Detection of Mycobacterium avium subspecies paratuberculosis: comparing fecal culture versus serum enzyme-linked immunosorbent assay and direct fecal polymerase chain reaction

Widespread circulation and transmission risk of Mycobacterium avium subsp. paratuberculosis at the livestock-wildlife-environment interface in a Mediterranean agro-forestry farmstead

Mycobacterium avium subsp. paratuberculosis (MAP) is the etiological agent of paratuberculosis, a chronic infection affecting ruminants and other species worldwide. Information on the ecological factors that increase infection risk at the livestock-wildlife-environment interface remains scarce. Thus, this work aimed at determining which factors modulate the exposure of a mammal community within a Mediterranean agro-forestry farmstead to MAP. Through field, molecular and ecological modeling approaches, MAP prevalence, distribution and spatial risk at the livestock-wildlife-environment was estimated in the study area by screening 436 samples (cattle, n = 150; wildlife, n = 206; soil, n = 80). Using molecular detection of IS900 as proxy, MAP was identified in ten wild mammal species. Being a central prey of mesocarnivores in Portugal, the high prevalence of MAP in the wild rabbit (19%) may be related with red fox's (22%). MAP was also detected in cattle managed in the farmstead (animal and herd prevalence, 54% and 100%) and in soil (44%), which may perpetuate intraspecies and interspecies transmission. Wildlife diversity showed a positive influence on MAP presence in wild mammals, while wildlife abundance showed a negative effect. Land use variables exerted distinct degrees of impact upon MAP detection in specific groups of mammals: mixed forest cover showed positive influence on carnivores, and shrubland showed positive effect on wild rabbits. The prevalence of MAP in cattle showed a negative influence on the detection of MAP in lagomorph, which may stem from wild rabbit lower density and avoidance of cattle areas. Based on explanatory variables, the spatial prediction of MAP occurrence in wildlife indicated two hotspots with increased exposure risk but future studies are needed to confirm this projection. This work represents the most comprehensive molecular survey of MAP occurrence and determinants in Mediterranean agroecosystems leveraging the principles and tools of community ecology, debating potential biological and ecological effects underlying MAP transmission.

Association between major histocompatibility complex haplotypes and susceptibility of unvaccinated and vaccinated cattle to paratuberculosis

Bovine Johne's disease (BJD) or paratuberculosis is caused by Mycobacterium avium spp. paratuberculosis (MAP) and is a worldwide problem among domestic and wild ruminants. While vaccines are available, natural differences in background immunity between breeds within species and between individuals within herds suggest that genetic differences may be able to be exploited in marker-assisted selection as an aid to disease control. The major histocompatibility complex (MHC) is an important component in immune recognition with considerable genetic variability. In this study, associations between the MHC and resistance to BJD were explored in dairy cattle across two herds in which some of the cattle had been vaccinated with Silirum® (n = 540 cows). A BJD susceptible animal was exposed to MAP and became infected, while a resistant animal was exposed but did not become infected. There are different ways to define both exposure and infection, with different levels of stringency, therefore many classifications of the same set of animals are possible and were included in the analysis. The polymorphic regions of major histocompatibility complex class I (MHC I) and class II (MHC II) genes were amplified from the genomic DNA by PCR and sequenced, targeting exons 2 and 3 of the classical and non-classical MHC I genes and exon 2 from the DRB3, DQA1, DQA2 + 3 and DQB MHC II genes. The frequencies of MHC I and MHC II haplotypes and alleles were determined in susceptible and resistant populations. In unvaccinated animals, seven MHC I haplotypes and seven MHC II haplotypes were associated with susceptibility while two MHC I and six MHC II haplotypes were associated with resistance (P < 0.05). In vaccinated animals, two MHC I and three MHC II haplotypes were associated with susceptibility, while one MHC I and two MHC II haplotypes were associated with resistance (P < 0.05). The alleles in significant haplotypes were also identified. Case definitions with higher stringency resulted in fewer animals being included in the analyses, but the power to detect an association was not reduced and there was an increase in strength and consistency of associations. Consistent use of stringent case definitions is likely to improve agreement in future association studies.

Associations between Johne's disease and fertility in UK dairy herds

The objective of this observational study was to quantify associations between Mycobacterium avium subspecies paratuberculosis (MAP) antibody status and a variety of fertility outcomes, in UK dairy cattle. Longitudinal milk recording, fertility and MAP antibody enzyme-linked immunosorbent assay (ELISA) milk test data were collated retrospectively from 121,762 lactations in 78 herds. Datasets were structured into appropriate units to suit outcomes and enable temporal association between current and future MAP status, and fertility measures. Current MAP status was categorised according to most recent status within 180 days, with time-related future MAP status assigned based on MAP antibody ELISA milk test data for each cow. Multilevel multivariable logistic regression models were used to evaluate associations between MAP status and 21-day pregnancy and submission rate and conception risk. Posterior predictions and cross-validation techniques were used to assess model fit and check model building assumptions. A negative association was found between risk of insemination (Odds Ratio [OR], 0.78; 95% Credible Interval [CI], 0.66-0.92) and conception occurring (OR, 0.65; CI, 0.5-0.84) and transition from negative to non-negative MAP test status in the next 30-90 days. A positive association was observed between risk of insemination (OR, 1.34; CI, 1.16-1.52) and conception occurring (OR, 1.26; CI, 1.11-1.43) and transition from negative to non-negative MAP test status in the next 90-180 days. Current positive MAP test status was negatively and positively associated with insemination (OR, 0.59; CI, 0.49-0.70) and conception risk (OR, 1.12; CI, 0.96-1.30), respectively. Herd managers will have had access to test results, declaring cows with past recent or multiple positive MAP antibody ELISA results not to be bred, negatively influencing insemination risk. Overall, these results demonstrate the temporal association between a positive MAP antibody ELISA result and dairy cow fertility outcomes, with particular variability prior to a positive MAP antibody ELISA result.

Bioprospective Role of Ocimum sanctum and Solanum xanthocarpum against Emerging Pathogen: Mycobacterium avium Subspecies paratuberculosis: A Review

Mycobacterium avium subspecies paratuberculosis (MAP) is a chronic, contagious, and typically life-threatening enteric disease of ruminants caused by a bacterium of the genus Mycobacterium, but it can also affect non-ruminant animals. MAP transmission occurs through the fecal-oral pathway in neonates and young animals. After infection, animals generate IL-4, IL-5, and IL-10, resulting in a Th2 response. Early detection of the disease is necessary to avoid its spread. Many detection methods, viz., staining, culture, and molecular methods, are available, and numerous vaccines and anti-tuberculosis drugs are used to control the disease. However, the prolonged use of anti-tuberculosis drugs leads to the development of resistance. Whereas vaccines hamper the differentiation between infected and vaccinated animals in an endemic herd. This leads to the identification of plant-based bioactive compounds to treat the disease. Bioactive compounds of Ocimum sanctum and Solanum xanthocarpum have been evaluated for their anti-MAP activity. Based on the MIC50 values, Ursolic acid (12 µg/mL) and Solasodine (60 µg/mL) were found to be suitable for anti-MAP activity.

Molecular and serological survey of paratuberculosis in cattle in selected districts of Western Uganda

Knowledge of Mycobacterium avium subsp. paratuberculosis (MAP) herd infection status is important to plan appropriate control and prevention strategies for Paratuberculosis (PTB); however, in Uganda MAP infection status of most herds is unknown. This study aimed at determining the MAP infection status of cattle herds and the associated risk factors for MAP infection in six western districts of Uganda. The survey covered a total of 93 herds where faecal and blood samples were collected from 1814 cattle. A Recombinase Polymerase Amplification (RPA) and an antibody-based (ELISA) assays were used to test for the presence of MAP DNA in faeces and MAP antibodies in serum, respectively. The apparent cow-level prevalence of MAP infection was 3.2 and 2.7% using ELISA and RPA respectively and the true cow-level prevalence using ELISA and RPA was 4.9 and 3% respectively. A herd-level prevalence of 43% (ELISA) and 40.8% (RPA) and a within-herd prevalence of 3.8 ± 2.1% based on ELISA were obtained. Among the risk factors investigated, long dry spells were significantly associated with high MAP infection (p < 0.05). These results indicate that MAP is actively present in most areas where surveillance was carried out. This poses a serious threat to the livestock industry and potentially to public health as MAP is highly suspected to play a role in the pathogenesis of several diseases in humans. Other areas of the country are to be surveyed as well in order to establish full data on MAP infection status to enable interventions for the control and prevention of the disease.

