Evaluation of the performance of the IFN-γ release assay in bovine tuberculosis free herds from five European countries

The diagnostic methods for granting and maintenance of the official tuberculosis-free (OTF) status and for intra-Community movement of cattle are the tuberculin skin tests (single or comparative) and the interferon-γ (IFN-γ) release assay (IGRA). However, until now, IGRAs have been primarily applied in infected farms in parallel to the skin test to maximize the number of infected animals detected. Therefore, an evaluation of the performance of IGRAs in OTF herds to assess whether if their specificity is equal to or higher than that of the skin tests is needed. For this, a panel of 4365 plasma samples coming from 84 OTF herds in six European regions (five countries) was assembled and analysed using two IGRA kits, the ID Screen^® Ruminant IFN-g (IDvet) and the Bovigam™ TB Kit (Bovigam). Results were evaluated using different cut-offs, and the impact of herd and animal-level factors on the probability of positivity was assessed using hierarchical Bayesian multivariable logistic regression models. The percentage of reactors ranged from 1.7 to 21.0% (IDvet: S/P ≥ 35%), and 2.1-26.3% (Bovigam: OD_bovis-OD_PBS ≥ 0.1 and OD_bovis-OD_avium ≥ 0.1) depending on the region, with Bovigam disclosing more reactors in all regions. The results suggest that specificity of IGRAs can be influenced by the production type, age and region of origin of the animals. Changes in the cut-offs could lead to specificity values above 98-99% in certain OTF populations, but no single cut-off yielding a sufficiently high specificity (equal or higher than that of skin tests) in all populations was identified. Therefore, an exploratory analysis of the baseline IFN-γ reactivity in OTF populations could help to assess the usefulness of this technique when applied for the purpose of maintaining OTF status.

Prostaglandin E2-Induced Immune Suppression via Cytotoxic T-Lymphocyte Antigen 4 in Paratuberculosis

Paratuberculosis is a chronic enteritis of ruminants caused by the facultative intracellular pathogen Mycobacterium avium subsp. paratuberculosis. The Th1 response inhibits the proliferation of M. avium subsp. paratuberculosis during the early subclinical stage. However, we have previously shown that immune inhibitory molecules, such as prostaglandin E₂ (PGE₂), suppress M. avium subsp. paratuberculosis-specific Th1 responses as the disease progresses. To date, the mechanism underlying immunosuppression during M. avium subsp. paratuberculosis infection has not been elucidated. Therefore, in the present study, we investigated the function of cytotoxic T-lymphocyte antigen 4 (CTLA-4) expressed by peripheral blood mononuclear cells (PBMCs) from cattle with paratuberculosis because CTLA-4 expression is known to be elevated in T cells under an M. avium subsp. paratuberculosis experimental infection. M. avium subsp. paratuberculosis antigen induced CTLA-4 expression in T cells from cattle experimentally infected with M. avium subsp. paratuberculosis. Interestingly, both PGE₂ and an E prostanoid 4 agonist also induced CTLA-4 expression in T cells. In addition, a functional assay with a bovine CTLA-4-immunogobulin fusion protein (CTLA-4-Ig) indicated that CTLA-4 inhibited gamma interferon (IFN-γ) production in M. avium subsp. paratuberculosis-stimulated PBMCs, while blockade by anti-bovine CTLA-4 monoclonal antibody increased the secretion of IFN-γ and tumor necrosis factor alpha production in these PBMCs. These preliminary findings show that PGE₂ has immunosuppressive effects via CTLA-4 to M. avium subsp. paratuberculosis. Therefore, it is necessary to clarify in the future whether CTLA-4-mediated immunosuppression facilitates disease progression of paratuberculosis in cattle.

Analysis of mRNA and circRNA Expression Profiles of Bovine Monocyte-Derived Macrophages Infected With Mycobacterium avium subsp. paratuberculosis

