estimated using a general linearized method (GLM) model with a susceptible-infected-susceptible model based on culture, followed by qPCR, of fecal samples collected during group housing. The R₀ was derived for IN and CE calves separately, due to a difference in susceptibility, as well as differences in duration of shedding events. Based on the FS model, interferon-γ results from blood samples resulted in a R₀^IG of 0.90 (0.24, 2.59) and tissue culture resulted in a R₀^T of 1.36 (0.45, 3.94). Based on the GLM model, the R₀ for CE calves to begin shedding (R₀^CE) was 3.24 (1.14, 7.41). We concluded that transmission of MAP infection between penmates occurred and that transmission among calves may be an important cause of persistent MAP infection on dairy farms that is currently uncontrolled for in current JD control programs.

Gene expression profiles during subclinical Mycobacterium avium subspecies paratuberculosis infection in sheep can predict disease outcome

Paratuberculosis in ruminants is caused by infection with Mycobacterium avium subspecies paratuberculosis (MAP) however exposure does not predetermine progression to clinical disease. The pathogenesis incorporates a subclinical phase during which MAP is capable of evading host immune responses through adaptation of host cellular immune mechanisms. Presented are results of transcriptomic analysis of Merino sheep experimentally exposed to MAP and repeatedly sampled over the subclinical phase, identifying genes consistently changed over time in comparison to unexposed controls and associated with different disease outcomes. MAP exposed sheep were classified as diseased 45% (n = 9) or resilient 55% (n = 11). Significant gene expression changes were identified in the white blood cells of paucibacillary (n = 116), multibacillary (n = 98) and resilient cohorts (n = 53) compared to controls. Members of several gene families were differentially regulated, including S100 calcium binding, lysozyme function, MHC class I and class II, T cell receptor and transcription factors. The microarray findings were validated by qPCR. These differentially regulated genes are presented as putative biomarkers of MAP exposure, or of the specified disease or resilience outcomes. Further, in silico functional analysis of genes suggests that experimental MAP exposure in Merino sheep results in adaptations to cellular growth, proliferation and lipid metabolism.

Immunopathological changes and apparent recovery from infection revealed in cattle in an experimental model of Johne's disease using a lyophilised culture of Mycobacterium avium subspecies paratuberculosis

Johne's disease (JD) or paratuberculosis is an economically significant, chronic enteropathy of ruminants caused by Mycobacterium avium subspecies paratuberculosis (MAP). Experimental models of JD in cattle are logistically challenging due to the need for long term monitoring, because the clinical disease can take years to manifest. Three trials were undertaken, the largest involving 20 cattle exposed orally to a low dose of C strain MAP and 10 controls studied for 4.75 years. Frequent blood and faecal sampling was used to monitor immunological and infection parameters, and intestinal biopsies were performed at two time points during the subclinical disease phase. Although clinical disease was not seen, there was evidence of infection in 35% of the animals and at necropsy 10% had histopathological lesions consistent with JD, similar to the proportions expected in naturally infected herds. Faecal shedding occurred in two distinct phases: firstly there was intermittent shedding <∼9 months post-exposure that did not correlate with disease outcomes; secondly, in a smaller cohort of animals, this was followed by more consistent shedding of increasing quantities of MAP, associated with intestinal pathology. There was evidence of regression of histopathological lesions in the ileum of one animal, which therefore had apparently recovered from the disease. Both cattle with histopathological lesions of paratuberculosis at necropsy had low MAP-specific interferon-gamma responses at 4 months post-exposure and later had consistently shed viable MAP; they also had the highest loads of MAP DNA in faeces 4.75 year s post-exposure. In a trial using a higher dose of MAP, a higher proportion of cattle developed paratuberculosis. The information derived from these trials provides greater understanding of the changes that occur during the course of paratuberculosis in cattle.