Estimating the sensitivity and specificity of serum ELISA and pooled and individual fecal PCR for detecting Mycobacterium avium subspecies paratuberculosis in Canadian cow-calf herds using Bayesian latent class models

While Johne's disease (JD) is less common in beef than in dairy herds, consolidation is increasing transmission risk. Estimates of Mycobacterium avium spp. paratuberculosis (MAP) prevalence and test performance in cow-calf herds are needed to inform control programs. Objectives of this study included describing the prevalence of MAP in Canadian cow-calf herds and comparing the relative performance of a serum ELISA, pooled fecal PCR and individual fecal PCR using Bayesian latent class models, and to investigate factors associated with positive MAP tests. Blood and fecal samples (n = 3,171) were collected from 159 Canadian cow-calf herds. All samples were analyzed using serum ELISA and fecal PCR (pools of five samples) and a subset of 913 fecal samples were also tested with individual PCR. Based on latent class analysis, MAP prevalence was higher in eastern compared to western Canada for both animals {East, 3% [95% Credible Interval (CrI) 1–7%]; West, 1% [95% CrI 0.2–2%]} and herds [East, 15% (95% CrI 2–35%); West, 10% (95% CrI 1–26%), based on one or more positive results]. Sensitivity (Se) and specificity (Sp) for animal level individual PCR were 96% (95% CrI 80–100%) and 98% (95% CrI 96–100%), respectively followed by pooled PCR [Se = 54% (95% CrI 36–72%), Sp > 99.9% (95% CrI 99.8–100%)] and ELISA [Se = 36% (95% CrI 22–52%), Sp = 98% (95% CrI 96–99%)]. Based on 20 samples per herd, the herd level Se of ELISA was 79% (95% CrI 47–100%) (at least one positive sample) compared to 43% (95% CrI 14–94%) for pooled PCR. Herd-level Sp was 99% (95% CrI 96–100%) for pooled PCR and 90% (95% CrI 83–100%) for ELISA. Cows from herds with dairy cattle on farm and cows with symptoms of JD in the past 3 years were more likely to be MAP positive. Herds that had animals with JD symptoms in the previous 3 years and those with more breeding females were most likely to test positive for MAP. While serum ELISA can be effective for herd screening, PCR performed better for animal testing. Pooled PCR testing could be a less costly option; however, determining the most cost-effective approach will require further economic analysis.

Use of uncoated magnetic beads to capture Mycobacterium smegmatis and Mycobacterium avium paratuberculosis prior detection by mycobacteriophage D29 and real-time-PCR

Uncoated tosyl-activated magnetic beads were evaluated to capture Mycobacterium smegmatis and Mycobacterium avium subspecies paratuberculosis (MAP) from spiked feces, milk, and urine. Centrifugation and uncoated magnetic beads recovered more than 99% and 93%, respectively, of 1.68 × 10⁷ CFU/mL, 1.68 × 10⁶ CFU/mL and 1.68 × 10⁵ CFU/mL M. smegmatis cells resuspended in phosphate buffer saline. The use of magnetic beads was more efficient to concentrate cells from 1.68 × 10⁴ CFU/mL of M. smegmatis than centrifugation. Likewise, the F57-qPCR detection of MAP cells was different whether they were recovered by beads or centrifugation; cycle threshold (Ct) was lower (p < 0.05) for the detection of MAP cells recovered by beads than centrifugation, indicative of greater recovery. Magnetic separation of MAP cells from milk, urine, and feces specimens was demonstrated by detection of F57 and IS900 sequences. Beads captured no less than 10⁹ CFU/mL from feces and no less than 10⁴ CFU/mL from milk and urine suspensions. In another detection strategy, M. smegmatis coupled to magnetic beads were infected by mycobacteriophage D29. Plaque forming units were observed after 24 h of incubation from urine samples containing 2 × 10⁵ and 2 × 10³ CFU/mL M. smegmatis. The results of this study provide a promising tool for diagnosis of tuberculosis and Johne's disease.

A rapid phage assay for detection of viable Mycobacterium avium subsp. paratuberculosis in milk

Paratuberculosis is an incurable gastroenteritis among ruminants that is promoted by Mycobacterium avium subsp. paratuberculosis (MAP), an acid-fast mycobacterium. To accelerate the detection of viable pathogen, a conventional (peptide mediated magnetic separation: PMS) and novel (phage-bead qPCR: PBQ) phage based assay was optimized. A superior limit of detection (LOD) of 10 MAP per 10 mL milk was suggested for PBQ compared to 100 cells/10 mL for PMS-phage assay. Via PBQ, viable MAP was found in 48.78% out 41 unpasteurized sheep and goat milk samples. Sheep milk samples (n = 29) that were tested by PMS-phage assay contained no viable MAP. The absence of viable MAP in milk collected from 21 of the recent sheep animals was also confirmed by PBQ after a 2-week gap. Although, the two phage assays comparably detected no viable MAP in the milk samples, MAP DNA and antibodies against MAP were recognized in milk and sera of some of these animals within two instances of sampling representing that some sheep animals were MAP shedders. In conclusion, PBQ and PMS-phage could be promising methods for the assessment of MAP viability in milk samples. However, PBQ was privileged over the PMS-phage assay due to the lower LOD, rapidity, higher sensitivity, lack of need to M. smegmatis and consequent virucidal treatment that are essential in PMS-phage assay for making lawn and inactivation of exogenous mycobacteriophages respectively.

MicroRNA profiling in bovine serum according to the stage of Mycobacterium avium subsp. paratuberculosis infection

Mycobacterium avium subsp. paratuberculosis (MAP) is the causative agent of Johne's disease (JD), and it causes diarrhea and weakness in cattle. During a long subclinical stage, infected animals without clinical signs shed pathogens through feces. For this reason, the diagnosis of JD during the subclinical stage is very important. Circulating miRNAs are attracting attention as useful biomarkers in various veterinary diseases because of their expression changes depending on the state of the disease. Based on current knowledge, circulating miRNAs extracted from bovine serum were used to develop a diagnostic tool for JD. In this study, the animals were divided into 4 groups according to fecal shedding, the presence of antibodies, and clinical signs. Gene expression was analyzed by performing miRNA sequencing for each group, and it was identified that the miRNA expression changed more as the MAP infection progressed. The eight miRNAs that were differentially expressed in all infected groups were selected as biomarker candidates based on their significant differences compared to the control group. These biomarker candidates were validated by qRT-PCR. Considering the sequencing data, two upregulated miRNAs and two downregulated miRNAs showed the same trend in the validation results. Network analysis was also conducted and the results showed that mRNAs (IL-10, TGF-β1) associated with regulatory T cells were predicted to be activated in the subclinical stage. Taken together, our data suggest that two miRNAs (bta-miR-374b, bta-miR-2887) may play major roles in the immune response to MAP infection during the subclinical stage.

Comparison of Mycobacterium avium subsp. paratuberculosis infection in cattle, sheep and goats in the Khuzestan Province of Iran: Results of a preliminary survey

Background

Paratuberculosis or Johne's disease, the chronic infectious granulomatous enteritis of ruminants, is a worldwide infection, which is caused by Mycobacterium avium subsp. paratuberculosis (MAP). The most common symptoms of this disease in cattle are loss of milk production, weight loss and diarrhoea, whereas in sheep and goats, the symptoms are emaciation, anorexia and severe disability.

Objectives

The aim of this study was to compare the seroprevalence of MAP in cattle, sheep and goats in the southwest of Iran.

Methods

Blood samples were randomly collected from 530 cattle, 568 sheep and 368 goats in southwest of Iran. Sera were tested by a commercial ELISA kit (ID vet; ID Screen® Paratuberculosis Indirect) for detection of antibodies of MAP.

Results

Overall apparent and true seroprevalence rate of MAP was 6.00% (95% CI: 4.90%–7.30%) and 13.25% (95% CI: 11.55%– 14.95%). Apparent and true seroprevalence of MAP, respectively, was 4.34% (95% CI: 3.88%–6.46%) and 9.19% (95% CI: 6.98%–11.98%) in cattle, 6.87% (95% CI: 5.05%–9.27%) and 15.37% (95% CI: 12.60%–16.60%) in sheep and 7.07% (95% CI: 4.82%–10.18%) and 15.86% (95% CI: 12.41%–20.01%) in goats, respectively. As a result, there was no significant relationship between animal species and MAP infection. Moreover, multivariate logistic regression showed that the infection rate is not associated with age, gender and geographical location in cattle, sheep and goats (P > 0.05).

Conclusion

This study confirms that the seroprevalence of MAP is relatively considerable in the cattle, sheep and goats in the southwest of Iran, although in cattle, it is less than goats and sheep. Therefore, preventive and control measures should be considered by animal health authorities and meat and dairy processing units.

New and rapid strategies for the diagnosis of bovine paratuberculosis "in situ" using latex particles

The chemical coupling of a protoplasmatic antigen from Mycobacterium avium subsp. paratubeculosis onto core-shell carboxylated particles was investigated with the aim of producing latex-protein complexes to be used in immunoagglutination assays capable of detecting bovine paratuberculosis disease. For this purpose, sensitizations were carried out using both colored and not colored carboxylated latexes as well as the protoplasmatic antigen at pH close to its isoelectric point to favor the antigenic protein to approach the particle surface. In all cases, higher fractions of proteins were chemically-bound to carboxyl groups on the surface of the particles. The assessment of the performance of the visual immunoagglutination assays consisted of evaluating 111 sera from healthy and infected bovines with Mycobacterium avium subsp. paratuberculosis. Complexes obtained from the colored latex allowed an acceptable visual discrimination between the studied positive and negative sera. Most of the positive samples showed strong to very strong agglutination and only a few samples reacted weakly, i.e. a sensitivity of 70%. The specificity of the assay, on the other hand, was 86%. Therefore, this rapid detection technique allows an easy and inexpensive identification of animals possibly infected with paratuberculosis "in situ" in the herds.