Mycobacterium avium subsp. paratuberculosis (MAP) is the pathogen of Johne’s disease (paratuberculosis), which mainly causes chronic infectious granulomatous enteritis in ruminants and has brought huge economic losses to animal husbandry. As a specific intracellular pathogen, when MAP invades the body, it is internalized by macrophages where it is able to replicate by inhibition of the phagosome maturation, escaping the host immune system and surviving, which leads to the spread of the disease. More recent studies have shown that circRNA is involved in many pathological and physiological processes of the body as the molecular sponge of miRNA, the scaffold of RNA binding protein and having the characteristic of being able to translate into protein. In this study, the mRNA and circRNA expression profiles of MAP-infected bovine monocyte-macrophages and uninfected bovine cells were analyzed by high-throughput sequencing. A total of 618 differentially expressed mRNA were screened out, including 322 upregulated mRNA and 296 downregulated mRNA. In addition, the analysis of circRNA differential expression profile showed 39 differentially expressed genes including 12 upregulated and 27 downregulated genes. Moreover, differential genes belonging to cytokine activity, chemokine activity, inflammatory reaction, apoptosis, and other functional groups related to macrophage immune response were significantly enriched in Gene Ontology (GO). Multiple signal pathways including NF-κB, MAPK, Toll-like receptor, IL-17, JAK-STAT, and other signaling pathways related to activating macrophage immune response were significantly enriched in Kyoto Encyclopedia of Genes and Genomes (KEGG). In addition, RT-qPCR technology verified the accuracy of the mRNA sequencing results. In this study, we have obtained the transcriptome information of mRNA and circRNA of bovine monocyte-macrophage infected with MAP. These results will provide data support for the further study of mRNA–miRNA–circRNA network and immune escape mechanism of MAP and will enrich the knowledge of the molecular immune mechanisms of Johne’s disease as well.

Transmission patterns of a Mycobacterium avium subsp. paratuberculosis clone within a single heard investigated by Whole Genome Sequencing

Mycobacterium avium subsp. paratuberculosis (MAP) is characterized by a low genomic rate of mutation. Current subtyping tools, such as Mini-Micro-satellite analyses, do to have not sufficient discriminatory power to disclose MAP's evolution on small spatial and temporal scales. The aim of the study was to investigate the population structure of MAP inside a single dairy herd using whole genome sequencing (WGS) approaches. For this purpose, the genomes of 43 field isolates, recovered from the faeces of 36 cows of the same dairy herd from 2012 to 2016, were sequenced by WGS. The isolates' genomes showed a low number (43) of polymorphic sites (SNPs), confirming the clonal origin of the herd infection. However, despite the limited genomic diversity found in WGS, the phylogenetic analysis was discriminatory enough to detect the presence of different genomic clades and sub-clades inside the herd population. In addition, the phylodynamic reconstruction showed the existence of an ancestor clade from which the other clades and sub-clades originated. Moreover, by reconstructing the putative within-herd transmission networks using WGS data, we demonstrated that: (i) in a herd where MAP is endemic, multiple isolates recovered from a single animal and differing from each other by few (three/four) SNPs can originate from different transmission or passive shedding events and not from intra-host evolution; and (ii) variability of minisatellites coupled with a few microsatellites does not represent reliable tracers of within-herd infection chains. Our findings show that WGS, coupled with relevant epidemiological information, represents a valuable tool to work out fine epidemiological and micro-evolutionary relationships such as those at herd-level scale.

Who infects whom?-Reconstructing infection chains of Mycobacterium avium ssp. paratuberculosis in an endemically infected dairy herd by use of genomic data

Recent evidence of circulation of multiple strains within herds and mixed infections of cows marks the beginning of a rethink of our knowledge on Mycobacterium avium ssp. paratuberculosis (MAP) epidemiology. Strain typing opens new ways to investigate MAP transmission. This work presents a method for reconstructing infection chains in a setting of endemic Johne’s disease on a well-managed dairy farm. By linking genomic data with demographic field data, strain-specific differences in spreading patterns could be quantified for a densely sampled dairy herd. Mixed infections of dairy cows with MAP are common, and some strains spread more successfully. Infected cows remain susceptible for co-infections with other MAP genotypes. The model suggested that cows acquired infection from 1–4 other cows and spread infection to 0–17 individuals. Reconstructed infection chains supported the hypothesis that high shedding animals that started to shed at an early age and showed a progressive infection pattern represented a greater risk for spreading MAP. Transmission of more than one genotype between animals was recorded. In this farm with a good MAP control management program, adult-to-adult contact was proposed as the most important transmission route to explain the reconstructed networks. For each isolate, at least one more likely ancestor could be inferred. Our study results help to capture underlying transmission processes and to understand the challenges of tracing MAP spread within a herd. Only the combination of precise longitudinal field data and bacterial strain type information made it possible to trace infection in such detail.

The enhancement of Th1 immune response by anti-PD-L1 antibody in cattle infected with Mycobacterium avium subsp. paratuberculosis

Johne's disease, caused by Mycobacterium avium subsp. paratuberculosis (MAP), is a chronic enteritis of ruminants. Previous studies have shown that programmed death-ligand 1 (PD-L1) is associated with the disease progression, and PD-L1 blockade activates MAP-specific Th1 responses in vitro. Here, we performed anti-PD-L1 antibody administration using 2 MAP-infected cattle at the late subclinical stage of infection. After administration, bacterial shedding was reduced or maintained at a low level. Additionally, MAP-specific Th1 cytokine production was upregulated, and CD69 expression was increased in T cells. Collectively, the treatment has a potential as a novel control method against Johne's disease.

