Paratuberculosis Infection In Cattle Research Articles

Association between High Interferon-Gamma Production in Avian Tuberculin-Stimulated Blood from Mycobacterium avium subsp. paratuberculosis-Infected Cattle and Candidate Genes Implicated in Necroptosis.

The mechanisms underlying host resistance to Mycobacterium avium subsp. paratuberculosis (MAP) infection are largely unknown. In the current study, we hypothesize that cows with an ability to produce higher levels of interferon-gamma (IFNɣ) might control MAP infection more successfully. To test this hypothesis, IFNɣ production was measured using a specific IFNɣ ELISA kit in avian purified protein derivative (aPPD)-stimulated blood samples collected from 152 Holstein cattle. DNA isolated from peripheral blood samples of the animals included in the study was genotyped with the EuroG Medium-Density Bead Chip, and the genotypes were imputed to whole-genome sequencing. A genome-wide association analysis (GWAS) revealed that high levels of IFNɣ in response to the aPPD were associated with a specific genetic profile (heritability = 0.64) and allowed the identification of 71 SNPs, 40 quantitative trait loci (QTL), and 104 candidate genes. A functional analysis using the 104 candidate genes revealed a significant enrichment of genes involved in the innate immune response and, more specifically, in necroptosis. Taken together, our results define a heritable and distinct immunogenetic profile associated with the production of high IFNɣ levels and with the capacity of the host to lyse MAP-infected macrophages by necroptosis.

Assessment of Tuberculosis Biomarkers in Paratuberculosis-infected Cattle.

Mycobacterium bovis and Mycobacterium avium subsp. paratuberculosis, respectively the causative agents of bovine tuberculosis (bTB) and bovine paratuberculosis (PTB), share a high number of antigenic proteins. This characteristics makes the differential diagnosis of the diseases difficult. The interferon gamma (IFN-γ), C-X-C motif chemokine ligand 10 (CXCL10), matrix metallopeptidase 9 (MMP9), interleukin 22 (IL-22) and thrombospondin 1 (THBS1) bovine genes have already been shown to be accurate transcriptional biomarkers of bTB. In order to improve the diagnosis of bTB and PTB, in the present study we evaluated the risk of false positivity of these bTB biomarkers in cattle with PTB. The transcription of these genes was studied in 13 PTB-infected cattle, using Mycobacterium avium subsp. paratuberculosis (MAP)-stimulated peripheral blood mononuclear cells (PBMC). Overall, the levels of IFN-γ, CXCL10, MMP9 and IL-22 transcripts in MAP-stimulated PBMC failed to differentiate animals with PTB from healthy animals. However, as bTB-afflicted cattle do, the MAP-infected group also displayed a lower level of THBS1 transcription than the non-infected animals. The results of this study add new specificity attributes to the levels of transcription of IFN-γ, CXCL10, MMP9 and IL-22 as biomarkers for bTB.

Identification of loci associated with susceptibility to Mycobacterium avium subsp. paratuberculosis infection in Holstein cattle using combinations of diagnostic tests and imputed whole-genome sequence data.

Bovine paratuberculosis (PTB) is a chronic inflammatory disease caused by Mycobacterium avium susbp. paratuberculosis (MAP). Genome-wide association studies (GWAS) have identified single nucleotide polymorphisms (SNPs) significantly associated with susceptibility to bovine PTB. The main objective of this study was to identify quantitative trait loci (QTLs) associated with MAP infection in Spanish Holstein cows (N = 983) using combinations of diagnostic tests and imputed whole-genome sequence (WGS) data. The infection status of these animals was defined by three diagnostic methods including ELISA for MAP-antibodies detection, and tissue culture and PCR for MAP detection. The 983 cows included in this study were genotyped with the Bovine MD SNP50 Bead Chip, and the corresponding genotypes were imputed to WGS using the 1,000 Bull genomes reference population. In total, 33.77 million SNP variants per animal were identified across the genome. Linear mixed models were used to calculate the heritability (h2) estimates for each diagnostic test and test combinations. Next, we performed a case-control GWAS using the imputed WGS datasets and the phenotypes and combinations of phenotypes with h2 estimates > 0.080. After performing the GWAS, the test combinations that showed SNPs with a significant association (PFDR ≤ 0.05), were the ELISA-tissue PCR-tissue culture, ELISA-tissue culture, and ELISA-tissue PCR. A total of twelve quantitative trait loci (QTLs) highly associated with MAP infection status were identified on the Bos taurus autosomes (BTA) 4, BTA5, BTA11, BTA12, BTA14, BTA23, BTA24, and BTA28, and some of these QTLs were linked to immune-modulating genes. The identified QTLs on BTA23 spanning from 18.81 to 22.95 Mb of the Bos taurus genome overlapped with several QTLs previously found to be associated with PTB susceptibility, bovine tuberculosis susceptibility, and clinical mastitis. The results from this study provide more clues regarding the molecular mechanisms underlying susceptibility to PTB infection in cattle and might be used to develop national genetic evaluations for PTB in Spain.