Preparation of immunomagnetic beads coupled with a rhodamine hydrazine immunosensor for the detection of Mycobacterium avium subspecies paratuberculosis in bovine feces, milk, and colostrum

The aim of this study was to develop and evaluate a method for detecting Mycobacterium avium ssp. paratuberculosis (MAP) bacteria in bovine fecal, milk, and colostrum samples using immunomagnetic beads (IMB) and a rhodamine hydrazone immunosensor. Immunomagnetic beads were prepared by using purified antibodies from hyperimmunized sera that were coupled to Fe nanoparticles with diethylene triamine pentaacetic acid (DTPA) or ethyl (dimethyl aminopropyl) carbodiimide (EDC)-N-hydroxy succinimide (NHS) as linkers. Rhodamine hydrazone particles were synthesized and coupled to IgY anti-MAP antibodies using DTPA or EDC-NHS linkers. Separation efficiency of the IMB was tested on bovine fecal, milk, and colostrum samples experimentally contaminated with MAP. The studied methods were evaluated on their ability to detect MAP and separate bacteria in complex mediums. The ELISA results indicated 95% efficacy in antibody coupling to IMB, with the DTPA-IMB method being more efficient than the EDC-NHS-IMB method. By using the DTPA-IMB method, MAP bacteria were successfully recovered from fecal, milk, and colostrum samples. The DTPA-IMB method used in combination with the rhodamine hydrazone immunosensor had a limit of detection equal to 30 and 30,000 MAP cells/mL using chromogenic and fluorescent properties, respectively. Combining the DTPA-IMB separation method with the rhodamine hydrazone immunosensor provides a fast, sensitive, and cost-beneficial method for detecting MAP in bovine feces, milk, and colostrum.

Genome-wide association analysis identified both RNA-seq and DNA variants associated to paratuberculosis in Canadian Holstein cattle 'in vitro' experimentally infected macrophages

Background

Mycobacterium avium ssp. paratuberculosis (MAP) is the causative agent of paratuberculosis, or Johne’s disease (JD), an incurable bovine disease. The evidence for susceptibility to MAP disease points to multiple interacting factors, including the genetic predisposition to a dysregulation of the immune system. The endemic situation in cattle populations can be in part explained by a genetic susceptibility to MAP infection. In order to identify the best genetic improvement strategy that will lead to a significant reduction of JD in the population, we need to understand the link between genetic variability and the biological systems that MAP targets in its assault to dominate macrophages. MAP survives in macrophages where it disseminates. We used next-generation RNA (RNA-Seq) sequencing to study of the transcriptome in response to MAP infection of the macrophages from cows that have been naturally infected and identified as positive for JD (JD (+); n = 22) or negative for JD (healthy/resistant, JD (−); n = 28). In addition to identifying genetic variants from RNA-seq data, SNP variants were also identified using the Bovine SNP50 DNA chip.

Results

The complementary strategy allowed the identification of 1,356,248 genetic variants, including 814,168 RNA-seq and 591,220 DNA chip variants. Annotation using SnpEff predicted that the 2435 RNA-seq genetic variants would produce high functional effect on known genes in comparison to the 33 DNA chip variants. Significant variants from JD(+/−) macrophages were identified by genome-wide association study and revealed two quantitative traits loci: BTA4 and 11 at (P < 5 × 10^− 7). Using BovineMine, gene expression levels together with significant genomic variants revealed pathways that potentially influence JD susceptibility, notably the energy-dependent regulation of mTOR by LKB1-AMPK and the metabolism of lipids.

Conclusion

In the present study, we succeeded in identifying genetic variants in regulatory pathways of the macrophages that may affect the susceptibility of cows that are healthy/resistant to MAP infection. RNA-seq provides an unprecedented opportunity to investigate gene expression and to link the genetic variations to biological pathways that MAP normally manipulate during the process of killing macrophages. A strategy incorporating functional markers into genetic selection may have a considerable impact in improving resistance to an incurable disease. Integrating the findings of this research into the conventional genetic selection program may allow faster and more lasting improvement in resistance to bovine paratuberculosis in dairy cattle.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07487-4.

Serological and Molecular Characterization of Mycobacterium avium Subsp. paratuberculosis (MAP) from Sheep, Goats, Cattle and Camels in the Eastern Province, Saudi Arabia

Simple Summary

Mycobacterium avium subsp. paratuberculosis (MAP) is the causative agent of Johne’s disease, affecting small and large ruminants and causing chronic diarrhea and severe emaciation. MAP is prevalent in many countries, including Saudi Arabia. Serological and molecular characterization of MAP and determination of the prevalent strains are essential for the control strategies. The results obtained from 31 herds showed that the sheep type (S-type) was the most prevalent MAP type and the molecular characterization revealed different strain profiles distributed among the sheep, goat, cattle, and camel herds in Eastern Province, Saudi Arabia.

Abstract

The objectives of the present study were to characterize Mycobacterium avium subsp. paratuberculosis (MAP) infection using serological and molecular tools and investigate the distribution and molecular characterization of MAP strains (cattle (C) and sheep (S) types) in sheep, goat, cattle, and camel herds in Eastern Province, Saudi Arabia. Serum and fecal samples were collected from all animals aged >2 years old in 31 herds (sheep = 8, goats = 6, cattle = 8 and camels = 9) from January to December 2019. Serum samples were tested by ELISA for the detection of MAP antibodies. Fecal samples were tested by PCR for the detection of MAP IS900 gene and the identification of MAP strains. MAP antibodies were detected in 19 (61.3%) herds. At the animal level, antibodies against MAP were detected in 43 (19.5%) sheep, 21 (17.1%) goats, 13 (19.7%) cattle and 22 (9.1%) camels. The IS900 gene of MAP was detected in 23 (74.2%) herds and was directly amplified from fecal samples of 59 (26.8%) sheep, 34 (27.6%) goats, 20 (30.3%) cattle and 36 (15.0%) camels. The S-type was the most prevalent MAP type identified in 15 herds, and all were identified as type-I, while the C-type was identified in only 8 herds. The IS900 sequences revealed genetic differences among the MAP isolates recovered from sheep, goats, cattle and camels. Results from the present study show that MAP was prevalent and confirm the distribution of different MAP strains in sheep, goat, cattle and camel herds in Eastern Province, Saudi Arabia.

Estimation of the sensitivity and specificity of four serum ELISA and one fecal PCR for diagnosis of paratuberculosis in adult dairy cattle in New Zealand using Bayesian latent class analysis

In New Zealand, a new diagnostic approach for the control of paratuberculosis in mixed aged milking cows has been developed using a combination of ELISA and quantitative fecal PCR (f-qPCR). Our analysis was designed to evaluate performance of these individual tests in infected or infectious mixed aged cows across the prevalence of infection typically encountered on NZ dairy farms and calculate test accuracy when used as a screening test of serological ELISAs for four separate antigens read in parallel followed by a confirmatory quantitative f-qPCR test. Data from a cross-sectional study of 20 moderate prevalence herds was combined with existing data from 2 low and 20 high prevalence herds forming a dataset of 3845 paired serum and fecal samples. Incidence of clinical Johne's disease (JD) was used to classify herds into three prevalence categories. High (≥ 3% annual clinical JD for the last three years), moderate (<3 - 1%) and low (<1% incidence for at least the last five years). Positive tests were declared if> 50 ELISA units and f-qPCR at two cut-points (≥1 × 10⁴ genomes/mL or >1 × 10³ genomes/mL). Fixed Bayesian latent class models at both f-qPCR cut-points, accounted for conditional independence and paired conditional dependence. Mixed models at both f-qPCR cut-points, using a different mechanism to account for conditional dependencies between tests were also implemented. Models (24 in number) were constructed using OpenBUGS. The aim was to identify Mycobacterium avium subsp. paratuberculosis (MAP) infected cows that met at least one of two criteria: shedding sufficient MAP in feces to be detected by f-qPCR or mounting a detectable MAP antibody response. The best fit to the data was obtained by modelling pairwise dependencies between tests in a fixed model or by accounting for dependencies in a mixed model at a fecal cut-off of ≥1 × 10⁴ genomes/mL. Test performance differed with prevalence, but models were robust to prior assumptions. For the fixed model, at a prevalence of 0.29 (95 % probability interval (PI) = 0.25-0.33), as a screening plus confirmatory f-qPCR, post-test probability for disease in a positive animal was 0.84 (95 %PI = 0.80-0.88) and 0.16 (95 %PI = 0.15-0.18) for disease in a test negative animal. In low prevalence herds (0.01(95 %PI = 0.00-0.04)) the equivalent figures were 0.84 (95 %PI = 0.08-0.92) and 0.00 (95 %PI = 0.00-0.02). These results suggest this is a useful tool to control JD on dairy farms, particularly in herds with higher levels of infection, where the sampling and testing cost per animal is defrayed across more detected animals.