Case definition terminology for paratuberculosis (Johne's disease)

Paratuberculosis (Johne's disease) is an economically significant condition caused by Mycobacterium avium subsp. paratuberculosis. However, difficulties in diagnosis and classification of individual animals with the condition have hampered research and impeded efforts to halt its progressive spread in the global livestock industry. Descriptive terms applied to individual animals and herds such as exposed, infected, diseased, clinical, sub-clinical, infectious and resistant need to be defined so that they can be incorporated consistently into well-understood and reproducible case definitions. These allow for consistent classification of individuals in a population for the purposes of analysis based on accurate counts. The outputs might include the incidence of cases, frequency distributions of the number of cases by age class or more sophisticated analyses involving statistical comparisons of immune responses in vaccine development studies, or gene frequencies or expression data from cases and controls in genomic investigations. It is necessary to have agreed definitions in order to be able to make valid comparisons and meta-analyses of experiments conducted over time by a given researcher, in different laboratories, by different researchers, and in different countries. In this paper, terms are applied systematically in an hierarchical flow chart to enable classification of individual animals. We propose descriptive terms for different stages in the pathogenesis of paratuberculosis to enable their use in different types of studies and to enable an independent assessment of the extent to which accepted definitions for stages of disease have been applied consistently in any given study. This will assist in the general interpretation of data between studies, and will facilitate future meta-analyses.

Knowledge gaps that hamper prevention and control of Mycobacterium avium subspecies paratuberculosis infection

In the last decades, many regional and country-wide control programmes for Johne's disease (JD) were developed due to associated economic losses, or because of a possible association with Crohn's disease. These control programmes were often not successful, partly because management protocols were not followed, including the introduction of infected replacement cattle, because tests to identify infected animals were unreliable, and uptake by farmers was not high enough because of a perceived low return on investment. In the absence of a cure or effective commercial vaccines, control of JD is currently primarily based on herd management strategies to avoid infection of cattle and restrict within-farm and farm-to-farm transmission. Although JD control programmes have been implemented in most developed countries, lessons learned from JD prevention and control programmes are underreported. Also, JD control programmes are typically evaluated in a limited number of herds and the duration of the study is less than 5 year, making it difficult to adequately assess the efficacy of control programmes. In this manuscript, we identify the most important gaps in knowledge hampering JD prevention and control programmes, including vaccination and diagnostics. Secondly, we discuss directions that research should take to address those knowledge gaps.

Modeling environmental transmission of MAP infection in dairy cows

Johne's disease is caused by Mycobacterium avium subspecies paratuberculosis(MAP). It is a chronic, progressive, and inflammatory disease which has a long incubation period. One main problem with the disease is the reduction of milk production in infected dairy cows. In our study we develop a system of ordinary differential equations to describe the dynamics of MAP infection in a dairy farm. This model includes the progression of the disease and the age structure of the cows. To investigate the effect of persistence of this bacteria on the farm on transmission in our model, we include environmental compartments, representing the pathogen input in an explicit way. The effect of indirect transmission from the bacteria in the environment and the culling of high-shedding adults can be seen in the numerical simulations. Since culling usually only happens once a year, we include a novel feature in the simulations with a discrete action of removing high-shedding adults once a year. We conclude that with culling of high shedders even at a high rate, the infection will persist in the modeled farm setting.

Field performance of six Mycobacterium avium subsp. paratuberculosis antigens in a 20h interferon gamma release assay in Belgium

Paratuberculosis, caused by Mycobacterium avium subsp. paratuberculosis (Map), is a chronic granulomatous enteritis which primarily affects domestic and wild ruminants, resulting in serious economic losses for dairy and beef industry around the world. There is no satisfactory cure or vaccine, and actual diagnostic tests need improvement, particularly for the initial stages of the disease. Map specific cell-mediated immune responses may allow early detection of the infection at subclinical stages. In this study, over a period of 39 months, we collected 548 blood samples in two culture-confirmed Map-infected herds, 95 blood samples in five dairy herds that scored negative during 3 consecutive years of Map serology testing and 79 samples in three culture-confirmed M. bovis infected herds. Based on criteria of bacteriology, serology and ratio of IFN-γ induced with bovine and avian purified protein derivative of tuberculin (PPD-B/PPD-A), we classified the samples in four groups: 415 samples as Map-exposed/infected (MAP), 58 samples as aspecific reactors (AR), 179 samples as non-responders (NI) and 70 samples as M. bovis infected (TB). Age of the animals influenced the IFN-γ response in the MAP group, with PPD specific IFN-γ levels (but not PPD-B/PPD-A IFN-γ ratio) being significantly higher in animals <18 months of age. Map specific antibodies were detected by IDEXX ELISA in 13/415 (3%) sera of the MAP group, whereas fecal culture was positive for only 7/405 (1.7%) samples. Animals in the MAP group could therefore be considered being at the very early stage of Map infection. Six purified, recombinant Map antigens (Ag5, Ag6, MAP1637c, MAP0388, MAP3547c and MAP0586c), previously identified using combined advanced proteomic or reverse genomic approaches, were tested for their diagnostic potential in a 20h IFN-γ release assay. In the age group >18 months old, Ag5 and MAP0388 were recognized by only 10.1% and 7.7% of the animals in the MAP group, whereas a total of 38.6.%, 29.4%, 25.6% and 39.0% of the animals in the MAP group reacted to Ag6, MAP1637c, MAP3547c and MAP0586c respectively. None of the animals in the TB group reacted to Ag6, MAP1637c or MAP586c. Except for MAP0388, the % of reactors in the MAP group was significantly higher in animals <18 months old: 28.0%, 24.0%, 45.5%, 47.1%, 49.8% and 47.4% respectively. Further studies of these candidates and their combination are needed to confirm their diagnostic potential for the detection of early Map infection.

