An enzyme-linked immunosorbent assay using immonoaffinity-purified antigen in the diagnosis of caprine paratuberculosis and its comparison with conventional ELISAs

Prevalence of paratuberculosis in organized and unorganized dairy cattle herds in West Bengal, India

Aim::

The aim of this study was to determine the prevalence pattern of Mycobacterium avium subsp. paratuberculosis, the causative agent of paratuberculosis or Johne’s disease, in unorganized as well as organized cattle herds in West Bengal.

Materials and Methods::

Four organized cattle farms with identical management practice in Nadia (n=3) and South 24 Parganas (n=1) districts and three unorganized cattle herds, one each from three districts, namely, Burdwan, North 24 Parganas, and Purba Midnapur, were selected randomly and screened for paratuberculosis by delayed-type hypersensitivity (DTH) and enzyme-linked immunosorbent assay (ELISA).

Results::

Of 191 animals tested by DTH, 57 (29.8%) were found to be positive in comparison to 72 (37.7%) by ELISA. In organized farms, seropositivity varied from 13.3% to 53.1%, whereas in unorganized sector, it ranged from 5% to 6.7% with one area having exceptionally high prevalence, i.e. 53.3%. The range of positivity detected by DTH both in organized farms and backyard sectors varied from 0% to 46.7%. By employing both DTH and ELISA together, the positivity of animals in organized and unorganized herds was 19.9% and 8%, respectively.

Conclusion::

The results indicate that animals in organized farms are much more prone to paratuberculosis than others. For screening the herd, both DTH and ELISA should be used simultaneously to increase the test sensitivity in order to minimize its further spread adopting control programs.

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

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

Sequential Development of Histologic Lesions and Their Relationship with Bacterial Isolation, Fecal Shedding, and Immune Responses during Progressive Stages of Experimental Infection of Lambs with Mycobacterium avium subsp. paratuberculosis

Understanding pathogenesis during progressive stages of infection by Mycobacterium avium subsp. paratuberculosis (MAP) and finding suitable methods for its diagnosis are key to the control of Johne's disease in animals. Paratuberculosis was experimentally produced in 20 crossbred lambs by oral administration of MAP to study the sequential development of lesions between 10 and 330 days postinfection and to assess commonly used diagnostic methods such as bacterial culture, lymphocyte stimulation test (LST), and enzyme-linked immunosorbent assay (ELISA) during progressive stages of infection. Histologic lesions were classified into four grades from grade 1 (least severe) to grade 4 (most severe) on the basis of location of granulomatous lesions in different regions and layers of intestines, their association with intestinal lymphoid tissues, pattern and distribution of lesions, types of cellular infiltration, and presence of acid-fast bacilli. It is evident that infection first establishes in lymphoid tissues of the small intestine, possibly at multiple sites, producing segmental lesions and from there spreads to lamina propria and local lymph nodes. Wide variability in the histologic lesions in relation to postinfection periods and initial tropism of MAP to the intestinal lymphoid tissues (Peyer's patches) suggests a differential susceptibility of young animals, possibly because of compositional phenotypic variation of Peyer's patches influencing subsequent course of infection. Histopathology was found to be a better indicator of paratuberculous infection than bacteriology in sheep. The LST (reflecting the cellular immune response) and ELISA (reflecting the humoral immune response) had overall sensitivities of 65% (11 of 17) and 42% (8 of 19), respectively, in sheep with different types of pathology but when employed together could detect about 88% of infected animals.