Detection of latent forms of Mycobacterium avium subsp. paratuberculosis infection using host biomarker-based ELISAs greatly improves paratuberculosis diagnostic sensitivity

Bovine paratuberculosis (PTB) is a chronic granulomatous enteritis, caused by Mycobacterium avium subsp. paratuberculosis (MAP), responsible for important economic losses in the dairy industry. Current diagnostic methods have low sensitivities for detection of latent forms of MAP infection, defined by focal granulomatous lesions and scarce humoral response or MAP presence. In contrast, patent infections correspond to multifocal and diffuse types of enteritis where there is increased antibody production, and substantial mycobacterial load. Our previous RNA-Seq analysis allowed the selection of five candidate biomarkers overexpressed in peripheral blood of MAP infected Holstein cows with focal (ABCA13 and MMP8) and diffuse (FAM84A, SPARC and DES) lesions vs. control animals with no detectable PTB-associated lesions in intestine and regional lymph nodes. The aim of the current study was to assess the PTB diagnostic potential of commercial ELISAs designed for the specific detection of these biomarkers. The ability of these ELISAs to identify animals with latent and/or patent forms of MAP infection was investigated using serum from naturally infected cattle (n = 88) and non-infected control animals (n = 67). ROC analysis revealed that the ABCA13-based ELISA showed the highest diagnostic accuracy for the detection of infected animals with focal lesions (AUC 0.837, sensitivity 79.25% and specificity 88.06%) and with any type of histological lesion (AUC 0.793, sensitivity 69.41% and specificity 86.57%) improving on the diagnostic performance of the popular IDEXX ELISA and other conventional diagnostic methods. SPARC and MMP8 showed the highest diagnostic accuracy for the detection of animals with multifocal (AUC 0.852) and diffuse lesions (AUC 0.831), respectively. In conclusion, our results suggest that quantification of ABCA13, SPARC and MMP8 by ELISA has the potential for implementation as a diagnostic tool to reliably identify MAP infection, greatly improving early detection of MAP latent infections when antibody responses and fecal shedding are undetectable using conventional diagnostic methods.

Identification of Mycobacterium avium subsp. paratuberculosis (MAP) in Sheep Milk, a Zoonotic Problem

Johne’s disease (JD) is a life-threatening gastrointestinal disease affecting ruminants, which causes crucial economical losses globally. This ailment is caused by Mycobacterium avium subsp. paratuberculosis (MAP), a fastidious intracellular pathogen that belongs to the Mycobacteriaceae family. This acid-fast, hard-to-detect bacterium can resist milk pasteurization and be conveyed to dairy product consumers. Many studies have emphasized the zoonotic nature of MAP, suggesting an association between MAP and some gastroenteric conditions such as Crohn’s disease in humans. This underlines the importance of utilizing efficient pasteurization alongside a state-of-the-art diagnostic system in order to minimize the possible ways this pathogen can be conveyed to humans. Until now, no confirmatory MAP screening technique has been developed that can reveal the stages of JD in infected animals. This is partially due to the lack of an efficient gold-standard reference method that can properly evaluate the performance of diagnostic assays. Therefore, the following research aimed to compare the merits of qPCR and ELISA assessments of milk for the detection of MAP in a total of 201 Sardinian unpasteurized sheep milk samples including 73 bulk tank milk (BTM) and 128 individual samples from a MAP-infected flock (MIF) applying various reference models. Accordingly, milk qPCR and ELISA assessments, together and individually, were used as reference models in the herd-level study, while serum ELISA and fecal PCR were similarly (together and in isolation) considered as the gold standards in the individual-level diagnosis. This study showed that the type of gold-standard test affects the sensitivity and specificity of milk qPCR and ELISA significantly. At the individual level in the MAP-infected flock, serum ELISA in isolation and together with fecal PCR were recognized as the best references; however, the best correlation was seen between milk and serum ELISA (p < 0.0001). Regarding the detection of MAP in BTM, qPCR IS900 was recognized as the most sensitive and specific diagnostic test (p < 0.0001) for monitoring the MAP shedders and animals with clinically developed symptoms within herds, under the condition that both milk qPCR and milk ELISA tests formed a binary reference model. The BTM analyses (qPCR and ELISA) revealed that MAP positivity has a seasonal pattern. This hypothesis was proven through a longitudinal study on 14 sheep herds.

Longitudinal Study of Mycobacterium avium Subsp. paratuberculosis Antibody Kinetics in Dairy Cattle Using Sera and Milk Throughout the Lactation Period

Mycobacterium avium subsp. paratuberculosis (MAP) is the causative agent of Johne's disease in dairy cattle populations around the world. The objective of this study was to evaluate MAP antibody kinetics in serum and milk samples throughout the lactation period in dairy cattle. The samples were collected simultaneously from eight MAP-positive and two healthy MAP-negative (control group) cows. The MAP antibody was detected by using serum and milk ELISA. The serum and milk MAP antibody titers fluctuated between the positive and negative cut-off values in this study. Specifically, cattle with low MAP antibody titer (<100) showed fluctuation between the cut-off values. Variable changes of MAP antibody titer were also observed after parturition. Between the serum and milk MAP antibody titers, there was a positive correlation (R² = 0.5358) observed throughout the assessment period. The milk MAP ELISA test had low diagnostic performance in cows with low MAP titer due to its weak correlation (R² = 0.0198). Finally, this study suggest that the periodic MAP ELISA test is recommended for the application of Johne's eradication program due to the fluctuating nature of MAP antibody kinetics.

Bayesian latent class estimation of sensitivity and specificity parameters of the PMS-PCR test for the diagnosis of cattle sub-clinically infected with Mycobacterium avium subsp. paratuberculosis

The objective of this study was to estimate the performance of the peptide magnetic separation PCR test (PMS-PCR) for the diagnosis of Mycobacterium avium subsp. paratuberculosis (MAP) in sub-clinically infected dairy cattle. Twenty-one herds were randomly selected from a source population of 131 commercial dairy herds with a known history of MAP infection, located in the De Los Rios and De Los Lagos regions, in southern Chile. In the selected herds, all milking cows with ≥2 parities and without any clinical signs were sampled, collecting feces and blood-serum samples. The PMS-PCR test was used to analyze the fecal samples, while serum samples were analyzed using a commercial ELISA kit. A Bayesian latent class model was used to estimate the sensitivity (Se) and specificity (Sp) of the diagnostic tests. A total of 1381 animals were sampled in the 21 selected dairy herds, with an average sample size of 65 animals per herd (range 10-721). The PMS-PCR test had a greater Se than the ELISA test, with a median of 85.5 % (posterior probability interval (PPI) 95 %: 79.3-91.0%), while the ELISA test presented a median of 21.7 % (95 % PPI: 18.3-25.4%). On the other hand, the ELISA test had a better Sp than the PMS-PCR test, with a median of 97.7 % (95 % PPI: 96.6-98.5%), whereas PMS-PCR presented a median of 90.8 % (95 % PPI: 88.3-93.9%). Model results showed that PMS-PCR has a better Se than all available tests for MAP diagnosis in subclinical animals. However, this test should be used with care in herds with high infection rates, where a high MAP environmental load is expected, potentially increasing the frequency of false positive cases due to the pass-through phenomenon.

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.

A pilot study using environmental screening to determine the prevalence of Mycobacterium avium subspecies paratuberculosis (MAP) and antimicrobial resistance (AMR) in Irish cattle herds

BACKGROUND

Dairy and beef cattle can be reservoirs of many pathogens, including Salmonella and Mycobacterium avium subsp. paratuberculosis (MAP), the causative agent of Johne's disease (JD). Farm environments may provide potential entry points for the transmission of infectious agents into the food chain. Antibiotics are used to treat a wide variety of infections on farms, and administration of antimicrobial agents to cattle is considered to be a driving factor for antimicrobial resistance (AMR). Control of JD and AMR are priority for animal health initiatives in Ireland. A national JD pilot programme was introduced by Animal Health Ireland in 2014, while the national action plan launched by Department of Health and Department of Agriculture, Food and Marine introduced in 2017 aims to improve the surveillance of AMR. The current investigation was undertaken as a pilot study to determine the proportion of herds positive for MAP, Salmonella species (Salmonella spp), commensal Escherichia coli (E. coli), Extended-spectrum beta-lactamase (ESBL) AmpC β-lactamase and carbapenemase-producing E. coli from 157 environmental faecal samples in Irish farms.

RESULTS

MAP was detected in 10.2% of samples collected; on culture in 4 (4.9%) of the dairy herds and from 1 (1.3%) of the beef/suckler herds, and by PCR in 10 (12.3%) and 6 (7.9%) of these herds respectively. All culture positive herds were also positive by PCR. An additional 11 herds were positive by PCR only. Salmonella was not detected, while commensal E. coli were isolated from 70.7% of the samples (111/157) with 101 of these isolates shown to be fully susceptible to all antimicrobials tested. Of the 27 presumptive ESBL AmpC β-lactamase producing E. coli detected, one isolate was resistant to ten antimicrobials, nine isolates were resistant to nine antimicrobials, and four isolates were resistant to eight antimicrobials. Carbapenemase-producing E. coli were not isolated.

CONCLUSIONS

The results highlight the importance of monitoring farm environments for Johne's disease. This disease is a growing concern for dairy and beef producers in Ireland, and sampling the farm environment may offer a useful means to rapidly screen for the presence of MAP. Non-pathogenic common enteric commensal and multiple-drug-resistant E. coli may contribute to AMR acting as a reservoir and transferring resistance to other species/pathogens in the environment.