Acanthamoeba castellanii as a Screening Tool for Mycobacterium avium Subspecies paratuberculosis Virulence Factors with Relevance in Macrophage Infection

The high prevalence of Johne's disease has driven a continuous effort to more readily understand the pathogenesis of the etiological causative bacterium, Mycobacterium avium subsp. paratuberculosis (MAP), and to develop effective preventative measures for infection spread. In this study, we aimed to create an in vivo MAP infection model employing an environmental protozoan host and used it as a tool for selection of bacterial virulence determinants potentially contributing to MAP survival in mammalian host macrophages. We utilized Acanthamoeba castellanii (amoeba) to explore metabolic consequences of the MAP-host interaction and established a correlation between metabolic changes of this phagocytic host and MAP virulence. Using the library of gene knockout mutants, we identified MAP clones that can either enhance or inhibit amoeba metabolism and we discovered that, for most part, it mirrors the pattern of MAP attenuation or survival during infection of macrophages. It was found that MAP mutants that induced an increase in amoeba metabolism were defective in intracellular growth in macrophages. However, MAP clones that exhibited low metabolic alteration in amoeba were able to survive at a greater rate within mammalian cells, highlighting importance of both category of genes in bacterial pathogenesis. Sequencing of MAP mutants has identified several virulence factors previously shown to have a biological relevance in mycobacterial survival and intracellular growth in phagocytic cells. In addition, we uncovered new genetic determinants potentially contributing to MAP pathogenicity. Results of this study support the use of the amoeba model system as a quick initial screening tool for selection of virulence factors of extremely slow-grower MAP that is challenging to study.

Peripheral blood bovine lymphocytes and MAP show distinctly different proteome changes and immune pathways in host-pathogen interaction

Mycobacterium avium subsp. paratuberculosis (MAP) is a pathogen causing paratuberculosis in cattle and small ruminants. During the long asymptomatic subclinical stage, high numbers of MAP are excreted and can be transmitted to food for human consumption, where they survive many of the standard techniques of food decontamination. Whether MAP is a human pathogen is currently under debate. The aim of this study was a better understanding of the host-pathogen response by analyzing the interaction of peripheral blood lymphocytes (PBL) from cattle with MAP in their exoproteomes/secretomes to gain more information about the pathogenic mechanisms of MAP. Because in other mycobacterial infections, the immune phenotype correlates with susceptibility, we additionally tested the interaction of MAP with recently detected cattle with a different immune capacity referred as immune deviant (ID) cows. In PBL, different biological pathways were enhanced in response to MAP dependent on the immune phenotype of the host. PBL of control cows activated members of cell activation and chemotaxis of leukocytes pathway as well as IL-12 mediated signaling. In contrast, in ID cows CNOT1 was detected as highly abundant protein, pointing to a different immune response, which could be favorable for MAP. Additionally, MAP exoproteomes differed in either GroEL1 or DnaK abundance, depending on the interacting host immune response. These finding point to an interdependent, tightly regulated response of the bovine immune system to MAP and vise versa.

Mycobacterium avium paratuberculosis and Mycobacterium avium complex and related subspecies as causative agents of zoonotic and occupational diseases

Mycobacterium avium complex (MAC) and Mycobacterium avium paratuberculosis (MAP) cause zoonotic infections transmitted by birds and livestock herds. These pathogens have remained as serious economic and health threats in most areas of the world. As zoonotic diseases, the risk of development of occupational disease and even death outcome necessitate implementation of control strategies to prevent its spread. Zoonotic MAP infections include Crohn's disease, inflammatory bowel disease, ulcerative colitis, sarcoidosis, diabetes mellitus, and immune-related diseases (such as Hashimoto's thyroiditis). Paratuberculosis has classified as type B epidemic zoonotic disease according to world health organization which is transmitted to human through consumption of dairy and meat products. In addition, MAC causes pulmonary manifestations and lymphadenitis in normal hosts and human immunodeficiency virus (HIV) progression (by serotypes 1, 4, and 8). Furthermore, other subspecies have caused respiratory abscesses, neck lymph nodes, and disseminated osteomyelitis in children and ulcers. However, the data over the occupational relatedness of these subspecies is rare. These agents can cause occupational infections in susceptible herd breeders. Several molecular methods have been recognized as proper strategies for tracking the infection. In this study, some zoonotic aspects, worldwide prevalence and control strategies regarding infections due to MAP and MAC and related subspecies has been reviewed.