Performance of a Johne's Disease Enzyme-Linked Immunosorbent Assay Adapted for Milk Samples from Goats

Antibody detection–based tests for paratuberculosis offer speed and economy, 2 diagnostic test attributes important to animal industries with narrow profit margins. Application of such tests to individual milk samples instead of serum samples can further improve testing efficiency and decrease testing cost. Accuracy of a commercial bovine paratuberculosis enzyme-linked immunosorbent assay (ELISA) adapted for use on goat serum and milk samples was determined. Fecal, blood, and milk samples were collected from 159 goats belonging to 2 Wisconsin goat herds with a prior history of paratuberculosis and 1 herd of 50 goats from a paratuberculosis-free Wisconsin herd. Fecal samples were cultured using the modified BACTEC 12B media. Sera were tested according to the manufacturer's instructions for bovine samples. Milk samples were centrifuged and mixed with the ELISA kit's Mycobacterium phlei–containing diluent at a ratio of 1:2. Using fecal culture as the “gold standard,” the sensitivity of the ELISA on goat serum was 64% and the sensitivity of the ELISA on goat milk was 48%. The milk ELISA had higher agreement with fecal culture results (kappa = 0.525) than the serum ELISA (kappa = 0.425). ELISA specificity was 100% on both serum and milk. Regression analysis also showed good correlation between serum and milk S/P values ( r2 = 0.67). Although less sensitive, the ELISA on goat milk samples appears to offer a useful, low-cost alternative for detection of goats with paratuberculosis that have progressed to the stage of shedding M. paratuberculosis in their feces.

Application of the Enfer chemiluminescent multiplex ELISA system for the detection of Mycobacterium bovis infection in goats

A study was conducted to optimise a multiplex serological immunoassay for use in identification of goats infected with Mycobacterium bovis. To assess assay specificity, 31 goats with a history of being free from M. bovis infection were used. To determine assay sensitivity, 180 Single Intradermal Comparative Tuberculin test (SICTT) positive goats were recruited. Additionally, 286 SICTT negative goats classed as potentially exposed animals present in the same positive herds were also included in the study. The results of the assay demonstrated a specificity of 100%. The multiplex assay detected 57/60 SICTT (95.0%) positive animals in one M. bovis infected herd and 120/120 (100%) in a second herd. In a separate experiment, 28 M. caprae culture confirmed infected goats from Spain were assayed, of which 24 (85.7%) were found positive in the test. The results show that inclusion of an antibody based assay can improve the ability to identify M. bovis and M. caprae infected goats. With further development and validation the multiplex assay may prove to be a useful tool for control of M. bovis and M. caprae infection in goats.

Diagnosis of paratuberculosis by fecal culture and ELISA on milk and serum samples in two types of Chilean dairy goat herds

Fecal culture has been the primary method used to diagnose paratuberculosis in goats. It is laborious, slow, and expensive. Validation of enzyme-linked immunosorbent assays (ELISAs) on milk samples could make paratuberculosis testing more widely available for goat farmers. The aim of this study was to determine the accuracy of serum and milk ELISAs for paratuberculosis, relative to fecal culture, in Chilean dairy goats. Eight dairy goat herds were selected. Feces, blood, and milk samples were collected from all female goats >2 years old. Fecal samples were cultured using Herrold egg yolk medium with mycobactin J and antibiotics. Serum and milk samples were tested using a commercial ELISA kit for Mycobacterium avium subsp. paratuberculosis antibody detection. A total of 383 goats were tested by ELISA and fecal culture. The sensitivity of ELISA on serum and milk relative to fecal culture was 74.3% (95% CI: 59.8-88.8) and 60% (95% CI: 43.8-76.2), respectively. The corresponding values for ELISA specificity based on the percentage of non- M. avium subsp. paratuberculosis-infected goats testing ELISA-negative were 98.6% (95% CI: 96.6-100) and 99.3% (95% CI: 97.9-100) on serum and milk, respectively. Proportions of positive results for serum and fecal samples were significantly different, whereas the proportions of positive results for milk and fecal samples were not significantly different. The milk ELISA had a moderate level of agreement with fecal culture results (Kappa = 0.57). The paratuberculosis ELISA on goat milk samples may be a cost-effective, accurate alternative to fecal culture.