Mastitis risk effect on the economic consequences of paratuberculosis control in dairy cattle: A stochastic modeling study

The benefits and efficacy of control programs for herds infected with Mycobacterium avium subsp. paratuberculosis (MAP) have been investigated under various contexts. However, most previous research investigated paratuberculosis control programs in isolation, without modeling the potential association with other dairy diseases. This paper evaluated the benefits of MAP control programs when the herd is also affected by mastitis, a common disease causing the largest losses in dairy production. The effect of typically suggested MAP controls were estimated under the assumption that MAP infection increased the rate of clinical mastitis. We evaluated one hundred twenty three control strategies comprising various combinations of testing, culling, and hygiene, and found that the association of paratuberculosis with mastitis alters the ranking of specific MAP control programs, but only slightly alters the cost-benefit difference of particular MAP control components, as measured by the distribution of net present value of a representative U.S. dairy operation. In particular, although testing and culling for MAP resulted in a reduction in MAP incidence, that control led to lower net present value (NPV) per cow. When testing was used, ELISA was more economically beneficial than alternative testing regimes, especially if mastitis was explicitly modeled as more likely in MAP-infected animals, but ELISA testing was only significantly associated with higher NPV if mastitis was not included in the model at all. Additional hygiene was associated with a lower NPV per cow, although it lowered MAP prevalence. Overall, the addition of an increased risk of mastitis in MAP-infected animals did not change model recommendations as much as failing to consider.

Development and validation of a loop-mediated isothermal amplification assay-a rapid and sensitive detection tool for Mycobacterium avium subsp. paratuberculosis in small ruminants

AIMS

The aim of this study was to design an assay for the identification of Mycobacterium avium subsp. paratuberculosis (MAP) to be used in faeces and milk samples of small ruminants with a loop-mediated isothermal amplification (LAMP) system, as a time-saving and user-friendly method in contrast to real-time PCR.

METHODS AND RESULTS

For the detection of MAP in milk and faeces of small ruminants, we developed a set of primers, specific for the target gene ISMap02. The analytical sensitivity of LAMP, when targeting ISMap02, showed a DNA detection limit of 10 fg μl^-1 . After performing spiking experiments with two MAP reference strains, DSM 44133 and ATCC 19698^T , the limit of detection, using the LAMP protocol described herein were 3·8 MAP CFU per ml milk and 12·5 MAP CFU per gram faeces. All LAMP results during the establishment of the assay were compared to those of the real-time PCR results. An internal amplification control was incorporated into the assay to exclude false-negative results produced and had no significant negative impact on the analytical sensitivity. Validation of the assay was confirmed by testing field samples of faeces and revising the results with real-time PCR.

CONCLUSION

Our study conducted the first MAP detection system with a LAMP targeting ISMap02. Due to the positive results we encourage the use of LAMP in combination with ISMap02, when detecting MAP in faeces samples, as an alternative to targeting other genes as f57 or IS900. Further research on MAP detection in different matrices like raw milk, tissue or sperm with this system is recommended.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides new achievements in MAP diagnostic. Especially small ruminants do not show signs of diarrhoea until the terminal stage of the illness. The greatest task in fighting MAP is to rule out animals, which shed MAP with faeces and milk before showing symptoms of Johne's disease. Worldwide there is a need to eradicate animals, which are low MAP shedders to stop the illness spreading in animal holdings. MAP detection with LAMP is time saving, easy to use, does not need expensive equipment, as, for example, PCR kits and can be used without access to laboratories. The target gene ISMap02 was shown to be a specific insertion element for MAP and is a reliable aim in future MAP detection studies.

Core profile of volatile organic compounds related to growth of Mycobacterium avium subspecies paratuberculosis - A comparative extract of three independent studies

Analysis of volatile organic compounds (VOC) derived from bacterial metabolism during cultivation is considered an innovative approach to accelerate in vitro detection of slowly growing bacteria. This applies also to Mycobacterium avium subsp. paratuberculosis (MAP), the causative agent of paratuberculosis, a debilitating chronic enteritis of ruminants. Diagnostic application demands robust VOC profiles that are reproducible under variable culture conditions. In this study, the VOC patterns of pure bacterial cultures, derived from three independent in vitro studies performed previously, were comparatively analyzed. Different statistical analyses were linked to extract the VOC core profile of MAP and to prove its robustness, which is a prerequisite for further development towards diagnostic application. Despite methodical variability of bacterial cultivation and sample pre-extraction, a common profile of 28 VOCs indicating cultural growth of MAP was defined. The substances cover six chemical classes. Four of the substances decreased above MAP and 24 increased. Random forest classification was applied to rank the compounds relative to their importance and for classification of MAP versus control samples. Already the top-ranked compound alone achieved high discrimination (AUC 0.85), which was further increased utilizing all compounds of the VOC core profile of MAP (AUC 0.91). The discriminatory power of this tool for the characterization of natural diagnostic samples, in particular its diagnostic specificity for MAP, has to be confirmed in future studies.

Control of Mycobacterium avium subsp. paratuberculosis infection on a New Zealand pastoral dairy farm

Background

Johne’s disease is a major production limiting disease of dairy cows caused by infection with Mycobacterium avium subsp. paratuberculosis in calf-hood. The disease is chronic, progressive, contagious and widespread with no treatment and no cure. Economic losses arise from decreased productivity through reduced growth, milk yield, fertility and also capital losses due to premature culling or death. Control chiefly centers upon removing those animals which actively shed bacteria and protecting calves from infection. A prolonged pre-clinical shedding phase, lack of test sensitivity, organism persistence and abundance in the environment as well as management systems that expose susceptible calves to infection make control challenging, particularly in pastoral, seasonal dairy systems. Combining a novel testing strategy to remove infected cows along with limited measures to protect vulnerable calves at pasture, this study reports the successful reduction over a four-year period of seroprevalence of cows testing positive for MAP infection in a New Zealand pastoral dairy herd.

Results

For all age groups considered the apparent seroprevalence of cows testing positive decreased from 297 / 1,122 (26%) in 2013–2014, to 24 / 1,030 (2.3%) in 2016–2017. Over the same period, the apparent seroprevalence in primiparous cows decreased from 39 / 260 (15%) to 7 / 275 (2.5%) and in multiparous cows from 258 / 862 (29.9%) to 17 / 755 (2.3%). The reported proportion of calved cows culled annually from suspected clinical Johne’s disease fell from 55 / 1,201 (5%) in the year preceding the control program to 5 / 1,283 (0.4%) in the final year of the study.

Conclusions

On this farm, reduction in the prevalence of infection was achieved by reducing the infectious pressure through targeted culling of heavily shedding animals together with limited measures to protect calves at pasture from exposure to Mycobacterium avium subsp. paratuberculosis. Whilst greater protection of young animals through separation from infected cows and their colostrum and milk would have reduced the risk of neonatal infection, this study demonstrates, in this case, that these management measures while prudent were not essential for effective reduction in the prevalence of MAP infection.

Mycobacterium tuberculosis extracellular vesicle-associated lipoprotein LpqH as a potential biomarker to distinguish paratuberculosis infection or vaccination from tuberculosis infection

BACKGROUND

Both bovine tuberculosis (TB) and paratuberculosis (PTB) are serious and widespread bacterial infections affecting many domestic and wild animal species. However, current vaccines do not confer complete protection and cause interference with other diagnostics tests, including bovine TB. Therefore, the development of "Differentiating Infected from Vaccinated Animals" (DIVA) tests are a pressing need. In this study, we have tested the feasibility of mycobacterial extracellular vesicles (EVs) as potential source of biomarkers to discriminate between Mycobacterium bovis infected, Mycobacterium avium subsp. paratuberculosis (MAP) infected and MAP-vaccinated cows. We have, initially, characterized vesicle production in the two most medically relevant species of mycobacteria for livestock, MAP and M. bovis, for being responsible for tuberculosis (TB) and paratuberculosis (PTB).

RESULTS

Our results indicate that these two species produce EVs with different kinetics, morphology and size distribution. Analysis of the immunogenicity of both type of EVs showed some cross reactivity with sera from PTB+ and TB+ cows, suggesting a limited diagnostic capacity for both EVs. Conversely, we noticed that Mycobacterium tuberculosis (Mtb) EVs showed some differential reactivity between sera from MAP-vaccinated or PTB+ cows from TB+ ones. Mass spectrometry analysis (MS) identified a 19-kDa EV-associated lipoprotein as the main source of the differential reactivity.

CONCLUSIONS

LpqH could be a good plasma biomarker with capacity to distinguish PTB+ or MAP-vaccinated cows from cows infected with TB.

