Comparative sensitivity of various faecal culture methods and ELISA in dairy cattle herds with endemic Johne's disease

Gold nanoparticle based immunochromatographic biosensor for rapid diagnosis of Mycobacterium avium subspecies paratuberculosis infection using recombinant protein

Highly infectious and obvious withstand ability of Mycobacterium avium subspecies paratuberculosis (MAP) to environment as well as lack of on-site field diagnostic methods notably hampers the paratuberculosis (PTB) control. The existing intricacy, time-consuming and complicated diagnostic methods of PTB accentuate the development of novel and easy-to-perform on-site test. A gold nanoparticle (GNP) based lateral-flow assay (LFA) using MAP recombinant protein (44 kDa) has been developed for sensitive and specific detection of PTB in field conditions. The diagnostic sensitivity and specificity of the LFA for MAP specific antibodies was found approximately 84.2% and 83.3% in comparison to indirect enzyme-linked immunosorbent assay. Consequently, the newly developed GNP based LFA offers on-site and cost-effective method for the prompt diagnosis of PTB and precludes the time-consuming laboratory screening.

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.

Isolation of Mycobacterium avium Subsp. Paratuberculosis in the Feces and Tissue of Small Ruminants Using a Non-Automated Liquid Culture Method

Paratuberculosis is a chronic disease of ruminants caused by Mycobacterium avium subsp. Paratuberculosis (MAP). Since isolation of MAP type I (S) is rarely reported in Italy, our research was aimed at isolating, by an inexpensive liquid culture manual method, this type of MAP isolates. At first, we used an ELISA to point out to serologically positive samples from five flocks. Secondly, we used a fecal direct IS900-qPCR on the ELISA positive samples, in order to detect shedder animals. Feces from IS900-qPCR positive samples were inoculated in solid and liquid culture media. IS900-qPCR was further used to test the growth of MAP isolates in liquid medium, which were further confirmed by f57-qPCR and submitted to typing by specific PCR in order to identify the MAP type. Twenty-eight samples (24 fecal and four tissutal samples) were processed by culture methods, resulting in the isolation of six type I MAP field isolates. Notably, no isolates were recovered by solid media, underlining the utility of this liquid method. Few data about this type of MAP are currently available in Italy, and further analyses should be carried out in order to study the origin and epidemiology of type I strains circulating in Italy.

Optimisation of decontamination method and influence of culture media on the recovery of Mycobacterium avium subspecies paratuberculosis from spiked water sediments

The recovery of Mycobacterium avium subspecies paratuberculosis (Map) from the environment can be a laborious process - owing to Map being fastidious, its low number, and also high numbers of other microbial populations in such settings. Protocols i.e. filtration, decontamination and modified elution were devised to recover Map from spiked water sediments. Three culture media: Herrold's Egg Yolk Media (HEYM), Middlebrook 7H10 (M-7H10) and Bactec 12B were then employed to grow the organism following its elution. In the sterile sediment samples the recovery of Map was significant between the time of exposure for each of HEYM and M-7H10, and insignificant between both media (P < 0.05). However, in the non-sterile sediment samples, the HEYM grew other background microflora including moulds at all the times of exposure whilst 4 h followed by M-7H10 culture yielded Map colonies without any background microflora. Using sterile samples only for the Bactec 12B, the recovery of Map decreased as time of exposure increased. Based on these findings, M-7H10 should be considered for the recovery of Map from the natural environment including water sediments where the recovery of diverse microbial species remains a challenge.

SIGNIFICANCE OF THE STUDY

Map is a robust pathogen that abides in the environment. In water treatment operations, Map associates with floccules and other particulate matter including sediments. It is also a fastidious organism, and its detection and recovery from the water environment is a laborious process and can be misleading within the abundance of other mycobacterial species owing to their close resemblance in phylogenetic traits. In the absence of a reliable recovery method, Map continues to pose public health risks through biofilm in household water tanks, hence the need for the development of a reliable recovery protocol to monitor the presence of Map in water systems in order to curtail its public health risks.

Risk factors associated with Mycobacterium avium subsp. paratuberculosis herd status in Québec dairy herds

Paratuberculosis is a chronic and contagious enteric disease of ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). Control of paratuberculosis is justified given the associated economic losses and the potential role of MAP in Crohn's disease in humans. Management practices that limit exposure of susceptible animals to MAP are more effective at reducing disease prevalence than testing and culling infected cows. The objective of this retrospective case-control study was to study the association between management practices and MAP status in dairy herds in Québec, Canada. A total of 26 case herds (MAP had been isolated from at least 1 environmental sample in each herd) and 91 control herds (no clinical cases of paratuberculosis and negative on 2 consecutive yearly environmental samplings) were selected among herds enrolled in the Québec Voluntary Paratuberculosis Control Program. A risk assessment questionnaire, completed at enrolment, was available for the selected herds. Culture of MAP was achieved using liquid media and the BACTEC 960 detection system. Multivariable logistic regression was used to evaluate the association between selected risk factors and MAP herd status. Herd size (OR = 1.17; 95% CI: 1.02-1.33) and proportion of cows purchased per year in the last 5 years (OR = 5.44; 95% CI: 1.23-23.98) were significantly associated with a positive MAP herd status. The management risk factors identified in the present study are in accord with previous studies. Management practices aiming to prevent the introduction of new animals into the herd and to reduce the contact of newborn calves with adult animals or their feces are key elements to minimize MAP introduction and transmission into a herd. These elements should be prioritized in control programs.

An intra-laboratory cultural and real-time PCR method comparison and evaluation for the detection of subclinical paratuberculosis in dairy herds

Mycobacterium avium subsp. paratuberculosis (MAP) is a vigorous microorganism which causes incurable chronic enteritis, Johne's disease (JD) in cattle. A target of control programmes for JD is to accurately detect MAP-infected cattle early to reduce disease transmission. The present study evaluated the efficacy of two different cultural procedures and a TaqMan real-time PCR assay for detection of subclinical paratuberculosis in dairy herds. Therefore, sixty-one faecal samples were collected from two Dutch dairy herds (n = 40 and n = 21, respectively) which were known to be MAP-ELISA positive. All individual samples were assessed using two different cultural protocols in two different laboratories. The first cultural protocol (first laboratory) included a decontamination step with 0.75% hexadecylpyridinium chloride (HPC) followed by inoculation on Herrold's egg yolk media (HEYM). The second protocol (second laboratory) comprised of a decontamination step using 4% NaOH and malachite green-oxalic acid followed by inoculation on two media, HEYM and in parallel on modified Löwenstein-Jensen media (mLJ). For the TaqMan real-time PCR assay, all faecal samples were tested in two different laboratories using TaqMan® MAP (Johne's) reagents (Life Technologies). The cultural procedures revealed positive reactions in 1.64% of the samples for cultivation protocol 1 and 6.56 and 8.20% of the samples for cultivation protocol 2, respectively. The results of the TaqMan real-time PCR performed in two different laboratories yielded 13.11 and 19.76% positive reaction. The kappa test showed proportional agreement 0.54 between the mLJ media (second laboratory) and TaqMan® real-time PCR method (second laboratory). In conclusion, the TaqMan real-time PCR could be a strongly useful and efficient assay for the detection of subclinical paratuberculosis in dairy cattle leading to an improvement in the efficiency of MAP control strategies.