Electrochemical Detection of Serum Antibodies Against Mycobacterium avium Subspecies paratuberculosis.

Mycobacterium avium subsp. paratuberculosis (MAP) causes a chronic inflammatory intestinal disease, called Johne's disease (JD) in many ruminants. In the dairy industry, JD is responsible for significant economic losses due to decreased milk production and premature culling of infected animals. Test-and-cull strategy in conjunction with risk management is currently recommended for JD control in dairy herds. However, current diagnostic tests are labor-intensive, time-consuming, and/or too difficult to operate on site. In this study, we developed a new method for the detection of anti-M. paratuberculosis antibodies from sera of M. paratuberculosis-infected animals. M. paratuberculosis antigen-coated magnetic beads were sequentially reacted with bovine serum followed by a horseradish peroxidase (HRP)-labeled secondary antibody. The reaction of HRP with its substrate was then quantitatively measured electrochemically using a redox-active probe, ferrocyanide. After optimization of electrochemical conditions and concentration of the redox-active probe, we showed that the new electrochemical detection method could distinguish samples of M. paratuberculosis-infected cattle from those of uninfected cattle with greater separation between the two groups of samples when compared with a conventional colorimetric testing method. Since electrochemical detection can be conducted with an inexpensive, battery-operated portable device, this new method may form a basis for the development of an on-site diagnostic system for JD.

Genetic Resistance to Johne's Disease in Cattle

Paratuberculosis (Johne's disease) is an economically significant, infectious disease of ruminants caused by Mycobacterium avium subsp paratuberculosis, and characterized by progressive weight loss and nonresponsive diarrhea. Genetic factors have been associated with differences in host susceptibility to bovine paratuberculosis. Research has been aimed at detecting associations between susceptibility and polymorphisms at candidate genes with no definitive results. Several gene products are candidates for this association. Interferon gamma is an inducible cytokine with a crucial role in the innate host response to intracellular bacteria. Toll-like receptors are trans-membrane structures responsible for coordination of innate and adaptive immune responses. The SLC11A1 gene plays an important role in innate immunity, preventing bacterial growth in macrophages during the initial stages of infection. The objective of this candidate gene case-control study was to characterize the distribution of polymorphisms in three candidate genes related to the immune function; interferon gamma (BoIFNG), toll-like receptor 4 (TLR4), and solute carrier family 11 member1 (SLC11A1) genes, and test their association with paratuberculosis infection in cattle.

Association between combinations of genetic polymorphisms and epidemiopathogenic forms of bovine paratuberculosis

Control of major mycobacterial diseases affecting livestock is a challenging issue that requires different approaches. The use of genetic markers for improving resistance to Mycobacterium avium subsp. paratuberculosis infection in cattle has been explored as a promising population strategy We performed paratuberculosis epidemiopathogenic phenotypic and genotypic characterization involving 24 SNPs in six candidate genes (NOD2, CD209, SLC11A1, SP110, TLR2 and TLR4) on 502 slaughtered Friesian cows. In the current study, we investigate whether recently proposed paratuberculosis (PTB) epidemiopathogenic (EP) forms (apparently free-AF, latent-LAT and patent-PAT) could be associated with some combination of these 24 SNPs. Best EP form grouping was obtained using a combination of 5 SNPs in four genes (CD209: rs210748127; SLC11A1: rs110090506; SP110: rs136859213 and rs110480812; and TLR2: rs41830058). These groups were defined according to the level of infection progression risk to patent epidemiopathogenic forms and showed the following distributions: LOWIN (low) with 39 (8%) cases (94.9% AF/5.1% LAT/0% PAT); LATIN (low) with 17 (3%) cases (5.9% AF/94.1% LAT/0% PAT); AVERIN (average) with 413 (82%) cases (52.1% AF/38.5% LAT/9.4% PAT) and PATIN (patent) with 33 (7%) cases (36.4% AF/24.2% LAT/39.4% PAT). Age of slaughter was significantly higher for LATIN (88.3 months) compared to AVERIN (65.3 months; p = 0.0007) and PATIN (59.1 months; p = 0.0004), and for LOWIN (73.9 months) compared to PATIN (p = 0.0233), and nearly significant compared to AVERIN (p = 0.0572) These results suggest that some selected genetic polymorphisms have a potential use as markers of PTB EP forms and thus add a new tool for the control of this widespread infection.