Candidate genes associated with the heritable humoral response to Mycobacterium avium ssp. paratuberculosis in dairy cows have factors in common with gastrointestinal diseases in humans

Infection of cattle with bovine paratuberculosis (i.e., Johne's disease) is caused by Mycobacterium avium ssp. paratuberculosis (MAP) and results in a chronic incurable gastroenteritis. This disease, which has economic ramifications for the cattle industry, is increasing in detected prevalence globally; subclinically infected animals can silently shed the bacterium into the environment for years, exposing contemporaries and hampering disease-control programs. The objective of the present study was to first quantify the genetic parameters for humoral response to MAP in dairy cattle. This was followed by a genome-based association analysis and subsequent downstream bioinformatic analyses from imputed whole genome sequence SNP data. After edits, ELISA test records were available on 136,767 cows; analyses were also undertaken on a subset of 33,818 of these animals from herds with at least 5 MAP ELISA-positive cows, with at least 1 of those positive cows being homebred. Variance components were estimated using univariate animal and sire linear mixed models. The heritability calculated from the animal model for humoral response to MAP using alternative phenotype definitions varied from 0.02 (standard error = 0.003) to 0.05 (standard error = 0.008). The genome-based associations were undertaken within a mixed model framework using weighted deregressed estimated breeding values as a dependent variable on 1,883 phenotyped animals that were ≥87.5% Holstein-Friesian. Putative susceptibility quantitative trait loci (QTL) were identified on Bos taurus autosome 1, 3, 5, 6, 8, 9, 10, 11, 13, 14, 18, 21, 23, 25, 26, 27, and 29; mapping the most significant SNP to genes within and overlapping these QTL revealed that the most significant associations were with the 10 functional candidate genes KALRN, ZBTB20, LPP, SLA2, FI3A1, LRCH3, DNAJC6, ZDHHC14, SNX1, and HAS2. Pathway analysis failed to reveal significantly enriched biological pathways, when both bovine-specific pathway data and human ortholog data were taken into account. The existence of genetic variation for MAP susceptibility in a large data set of dairy cows signifies the potential of breeding programs for reducing MAP susceptibility. Furthermore, the identification of susceptible QTL facilitates greater biological understanding of bovine paratuberculosis and potential therapeutic targets for future investigation. The novel molecular similarities identified between bovine paratuberculosis and human inflammatory bowel disease suggest potential for human therapeutic interventions to be translated to veterinary medicine and vice versa.

Analysis of long non-coding RNA and mRNA expression in bovine macrophages brings up novel aspects of Mycobacterium avium subspecies paratuberculosis infections

Paratuberculosis is a major disease in cattle that severely affects animal welfare and causes huge economic losses worldwide. Development of alternative diagnostic methods is of urgent need to control the disease. Recent studies suggest that long non-coding RNAs (lncRNAs) play a crucial role in regulating immune function and may confer valuable information about the disease. However, their role has not yet been investigated in cattle with respect to infection towards Paratuberculosis. Therefore, we investigated the alteration in genomic expression profiles of mRNA and lncRNA in bovine macrophages in response to Paratuberculosis infection using RNA-Seq. We identified 397 potentially novel lncRNA candidates in macrophages of which 38 were differentially regulated by the infection. A total of 820 coding genes were also significantly altered by the infection. Co-expression analysis of lncRNAs and their neighbouring coding genes suggest regulatory functions of lncRNAs in pathways related to immune response. For example, this included protein coding genes such as TNIP3, TNFAIP3 and NF-κB2 that play a role in NF-κB2 signalling, a pathway associated with immune response. This study advances our understanding of lncRNA roles during Paratuberculosis infection.

Enhanced sensitivity and fast turnaround time in laboratory diagnosis for bovine paratuberculosis in faecal samples

Bovine paratuberculosis (Johne's disease in cattle) is caused by the pathogen Mycobacterium avium subsp. paratuberculosis (MAP) and is a widespread chronic bacterial infectious disease in cattle. Due to the peculiarities of the pathogen, detection of MAP in faeces remains difficult. DNA extraction and real-time PCR for detection of MAP in bovine faeces (direct PCR) have been refined and feasible procedures for rapid, sensitive and automatable detection of the pathogen agent have been developed. Accordingly, in a first step we tested 20 faecal samples using two MAP complete kits (DNA extraction kits based on magnetic beads combined with real-time PCR assays) and six other DNA extraction kits for faeces. MAP-specific DNA was detected by real-time PCR assays. Cultivation of MAP on the solid medium HEYM and in the liquid medium M7H9C served as reference standards. The two complete kits detected significantly more MAP-DNA positive samples than the other procedures applied (p < 0.04). Ct values of 37 and 38 served as cut-off for the respective real-time PCR assays calculated on the basis of standard curves and droplet digital PCR (ddPCR). In a second step, the two MAP complete kits were employed for a comprehensive study including 107 positive and 50 negative faecal samples which had been previously tested on HEYM cultivation. The MAP complete kits yielded sensitivity values of 86% and 89% and specificity values of 100% compared to cultivation of MAP in the liquid medium M7H9C. In detail, cultivation of MAP in M7H9C detected the pathogen in 97% and 100% of the samples tested after an incubation period of six and twelve weeks, respectively. However, the cultivation of MAP on HEYM succeeded in only 74% after twelve weeks of incubation. In all these solid culture positive samples, MAP was also detected using the two complete kits. Additionally, the impact of repeated freezing and thawing of samples on re-cultivation of MAP was tested using 20 faecal samples and resulted in a reduction to 75% and 25% of bacterial growth when using liquid medium M7H9C and solid medium HEYM, respectively. The results of this study show that complete kits with refined automatable protocols for DNA extraction in combination with real-time PCR assays for detection of MAP can compete with sensitive cultivation of the pathogen in liquid medium.

An agent-based model evaluation of economic control strategies for paratuberculosis in a dairy herd

This paper uses an agent-based simulation model to estimate the costs associated with Mycobacterium avium ssp. paratuberculosis (MAP), or Johne's disease, in a milking herd, and to determine the net benefits of implementing various control strategies. The net present value (NPV) of a 1,000-cow milking herd is calculated over 20 yr, parametrized to a representative US commercial herd. The revenues of the herd are generated from sales of milk and culled animals. The costs include all variable and fixed costs necessary to operate a representative 1,000-cow milking herd. We estimate the NPV of the herd with no MAP infection, under an expected endemic infection distribution with no controls, and under an expected endemic infection distribution with various controls. The initial number of cows in a herd with an endemic MAP infection is distributed as 75% susceptible, 13% latent, 9% low MAP shedding, and 3% high MAP shedding. Control strategies include testing using ELISA and fecal culture tests and culling of cows that test positive, and culling based on observable milk production decrease. Results show that culling cows based on test results does not increase the herd's NPV and in most cases decreases NPV due to test costs as well as false positives and negatives with their associated costs (e.g., culling healthy cows and keeping infected cows). Culling consistently low producing cows when MAP is believed to be present in the herd produces higher NPV over the strategy of testing and culling MAP infected animals, and over the case of no MAP control.

The effect of sub-clinical infection with Mycobacterium avium subsp. paratuberculosis on milk production in a New Zealand dairy herd

Background

Johne’s disease is a major production limiting disease of dairy cows. The disease is chronic, progressive, contagious and widespread; there is no treatment and there is no cure. Economic losses arise from decreased productivity through reduced growth, milk yield and fertility and capital losses due to premature culling or death. This study attempts to address the effect of subclinical JD on milk production under New Zealand pastoral dairy farming conditions using a new testing approach. Blood samples were taken from all lactating animals from a single seasonally calving New Zealand dairy herd in the autumn of 2013 and 2014. Samples were subject to serological assay for antibodies to Mycobacterium avium subsp. paratuberculosis using a combination of four ELISA tests in parallel followed by selective quantitative fecal PCR to confirm the fecal shedding characteristics of ELISA positive cows. ELISA status was classified as Not-Detected, Low, Moderate or High and fecal PCR status as Not-Detected, Moderate or High.

Results

A mixed generalized regression model indicated that, compared to cows where MAP was not detected, daily milk solids production was 4% less for high ELISA positive cows (p = 0.004), 6% less for moderate fPCR cows (p = 0.036) and 12% less for high fPCR cows (p < 0.001).

Conclusions

This study confirms that sub-clinical JD can have a significant impact on milk production and that the testing methodology used stratified the animals in this herd on their likely impact on production and disease spread. This allowed the farmer to prioritize removal of heavily shedding, less-productive animals and so reduce the risk of infection of young stock. This is the first longitudinal study based in New Zealand looking at the effect of Johne’s infection status on daily milk production allowing for intermediary and confounding factors.

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

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

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.

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.

PCR Inhibition of a Quantitative PCR for Detection of Mycobacterium avium Subspecies Paratuberculosis DNA in Feces: Diagnostic Implications and Potential Solutions

Molecular tests such as polymerase chain reaction (PCR) are increasingly being applied for the diagnosis of Johne's disease, a chronic intestinal infection of ruminants caused by Mycobacterium avium subspecies paratuberculosis (MAP). Feces, as the primary test sample, presents challenges in terms of effective DNA isolation, with potential for PCR inhibition and ultimately for reduced analytical and diagnostic sensitivity. However, limited evidence is available regarding the magnitude and diagnostic implications of PCR inhibition for the detection of MAP in feces. This study aimed to investigate the presence and diagnostic implications of PCR inhibition in a quantitative PCR assay for MAP (High-throughput Johne's test) to investigate the characteristics of samples prone to inhibition and to identify measures that can be taken to overcome this. In a study of fecal samples derived from a high prevalence, endemically infected cattle herd, 19.94% of fecal DNA extracts showed some evidence of inhibition. Relief of inhibition by a five-fold dilution of the DNA extract led to an average increase in quantification of DNA by 3.3-fold that consequently increased test sensitivity of the qPCR from 55 to 80% compared to fecal culture. DNA extracts with higher DNA and protein content had 19.33 and 10.94 times higher odds of showing inhibition, respectively. The results suggest that the current test protocol is sensitive for herd level diagnosis of Johne's disease but that test sensitivity and individual level diagnosis could be enhanced by relief of PCR inhibition, achieved by five-fold dilution of the DNA extract. Furthermore, qualitative and quantitative parameters derived from absorbance measures of DNA extracts could be useful for prediction of inhibitory fecal samples.