Evaluation of a PCR assay on overgrown environmental samples cultured for Mycobacterium avium subsp. paratuberculosis

Culture of Mycobacterium avium subsp. paratuberculosis (MAP) is the definitive antemortem test method for paratuberculosis. Microbial overgrowth is a challenge for MAP culture, as it complicates, delays, and increases the cost of the process. Additionally, herd status determination is impeded when noninterpretable (NI) results are obtained. The performance of PCR is comparable to fecal culture, thus it may be a complementary detection tool to classify NI samples. Our study aimed to determine if MAP DNA can be identified by PCR performed on NI environmental samples and to evaluate the performance of PCR before and after the culture of these samples in liquid media. A total of 154 environmental samples (62 NI, 62 negative, and 30 positive) were analyzed by PCR before being incubated in an automated system. Growth was confirmed by acid-fast bacilli stain and then the same PCR method was again applied on incubated samples, regardless of culture and stain results. Change in MAP DNA after incubation was assessed by converting the PCR quantification cycle (Cq) values into fold change using the 2−ΔCq method (ΔCq = Cq after culture − Cq before culture). A total of 1.6% (standard error [SE] = 1.6) of the NI environmental samples had detectable MAP DNA. The PCR had a significantly better performance when applied after culture than before culture ( p = 0.004). After culture, a 66-fold change (SE = 17.1) in MAP DNA was observed on average. Performing a PCR on NI samples improves MAP culturing. The PCR method used in our study is a reliable and consistent method to classify NI environmental samples.

Trends and advances in the diagnosis and control of paratuberculosis in domestic livestock

Paratuberculosis (pTB) is a chronic granulomatous enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP) in a wide variety of domestic and wild animals. Control of pTB is difficult due to the lack of sensitive, efficacious and cost-effective diagnostics and marker vaccines. Microscopy, culture, and PCR have been used for the screening of MAP infection in animals for quite a long time. Besides, giving variable sensitivity and specificity, these tests have not been considered ideal for large-scale screening of domestic livestock. Serological tests like ELISA easily detects anti-MAP antibodies. However, it cannot differentiate between the vaccinated and infected animals. Nanotechnology-based diagnostic tests are underway to improve the sensitivity and specificity. Newer generation diagnostic tests based on recombinant MAP secretory proteins would open new paradigm for the differentiation between infected and vaccinated animals and for early detection of the infection. Due to higher seroreactivity of secretory proteins vis-à-vis cellular proteins, the secretory proteins may be used as marker vaccine, which may aid in the control of pTB infection in animals. Secretory proteins can be potentially used to develop future diagnostics, surveillance and monitoring of the disease progression in animals and the marker vaccine for the control and eradication of pTB.

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.

Evaluation of performance of bacterial culture of feces and serum ELISA across stages of Johne's disease in cattle using a Bayesian latent class model

The objective of this study was to evaluate the performance of bacterial culture of feces and serum ELISA to correctly identify cows with Mycobacterium avium ssp. paratuberculosis (MAP) at heavy, light, and non-fecal-shedding levels. A total of 29,785 parallel test results from bacterial culture of feces and serum ELISA were collected from 17 dairy herds in Minnesota, Pennsylvania, and Colorado. Samples were obtained from adult cows from dairy herds enrolled for up to 10 yr in the National Johne's Disease Demonstration Herd Project. A Bayesian latent class model was fitted to estimate the probabilities that bacterial culture of feces (using 72-h sedimentation or 30-min centrifugation methods) and serum ELISA results correctly identified cows as high positive, low positive, or negative given that cows were heavy, light, and non-shedders, respectively. The model assumed that no gold standard test was available and conditional independency existed between diagnostic tests. The estimated conditional probabilities that bacterial culture of feces correctly identified heavy shedders, light shedders, and non-shedders were 70.9, 32.0, and 98.5%, respectively. The same values for the serum ELISA were 60.6, 18.7, and 99.5%, respectively. Differences in diagnostic test performance were observed among states. These results improve the interpretation of results from bacterial culture of feces and serum ELISA for detection of MAP and MAP antibody (respectively), which can support on-farm infection control decisions and can be used to evaluate disease-testing strategies, taking into account the accuracy of these tests.

Efficient, validated method for detection of mycobacterial growth in liquid culture media by use of bead beating, magnetic-particle-based nucleic acid isolation, and quantitative PCR

Pathogenic mycobacteria are difficult to culture, requiring specialized media and a long incubation time, and have complex and exceedingly robust cell walls. Mycobacterium avium subsp. paratuberculosis (MAP), the causative agent of Johne's disease, a chronic wasting disease of ruminants, is a typical example. Culture of MAP from the feces and intestinal tissues is a commonly used test for confirmation of infection. Liquid medium offers greater sensitivity than solid medium for detection of MAP; however, support for the BD Bactec 460 system commonly used for this purpose has been discontinued. We previously developed a new liquid culture medium, M7H9C, to replace it, with confirmation of growth reliant on PCR. Here, we report an efficient DNA isolation and quantitative PCR methodology for the specific detection and confirmation of MAP growth in liquid culture media containing egg yolk. The analytical sensitivity was at least 10(4)-fold higher than a commonly used method involving ethanol precipitation of DNA and conventional PCR; this may be partly due to the addition of a bead-beating step to manually disrupt the cell wall of the mycobacteria. The limit of detection, determined using pure cultures of two different MAP strains, was 100 to 1,000 MAP organisms/ml. The diagnostic accuracy was confirmed using a panel of cattle fecal (n=54) and sheep fecal and tissue (n=90) culture samples. This technique is directly relevant for diagnostic laboratories that perform MAP cultures but may also be applicable to the detection of other species, including M. avium and M. tuberculosis.