Early detection of Mycobacterium avium subsp. paratuberculosis infection in cattle with multiplex-bead based immunoassays.

Johne’s Disease (JD), caused by Mycobacterium avium subspecies paratuberculosis (MAP), results in significant economic loss to livestock production. The early detection of MAP infection in animals with extant serological assays has remained challenging due to the low sensitivity of commercially available ELISA tests, a fact that has hampered the development of effective JD control programs. Our recent protein microarray-based studies identified several promising candidate antigens that are immunogenic during different stages of MAP infection. To evaluate these antigens for use in diagnostic assays and reliably identify animals with MAP infection, a multiplex (Luminex®) assay was developed using color-coded flourescent beads coupled to 6 MAP recombinant proteins and applied to screen 180 serum and 90 milk samples from cows at different stages of MAP infection including negative (NL), fecal test positive/ELISA negative (F+E-), and fecal positive/ELISA positive (F+E+). The results show that while serum antibody reactivities to each of the 6 antigens were highest in F+E+ group, antibody reactivity to three of the six antigens were identified in the F+E- group, suggesting that these three antigens are expressed and provoke antibody responses during the early infection stages with MAP. Further, antibodies against all six antigens were elevated in milk samples from both the F+E- and F+E+ groups in comparison to the NL group (p<0.01). Taken together, the results of our investigation suggest that multiplex bead-based assays are able to reliably identify MAP infection, even during early stages when antibody responses in animals are undetectable with widely used commercial ELISA tests.

Identification of Novel Seroreactive Antigens in Johne's Disease Cattle by Using the Mycobacterium tuberculosis Protein Array.

Johne's disease, a chronic gastrointestinal inflammatory disease caused by Mycobacterium avium subspecies paratuberculosis, is endemic in dairy cattle and other ruminants worldwide and remains a challenge to diagnose using traditional serological methods. Given the close phylogenetic relationship between M. avium subsp. paratuberculosis and the human pathogen Mycobacterium tuberculosis, here, we applied a whole-proteome M. tuberculosis protein array to identify seroreactive and diagnostic M. avium subsp. paratuberculosis antigens. A genome-scale pairwise analysis of amino acid identity levels between orthologous proteins in M. avium subsp. paratuberculosis and M. tuberculosis showed an average of 62% identity, with more than half the orthologous proteins sharing >75% identity. Analysis of the M. tuberculosis protein array probed with sera from M. avium subsp. paratuberculosis-infected cattle showed antibody binding to 729 M. tuberculosis proteins, with 58% of them having ≥70% identity to M. avium subsp. paratuberculosis orthologs. The results showed that only 4 of the top 40 seroreactive M. tuberculosis antigens were orthologs of previously reported M. avium subsp. paratuberculosis antigens, revealing the existence of a large number of previously unrecognized candidate diagnostic antigens. Enzyme-linked immunosorbent assay (ELISA) testing of 20 M. avium subsp. paratuberculosis recombinant proteins, representing reactive and nonreactive M. tuberculosis orthologs, further confirmed that the M. tuberculosis array has utility as a screening tool for identifying candidate antigens for Johne's disease diagnostics. Additional ELISA testing of field serum samples collected from dairy herds around the United States revealed that MAP2942c had the strongest seroreactivity with Johne's disease-positive samples. Collectively, our studies have considerably expanded the number of candidate M. avium subsp. paratuberculosis proteins with potential utility in the next generation of rationally designed Johne's disease diagnostic assays.