Economic consequences of paratuberculosis control in dairy cattle: A stochastic modeling study

The cost of paratuberculosis to dairy herds, through decreased milk production, early culling, and poor reproductive performance, has been well-studied. The benefit of control programs, however, has been debated. A recent stochastic compartmental model for paratuberculosis transmission in US dairy herds was modified to predict herd net present value (NPV) over 25 years in herds of 100 and 1000 dairy cattle with endemic paratuberculosis at initial prevalence of 10% and 20%. Control programs were designed by combining 5 tests (none, fecal culture, ELISA, PCR, or calf testing), 3 test-related culling strategies (all test-positive, high-positive, or repeated positive), 2 test frequencies (annual and biannual), 3 hygiene levels (standard, moderate, or improved), and 2 cessation decisions (testing ceased after 5 negative whole-herd tests or testing continued). Stochastic dominance was determined for each herd scenario; no control program was fully dominant for maximizing herd NPV in any scenario. Use of the ELISA test was generally preferred in all scenarios, but no paratuberculosis control was highly preferred for the small herd with 10% initial prevalence and was frequently preferred in other herd scenarios. Based on their effect on paratuberculosis alone, hygiene improvements were not found to be as cost-effective as test-and-cull strategies in most circumstances. Global sensitivity analysis found that economic parameters, such as the price of milk, had more influence on NPV than control program-related parameters. We conclude that paratuberculosis control can be cost effective, and multiple control programs can be applied for equivalent economic results.

Comparison of commercial DNA extraction kits and quantitative PCR systems for better sensitivity in detecting the causative agent of paratuberculosis in dairy cow fecal samples

Mycobacterium avium ssp. paratuberculosis (MAP) causes ruminant paratuberculosis (Johne's disease) worldwide. Oral-fecal contamination is the most important mode of transmission of paratuberculosis, so eradicating MAP-shedding animals could prevent disease propagation. Fecal culture, a well-known method for MAP diagnosis, requires costly specialized media and a long incubation time that sometimes ends in disappointing bacterial contamination. To facilitate the efforts of control programs, we evaluated the performance of direct fecal quantitative PCR (qPCR) assays for their sensitivity and robustness for MAP detection. Commercial kits use different strategies for extracting DNA, combined with qPCR systems, to detect the presence of MAP in fecal samples. In this study, we compared the sensitivity of 3 commercially available DNA extraction kits (A, B, and C) combined with 2 qPCR systems (T and V) for the detection of MAP in infectious cows. A total of 49 dairy cows from 5 herds were sampled twice a year for 3 yr and diagnosed using fecal culture and ELISA. Eight replicates of their fecal samples from the first sampling were tested using each DNA extraction method and qPCR detection system. Although all 3 of the commercial DNA extraction kits have been previously described as very efficient for the diagnosis of paratuberculosis, kit B provided the highest sensitivity. Indeed, 89% of the cows declared positive for paratuberculosis by both fecal culture and ELISA were identified with kit B, whereas only 23 and 43% of the cows were identified with kits A and C, respectively. Interestingly, kit B was able to detect some low-MAP shedders. The qPCR detection system also played a critical role: system T yielded qPCR with the highest sensitivity. The results of this study suggest that DNA extraction kit B combined with detection system T provides the best amplification of MAP DNA from fecal samples with the highest sensitivity and specificity. Although 1 DNA extraction and qPCR analysis should be adequate to confirm that an animal with diarrhea or other signs of paratuberculosis is positive, detecting low shedders at the highest sensitivity should include repetitive testing. This study demonstrates the importance of repetitions using the most appropriate method for extracting DNA from fecal samples, combined with a compatible qPCR system for identifying MAP-shedding animals.

Assessment of the relative sensitivity of milk ELISA for detection of Mycobacterium avium ssp. paratuberculosis infectious dairy cows

Milk ELISA are commonly used for detection of Mycobacterium avium ssp. paratuberculosis (MAP) antibodies in dairy cows, due to low cost and quick processing for large numbers of samples. However, low sensitivity and variations from host and environmental factors can impede detection of MAP antibodies at early disease stages. The objectives of our study were to assess the sensitivity of milk ELISA in comparison with fecal tests and to evaluate how detectable antibody concentrations in milk vary with changes in fecal shedding of MAP, cow age, cow parity, days in milk, and time of year. To compare the sensitivity of a commercial milk ELISA with solid and broth fecal culture and with fecal real-time PCR, a longitudinal study was performed for the identification of MAP-infectious animals as determined by prior fecal testing for MAP shedding. In addition, associations between variation in milk MAP ELISA score and changes in fecal MAP shedding, host age, days in milk, and season were evaluated. Monthly milk and fecal samples were collected over 1 yr from 46 cows that were previously shedding MAP in their feces. Sensitivity of milk ELISA was 29.9% (95% CI: 24.8 to 35.1%), compared with 46.7% (40.7 to 52.7%) for fecal solid culture, 55.0% (49.3 to 60.7%) for fecal broth culture, and 78.4% (73.3 to 83.1%) for fecal direct real-time PCR. The effect of stage of lactation could not be separated from the effect of season, with increased milk ELISA scores at greater days in milk in winter. However, unpredictable monthly variations in results were observed among the 3 assays for individual cow testing, which highlights the importance of identifying patterns in pathogen and antibody detection over time in MAP-positive herds.

Responses of Bovine Innate Immunity to Mycobacterium avium subsp. paratuberculosis Infection Revealed by Changes in Gene Expression and Levels of MicroRNA

Paratuberculosis in cattle is a chronic granulomatous gastroenteritis caused by Mycobacterium avium subsp. paratubercolosis (MAP) which is endemic worldwide. In dairy herds, it is responsible for huge economic losses. However, current diagnostic methods do not detect subclinical infection making control of the disease difficult. The identification of MAP infected animals during the sub-clinical phase of infection would play a key role in preventing the dissemination of the pathogen and in reducing transmission. Gene expression and circulating microRNA (miRNA) signatures have been proposed as biomarkers of disease both in the human and veterinary medicine. In this paper, gene expression and related miRNA levels were investigated in cows positive for MAP, by ELISA and culture, in order to identify potential biomarkers to improve diagnosis of MAP infection. Three groups, each of 5 animals, were used to compare the results of gene expression from positive, exposed and negative cows. Overall 258 differentially expressed genes were identified between unexposed, exposed, but ELISA negative and positive groups which were involved in biological functions related to inflammatory response, lipid metabolism and small molecule biochemistry. Differentially expressed miRNA was also found among the three groups: 7 miRNAs were at a lower level and 2 at a higher level in positive animals vs unexposed animals, while 5 and 3 miRNAs were respectively reduced and increased in the exposed group compared to the unexposed group. Among the differentially expressed miRNAs 6 have been previously described as immune-response related and two were novel miRNAs. Analysis of the miRNA levels showed correlation with expression of their target genes, known to be involved in the immune process. This study suggests that miRNA expression is affected by MAP infection and play a key role in tuning the host response to infection. The miRNA and gene expression profiles may be biomarkers of infection and potential diagnostic of MAP infection earlier than the current ELISA based diagnostic tests.

Invited review: The economic impact and control of paratuberculosis in cattle

Paratuberculosis (also called Johne's disease) is a chronic disease caused by Mycobacterium avium ssp. paratuberculosis (MAP) that affects ruminants and other animals. The epidemiology of paratuberculosis is complex and the clinical manifestations and economic impact of the disease in cattle can be variable depending on factors such as herd management, age, infection dose, and disease prevalence, among others. Additionally, considerable challenges are faced in the control of paratuberculosis in cattle, such as the lack of accurate and reliable diagnostic tests. Nevertheless, efforts are directed toward the control of this disease because it can cause substantial economic losses to the cattle industry mainly due to increased premature culling, replacement costs, decreased milk yield, reduced feed conversion efficiency, fertility problems, reduced slaughter values, and increased susceptibility to other diseases or conditions. The variability and uncertainty surrounding the estimations of paratuberculosis prevalence and impact influence the design, implementation, and efficiency of control programs in diverse areas of the world. This review covers important aspects of the economic impact and control of paratuberculosis, including challenges related to disease detection, estimations of the prevalence and economic effects of the disease, and the implementation of control programs. The control of paratuberculosis can improve animal health and welfare, increase productivity, reduce potential market problems, and increase overall business profitability. The benefits that can derive from the control of paratuberculosis need to be communicated to all industry stakeholders to promote the implementation of control programs. Moreover, if the suspected link between Johne's disease in ruminants and Crohn's disease in humans was established, significant economic losses could be expected, particularly for the dairy industry, making the control of this disease a priority across dairy industries internationally.

