Analysis of repeated tests for interferon-gamma (IFN-gamma) response and faecal excretion for diagnosis of subclinical paratuberculosis in Danish cattle

Selection of vaccine-candidate peptides from Mycobacterium avium subsp. paratuberculosis by in silico prediction, in vitro T-cell line proliferation, and in vivo immunogenicity

Mycobacterium avium subspecies paratuberculosis (MAP) is a global concern in modern livestock production worldwide. The available vaccines against paratuberculosis do not offer optimal protection and interfere with the diagnosis of bovine tuberculosis. The aim of this study was to identify immunogenic MAP-specific peptides that do not interfere with the diagnosis of bovine tuberculosis. Initially, 119 peptides were selected by either (1) identifying unique MAP peptides that were predicted to bind to bovine major histocompatibility complex class II (MHC-predicted peptides) or (2) selecting hydrophobic peptides unique to MAP within proteins previously shown to be immunogenic (hydrophobic peptides). Subsequent testing of peptide-specific CD4+ T-cell lines from MAP-infected, adult goats vaccinated with peptides in cationic liposome adjuvant pointed to 23 peptides as being most immunogenic. These peptides were included in a second vaccine trial where three groups of eight healthy goat kids were vaccinated with 14 MHC-predicted peptides, nine hydrophobic peptides, or no peptides in o/w emulsion adjuvant. The majority of the MHC-predicted (93%) and hydrophobic peptides (67%) induced interferon-gamma (IFN-γ) responses in at least one animal. Similarly, 86% of the MHC-predicted and 89% of the hydrophobic peptides induced antibody responses in at least one goat. The immunization of eight healthy heifers with all 119 peptides formulated in emulsion adjuvant identified more peptides as immunogenic, as peptide specific IFN-γ and antibody responses in at least one heifer was found toward 84% and 24% of the peptides, respectively. No peptide-induced reactivity was found with commercial ELISAs for detecting antibodies against Mycobacterium bovis or MAP or when performing tuberculin skin testing for bovine tuberculosis. The vaccinated animals experienced adverse reactions at the injection site; thus, it is recommend that future studies make improvements to the vaccine formulation. In conclusion, immunogenic MAP-specific peptides that appeared promising for use in a vaccine against paratuberculosis without interfering with surveillance and trade tests for bovine tuberculosis were identified by in silico analysis and ex vivo generation of CD4+ T-cell lines and validated by the immunization of goats and cattle. Future studies should test different peptide combinations in challenge trials to determine their protective effect and identify the most MHC-promiscuous vaccine candidates.

Interferon-γ Response of Mycobacterium avium subsp. paratuberculosis Infected Goats to Recombinant and Synthetic Mycobacterial Antigens

Despite its potential for early diagnosis of Mycobacterium avium subsp. paratuberculosis (MAP) infection, the IFN-γ release assay is not used routinely, because of low specificity of the established crude antigen preparation Johnin (PPDj). Limited data are available assessing the potential of MAP-derived protein and lipopeptide antigens to replace PPDj in assays for goats, while cattle and sheep have been studied more extensively. Furthermore, MAP infection is claimed to interfere with the diagnosis of bovine tuberculosis when other crude antigen preparations (PPDb, PPDa) are applied. In this study, the diagnostic potential of MAP-derived recombinant protein antigens, synthetic MAP lipopentapeptides and of Mycobacterium bovis-specific peptide cocktails was assessed compared to crude mycobacterial antigen preparations in experimentally infected goats. Goats were inoculated with MAP, or Mycobacterium avium subsp. hominissuis (MAH) as surrogate for environmental mycobacteria, non-exposed animals served as controls. Mycobacterium avium Complex-specific antibody and PPDj-induced IFN-γ responses were monitored in vivo. Infection status was assessed by pathomorphological findings and bacteriological tissue culture at necropsy 1 year after inoculation. The IFN-γ response to 13 recombinant protein antigens of MAP, two synthetic MAP lipopentapeptides and three recombinant peptide cocktails of Mycobacterium bovis was investigated at three defined time points after infection. At necropsy, MAP or MAH infection was confirmed in all inoculated goats, no signs of infection were found in the controls. Antibody formation was first detected 3-6 weeks post infection (wpi) in MAH-inoculated and 11-14 wpi in the MAP-inoculated goats. Maximum PPDj-induced IFN-γ levels in MAH and MAP exposed animals were recorded 3-6 and 23-26 wpi, respectively. Positive responses continued with large individual variation. Antigens Map 0210c, Map 1693c, Map 2020, Map 3651cT(it), and Map 3651c stimulated increased whole blood IFN-γ levels in several MAP-inoculated goats compared to MAH inoculated and control animals. These IFN-γ levels correlated with the intensity of the PPDj-induced responses. The two synthetic lipopentapeptides and the other MAP-derived protein antigens had no discriminatory potential. Stimulation with Mycobacterium bovis peptide cocktails ESAT6-CFP10, Rv3020c, and Rv3615c did not elicit IFN-γ production. Further work is required to investigate if test sensitivity will increase when mixtures of the MAP-derived protein antigens are applied.