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.

Inferring biomarkers for Mycobacterium avium subsp. paratuberculosis infection and disease progression in cattle using experimental data

Available diagnostic assays for Mycobacterium avium subsp. paratuberculosis (MAP) have poor sensitivities and cannot detect early stages of infection, therefore, there is need to find new diagnostic markers for early infection detection and disease stages. We analyzed longitudinal IFN-γ, ELISA-antibody and fecal shedding experimental sensitivity scores for MAP infection detection and disease progression. We used both statistical methods and dynamic mathematical models to (i) evaluate the empirical assays (ii) infer and explain biological mechanisms that affect the time evolution of the biomarkers, and (iii) predict disease stages of 57 animals that were naturally infected with MAP. This analysis confirms that the fecal test is the best marker for disease progression and illustrates that Th1/Th2 (IFN-γ/ELISA antibodies) assays are important for infection detection, but cannot reliably predict persistent infections. Our results show that the theoretical simulated macrophage-based assay is a potential good diagnostic marker for MAP persistent infections and predictor of disease specific stages. We therefore recommend specifically designed experiments to test the use of a based assay in the diagnosis of MAP infections.

Development of vaccines to Mycobacterium avium subsp. paratuberculosis infection

Johne's disease or paratuberculosis is a chronic debilitating disease in ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). The disease causes significant economic losses in livestock industries worldwide. There are no effective control measures to eradicate the disease because there are no appropriate diagnostic methods to detect subclinically infected animals. Therefore, it is very difficult to control the disease using only test and cull strategies. Vaccination against paratuberculosis has been considered as an alternative strategy to control the disease when combined with management interventions. Understanding host-pathogen interactions is extremely important to development of vaccines. It has long been known that Th1-mediated cellular immune responses are play a crucial role in protection against MAP infection. However, recent studies suggested that innate immune responses are more closely related to protective effects than adaptive immunity. Based on this understanding, several attempts have been made to develop vaccines against paratuberculosis. A variety of ideas for designing novel vaccines have emerged, and the tests of the efficacy of these vaccines are conducted constantly. However, no effective vaccines are commercially available. In this study, studies of the development of vaccines for MAP were reviewed and summarized.

The Features of Fecal and Ileal Mucosa-Associated Microbiota in Dairy Calves during Early Infection with Mycobacterium avium Subspecies paratuberculosis

Current diagnostic tests for Johne's disease (JD), a chronic granulomatous inflammation of the gastrointestinal tract of ruminants caused by Mycobacterium avium subspecies paratuberculosis (MAP), lack the sensitivity to identify infected animals at early (asymptomatic) stages of the disease. The objective was to determine the pattern of MAP-associated dysbiosis of intestinal microbiota as a potential biomarker for early detection of infected cattle. To that end, genomic DNA was extracted from ileal mucosa and fecal samples collected from 28 MAP-positive and five control calves. High-throughput Illumina sequencing of the V4 hypervariable region of the 16S rRNA gene was used for community profiling of ileal mucosa-associated (MAM) or fecal microbiota. The PERMANOVA analysis of unweighted UniFrac distances revealed distinct clustering of ileal MAM (P = 0.049) and fecal microbiota (P = 0.068) in MAP-infected vs. control cattle. Microbiota profile of MAP-infected animals was further investigated by linear discriminant analysis effective size (LEfSe); several bacterial taxa within the phylum Proteobacteria were overrepresented in ileal MAM of control calves. Moreover, based on reconstructed metagenomes (PICRUSt) of ileal MAM, functional pathways associated with MAP infection were inferred. Enrichment of lysine and histidine metabolism pathways, and underrepresentation of glutathione metabolism and leucine and isoleucine degradation pathways in MAP-infected calves suggested potential contributions of ileal MAM in development of intestinal inflammation. Finally, simultaneous overrepresentation of families Planococcaceae and Paraprevotellaceae, as well as underrepresentation of genera Faecalibacterium and Akkermansia in the fecal microbiota of infected cattle, served as potential biomarker for identifying infected cattle during subclinical stages of JD. Collectively, based on compositional and functional shifts in intestinal microbiota of infected cattle, we inferred that this dynamic network of microorganisms had an active role in intestinal homeostasis.