Development and validation of a liquid medium (M7H9C) for routine culture of Mycobacterium avium subsp. paratuberculosis to replace modified Bactec 12B medium

Liquid culture of Mycobacterium avium subsp. paratuberculosis from clinical samples, such as feces, is the most sensitive antemortem test for the diagnosis of Johne's disease in ruminants. In Australia, New Zealand, the United States, and some other countries, the Bactec 460 system with modified Bactec 12B medium (Becton, Dickinson) has been the most commonly used liquid culture system, but it was discontinued in 2012. In this study, a new liquid culture medium, M7H9C, was developed. It consists of a Middlebrook 7H9 medium base with added Casitone, albumin, dextrose, catalase, egg yolk, mycobactin J, and a cocktail of antibiotics. We found that polyoxyethylene stearate (POES) was not essential for the cultivation of M. avium subsp. paratuberculosis in either the Bactec 12B or the M7H9C medium. The limit of detection determined using pure cultures of the C and S strains of M. avium subsp. paratuberculosis was 7 bacilli per 50 μl inoculum in the two media. The new medium was validated using 784 fecal and tissue samples from sheep and cattle, >25% of which contained viable M. avium subsp. paratuberculosis. Discrepant results for the clinical samples between the two media were mostly associated with samples that contained <10 viable bacilli per gram, but these results were relatively uncommon, and the performances of the two media were not significantly different. M7H9C medium was less than half the cost of the Bactec 12B medium and did not require regular examination during incubation, but a confirmatory IS900 PCR test had to be performed on every culture after the predetermined incubation period.

Contrasting results of culture-dependent and molecular analyses of Mycobacterium avium subsp. paratuberculosis from wood bison

Reduced to near extinction in the late 1800s, a number of wood bison populations (Bison bison athabascae) have been re-established through reintroduction initiatives. Although an invaluable tool for conservation, translocation of animals can spread infectious agents to new areas or expose animals to pathogens in their new environment. Mycobacterium avium subsp. paratuberculosis, a bacterium that causes chronic enteritis in ruminants, is among the pathogens of potential concern for wood bison management and conservation. In order to inform translocation decisions, our objectives were to determine the M. avium subsp. paratuberculosis infection status of wood bison herds in Canada and to culture and genetically characterize the infective strain(s). We tested fecal samples from bison (n = 267) in nine herds using direct PCR for three M. avium subsp. paratuberculosis-specific genetic targets with different copy numbers within the M. avium subsp. paratuberculosis genome. Restriction enzyme analysis (REA) and sequencing of IS1311 were performed on seven samples from five different herds. We also evaluated a panel of different culture conditions for their ability to support M. avium subsp. paratuberculosis growth from feces and tissues of direct-PCR-positive animals. Eighty-one fecal samples (30%) tested positive using direct IS900 PCR, with positive samples from all nine herds; of these, 75% and 21% were also positive using ISMAP02 and F57, respectively. None of the culture conditions supported the growth of M. avium subsp. paratuberculosis from PCR-positive samples. IS1311 REA and sequencing indicate that at least two different M. avium subsp. paratuberculosis strain types exist in Canadian wood bison. The presence of different M. avium subsp. paratuberculosis strains among wood bison herds should be considered in the planning of translocations.

Genomic variations associated with attenuation in Mycobacterium avium subsp. paratuberculosis vaccine strains

BACKGROUND

Mycobacterium avium subspecies paratuberculosis (MAP) whole cell vaccines have been widely used tools in the control of Johne's disease in animals despite being unable to provide complete protection. Current vaccine strains derive from stocks created many decades ago; however their genotypes, underlying mechanisms and relative degree of their attenuation are largely unknown.

RESULTS

Using mouse virulence studies we confirm that MAP vaccine strains 316 F, II and 2e have diverse but clearly attenuated survival and persistence characteristics compared with wild type strains. Using a pan genomic microarray we characterise the genomic variations in a panel of vaccine strains sourced from stocks spanning over 40 years of maintenance. We describe multiple genomic variations specific for individual vaccine stocks in both deletion (26-32 Kbp) and tandem duplicated (11-40 Kbp) large variable genomic islands and insertion sequence copy numbers. We show individual differences suitable for diagnostic differentiation between vaccine and wild type genotypes and provide evidence for functionality of some of the deleted MAP-specific genes and their possible relation to attenuation.

CONCLUSIONS

This study shows how culture environments have influenced MAP genome diversity resulting in large tandem genomic duplications, deletions and transposable element activity. In combination with classical selective systematic subculture this has led to fixation of specific MAP genomic alterations in some vaccine strain lineages which link the resulting attenuated phenotypes with deficiencies in high reactive oxygen species handling.

Heritability estimates for Mycobacterium avium subspecies paratuberculosis status of German Holstein cows tested by fecal culture

The objective of this study was to estimate genetic manifestation of Mycobacterium avium ssp. paratuberculosis (MAP) infection in German Holstein cows. Incorporated into this study were 11,285 German Holstein herd book cows classified as MAP-positive and MAP-negative animals using fecal culture results and originating from 15 farms in Thuringia, Germany involved in a paratuberculosis voluntary control program from 2008 to 2009. The frequency of MAP-positive animals per farm ranged from 2.7 to 67.6%. The fixed effects of farm and lactation number had a highly significant effect on MAP status. An increase in the frequency of positive animals from the first to the third lactation could be observed. Threshold animal and sire models with sire relationship were used as statistical models to estimate genetic parameters. Heritability estimates of fecal culture varied from 0.157 to 0.228. To analyze the effect of prevalence on genetic parameter estimates, the total data set was divided into 2 subsets of data into farms with prevalence rates below 10% and those above 10%. The data set with prevalence above 10% show higher heritability estimates in both models compared with the data set with prevalence below 10%. For all data sets, the sire model shows higher heritabilities than the equivalent animal model. This study demonstrates that genetic variation exists in dairy cattle for paratuberculosis infection susceptibility and furthermore, leads to the conclusion that MAP detection by fecal culture shows a higher genetic background than ELISA test results. In conclusion, fecal culture seems to be a better trait to control the disease, as well as an appropriate feature for further genomic analyses to detect MAP-associated chromosome regions.

Proteomic analysis of plasma from Holstein cows testing positive for Mycobacterium avium subsp. paratuberculosis (MAP)

Johne's disease (JD) is a widespread and economically important chronic inflammatory disease of the small intestine of ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). Although there are several techniques available for diagnosis of JD, their sensitivity is questionable. New proteome profiling methods, such as serum/plasma protein fingerprinting by 2-Dimensional Fluorescence Difference Gel Electrophoresis (2D-DIGE), may therefore be useful for identifying novel protein biomarkers of MAP infection. In this study, plasma samples were collected from 380 Holstein cows and screened for the presence of MAP infection using the M.pt. Johne's antibody Kit (IDEXX). Five negative (MAP-), and 5 strongly positive (MAP+) cows were selected for proteomic analysis. Highly abundant proteins were depleted from the plasma samples using the ProteoMiner technology (Bio-Rad) to enhance the resolution of low abundance proteins. Plasma samples from MAP-, MAP+, and a pooled internal control were labelled with different fluorescent dyes and separated based on their isoelectrical point (IP) and then their molecular weight. Gel images of the fluorescent plasma protein maps were acquired using a Typhoon scanner and analyzed using the DeCyder software. Proteins that were differentially expressed were excised from the gels, trypsin digested, and subjected to MS/MS analysis for identification. Six proteins were identified as being up-regulated at least 2-fold in MAP+ cows including: transferrin, gelsolin isoforms α & β (actin binding protein - ABP), complement subcomponent C1r, complement component C3, amine oxidase - copper containing 3 (AOC3), and coagulation factor II (thrombin) (p<0.05). Two proteins that were down-regulated approximately 2-fold in the MAP+ cows included coagulation factor XIII -B polypeptide (COAFXIII), and fibrinogen γ chain (FGG) and its precursor.