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

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

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.

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.

Interferon-gamma responses in sheep exposed to virulent and attenuated Brucella melitensis strains

Antibody detection is the basis of large-scale sheep brucellosis diagnosis because of its sensitivity and specificity. In contrast, information on the cellular mediated immune (CMI) response triggered after Brucella melitensis infection, a cornerstone in the protection against this pathogen, is more limited, particularly regarding the effect of the virulence of the infecting strain in the induced CMI reaction. Here, the interferon-gamma (IFN-γ) profiles evoked after exposure by different routes to virulent (H38) and attenuated (Rev.1) B. melitensis strains in 14 pregnant sheep and 87 ewe lambs, respectively, were characterized accounting for different host-related factors, and compared with their serological response and with the basal IFN-γ responses observed in 155 animals non exposed to Brucella. No significant differences in the IFN-γ response of Rev.1 vaccinated animals depending on the inoculation route was observed, in contrast with their serological results. Response in H38-challenged followed a similar trend although peaked later, and an effect of the abortion on the IFN-γ response was detected. This information could help to understand the interaction bacteria-host that leads to its intracellular survival and could be useful for the design of new diagnostic approaches.

Specific antibody and interferon-gamma responses associated with immunopathological forms of bovine paratuberculosis in slaughtered Friesian cattle

Mycobacterium avium subsp. paratuberculosis (MAP) infection causes a chronic granulomatous inflammatory regional enteritis in ruminants. Cell-mediated immune responses are assumed to be protective and therefore, to be associated with its more delimited lesion types, while humoral responses are mainly associated with diffuse histopathological lesions. However, this duality of immune responses has been recently questioned. The aim of this study was to assess the relationship between both types of immunological responses and the type and extension of intestinal lesions and the presence of MAP in bovine tissues. Standard histopathological examinations, two microbiological procedures (culture and real time PCR (rtPCR)), as well as MAP specific antibody and interferon gamma (IFN-γ) release assays (IGRA) were performed on tissues and blood of 333 slaughtered Holstein-Friesian animals. Paratuberculous lesions were observed in 176 (52.9%) of the animals and overall MAP detection rates were estimated at 13.5% and 28.5% for tissue culture and rtPCR, respectively. Unlike the relatively constant non-specific IFN-γ release, both the antibody levels and the specific IFN-γ release significantly increased with tissue damage. Delimited immunopathological forms, which accounted for 93.2% of all forms, were mostly related to positive testing in the IGRA (38.4%) whereas diffuse ones (6.8%) were associated with antibody seropositivity (91.7%). However, since the frequency of positive immune responses in both tests increased as the lesions severity increased, polarization of Th1/Th2 responses was less prominent than expected. MAP was detected in the majority of ELISA-positive animals (culture+: 90%, rtPCR+: 85%) but the bacteria was only confirmed in the 36.1% of IGRA-positive animals by any of the two microbiological tests. In terms of diagnosis, the antibody test was a good indicator of advanced tissue damage (diffuse forms), but the IGRA did not associate well with more delimited forms or with MAP detection.