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.

Envelope protein complexes of Mycobacterium avium subsp. paratuberculosis and their antigenicity

Mycobacterium avium subsp. paratuberculosis (MAP) is the causative agent of Johne's disease, a chronic enteric disease of ruminant animals. In the present study, blue native PAGE electrophoresis and 2D SDS-PAGE were used to separate MAP envelope protein complexes, followed by mass spectrometry (MS) to identify individual proteins within the complexes. Identity of individual proteins within complexes was further confirmed by MS upon excision of spots from 2D SDS-PAGE gels. Among the seven putative membrane complexes observed, major membrane protein (MAP2121c), a key MAP antigen involved in invasion of epithelial cells, was found to form a complex with cysteine desulfurase (MAP2120c). Other complexes found included those involved in energy metabolism (succinate dehydrogenase complex) as well as a complex formed by Cfp29, a characterized T cell antigen of Mycobacterium tuberculosis. To determine antigenicity of proteins, Western blot was performed on replicate 2D SDS-PAGE gels with sera from noninfected control cows (n=9) and naturally infected cows in the subclinical (n=10) and clinical (n=13) stages of infection. Clinical animals recognized MAP2121c in greater proportion than subclinical and control cows, whereas cysteine desulfurase recognition was not differentiated by infection status. To further characterize antigenicity, recombinant proteins were expressed for 10 of the proteins identified and evaluated in an interferon-gamma (IFN-γ) release assay as well as immunoblots. This study reveals the presence of protein complexes in the cell envelope of MAP, suggesting protein interactions in the envelope of this pathogen. Furthermore the identification of antigenic proteins with potential as diagnostic targets was characterized.

Metabolomic profiling in cattle experimentally infected with Mycobacterium avium subsp. paratuberculosis

The sensitivity of current diagnostics for Johne's disease, a slow, progressing enteritis in ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP), is too low to reliably detect all infected animals in the subclinical stage. The objective was to identify individual metabolites or metabolite profiles that could be used as biomarkers of early MAP infection in ruminants. In a monthly follow-up for 17 months, calves infected at 2 weeks of age were compared with aged-matched controls. Sera from all animals were analyzed by 1H nuclear magnetic resonance spectrometry. Spectra were acquired, processed, and quantified for analysis. The concentration of many metabolites changed over time in all calves, but some metabolites only changed over time in either infected or non-infected groups and the change in others was impacted by the infection. Hierarchical multivariate statistical analysis achieved best separation between groups between 300 and 400 days after infection. Therefore, a cross-sectional comparison between 1-year-old calves experimentally infected at various ages with either a high- or a low-dose and age-matched non-infected controls was performed. Orthogonal Projection to Latent Structures Discriminant Analysis (OPLS DA) yielded distinct separation of non-infected from infected cattle, regardless of dose and time (3, 6, 9 or 12 months) after infection. Receiver Operating Curves demonstrated that constructed models were high quality. Increased isobutyrate in the infected cattle was the most important agreement between the longitudinal and cross-sectional analysis. In general, high- and low-dose cattle responded similarly to infection. Differences in acetone, citrate, glycerol and iso-butyrate concentrations indicated energy shortages and increased fat metabolism in infected cattle, whereas changes in urea and several amino acids (AA), including the branched chain AA, indicated increased protein turnover. In conclusion, metabolomics was a sensitive method for detecting MAP infection much sooner than with current diagnostic methods, with individual metabolites significantly distinguishing infected from non-infected cattle.