Crohn's disease and the mycobacterioses: a quarter century later. Causation or simple association?

It has been more than 25 years since Mycobacterium paratuberculosis was first proposed as an etiologic agent in Crohn's disease based on the isolation of this organism from several patients. Since that time, a great deal of information has been accumulated that clearly establishes an association between M. paratuberculosis and Crohn's disease. However, data are conflicting and difficult to interpret and the field has become divided into committed advocates and confirmed skeptics. This review is an attempt to provide a thorough and objective summary of current knowledge from both basic and clinical research from the views and interpretations of both the antagonists and proponents. The reader is left to draw his or her own conclusions related to the validity of the issues and claims made by the opposing views and data interpretations. Whether M. paratuberculosis is a causative agent in some cases or simply represents an incidental association remains a controversial topic, but current evidence suggests that the notion should not be so readily dismissed. Remaining questions that need to be addressed in defining the role of M. paratuberculosis in Crohn's disease and future implications are discussed.

Sample handling substantially affects Johne's ELISA

Detection methods for Mycobacterium avium subsp. paratuberculosis (MAP) are imperfect, yet crucial for diagnosis of Johne's disease. Our purpose was to test for significant and biologically relevant changes in Johne's ELISA results associated with how field-collected blood samples were transported to the laboratory, prepared and stored prior to testing, while removing potential confounding by test kit and laboratory variables. Blood samples were collected from 21 cows that previously had MAP ELISA scores ranging from negative to highly positive. Samples for immediate laboratory processing were subjected to different transportation temperatures (on ice, 26 degrees C) and preparation methods (serum separated, hemolyzed and serum separated, clotted whole blood), but were tested using the same ELISA kit in the same laboratory. Samples for laboratory processing after one week of storage were subjected to different storage temperatures (4 degrees C, -20 degrees C) and preparation methods (serum separated, hemolyzed and serum separated, clotted whole blood), and again were tested using the same ELISA kit in the same laboratory. Finally, samples were evaluated by time to processing (one day, one week) and storage temperature (4 degrees C, -20 degrees C). Data were checked for normality and analyzed with repeated measures ANOVAs. Significantly (P=0.027) higher MAP ELISA scores were recorded for whole blood and hemolyzed samples transported at 26 degrees C than serum separated samples. Sample storage for one week at -20 degrees C resulted in significantly (P<0.001) lower MAP ELISA scores, regardless of handling method, compared to samples stored at 4 degrees C for one week. Method of sample preparation, as well as transportation temperature and medium-term storage temperature, affects MAP ELISA results. Such discrepancies will inevitably result in improper classification of MAP-infected cattle, impeding both biosecurity measures on uninfected farms and MAP control programs.

Factors affecting isolation and identification of Mycobacterium avium subsp. paratuberculosis from fecal and tissue samples in a liquid culture system

Culture of Mycobacterium avium subsp. paratuberculosis is the definitive diagnostic test for Johne's disease, a chronic granulomatous enteropathy of animals. Compared to solid media, the identification of all strains of the organism in liquid media can be more difficult because the appearance of colonies and mycobactin dependence are not observable, and the growth of other organisms needs to be distinguished, commonly by PCR. Factors affecting the isolation rate of S strains and the contamination rate in modified Middlebrook 7H9 broth (Bactec 12B) and 7H10 agar were studied using 11,598 fecal samples and 2,577 tissue samples from sheep from 1,421 farms over 10 years. Minimization of contamination in Bactec cultures required the avoidance of the carryover of fecal particles from the first sedimentation step in the double-incubation centrifugation method, and contamination was reduced significantly by incubating the sample in a solution containing vancomycin, amphotericin B, and nalidixic acid for 3 days compared to 2 days. The growth of irrelevant microorganisms confounded the identification of M. avium subsp. paratuberculosis in liquid culture by inhibiting IS900 PCR and in solid medium culture by inhibiting the growth of M. avium subsp. paratuberculosis or obscuring colonies. The contamination of samples was clustered in certain laboratory submissions and was reduced by including ampicillin in Bactec medium without affecting the odds of isolation of M. avium subsp. paratuberculosis. The long-term contamination rate for fecal cultures was about 7%, and that for tissue cultures was <0.2%. Liquid medium was more sensitive than solid medium culture for M. avium subsp. paratuberculosis. The applicability of these findings for C strains is discussed.

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

Mycobacterium avium ssp. paratuberculosis (MAP) is the etiologic agent of Johne's disease in cattle. The disease causes diarrhea, reduced milk production, poor reproductivity, emaciation, and eventually death. Culture on Herrold's egg yolk agar is considered to be the definitive test for diagnosis of Johne's in cattle. This method has moderate sensitivity (30 to 50%) and is 100% specific; however, it can take up to 16 wk due to the slow growth of MAP. Currently, serum ELISA is used to screen herds for Johne's disease, but positive tests must be confirmed culturally or by PCR. The current research sought to evaluate an in-house direct fecal PCR procedure and directly compare it to ELISA using culture as the gold standard. Serum and fecal samples were collected from cows (n = 250) with unknown Johne's status. Fecal samples were processed for culture on Herrold's egg yolk agar and direct PCR. Serum samples were tested using the Parachek serum ELISA. Overall, 67/250 [26.8%, 95% confidence interval (CI) 21.4 to 32.8] animals were culturally confirmed to be shedding MAP. The PCR and ELISA detected 74/250 (29.6%, 95% CI 24 to 35.7) and 25/250 (10%, 95% CI 6.6 to 14.4), respectively. Culture and PCR were able to detect more positive animals than ELISA. Overall, direct fecal PCR was 70.2% sensitive and 85.3% specific when using culture as the gold standard. The ELISA method was 31.3% sensitive and 97.8% specific. When culture reported <10 cfu, the sensitivity and specificity of PCR and ELISA were 57.1 and 85.3%, and 4.8 and 97.8%, respectively. When culture reported 10 to <40 cfu, the sensitivity of PCR and ELISA were 75 and 50%, respectively. When culture reported > or =40 cfu, the sensitivity of PCR and ELISA were 100 and 88.2%, respectively. Specificity could not be calculated at these levels because there were no negative samples. The direct PCR outperformed the ELISA in detecting animals potentially infected with MAP and was not significantly different when compared with culture. The direct fecal PCR method described here provides faster results than traditional culture and is more sensitive than ELISA at detecting animals suspected of Johne's disease. These data support the use of PCR as an alternative method for screening herds for prevalence and diagnosis of Johne's disease.