Exposure to viral and bacterial pathogens among Soay sheep (Ovis aries) of the St Kilda archipelago

We assessed evidence of exposure to viruses and bacteria in an unmanaged and long-isolated population of Soay sheep (Ovis aries) inhabiting Hirta, in the St Kilda archipelago, 65 km west of Benbecula in the Outer Hebrides of Scotland. The sheep harbour many metazoan and protozoan parasites but their exposure to viral and bacterial pathogens is unknown. We tested for herpes viral DNA in leucocytes and found that 21 of 42 tested sheep were infected with ovine herpesvirus 2 (OHV-2). We also tested 750 plasma samples collected between 1997 and 2010 for evidence of exposure to seven other viral and bacterial agents common in domestic Scottish sheep. We found evidence of exposure to Leptospira spp., with overall seroprevalence of 6·5%. However, serological evidence indicated that the population had not been exposed to border disease, parainfluenza, maedi-visna, or orf viruses, nor to Chlamydia abortus. Some sheep tested positive for antibodies against Mycobacterium avium subsp. paratuberculosis (MAP) but, in the absence of retrospective faecal samples, the presence of this infection could not be confirmed. The roles of importation, the pathogen-host interaction, nematode co-infection and local transmission warrant future investigation, to elucidate the transmission ecology and fitness effects of the few viral and bacterial pathogens on Hirta.

Comparison of fecal pooling methods and DNA extraction kits for the detection of Mycobacterium avium subspecies paratuberculosis

The aim of the study was to develop a sensitive method using quantitative real‐time polymerase chain reaction (qPCR) with pooled fecal samples for the screening of Johne's disease (JD). Manufacturer‐specified and our new pooling method in combination with five commercial kits for DNA extraction and purification were compared. Different volumes of pooled fecal suspensions were tested, and the results were compared for individual samples and three pool sizes (5, 10, and 50 samples); each of the fecal suspensions, which were prepared from healthy dairy and beef cattle was spiked with 0, 10, 100, or 1000 cultured Mycobacterium avium subspecies paratuberculosis (MAP) organisms or was mixed with fecal suspensions from experimentally infected cattle. The MAP DNA detection proportion with our pooling method in combination with Johne‐Spin kit (Fasmac, Japan) was 100% for all models and all pool sizes, except for the low shedder model with a pool size of 50. There was no loss of sensitivity in pools of 10 subjects or less by using the new method. These results suggest that new method is a sensitive, practical, and cost‐effective screening test for the detection of MAP‐infected cattle and the monitoring of JD‐free herds.

Potential application of emerging diagnostic techniques to the diagnosis of bovine Johne's disease (paratuberculosis)

Mycobacterium avium subspecies paratuberculosis (MAP) causes Johne's disease (paratuberculosis), a chronic wasting disease in cattle with important welfare, economic and potential public health implications. Current tests are unable to recognise all stages of the disease, which makes it difficult to diagnose and control. This review explores emerging diagnostic techniques that could complement and enhance the diagnosis of MAP infection, including bacteriophage analysis, new MAP-specific antigens, host protein expression in response to infection, transcriptomic studies, analysis of microRNAs and investigation of the gastrointestinal microbiome. It emphasises the inherent challenges of diagnosing bovine Johne's disease and investigates novel areas which may have the potential both to advance our understanding of the immunopathology of MAP infection and to augment current diagnostic tests.

The Identification of Circulating MiRNA in Bovine Serum and Their Potential as Novel Biomarkers of Early Mycobacterium avium subsp paratuberculosis Infection

Mycobacterium avium subspecies paratuberculosis (MAP) is the aetiological agent of Johne's disease (JD), a chronic enteritis in ruminants that causes substantial economic loses to agriculture worldwide. Current diagnostic assays are hampered by low sensitivity and specificity that seriously complicate disease control; a new generation of diagnostic and prognostic assays are therefore urgently needed. Circulating microRNAs (miRNAs) have been shown to have significant potential as novel biomarkers for a range of human diseases, but their potential application in the veterinary sphere has been less well characterised. The aim of this study was therefore to apply RNA-sequencing approaches to serum from an experimental JD infection model as a route to identify novel diagnostic and prognostic miRNA biomarkers. Sera from experimental MAP-challenged calves (n = 6) and age-matched controls (n = 6) were used. We identified a subset of known miRNAs from bovine serum across all samples, with approximately 90 being at potentially functional abundance levels. The majority of known bovine miRNAs displayed multiple isomiRs that differed from the canonical sequences. Thirty novel miRNAs were identified after filtering and were found within sera from all animals tested. No significant differential miRNA expression was detected when comparing sera from MAP-challenged animals to their age-matched controls at six-month's post-infection. However, comparing sera from pre-infection bleeds to six-month's post-infection across all 12 animals did identify increased miR-205 (2-fold) and decreased miR-432 (2-fold) within both challenged and control groups, which suggests changes in circulating miRNA profiles due to ageing or development (P<0.00001). In conclusion our study has identified a range of novel miRNA in bovine serum, and shown the utility of small RNA sequencing approaches to explore the potential of miRNA as novel biomarkers for infectious disease in cattle.

Resolution of Crohn's disease and complex regional pain syndrome following treatment of paratuberculosis

A cohort of family members with various chronic diseases including Crohn's disease, asthma, complex regional pain syndrome, hypothyroidism, type 1 diabetes mellitus, and lymphangiomatosis and/or evidence of infection by Mycobacterium avium subsp. paratuberculosis (MAP) are described in this series of case reports. MAP was cultured from the blood of three members affected by the first five diseases and there was accompanying elevated anti-MAP IgG in two members. The patient affected by the sixth disease has a markedly elevated anti-MAP titer. The two patients affected by the first four diseases have been treated with a combination of anti-MAP antibiotics and ultraviolet blood irradiation therapy with resolution of the disease symptomatology and inability to culture MAP in post treatment blood samples. These case reports of patients with MAP infections provide supportive evidence of a pathogenic role of MAP in humans.

A longitudinal study of factors influencing the result of a Mycobacterium avium ssp. paratuberculosis antibody ELISA in milk of dairy cows

The influence of milk yield and milk composition on the diagnosis of Mycobacterium avium ssp. paratuberculosis (MAP) by milk ELISA in the context of the total IgG secretion patterns in milk throughout lactation and serum concentrations were investigated. A 2-yr trial was performed in which 1,410 dairy cows were sampled monthly and MAP milk ELISA status and milk yield and composition were determined. Data were analyzed by mixed model analysis. Milk yield was found to significantly influence ELISA results expressed as sample-to-positive (S/P) ratios. For each 5-kg increase in milk, the S/P ratio has to be multiplied by 0.89; therefore, high milk yield can change the MAP milk ELISA outcome of a cow in early infection from positive to negative. Parity influenced ELISA outcome significantly, indicating that cows with a parity >1 are more likely to be identified by milk testing. Also, herd was an important predictor, showing that herd prevalence influences the milk ELISA strongly. Other factors influencing the S/P ratios were protein concentration, somatic cell count, and days in milk. The IgG concentration and mass excreted per day were determined longitudinally in a subset of 41 cows of which samples and data of a complete lactation were available. Again, the IgG concentration in milk was mainly influenced by milk yield. The total IgG mass secreted per day in milk was found to be relatively constant, with a mean of 8.70 ± 5.38 g despite an increasing IgG concentration in serum at the same time. The variation of IgG concentration in milk can be mainly attributed to dilution through changes in milk yield. This supports the assumption that concentrations of MAP-specific antibodies are influenced by changes in milk yield similarly. In conclusion, we confirmed that antibody concentrations, and therefore MAP ELISA outcome, were influenced by milk yield, herd, and parity. To enhance performance, milk ELISA tests should either be performed in early or late lactation, when milk yield is low. From a management perspective, sampling should be done during early lactation before cows are bred again. Based on the slow progressive infection dynamics, only first-parity cows should be preferentially tested at the end of their first lactation to avoid false-negative results.

Association between caudal fold tuberculin test responses and results of an ELISA for Mycobacterium avium subsp paratuberculosis and mycobacterial culture of feces in tuberculosis-free dairy herds

OBJECTIVE--To evaluate associations between Mycobacterium avium subsp paratuberculosis (MAP) and caudal fold tuberculin (CFT) test results in cattle. DESIGN--Longitudinal and cross-sectional evaluations. ANIMALS--1 California (approx 3,600 cows) and 3 Colorado (approx 640, 1,190, and 1,480 cows) dairy herds considered free of Mycobacterium bovis infection. PROCEDURES--In the California herd, the association between CFT response and MAP status was determined with ELISA and mycobacterial culture of feces within 1 year before and after CFT testing. The association between CFT and MAP status in all herds was modeled with mixed-effects logistic regression. RESULTS--In the California herd, significantly higher odds of being classified as suspect by CFT were found for cows with results of MAP ELISA negative before and positive after CFT testing (OR, 5.6) and cows positive before and after CFT testing (OR, 8.1). Higher odds were found for cows positive for mycobacterial culture of feces before and negative for culture after CFT testing (OR, 4.6) and cows negative for mycobacterial culture of feces before and positive for culture after CFT testing (OR, 13.2). All herds had higher odds of being classified as suspect by CFT testing for cows with positive results for ELISA (OR, 2.9) or mycobacterial culture of feces (OR, 5.0), compared with cows with negative results of the same tests. CONCLUSIONS AND CLINICAL RELEVANCE--A strong association was found between positive MAP test results and being classified as a suspect by CFT testing. Within-herd MAP prevalence may affect specificity of CFT testing for tuberculosis in cattle.