A data-driven individual-based model of infectious disease in livestock operation: A validation study for paratuberculosis

Chronic livestock diseases cause large financial loss and affect animal health and welfare. Controlling these diseases mostly requires precise information on both individual animal and population dynamics to inform the farmer’s decisions, but even successful control programmes do by no means assure elimination. Mathematical models provide opportunities to test different control and elimination options rather than implementing them in real herds, but these models require robust parameter estimation and validation. Fitting these models to data is a difficult task due to heterogeneities in livestock processes. In this paper, we develop an infectious disease modeling framework for a livestock disease (paratuberculosis) that is caused by Mycobacterium avium subsp. paratuberculosis (MAP). Infection with MAP leads to reduced milk production, pregnancy rates, and slaughter value and increased culling rates in cattle and causes significant economic losses to the dairy industry. These economic effects are particularly important motivations in the control and elimination of MAP. In this framework, an individual-based model (IBM) of a dairy herd was built and MAP infection dynamics was integrated. Once the model produced realistic dynamics of MAP infection, we implemented an evaluation method by fitting it to data from three dairy herds from the Northeast region of the US. The model fitting exercises used least-squares and parameter space searching methods to obtain the best-fitted values of selected parameters. The best set of parameters were used to model the effect of interventions. The results show that the presented model can complement real herd statistics where the intervention strategies suggest a reduction in MAP prevalence without elimination. Overall, this research not only provides a complete model for MAP infection dynamics in a dairy herd but also offers a method for estimating parameters by fitting IBM models.

Prostaglandin E2 Induction Suppresses the Th1 Immune Responses in Cattle with Johne's Disease

Johne's disease, caused by Mycobacterium avium subsp. paratuberculosis, is a bovine chronic infection that is endemic in Japan and many other countries. The expression of immunoinhibitory molecules is upregulated in cattle with Johne's disease, but the mechanism of immunosuppression is poorly understood. Prostaglandin E₂ (PGE₂) is immunosuppressive in humans, but few veterinary data are available. In this study, functional and kinetic analyses of PGE₂ were performed to investigate the immunosuppressive effect of PGE₂ during Johne's disease. In vitro PGE₂ treatment decreased T-cell proliferation and Th1 cytokine production and upregulated the expression of immunoinhibitory molecules such as interleukin-10 and programmed death ligand 1 (PD-L1) in peripheral blood mononuclear cells (PBMCs) from healthy cattle. PGE₂ was upregulated in sera and intestinal lesions of cattle with Johne's disease. In vitro stimulation with Johnin purified protein derivative (J-PPD) induced cyclooxygenase-2 (COX-2) transcription, PGE₂ production, and upregulation of PD-L1 and immunoinhibitory receptors in PBMCs from cattle infected with M. avium subsp. paratuberculosis Therefore, Johnin-specific Th1 responses could be limited by the PGE₂ pathway in cattle. In contrast, downregulation of PGE₂ with a COX-2 inhibitor promoted J-PPD-stimulated CD8⁺ T-cell proliferation and Th1 cytokine production in PBMCs from the experimentally infected cattle. PD-L1 blockade induced J-PPD-stimulated CD8⁺ T-cell proliferation and interferon gamma production in vitro Combined treatment with a COX-2 inhibitor and anti-PD-L1 antibodies enhanced J-PPD-stimulated CD8⁺ T-cell proliferation in vitro, suggesting that the blockade of both pathways is a potential therapeutic strategy to control Johne's disease. The effects of COX-2 inhibition warrant further study as a novel treatment of Johne's disease.

The investigation of the truncated mbtA gene within the mycobactin cluster of Mycobacterium avium subspecies paratuberculosis as a novel diagnostic marker for real-time PCR