Association among results of serum ELISA, faecal culture and nested PCR on milk, blood and faeces for the detection of paratuberculosis in dairy cows

Paratuberculosis is a chronic, infectious disease of ruminants that entails a serious concern for the cattle industry. One of the main issues relates to the efficiency of diagnosis of subclinically infected animals. The objective of this field study was to analyse the association among results of a serum enzyme-linked immunosorbent assays (ELISA), faecal culture and nested PCR tests on milk, blood and faeces for Mycobacterium avium subsp. paratuberculosis detection in dairy cows. Faeces, blood and milk samples were collected from 328 lactating dairy cows in four known infected herds. Results were analysed to determine associations and levels of agreement between pairs of tests. A total of 61 animals (18.6%) tested positive when all the tests were interpreted in parallel. The agreement between results in different pairs of tests was poor, slight and fair in two, five and three of the 10 possible combinations respectively. Faecal culture and faecal polymerase chain reaction (PCR) resulted in the highest kappa coefficient (0.39; fair agreement), with the lowest agreement being for ELISA and blood PCR (-0.036; poor agreement). Fisher's exact test resulted in statistically significant associations (P < or = 0.05) between the following test pairs: ELISA : faecal culture; ELISA : faecal PCR; milk PCR : faecal PCR, blood PCR : faecal PCR and faecal culture : faecal PCR. Enzyme-linked immunosorbent assays showed the highest complementary sensitivity values for all the possible two-test combinations, followed by faecal PCR. The combined use of ELISA and faecal PCR has the potential to increase the overall sensitivity for the diagnosis of paratuberculosis infection.

Evaluation of radiometric faecal culture and direct PCR on pooled faeces for detection of Mycobacterium avium subsp. paratuberculosis in cattle

Dilution rates for pooled faecal culture (PFC) and direct IS900 polymerase chain reaction (D-PCR) tests were evaluated on faecal samples from infected cows mixed with uninfected faeces in dilutions from 1 in 5 to 1 in 50. PFC was performed by radiometric culture, with confirmation by IS900 PCR and restriction endonuclease analysis (PCR/REA) on growth, and by mycobactin dependency testing on solid medium. Using 37 culture positive faecal samples from 12 subclinical cows, 83.8% and 94.6% of samples were confirmed positive in the PFC assay at dilutions of 1 in 50 and 1 in 30, respectively. Lower dilutions (1 in 5 to 1 in 20) provided only marginally better sensitivity, and confirmation of PFC growth by PCR/REA was significantly more sensitive than mycobactin dependency. D-PCR had significantly lower sensitivity than PFC confirmed by PCR/REA, with pools of 1 in 50, 30, 10 and 5 yielding positive results in 64.9%, 70.3%, 78.4% and 83.8% of samples, respectively. Cattle considered to be shedding 1.5 x 10(6) viable M. avium subsp. paratuberculosis (Map)/g faeces (on the basis of estimated losses in processing and growth rates in radiometric broth) were positive at dilutions up to 1 in 50 in the PFC and D-PCR. Those shedding 5 x 10(5) viable Map/g were positive in the PFC at dilutions up to 1 in 40, but required a 1 in 10 dilution or less for D-PCR. The results suggest that for cattle shedding relatively high concentrations of Map in faeces (>2 x 10(5) viable Map/g), maximal dilutions of 1 in 30 for PFC and 1 in 10 for D-PCR would be applicable.

Detection of Mycobacterium avium subsp. paratuberculosis in ovine faeces by direct quantitative PCR has similar or greater sensitivity compared to radiometric culture

The aims of this study were to develop a new real-time quantitative PCR (QPCR) assay based on IS900 for detection and quantification of Mycobacterium avium subsp. paratuberculosis (MAP) DNA in faeces, and to use this to detect infected sheep. Both the C and S strains of MAP were detected by the QPCR assay, and no cross reactions were detected with 51 other species of mycobacteria including 10 which contained IS900-like sequences. One copy of IS900 fragment cloned into plasmid pCR2.1 and 1 fg of MAP genomic DNA were consistently detected, while in spiked faecal samples the detection limit was 10 viable MAP per gram of ovine faeces. A total of 506 individual ovine faecal samples and 27 pooled ovine faecal samples with known culture results were tested. The QPCR assay detected 68 of 69 BACTEC culture positive individual faeces and there was a strong relation between time to detection in culture and DNA quantity measured by QPCR (r= -0.70). In pooled faecal samples, QPCR also agreed with culture (kappa=0.59). MAP DNA was detected from some culture negative faecal samples from sheep exposed to MAP, suggesting that the QPCR has very high analytical sensitivity for MAP in faecal samples and detects non-viable MAP in ovine faeces. None of the faecal samples from 176 sheep that were not exposed to MAP were positive in QPCR. This is the first report of a direct faecal QPCR assay that has similar sensitivity to a gold standard radiometric culture assay.

Sampling and repeatability of radiometric faecal culture in bovine Johne's disease

The repeatability of detection of Mycobacterium avium subsp. paratuberculosis (Map) within and between samplings from 16 paratuberculous dairy cows (13 subclinical; 3 clinical) was investigated by radiometric culture of quadrants of faecal dung pats collected on four to seven occasions over a 10-16-day period. Results were compared to serological status and to pathological and bacteriological findings in multiple tissues obtained at slaughter from 15 of the animals 2-6 weeks after the faecal samplings. From faecal samples taken on 77 occasions over the 2-week period, 296/308 (96%) quadrants were culture positive, with samples from all cattle showing evidence of faecal shedding of Map. Histological lesions typical of paratuberculosis were present in 14 of the 15 cows examined at slaughter, varying in severity from mild (two animals) to moderate (4) and advanced (8), and all predilection tissue sites yielded Map. The negative faecal samples were derived from a single animal that was culture positive in two quadrants on each of the first two (of four) sampling occasions (i.e. culture positive in only 4 of 16 collected quadrants). This animal was found to be histologically negative at slaughter, and culture positive from three of five predilection tissue sites. Faecal samples from cows with subclinical and clinical paratuberculosis, with lesion severity ranging from mild to severe at multiple predilection sites, produced faeces with relatively consistent concentrations of Map within samples. There was significant variation in concentrations of Map between samples in individual animals over a period of 2 weeks, but this did not affect the dichotomous positive-negative culture status for 15 of the 16 cattle. A faecal sample collected non-randomly per rectum thus provides a representative specimen for detection of Map by radiometric culture on a single sampling occasion.