Seroepidemiology of paratuberculosis in cattle population of organized and unorganized farms of India

Serum samples (531) collected randomly from cattle of organized (200) and unorganized (331) farms of Central and Northern parts of India were subjected to a commercial ELISA to know the seroprevalence of paratuberculosis. These serum samples were also tested by an in-house absorbed ELISA developed in the laboratory and the results were compared. The overall seroprevalence of paratuberculosis in cattle was 8.09% with significantly higher prevalence in cattle of organized farms (13.5%) than unorganized farms (4.83%). The seroprevalence was also significantly higher in calves (17.24%) than adults (7.57%); whereas there was no significant difference in prevalence rate among male (6.71%) and female (9.87%) cattle. Region wise the seroprevalence was slightly higher in organized farms of Northern India (16.43%) than that of Central India (11.81%). The sensitivity and specificity of in-house ELISA were 71.11% and 98.76%, respectively, with the accuracy of over 96%. On the basis of Kappa-test, the inhouse ELISA was in good agreement with commercial Pourquier ® ELISA and can be recommended for screening of paratuberculosis infection in cattle in India.

Evidence for gene-gene epistatic interactions between susceptibility genes for Mycobacterium avium subsp. paratuberculosis infection in cattle

Johne's disease is a chronic granulomatous inflammatory disease caused by Mycobacterium avium subsp. paratuberculosis (MAP), with a particularly negative impact on the economy of the dairy industry. In recent years, several whole genome and candidate gene association studies have been published reporting MAP susceptibility genes, but the putative interaction between them remains unknown. Here, twenty-four single nucleotide polymorphisms in the bovine SLC11A1, NOD2, SP110, TLR2, TLR4, and CD209 genes, previously related with paratuberculosis disease, have been analyzed. Several significant (P<0.05) pair-wise genetic interactions were detected: CD209-TLR4, CD209-TLR2, TLR4-TLR2, SP110-SLC11A1, SP110-TLR2, and SP110-NOD2. The statistical interaction described here between bovine CD209 and TLR4 genes may be indicative of the biological interaction between their protein products upon infection by mycobacteria, as has been reported to occur in humans. Overall, this is the first evidence of epistasis among bovine innate immunity genes affecting susceptibility to MAP infection, corroborating, in turn, their implication in the disease.

Bovine Immunoinhibitory Receptors Contribute to Suppression of Mycobacterium avium subsp. paratuberculosis-Specific T-Cell Responses.

Johne's disease (paratuberculosis) is a chronic enteritis in cattle that is caused by intracellular infection with Mycobacterium avium subsp. paratuberculosis. This infection is characterized by the functional exhaustion of T-cell responses to M. avium subsp. paratuberculosis antigens during late subclinical and clinical stages, presumably facilitating the persistence of this bacterium and the formation of clinical lesions. However, the mechanisms underlying T-cell exhaustion in Johne's disease are poorly understood. Thus, we performed expression and functional analyses of the immunoinhibitory molecules programmed death-1 (PD-1)/PD-ligand 1 (PD-L1) and lymphocyte activation gene 3 (LAG-3)/major histocompatibility complex class II (MHC-II) in M. avium subsp. paratuberculosis-infected cattle during the late subclinical stage. Flow cytometric analyses revealed the upregulation of PD-1 and LAG-3 in T cells in infected animals, which suffered progressive suppression of interferon gamma (IFN-γ) responses to the M. avium subsp. paratuberculosis antigen. In addition, PD-L1 and MHC-II were expressed on macrophages from infected animals, consistent with PD-1 and LAG-3 pathways contributing to the suppression of IFN-γ responses during the subclinical stages of M. avium subsp. paratuberculosis infection. Furthermore, dual blockade of PD-L1 and LAG-3 enhanced M. avium subsp. paratuberculosis-specific IFN-γ responses in blood from infected animals, and in vitro LAG-3 blockade enhanced IFN-γ production from M. avium subsp. paratuberculosis-specific CD4(+) and CD8(+) T cells. Taken together, the present data indicate that M. avium subsp. paratuberculosis-specific T-cell exhaustion is in part mediated by PD-1/PD-L1 and LAG-3/MHC-II interactions and that LAG-3 is a molecular target for the control of M. avium subsp. paratuberculosis-specific T-cell responses.