Opportunities for improved serodiagnosis of human tuberculosis, bovine tuberculosis, and paratuberculosis

Mycobacterial infections—tuberculosis (TB), bovine tuberculosis (bTB), and Johne's disease (JD)—are major infectious diseases of both human and animals. Methods presently in use for diagnosis of mycobacterial infections include bacterial culture, nucleic acid amplification, tuberculin skin test, interferon-γ assay, and serology. Serological tests have several advantages over other methods, including short turn-around time, relatively simple procedures, and low cost. However, current serodiagnostic methods for TB, bTB and JD exhibit low sensitivity and/or specificity. Recent studies that have aimed to develop improved serodiagnostic tests have mostly focused on identifying useful species-specific protein antigens. A review of recent attempts to improve diagnostic test performance indicates that the use of multiple antigens can improve the accuracy of serodiagnosis of these mycobacterial diseases. Mycobacteria also produce a variety of species-specific nonprotein molecules; however, only a few such molecules (e.g., cord factor and lipoarabinomannan) have so far been evaluated for their effectiveness as diagnostic antigens. For TB and bTB, there has been recent progress in developing laboratory-free diagnostic methods. New technologies such as microfluidics and “Lab-on-Chip” are examples of promising new technologies that can underpin development of laboratory-free diagnostic devices for these mycobacterial infections.

Production and proteomic characterisation of purified protein derivative from Mycobacterium avium subsp. paratuberculosis

Background

Effective diagnosis of Johne's disease (JD), particularly at the stage of early subclinical infection, remains one of the greatest challenges for the control of JD worldwide. The IFN-γ test of cell mediated immunity is currently one of the most suitable diagnostics for subclinical infections, however a major limitation of this test is the lack of a standardised purified protein derivative (PPD) antigen (also referred to as Johnin PPD or PPDj). While attempting to replace PPDj with more specific individual antigens is an attractive proposition, bacterial culture derived PPDj remains the most effective antigen preparation for the diagnosis of subclinical JD. It may be possible to increase the reproducibility and specificity of PPDj preparations by further characterising and standardising the PPDj production.

Results

Using a standardised protocol, five in-house preparations of PPDj were prepared from cultures of Mycobacterium avium subsp. paratuberculosis (MAP). Compared to PPDs obtained from other institutes/laboratories, these preparations appeared to perform similarly well in the IFN-γ test. Although the broad proteomic composition of all PPDj preparations was remarkably similar, the absolute abundance of individual proteins varied markedly between preparations. All PPDj preparations contained common immunogenic proteins which were also observed in PPD preparations from Mycobacterium avium subsp. avium (PPDa) and Mycobacterium bovis (PPDb). Temporal difference in protein secretion of in vitro cultured MAP was observed between 20 and 34 weeks suggesting that the age of MAP culture used for PPDj preparations may markedly influence PPDj composition.

Conclusions

This study describes a protocol for the production of PPDj and its subsequent proteomic characterisation. The broad proteomic composition of different preparations of PPDj was, for the most part, highly similar. Compositional differences between PPDj preparations were found to be a direct reflection of genetic differences between the MAP strain types used to produce these preparations and the age of MAP cultures they were derived from. A number of conserved immunogenic proteins, such as members of the cutinase-like protein family, were found to be more abundant in PPDj compared to PPDa and should be considered as possible diagnostic antigens for the future.