Consensus recommendations on diagnostic testing for the detection of paratuberculosis in cattle in the United States

The report provided here contains a simplified set of diagnostic testing recommendations. These recommendations were developed on the basis of research funded by the USDA-Animal and Plant Health Inspection Service-Veterinary Services through a cooperative agreement. The report is intended to provide simple, practical, cost-effective consensus testing recommendations for cattle herds that are not enrolled in the US Test-Negative Program. The information has been reviewed by paratuberculosis (Johne's disease) experts at the USDA and academic centers as well as stakeholders in various segments of the cattle industry. The recommendations were accepted by the National Johne's Working Group and Johne's Disease Committee of the US Animal Health Association during their annual meetings in October 2006. The report is intended to aid veterinarians who work with cattle producers in the United States. The recommendations are based on information available up to October 2006. There is a paucity of large-scale, high-quality studies of multiple tests conducted on samples obtained from the same cattle. It is understood that there may be special circumstances that require deviation from these recommendations. Furthermore, as new information becomes available and assays are improved and their accuracy is critically evaluated, changes to these recommendations may be necessary.

Application of a semi-dependent latent model in the Bayesian estimation of the sensitivity and specificity of two faecal culture methods for diagnosis of paratuberculosis in sub-clinically infected Greek dairy sheep and goats

In this study, we compared the frequency of isolation of Mycobacterium avium subsp. paratuberculosis (MAP) from faecal samples grown on Herrold's egg-yolk medium (HEYM) or on Lowenstein-Jensen (LJ) medium and estimated the sensitivity (Se) and specificity (Sp) of the methods separately in sub-clinically infected Greek dairy sheep and goats, using latent-class models and Bayesian estimation procedures. Faecal and blood samples were collected from 400 animals > or =1 year old in April-May 2002. The HEYM supported growth of MAP better than the LJ method and their agreement was very poor (weighted kappa=0.062 (95% CI: -0.098, 0.222)). There was no evidence of dependence between the Ses whereas the Sps were positively correlated. Thus, a semi-dependent model that assumed independence of Ses and accounted for the dependence of Sps was adopted. Under this model, the parallel interpretation of the results of the two methods gave median estimates and 95% credible intervals (CrIs) for Se(par), Sp(par) of 15% (CrIs: 3, 45%), 96% (92, 98%) in sheep and 16% (6, 36%) and 97% (94, 99%) in goats.

Evaluation of a rapid fecal PCR test for detection of Mycobacterium avium subsp. paratuberculosis in dairy cattle

A high-throughput TaqMan PCR assay for detection of bovine paratuberculosis was evaluated by using fecal samples from 1,808 dairy cattle in seven naturally infected herds and 347 dairy cattle in seven herds considered free of paratuberculosis. Fecal, blood, and milk samples were submitted to laboratories where the PCR-based assay, three different fecal culture procedures for Mycobacterium avium subsp. paratuberculosis (centrifugation, sedimentation, and the BACTEC filter concentration method), two serologic enzyme-linked immunosorbent assays (ELISAs), and one milk ELISA were performed. Results from testing of dairy cattle in herds free of M. avium subsp. paratuberculosis showed that the PCR assay's specificity was 99.7%. Twenty-three percent of the dairy cows that were fecal culture positive by at least one of the three methods were positive by the PCR assay. By Bayesian non-"gold standard" analysis methods, the TaqMan PCR assay had a higher specificity than the serum ELISAs (99.3%; 95% confidence interval [CI]=98.6 to 99.7%) and a test sensitivity similar to that of the serum ELISAs (29%; 95% CI=24 to 35%). By classical methods, the estimated relative sensitivity of the fecal PCR assay was 4% for light and moderate fecal shedders (compared to 12 to 13% for the ELISAs) and 76% for heavy fecal shedders (compared to 67% for the milk ELISA). The PCR assay has higher sensitivity for detection of heavy fecal shedders than the evaluated milk ELISA but lower sensitivity than a serum or milk ELISA for detection of light and moderate fecal shedders. This assay can be used as a quick test for detection of cattle with heavy fecal shedding, those cattle with the highest risk of transmitting infection to susceptible cattle.

Efficacy of monensin sodium for the reduction of fecal shedding of Mycobacterium avium subsp. paratuberculosis in infected dairy cattle

Reducing the quantity of Mycobacterium avium subsp. paratuberculosis (MAP) being shed by cows with Johne's disease should decrease the risk of spread of this disease to young stock. Previous work has suggested that monensin sodium decreases the pathologic lesions associated with Johne's disease, but the impact on shedding of viable MAP remains unknown. After serologic screening of 32 dairy herds in southwestern Ontario, 228 cows from 13 of these herds were enrolled into a randomized clinical trial. Fecal culture and PCR were used to identify 114 cows as potential fecal shedders, while another 114 cows were enrolled as ELISA negative, herd and parity matched controls. All cows were randomized to receive either a monensin controlled release capsule (CRC) or a placebo capsule. Serial fecal and blood samples were collected for fecal culture and serum ELISA testing over a 98-day period. On day 98 of the study, treatments were switched for all cows continuing in the trial. These remaining cows were followed for another 98 days with a similar sampling protocol. Mixed effect models were used to measure the impact of treatment on the number of colony forming units identified on fecal cultures over time. During the first 98 days of the study, cows treated with a monensin CRC were found to shed 3.4cfu per tube less than placebo treated cows (P=0.05). The serum ELISA S/P ratio was reduced by 1.39 units in cows given monensin (P=0.06). However, treatment with monensin did not reduce the odds of testing positive on serology. Only the cows shedding MAP on day 0 were found to have a reduced odds of testing positive on fecal culture when treated with monensin (OR=0.27; P=0.03). Monensin sodium administered to infected animals at 335mg/day marginally reduced fecal shedding of MAP in mature dairy cattle, but the biological significance of this reduction is unknown.

Differential expression of genes encoding CD30L and P-selectin in cattle with Johne's disease: Progress toward a diagnostic gene expression signature

Mycobacterium avium subspecies paratuberculosis (Mycobacterium paratuberculosis), the causative agent of paratuberculosis (paraTB) or Johne's disease in ruminants, is a health problem for the global cattle industry with significant economic losses related to decreased milk production and reduced fertility. Commonly paraTB in cattle is diagnosed by antibody detection by serum enzyme-linked immunosorbent assay (ELISA), by detection of the pathogen by cultivation of individual faecal samples, or by in vitro measurement of cell mediated immune responses using the IFN-gamma test. There is an ongoing need for developing new diagnostic approaches as all currently available diagnostic tests for paraTB may fail to detect sub-clinical infection. We used cDNA microarrays to simultaneously measure expression of over 1300 host genes to help identify a subset of gene expression changes that might provide a unique gene expression signature for paraTB infection. In the present study, non-stimulated leukocytes isolated from 10 sub-clinical paraTB infected cows were examined for genes being expressed at significantly different levels than in similar cells from control cows with the same herd background. We included cattle (Holstein) from two locations (Denmark and USA) for the microarray experiment. Our results indicate that expression profiles of at least 52 genes are different in leukocytes from M. paratuberculosis infected cattle compared to control cattle. Gene expression differences were verified by quantitative real-time reverse transcriptase polymerase chain reactions (qRT-PCR) on the same group of cattle (Holstein) used for the microarray experiment. In order to assess the generality of the observed gene expression, a second and different group of cattle (Jersey) was also examined using qRT-PCR. Out of the seven genes selected for qRT-PCR, CD30 ligand (CD30L) and P-selectin were consistently differentially expressed in freshly isolated leukocytes from paraTB infected and control animals of both breeds of cattle. Although further work is clearly needed to develop a more complete gene expression signature specific for paraTB, our results demonstrate that a subset of genes in leukocytes are consistently expressed at different levels, depending upon M. paratuberculosis infection status.