An association study of SNPs with susceptibility to bovine paratuberculosis infection in cattle

The study was conducted to identify SNPs of quantitative trait loci (QTL) associated with susceptibility to Mycobacterium avium ssp. paratuberculosis (MAP) infection in cattle. Total 20 SNPs from the cattle QTL database were selected on the basis of the potential role in Mycobacterium susceptibility and a case: control association study was conducted in cattle. Out of 20 SNPs total 17 SNPs were polymorphic and 3 were monomorphic in population. The SNP (rs41945014) was significantly associated with MAP and revealed that ODDs of GG and GT genotypes verses TT genotype were 1.22 (0.33–4.49; 95% CI) and 3.37 (1.23–9.23; 95% CI), respectively. The proportion of GG and GT genotypes were significantly higher in bovine paratuberculosis positive animals suggested that selection against these 2 genotypes may confer resistance against bovine paratuberculosis. The all other 16 polymorphic SNPs of the present investigation were not differing significantly in case-control animals.

Expression of genes associated with cholesterol and lipid metabolism identified as a novel pathway in the early pathogenesis of Mycobacterium avium subspecies paratuberculosis-infection in cattle

Johne's disease (JD) is a chronic disease affecting ruminants and other species caused by the pathogenic mycobacterium, Mycobacterium avium subsp. paratuberculosis (MAP). MAP has developed a multitude of mechanisms to persist within the host, and these in turn are counteracted by the host through various immune pathways. Identifying and characterising the different strategies employed by MAP to alter the host immune system in its favour, and thereby persist intracellularly, could hold the key to developing strategies to fight this disease. In this study we analysed a subset of bovine microarray data derived from early time points after experimental infection with MAP. A specifically developed integrated approach was used to identify and validate host genes involved in cholesterol homeostasis (24DHCR, LDLR, SCD-1), calcium homeostasis and anti-bacterial defence mechanisms, (CD38, GIMAP6) which were downregulated in response to MAP exposure. A trend for upregulation of granulysin gene expression in MAP-exposed cattle in comparison to unexposed cattle was also observed. From these analyses, a model of potential pathogen-host interactions involving these novel pathways was developed which indicates an important role for host lipids in mycobacterial survival and persistence.

Increased blood-circulating interferon-γ, interleukin-17, and osteopontin levels in bovine paratuberculosis

Paratuberculosis-infected cattle initially develop an effective cell-mediated immune response that declines as the disease progresses. Blood is one of best sources for characterizing the inflammatory status of infected cows and for studying mediators related to chronic diseases. The aim of this study was to evaluate the cow-level association between blood cytokine concentration, the influence of serum on immune cell proliferation, and dairy cows naturally infected with Mycobacterium avium ssp. paratuberculosis (MAP). Positive animals (n=41) from 19 herds were selected on the basis of 2 positive fecal culture results and divided into 2 groups: single-positive, or serum ELISA-negative cows (n=32), and double-positive, or cows that gave positive results for both mycobacterial culture and serum ELISA (n=9). Negative animals (n=39) were selected from paratuberculosis-negative herds in which at least 80% of the animals had been diagnosed as negative by fecal culture and ELISA and that did not produce positive results during the 2-yr study. Analysis of plasma levels of the cytokines IL-4, IL-10, IL-17, IFN-γ, and osteopontin was performed, revealing distinct patterns. The ELISA-positive cows with MAP shedding had similar plasma concentrations of IL-4 and IL-10 but elevated levels of IFN-γ, IL-17, and osteopontin, which is indicative of inflammatory disease in these subclinical positive cows. In vitro MAP infection of bovine macrophages showed increased gene expression of tumor necrosis factor-α, IL-1β, IL-6, IL-23, and transforming growth factor-β as early as 6h postinfection for all of the cytokines involved in the establishment of a T-helper type-17 immune response. To determine the systemic influence of serum on immune cell functions, lymphoproliferation assays were also performed in presence of JD serum. The serum from shedding cows showed 15% less proliferation. These results indicate that infected cows have a lower systemic capacity to maintain a protective immune response and that, as the disease progresses, an emerging T-helper type-17 immune response is established.

Mycobacterium avium subsp. paratuberculosis Antibody Response, Fecal Shedding, and Antibody Cross-Reactivity to Mycobacterium bovis in M. avium subsp. paratuberculosis-Infected Cattle Herds Vaccinated against Johne's Disease