The inability of Mycobacterium avium subspecies paratuberculosis (MAP) to produce endogenous mycobactin in-vitro is most likely due to the presence of a truncated mbtA gene within the mycobactin cluster of MAP. The main goal of this study was to investigate this unique mbtA truncation as a potential novel PCR diagnostic marker for MAP. Novel primers were designed that were located within the truncated region and the contiguous MAP2179 gene. Primers were evaluated against non-MAP isolates and no amplicons were generated. The detection limit of this mbtA-MAP2179 target was evaluated using a range of MAP DNA concentrations, MAP inoculated faecal material and 20 MAP isolates. The performance of mbtA-MAP2179 was compared to the established f57 target. The detection limits recorded for MAP K-10 DNA and from MAP K-10 inoculated faecal samples were 0.34pg and 10⁴CFU/g respectively for both f57 and mbtA-MAP2179. A detection limit of 10³CFU/g was recorded for both targets, but not achieved consistently. The detection limit of MAP from inoculated faecal material was successful at 10³CFU/g for mbtA-MAP2179 when FAM probe real-time PCR was used. A MAP cell concentration of 10²CFU/g was detected successfully, but again not consistently achieved. All 20 mycobacterial isolates were successfully identified as MAP by f57 and mbtA-MAP2179. Interestingly, the mbtA-MAP2179 real-time PCR assay resulted in the formation of a unique melting curve profile that contained two melting curve peaks rather than one single peak. This melting curve phenomenon was attributed towards the asymmetrical GC% distribution within the mbtA-MAP2179 amplicon. This study investigated the implementation of the mbtA-MAP2179 target as a novel diagnostic marker and the detection limits obtained with mbtA-MAP2179 were comparable to the established f57 target, making the mbtA-MAP2179 an adequate confirmatory target. Moreover, the mbtA-MAP2179 target could be implemented in multiplex real-time PCR assays and with its unique melting curve profile adds increased specificity to MAP diagnostic tests.

Exploring MALDI-TOF MS approach for a rapid identification of Mycobacterium avium ssp. paratuberculosis field isolates

AIMS

The aim of the study was to explore the suitability of matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) for a rapid and correct identification of Mycobacterium avium ssp. paratuberculosis (MAP) field isolates.

METHODS AND RESULTS

MALDI-TOF MS approach is becoming one of the most popular tests for the identification of intact bacterial cells which has been shown to be fast and reliable. For this purpose, 36 MAP field isolates were analysed through MALDI-TOF MS and the spectra compared with two different databases: one provided by the vendor of the system employed (Biotyper ver. 3·0; Bruker Daltonics) and a homemade database containing spectra from both tuberculous and nontuberculous Mycobacteria. Moreover, principal component analysis procedure was employed to confirm the ability of MALDI-TOF MS to discriminate between very closely related subspecies. Our results suggest MAP can be differentiated from other Mycobacterium species, both when the species are very close (M. intracellulare) and when belonging to different subspecies (M. avium ssp. avium and M. avium ssp. silvaticum).

CONCLUSIONS

The procedure applied is fast, easy to perform, and achieves an earlier accurate species identification of MAP and nontuberculous Mycobacteria in comparison to other procedures.

SIGNIFICANCE AND IMPACT OF THE STUDY

The gold standard test for the diagnosis of paratuberculosis is still isolation of MAP by cultural methods, but additional assays, such as qPCR and subculturing for determination of mycobactin dependency are required to confirm its identification. We have provided here evidence pertaining to the usefulness of MALDI-TOF MS approach for a rapid identification of this mycobacterium among other members of M. avium complex.

The seroprevalence of Mycobacterium avium subspecies paratuberculosis in dairy cattle in Xinjiang, Northwest China

Background

Mycobacterium avium subspecies paratuberculosis (MAP) causes chronic, wasting, and progressive enteritis in cattle, bringing significant economic losses in livestock industries. MAP has spread worldwide mainly due to movement of animals. The objective of this study was to determine the MAP seroprevalence in cattle in the Xinjiang Uygur Autonomous Region, Northwest China, and evaluate the difference between intensive farming herds (cattle number in a herd is more than 200, and the cattle cannot have access to pasture) and free-range herds (the cattle are bred by individual households, a herd is defined as the cattle are bred in a village or town in this study).

Results

A total of 3157 serum specimens were collected from 42 herds in nine different regions. This included 1481 specimens from 18 intensive farming herds in four regions and 1676 specimens from 24 free-range herds in six regions. Antibody against MAP was tested with commercial ELISA test kits. The results showed that the overall apparent prevalence was 4.8% (95% CI, 4.1 to 5.6%) at animal level, and 50.0% (21/42) at herd level. The apparent prevalence in intensive farming herds and free-range herds were 9.5% (141/1481) and 0.7% (11/1676) at the animal-level, 88.9%(16/18) and 20.8% (5/24) at herd level, respectively, with a significant statistical difference between these two farming modes (p < 0.01). Cattle in intensive farming herds had a relatively higher risk to be infected with MAP than those in free-range herds (RR = 14.4).

Conclusion

This study demonstrates that apparent prevalence of MAP infection in dairy cattle differs with farming modes at the animal level and herd level, and farming density could be an important risk factor associated with the presence of MAP infected cattle. This study provides important epidemiological data for bovine MAP control in Xinjiang, Northwest China.