Growth of Mycobacterium avium subsp. paratuberculosis in the presence of hexadecylpyridinium chloride, natamycin, and vancomycin

A design-of-experiments approach was used to examine the effect of hexadecylpyridinium chloride (HPC), alone or in combination with the antibiotics vancomycin and natamycin, on the growth of Mycobacterium avium subsp. paratuberculosis (MAP). At concentrations above 74.4 microg/ml, HPC had a highly significant detrimental effect on the growth of MAP, whereas natamycin at 10.8 and 21.6 microg/ml and vancomycin at 5.2 and 10.4 microg/ml did not have such an effect. Titration of the amount of HPC tolerated by MAP indicated that growth can occur in the presence of 24.8 microg/ml or lower. Processing of bovine fecal specimens indicated that reducing the concentration of HPC from 32.22 to 1.07 mg/ml during decontamination may improve detection when cultures are grown on solid medium but not when cultures are grown in liquid medium. Further investigation into optimizing HPC concentration during processing of fecal samples is warranted. Natamycin, in conjunction with vancomycin, may be useful for controlling fungal contamination during isolation of MAP from fecal samples.

Effect of egg yolk on the detection of Mycobacterium avium subsp. paratuberculosis using the ESP II liquid culture system

Rapid diagnosis of paratuberculosis in infected cattle is important for the successful control of Johne disease within herds. Thus, improving culture methods for Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) will aid in the identification of asymptomatic animals. Egg yolk is a component of the media used for growing M. paratuberculosis, but its requirement as a supplement has not been reported. Using the ESP II liquid culture system, 2 different sources and 5 concentrations (3.3%, 1.6%, 0.8%, 0.4%, and 0%) of egg yolk were analyzed. Egg yolk source did not affect either recovery rate or time to detection, but both parameters were significantly improved when the 3.3% egg yolk concentrations (final volume) were used over media containing no egg yolk. This study also assessed the recovery of M. paratuberculosis from fecal samples that were cultured multiple times using Herrold egg yolk agar (HEY). Specimens containing greater than 70 cfu/g feces could routinely be identified as positive for M. paratuberculosis after only 1 culture attempt, whereas specimens with fewer bacteria were only intermittently positive, even after 5 replicate cultures. Therefore, this study indicates that the sensitivity of the Trek Diagnostic ESP II liquid culture system for M. paratuberculosis is affected by egg yolk concentration and that single culture attempts using HEY solid media may not identify specimens containing low numbers of bacteria.

Evaluation of Mycobacterium avium subsp. paratuberculosis faecal culture protocols and media

Paratuberculosis is an important enteritis of ruminants caused by Mycobacterium avium subsp. paratuberculosis (Map). The disease is officially considered exotic in Brazil, but recent serological surveys and the isolation of the agent suggest it may occur in our herds. The aim of this study was to evaluate three different formulations of Herrold's egg yolk agar with mycobactin J (HEYM) and four faecal culture protocols considering their ability for Map growth as well as cost and ease of application. Three formulations of HEYM were inoculated with two suspensions of Map. Spiked faeces and naturally contaminated faecal samples were treated by the four faecal culture protocols. Centrifugation protocol and HEYM recommended by OIE showed the best results on the recovery of Map.

Evaluation of three ELISAs for Mycobacterium avium subsp. paratuberculosis using tissue and fecal culture as comparison standards

Three serum ELISAs for detection of antibodies against Mycobacterium avium subsp. paratuberculosis (Mptb) were evaluated against culture of tissue and feces samples from 994 dairy cows collected at slaughter. Culture of ileum and associated lymph nodes for Mptb were positive for 160 (16.1%) of the 994 cows and 36 (3.6%) were fecal culture-positive for Mptb. Two of the ELISAs evaluated were absorbed indirect assays and the third was a non-absorbed indirect assay. Estimated sensitivities of the absorbed ELISAs when compared to tissue culture were 8.8% and 6.9%, while the unabsorbed ELISA had a sensitivity of 16.9%. Specificities were 97.6%, 96.0% and 90.8%, respectively. When compared to fecal culture, the sensitivities of the absorbed ELISAs were 16.6% and 13.9%, respectively, and the sensitivity of the unabsorbed ELISA was 27.8%. Specificities were 97.1%, 95.9% and 90.1%, respectively. Area under the curve (AUC) of receiver operator characteristic curves for the absorbed ELISAs when tissue culture was the standard were 0.553 and 0.547, while the unabsorbed ELISA had an AUC of 0.540. When fecal culture was the comparison standard, the AUC of the absorbed ELISAs was 0.575 and 0.574, while the unabsorbed ELISA was 0.529. Overall, the sensitivities of the ELISAs when compared to tissue culture were low. The apparent advantage of the unabsorbed ELISA with respect to sensitivity is at the cost of lowered specificity and test accuracy.

Routes of intraspecies transmission of Mycobacterium avium subsp. paratuberculosis in rabbits (Oryctolagus cuniculus): a field study

Rabbits have been increasingly linked to the persistence of paratuberculosis (Johne's disease) in domestic ruminants in the United Kingdom. The aims of this study were to determine the routes of intraspecies transmission of Mycobacterium avium subspecies paratuberculosis (MAP) in rabbits and to estimate the probability of transmission via each route, in order to gain understanding of the dynamics of MAP in this host. Rabbits were sampled from two sites where MAP had previously been isolated from the livestock and rabbit populations. No pathology was noted in any animals, but the overall prevalence of MAP in rabbits was high at both sites studied, 39.7% and 23.0%, respectively. MAP was isolated from the testes, uterus, placenta, fetuses, and milk. This is the first time that the bacterium has been isolated from any of these tissues in a nonruminant wildlife species. These results suggest that transmission may occur vertically, pseudovertically, and horizontally. Vertical, i.e., transplacental, and/or pseudo-vertical, i.e., through the ingestion of contaminated milk and/or feces, transmission occurred in 14% of offspring entering the population at 1 month of age. As infection via these routes is only possible from infected adult females, this equates to a probability of infection via this route of 0.326. Probability of infection via horizontal transmission (including interspecies transmission) occurred at up to 0.037 per month. The presence of these routes of transmission within natural rabbit populations will contribute to the maintenance of MAP infections within such populations and, therefore, the environment.