Vaccination for Johne's disease with killed inactivated vaccine in cattle herds has shown variable success. The vaccine delays the onset of disease but does not afford complete protection. Johne's disease vaccination has also been reported to interfere with measurements of cell-mediated immune responses for the detection of bovine tuberculosis. Temporal antibody responses and fecal shedding of Mycobacterium avium subsp. paratuberculosis, the causative agent of Johne's disease, were measured in 2 dairy cattle herds using Johne's disease vaccine (Mycopar) over a period of 7 years. Vaccination against Johne's disease resulted in positive serum M. avium subsp. paratuberculosis antibody responses in both herds, and the responses persisted in vaccinated cattle up to 7 years of age. Some vaccinated animals (29.4% in herd A and 36.2% in herd B) showed no serological reactivity to M. avium subsp. paratuberculosis. M. avium subsp. paratuberculosis-specific antibody responses were also detected in milk from Johne's disease-vaccinated animals, but fewer animals (39.3% in herd A and 49.4% in herd B) had positive results with milk than with serum samples. With vaccination against M. avium subsp. paratuberculosis, fecal shedding in both dairy herds was reduced significantly (P < 0.001). In addition, when selected Johne's disease-vaccinated and -infected animals were investigated for serological cross-reactivity to Mycobacterium bovis, no cross-reactivity was observed.

A murine oral model for Mycobacterium avium subsp. paratuberculosis infection and immunomodulation with Lactobacillus casei ATCC 334

Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) the causative agent of Johne's disease, is one of the most serious infectious diseases in dairy cattle worldwide. Due to the chronic nature of this disease and no feasible control strategy, it is essential to have an efficient animal model which is representative of the natural route of infection as well as a viable treatment option. In this report, we evaluated the effect of different doses of M. paratuberculosis in their ability to colonize murine tissues following oral delivery and the ability of Lactobacillus casei ATCC 334, a nascent probiotic, to combat paratuberculosis. Oral inoculation of mice was able to establish paratuberculosis in a dose-dependent manner. Two consecutive doses of approximately 109 CFU per mouse resulted in a disseminated infection, whereas lower doses were not efficient to establish infection. All inoculated mice were colonized with M. paratuberculosis, maintained infection for up to 24 weeks post infection and generated immune responses that reflect M. paratuberculosis infection in cattle. Notably, oral administration of L. casei ATCC 334 did not reduce the level of M. paratuberculosis colonization in treated animals. Interestingly, cytokine responses and histology indicated a trend for the immunomodulation and reduction of pathology in animals receiving L. casei ATCC 334 treatment. Overall, a reproducible oral model of paratuberculosis in mice was established that could be used for future vaccine experiments. Although the L. casei ATCC 334 was not a promising candidate for controlling paratuberculosis, we established a protocol to screen other probiotic candidates.

T lymphocyte responses during early enteric Mycobacterium avium subspecies paratuberculosis infection in cattle

Johne's disease (JD) is a costly intestinal disease of ruminants caused by Mycobacterium avium subspecies paratuberculosis (Map), which is transmitted to perinatal calves by the fecal-oral route. Disease control efforts focus on identification and culling of infected cattle from herds; therefore failure to identify animals early is a major obstacle to reducing transmission. Development of host immunity during early JD remain incompletely characterized so detecting subclinical JD using immunologic techniques is a substantial challenge in the field. Development of a test with high sensitivity and specificity is a major research goal with significant implications for the cattle industry. The objectives of this study were to compare early Map-specific T lymphocyte responses in naive, experimentally Map infected and Map vaccinated calves using a subcutaneous matrigel biopolymer-based assay. We examined the phenotype of recruited lymphocytes and local interferon gamma (IFNγ) production within subcutaneously placed matrigel containing Map antigen 30 days after experimentally induced intestinal Map infection or Map vaccination. We show that IFNγ-secreting CD4+ T cells are recruited to matrigel sites in vaccinated but not infected or naïve calves. γδ T cells recruited to matrigel sites of Map-infected calves were mostly WC1-, while γδ T cells recruited to matrigel sites of Map-vaccinated calves were predominantly WC1+. IFNγ at matrigel sites was a discriminating factor between infected calves, naïve calves and vaccinated calves. These data contribute to our understanding of early anti-Map immunity, and may be useful for detecting early intestinal Map infections in calves or for enhancing our ability to discriminate between Map-infected and Map-vaccinated calves.