Expression of genes associated with the antigen presentation and processing pathway are consistently regulated in early Mycobacterium avium subsp. paratuberculosis infection

The primary objective of this study was to evaluate early gene expression profiles associated with paratuberculosis in cattle exposed to known infectious doses of Mycobacterium avium sub-species paratuberculosis (MAP). A Johne's disease experimental infection field trial was conducted on a mixed population of Holstein and Holstein Red cattle. Blood samples from four MAP exposed and four unexposed cattle, selected based on IFNγ expressions were taken at 9, 13 and 21 weeks and RNA processed to Affymetrix GeneChip™ Bovine Genome arrays. Ontological analysis revealed consistent differences in gene expression between MAP exposed and control animals. A stark variation was observed in expression of a number of genes along antigen presentation pathways, suggesting that MAP exposure potentially results in the host immune response switching to a CD8(+) biased antigen presentation profile. This requires further in-depth analysis since it exposes a hitherto unconfirmed association between MAP exposure and in vivo MHC gene modulation.

Peptides specific for Mycobacterium avium subspecies paratuberculosis infection: diagnostic potential

Mycobacterium avium subspecies paratuberculosis (Map) is the causative agent of Johne's disease (JD). Current serological diagnostic tests for JD are limited by their sensitivity when used in sub-clinical stages of the disease. Our objective was to identify peptides that mimic diagnostically important Map epitopes that might be incorporated into a new-generation JD diagnostic. Four peptides were isolated from a phage-displayed random peptide library by screening on antibodies derived from Map-infected goats. The peptides were recognised by antibodies from Map-infected goats but not by antibodies from uninfected goats. The peptides elicited immune responses in rabbits, which reacted strongly with bona fide Map antigens proving the peptides were true epitope mimics. To assess the diagnostic value a panel of goat sera was screened for reactivity's with peptides. The peptides were recognised by antibodies from a proportion of goats infected with Map compared with control animals with a diagnostic specificity of 100% and the sensitivity ranged from 50 to 75%. Combinations of any two peptides improved sensitivity 62.5-87.5% and 100% sensitivity was achieved with three of the four peptides in combination. These data suggest peptides representing diagnostically important Map epitopes could be incorporated into a sensitive diagnostic test.

Transmission parameters of Mycobacterium avium subspecies paratuberculosis infections in a dairy herd going through a control program

A Johne's disease control program, including stringent management practices and a test-and-cull program (whole-herd fecal-samples taken twice a year), was implemented on a medium-sized Pennsylvania dairy farm that was suffering losses from clinical Johne's disease. The data that emerged from the control program, combined with birthdates, culling dates, lactation information and pedigrees, yielded an extensive longitudinal dataset. The dataset was processed through SAS 9.1 for statistical analysis; herd-level disease dynamics and dam-to-daughter transmission parameters were calculated. After the implementation of the program in 1984, prevalence dropped dramatically from 60% to less than 20% in 1989. After an apparent prevalence peak (25%) in 1991 due to improved test sensitivity, prevalence maintained a plateau of 10% from 1996 to 2000. After the implementation of the program, 9.5% of the offspring from test-negative dams and 26.8% of the offspring from known-infected dams became infected with Mycobacterium avium subspecies paratuberculosis (Map) (chi(2)=14.7; p=0.0001). Calves born shortly following the calving of an infected dam and calves growing up with a future high shedder were more likely to be infected compared to calves without this risk profile. It was concluded that, after the implementation of the control program, the most important causes of infections of susceptible calves were their own dams or infected animals which had calved recently.

Comparison of the proteosomes and antigenicities of secreted and cellular proteins produced by Mycobacterium paratuberculosis