Cow-level evaluation of a kinetics ELISA with multiple cutoff values to detect fecal shedding of Mycobacterium avium subspecies paratuberculosis in New York State dairy cows

In control programs for Mycobacterium avium subsp. paratuberculosis (Map), the infection status of the cows in a herd is often obtained by testing (a sample of) the herd with an ELISA that may lack some sensitivity and specificity but that is fast and inexpensive. In New York State (NYS), an unabsorbed kinetics ELISA (KELA) has been used extensively for Map control. The objective of this study was to determine the relative sensitivity and specificity of the KELA for detection of fecal shedding of Map for the NYS dairy cow population, taking into account possible confounders such as different antigen batches and Map prevalence in a herd. The data for the study consisted of all serum samples from NYS dairy cows with concurrent fecal culture results submitted to the NY Animal Health Diagnostic Laboratory (NYAHDL) between 1991 and 1996 (n=10,562). The data represented cows with different levels of fecal shedding from herds with different within-herd Map prevalence, including herds that were whole herd fecal culture negative on repeated testing. The cutoff values were based on the predictive value for fecal shedding obtained with a multiple logistic regression model that included variables for the three antigen batches and the Map prevalence in the herd. The KELA could not distinguish between non-shedders and low shedders (<or=30 total colony forming units (TCFU)) and thus the predictive value of the KELA to detect moderate to heavy fecal shedders (>30 TCFU) was modeled. The three cutoff values of 65, 135 and 170 were based on low (<0.2), moderate (<0.80) and high (>0.95) probabilities for moderate to heavy fecal shedding. The sensitivity and specificity values relative to culture were 67% and 95.2%, 31% and 99.7%, and 11% and 99.9% for the three cutoff values, respectively. Cutoff values for the KELA decreased for herds with increasing within-herd Map prevalence. For the best positive predictive value of a KELA for moderate to heavy fecal shedding, the cutoff values should be determined based on the apparent within-herd prevalence in a herd.

Description of the infection status in a Norwegian cattle herd naturally infected by Mycobacterium avium subsp. paratuberculosis

The Norwegian surveillance and control programme for paratuberculosis revealed 8 seroreactors in a single dairy cattle herd that had no clinical signs of Mycobacterium avium subsp. paratuberculosis (M. a. paratuberculosis) infection. Paratuberculosis had been a clinical problem in goats several years previously in this herd. All 45 cattle were culled and a thorough investigation of the infection status was conducted by the use of interferon-γ (IFN-γ) immunoassay, measurement of antibodies, and pathological and bacteriological examination.

In the IFN-γ immunoassay, 9 animals gave positive results, and 13 were weakly positive, while 19 animals were negative. In the serological test,10 animals showed positive reactions, and 5 were doubtful, while 30 animals gave negative reactions. There appeared to be a weak trend toward younger animals having raised IFN-γ and older animals having raised serological tests. Histopathological lesions compatible with paratuberculosis were diagnosed in 4 animals aged between 4 and 9 years. Three of these animals had positive serological reaction and one animal gave also positive results in the IFN-γ immunoassay. Infection was confirmed by isolation of M. a. paratuberculosis from 2 of these 4 animals. One single bacterial isolate examined by restriction fragment length polymorphism (RFLP) had the same profile, B-C1, as a strain that had been isolated from a goat at the same farm several years previously.

Despite many animals being positive in one or both of the immunological tests, indicative of a heavily infected herd, none of the animals showed clinical signs and only one cow was shown to be shedding bacteria. A cross-reaction with other mycobacteria might have caused some of the immunoreactions in these animals. It is also possible that the Norwegian red cattle breed is resistant to clinical infection with M. a. paratuberculosis.

Fecal shedding of Mycobacterium avium subsp. paratuberculosis by dairy cows

Between 1982 and 2000, fecal samples were obtained from 786 cows that were shedding Mycobacterium avium subsp. paratuberculosis (Map). These cows were resident on 93 Pennsylvania dairies (mean herd size, 64 milk cows) that had no or minimal previous testing for Map. Feces were cultured on four tubes of Herrold's egg yolk medium and the distribution of mean Map colony forming units (CFU) was evaluated. Most cows were light (< 10 CFU/tube, 51.4%) or high (> 50 CFU/tube, 30.8%) fecal shedders with fewer cows in the moderate category (10-50 CFU/tube). Of the 786 cows, 192 (24.4%) had colonies in only one of four tubes. In the multivariable negative binomial model, there were significant associations between mean CFU/tube and prevalence, herd size, and season and an interaction between herd size and season. The linear mixed model of continuous tube counts with a random herd effect yielded similar findings with associations with herd size as a continuous variable, season, and an interaction between categorized prevalence and continuous herd size. Variability in CFU/tube was greatest among cows in the same herd, intermediate for replicate tubes from the same cow, and smallest among cows in different herds. Reduction in the number of replicate tubes from four would have reduced the sensitivity of fecal culture for Map by approximately 6% (for three tubes) to 12% (for two tubes).

Certification of herds as free of Mycobacterium paratuberculosis infection: actual pooled faecal results versus certification model predictions

Dutch dairy herds closed for at least 3 years with no history of paratuberculosis were recruited for a study on herd-certification. One hundred dairy herds were tested for Mycobacterium paratuberculosis at 6-month intervals by pooled faecal culture (five individual animal samples per pool) with solid media. Ninety of the herds completed 9 herd tests and 10 herds dropped out of the study for reasons other than a paratuberculosis diagnosis. Of the 90 herds completing the full study, 61% eventually were found to be M. paratuberculosis-infected. The number of infected herds detected decreased with each round of testing. Assuming that all infected herds had been detected by the ninth herd test, the observed percentage of herds that were truly noninfected (P-free) after each round of testing was calculated. The observed P-free was compared to the predicted P-free based on a previously reported herd-certification model. The P-free predicted by the model was significantly different from the observed P-free. When a single assumption in the model was changed and a diagnostic sensitivity of 40-50% was selected, the predicted P-free closely approximated the observed P-free for the 90 Dutch dairy herds studied. The critical assumption that was changed for Version 2.0 of the model was within-herd infection prevalence for infected but test-negative herds after each round of serial testing. Model Version 1.0 had assumed a 50% decrease in within-herd prevalence but Version 2.0 assumed a stable within-herd prevalence. Culture of pooled faecal samples provides a high-sensitive, high-specific, low-cost test for herd-certification programs.