Novel Secreted Antigens of Mycobacterium paratuberculosis as Serodiagnostic Biomarkers for Johne's Disease in Cattle

Johne's disease is a chronic gastroenteritis of cattle caused by Mycobacterium avium subsp. paratuberculosis that afflicts 40% of dairy herds worldwide. M. avium subsp. paratuberculosis-infected cattle can remain asymptomatic for years while transmitting the pathogen via fecal contamination and milk. Current serodiagnosis with enzyme-linked immunosorbent assays (ELISAs) fails to detect asymptomatic M. avium subsp. paratuberculosis-infected cattle due to the use of poorly defined antigens and knowledge gaps in our understanding of M. avium subsp. paratuberculosis components eliciting pathogen-specific immune responses. We set out to (i) define a subset of proteins that contain putative antigenic targets and (ii) screen these antigen pools for immunogens relevant in detecting infection. To accomplish our first objective, we captured and resolved M. avium subsp. paratuberculosis-secreted proteins using a 2-step fractionation method and reverse-phase liquid chromatography to identify 162 unique proteins, of which 66 had not been previously observed in M. avium subsp. paratuberculosis culture filtrates. Subsequent screening of M. avium subsp. paratuberculosis-secreted proteins showed four antigens, of which one or more reacted on immunoblotting with individual serum samples from 35 M. avium subsp. paratuberculosis-infected cows. Moreover, these novel antigens reacted with sera from 6 low M. avium subsp. paratuberculosis shedders and 3 fecal-culture-positive cows labeled as ELISA seronegative. The specificity of these antigens was demonstrated using negative-control sera from uninfected calves (n = 5) and uninfected cows (n = 5), which did not react to any of these antigens in immunoblotting. As three of the four antigens are novel, their characterization and incorporation into an ELISA-based format will aid in detecting asymptomatic cattle in early or subclinical stages of disease.

Host Responses to Persistent Mycobacterium avium Subspecies paratuberculosis Infection in Surgically Isolated Bovine Ileal Segments

A lack of appropriate disease models has limited our understanding of the pathogenesis of persistent enteric infections with Mycobacterium avium subsp. paratuberculosis. A model was developed for the controlled delivery of a defined dose of M. avium subsp. paratuberculosis to surgically isolated ileal segments in newborn calves. The stable intestinal segments enabled the characterization of host responses to persistent M. avium subsp. paratuberculosis infections after a 9-month period, including an analysis of local mucosal immune responses relative to an adjacent uninfected intestinal compartment. M. avium subsp. paratuberculosis remained localized at the initial site of intestinal infection and was not detected by PCR in the mesenteric lymph node. M. avium subsp. paratuberculosis-specific T cell proliferative responses included both CD4 and γδ T cell receptor (γδTcR) T cell responses in the draining mesenteric lymph node. The levels of CD8(+) and γδTcR(+) T cells increased significantly (P < 0.05) in the lamina propria, and M. avium subsp. paratuberculosis-specific tumor necrosis factor alpha (TNF-α) and gamma interferon secretion by lamina propria leukocytes was also significantly (P < 0.05) increased. There was a significant (P < 0.05) accumulation of macrophages and dendritic cells (DCs) in the lamina propria, but the expression of mucosal toll-like receptors 1 through 10 was not significantly changed by M. avium subsp. paratuberculosis infection. In conclusion, surgically isolated ileal segments provided a model system for the establishment of a persistent and localized enteric M. avium subsp. paratuberculosis infection in cattle and facilitated the analysis of M. avium subsp. paratuberculosis-specific changes in mucosal leukocyte phenotype and function. The accumulation of DC subpopulations in the lamina propria suggests that further investigation of mucosal DCs may provide insight into host responses to M. avium subsp. paratuberculosis infection and improve vaccine strategies to prevent M. avium subsp. paratuberculosis infection.

A modeller's perspective on infection dynamics within and between hosts

The goal of this case-series was to increase our understanding of some complex within and between-host infection dynamics through the creation of mathematical and computational models that are able to capture the existing host and/or parasite heterogeneity. This goal was reached through a series of research projects (regarding experimental autoimmune encephalomyelitis (EAE) in mice, Mycobacterium avium subspecies paratuberculosis infection in cattle, Eimeria acervulina infection in chicken and human malaria) that gradually build up in complexity of both the system modelled and the modelling techniques used. In this case-series, the vast majority of model components have a direct link with reality. The results have shown some detailed examples of the valuable contribution that models have in understanding infection processes. The most satisfying achievements have come from those models that were able to, in hindsight, make complicated experimental results seem obvious and logical, and where the process of building the model was as insightful as the final results. The models created in these projects help to explain a wide range of sometimes contradictory experimental results and are used to predict the effect of control measures. In addition, they generate ideas for the development of new methods of control.