The protein expression profiles and antigenicities of both culture filtrates (CF) and cellular extracts (CE) of Mycobacterium paratuberculosis were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), one-dimensional electrophoresis (1-DE) and 2-DE immunoblotting, and enzyme-linked immunosorbent assay (ELISA). The CF proteins were harvested from supernatants of stationary-phase liquid cultures and concentrated by size exclusion filtration. The CE proteins were extracted by mechanical disruption of cells using glass beads and a high-speed agitator. Analysis of SDS-PAGE gels showed that the majority of CF proteins had low molecular masses (<50 kDa), whereas CE protein mass ranged more evenly over a broader range up to 100 kDa. By 2-DE, CF proteins had a narrow array of pI values, with most being between pH 4.0 and 5.5; CE proteins spanned pI values from pH 4.0 to 7.0. The antigenicities of CF and CE proteins were first determined by 1-DE and 2-DE immunoblotting with serum from a cow naturally infected with M. paratuberculosis. The serum reacted strongly to more proteins in the CF than the CE. Sera from 444 infected and 412 uninfected cattle were tested by ELISA with CF and CE as solid-phase antigens. Receiver-operator characteristic curve analysis of the ELISA results showed a significantly greater area under the curve for CF compared to CE (P<0.05). A high degree of variability in protein binding patterns was shown with 1-DE immunoblot analysis with 31 sera from M. paratuberculosis-infected cattle. Collectively, these results indicate that serologic tests for bovine paratuberculosis may be improved by using proteins derived from CF instead of CE. To maximize the diagnostic sensitivity of serologic tests, multiple proteins will be required. Even so, a CF ELISA may not be able to detect all M. paratuberculosis-infected cattle, in particular those in the early stages of infection that have yet to mount an antibody response.

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.

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 the gamma interferon test for diagnosis of paratuberculosis in goats

The gamma interferon assay was evaluated for diagnosis of paratuberculosis in goats with special emphasis on false positive reactions. Four categories of herds were tested: (A) herds that had a history of paratuberculosis, had given positive Mycobacterium avium subsp. paratuberculosis fecal samples and were vaccinated against paratuberculosis; (B) herds that had been vaccinated but had never shown clinical signs of paratuberculosis nor given positive M. a. paratuberculosis fecal samples; and (C) non-vaccinated herds without paratuberculosis. To extend the analysis of samples from young goats free of paratuberculosis, animals less than 18 months of age from non-vaccinated herds without paratuberculosis, category D, were included. Heparinized blood was stimulated with purified protein derivate (PPD) from M. a. paratuberculosis for 24 h and plasma was assayed for the presence of gamma interferon. Results were recorded as the difference between OD values of PPD stimulated and control samples. Vaccinated animals from herds with paratuberculosis, category A, showed significant higher gamma interferon responses than animals from vaccinated herds without paratuberculosis, category B. In both these groups the responses were correlated to age with higher responses in younger animals. Some of the vaccinated animals in herds without paratuberculosis had a gamma interferon response lasting for several years, which demonstrate a long lasting interference with diagnostic testing in vaccinated goats. Only three of the 121 non-vaccinated animals free of paratuberculosis in category C had responses against PPD (corrected OD values at 0.2, 0.24 and 0.5), and none of the 255 young animals in category D had corrected OD values exceeding 0.2. This indicates that false positive reactions do not appear to the same extent in young goats as in young cattle. We conclude that the low responses of non-infected goats could make the gamma interferon assay useful in monitoring the paratuberculosis status of non-vaccinated herds. However, more information about the early gamma interferon responses of naturally infected goats and the presence of false negative samples are needed.

Evaluation of cell-mediated immune responses and bacterial clearance in 6–10 months old water buffalo (Bubalus bubalis) experimentally vaccinated with four dosages of commercial Brucella abortus strain RB51 vaccine

Thirty water buffalo, obtained from a brucellosis-free farm, were used to evaluate cell-mediated immune responses and bacterial clearance in response to vaccination with Brucella abortus strain RB51 (RB51) in a dose-response study. The animals were randomly divided into five treatment groups. Groups I--V received the recommended dose (RD) of RB51 vaccine once, RD twice 4 weeks apart, double RD once, double RD twice 4 weeks apart and saline once, respectively. Cell-mediated immune response to RB51 was assessed by the histological examination of haematoxylin and eosin (H&E) stained sections of lymph nodes draining the sites of inoculation and by comparison of stimulation indices (SI) derived from gamma interferon (IFN-gamma) assay. A mixture of cytoplasmic proteins from B. melitensis B115 (brucellergene) was used as a specific antigenic stimulus to peripheral blood mononuclear cells (PBMC) and lymph node mononuclear cells (LNMC) up to 22 post-initial-inoculation week (PIW). Supernatants harvested at 18-24h after the in vitro antigenic stimulus were assayed for their IFN-gamma content by using a commercial sandwich enzyme-linked immunosorbent assay (ELISA) kit. Clearance of RB51 was assessed by the sequential immunohistochemical examination of sections of draining lymph nodes post-inoculation. There was no observable expansion of the deep cortex of lymph nodes on H&E sections indicating poor T-cell stimulation. All group V (control) water buffalo PBMC ELISA values were negative (SI<2.2) at all PIW sampling intervals. Overall PBMC IFN-gamma assay detected vaccinates from treatment groups' I--IV 67% (4/6), 83% (5/6), 33% (2/6) and 67% (4/6), respectively. LNMC IFN-gamma assay was unimpressive and there was a negative correlation (--.08) between the results of PBMC and LNMC of IFN-gamma assay. Clearance of RB51 occurred between 4 and 6 PIW in treatment groups I and III and between 6 and 12 PIW in groups II and IV. RB51 was not detected in any of the control animals at sampling intervals post-inoculation.

Longitudinal study of interferon-gamma, serum antibody and milk antibody responses in cattle infected with Mycobacterium avium subsp. paratuberculosis

During a 2-year study period, 252 animals from dairy herds infected with Mycobacterium avium subsp. paratuberculosis, and 119 animals from non-infected herds were subjected to repeated blood and faecal sampling. Animals were retrospectively grouped by infection status as infected, exposed (culture negative animals from infected herds), or non-infected animals, and by age, 12-23 months (1+ year), 24-35 months (2+ years), or 36 months and older (3+ years). Samples were collected for culture of faeces, assessment of interferon-gamma (IFN-gamma) secreted by M. paratuberculosis antigen stimulated whole-blood lymphocytes (IFN-gamma test), and measurement of antibody responses against M. paratuberculosis in serum and milk by an in-house absorbed ELISA. The IFN-gamma test diagnosed higher proportions of infected and exposed animals than the antibody ELISAs. The highest sensitivity of IFN-gamma test was in infected cattle of 2+ years of age. Receiver-operating characteristic (ROC) analyses supported the assumption that the IFN-gamma test had a better performance than antibody tests of animals of 1+ and 2+ years of age. However, for animals of 3+ years all tests performed equally well. Application of single sampling compared with repeated samplings showed better performance of the IFN-gamma test by repeated samplings, and the milk antibody ELISA in animals of 3+ years of age performed significantly better with repeated sampling compared with single sampling. In conclusion, the IFN-gamma test may be applied for screening of cattle of 1 and 2 years of age for exposure to M. paratuberculosis and the antibody ELISAs from 3 years of age.

Comparison of Histopathology, Cultivation of Tissues and Rectal Contents, and Interferon-gamma and Serum Antibody Responses for the Diagnosis of Bovine Paratuberculosis

The diagnosis of infection with Mycobacterium avium subsp. paratuberculosis was studied in 12 cattle from infected dairy herds and four from non-infected herds. A comparison was made of (1) histopathological examination and bacterial culture of tissues, (2) culture of serial samples of rectal contents, and (3) examination of repeated blood samples for interferon-gamma (IFN-gamma) and antibody responses. Tissue samples were taken from the small and large intestine and corresponding mesenteric lymph nodes, and from the pharyngeal tonsil and other lymphoid nodes (retropharyngeal, mediastinal, hepatic and supramammary). Histopathological examination and bacterial culture of tissues each revealed that six of the 16 cattle were infected, whereas repeated culture of rectal contents revealed only five infected animals. Except for the hepatic lymph node of a single animal, culture-positive tissues were confined to the intestinal tract and related lymph nodes. Bacterial culture of tissues from the ileum, caecum and lymph nodes draining the jejunum revealed the highest number of infected animals. Moreover, slightly greater numbers of positive tissues were revealed by culture than by histopathological examination. For both the IFN-gamma response and the antibody response, the means of the values for the final three samples before slaughter were significantly higher in infected than in non-infected cattle. However, these immunological responses were too variable to provide a reliable indication of infection.