Impact of Corynebacterium pseudotuberculosis infection on serologic surveillance for Johne's disease in goats

False-positive results on serologic assays for Mycobacterium avium subsp. paratuberculosis (MAP) are believed to occur due to cross-reacting antibody produced by Corynebacterium pseudotuberculosis (C. pstb) infection in goats. This issue of compromised specificity was evaluated by testing 771 adult goats from 10 Midwestern goat herds in 2004. Assays for MAP infection included radiometric fecal culture and 2 enzyme-linked immunosorbent assays (ELISAs); ELISA-positive samples were tested by agar gel immunodiffusion (AGID). A synergistic hemolysin inhibition assay (SHI) was used to detect C. pstb antibody. Four infection status categories were evaluated. Category 1 goats (free of both MAP and C. pstb infection) tested negative on all MAP fecal cultures and SHI tests. Five of 181 goats were positive in both ELISAs, and 2 more were positive in ELISA-1 only. For Category 2 (MAP infected; no C. pstb infection), all animals were SHI negative. Six goats were fecal culture positive and strongly positive in both ELISAs; 2 more goats were positive only in ELISA-1. For Category 3 (C. pstb infected or vaccinated; no history of MAP infection), all fecal cultures were negative and 91% were SHI test-positive. In this population, only 2 goats were positive in both MAP ELISAs, while 84 additional goats were test-positive only on ELISA-1. In the absence of C. pstb infection, both ELISAs performed comparably, but when C. pstb infection was present the performance of ELISA-1 was significantly perturbed. Use of the ELISA-2 for goats is an effective and efficient method for Johne's disease surveillance in any goat herd.

Lymphoproliferative response and its relationship with histological lesions in experimental ovine paratuberculosis and its diagnostic implications

Lymphoproliferative response (LPR) was studied in 19 lambs orally infected (Group I) with Mycobacterium avium subsp. paratuberculosis (MAP) with in vitro lymphocyte stimulation test using MTT dye reduction assay. The non-specific LPR against Con A and specific LPR against sonicated antigen and johnin PPD (purified protein derivatives) were estimated on preinfection (0 day) and various days postinfection period (15 to 330 dpi) in the animals, which were classified according to histological and bacteriological evidence of paratuberculosis infection. Of the two antigens used, johnin PPD was found to be superior in terms of consistency and uniformity of response over an observation period of about a year. Significantly (P<0.05) higher LPR were observed in the infected sheep during postinfection period, as compared with preinfection values and values from uninfected control sheep. It was evident from the present study that the LPR in histologically infected animals fluctuated during the long course of infection and had a definite relationship with the gut pathology and the mycobacterial load. The LPR were stronger but variable in sheep with grades 1, 2 and 3 lesions (paucibacillary) and increased progressively from 30 dpi onwards. The sheep with the advanced lesions (grade 4, multibacillary) showed progressive decline in LPR till 120 dpi after initial stronger response at 30 dpi. Most of the animals were detected by LPR before initiation of faecal shedding of MAP. The results suggested that repeated testing was required while screening an infected flock for detecting most of the positive animals.

Application of Different Methods for the Diagnosis of Experimental Paratuberculosis in Goats

The diagnosis of subclinical paratuberculosis is still considered a major problem worldwide. As part of investigating diagnostic strategies for the paratuberculosis infection, sequential results of various diagnostic methods in a progressive experimental infection in goats were evaluated. Twenty-three goat kids were divided into three groups: the infected, contact and control, comprising 10, five and eight goats respectively. Animals of the infected group were orally inoculated on seven occasions with 5 ml of inoculum containing 2 x 10(9)Mycobacterium avium ssp. paratuberculosis per ml. Lymphoycte proliferation test using johnin PPD detected paratuberculosis infection from 60 days post-infection (DPI) onwards. The johnin PPD was found to be a better antigen for the proliferative assays as compared with the sonicated antigen. The faecal smear examination with acid-fast staining detected more goats as positive than bacterial culture and polymerase chain reaction (PCR). Lipoarabinomannan enzyme-linked immunosorbent assay (ELISA) started detecting infected goats from 150 DPI onwards followed by indirect ELISA and agar gel immunodiffusion from 180 DPI onwards. Histological examination was confirmatory and detected five infected goats as positive.

Bayesian estimation of sensitivity and specificity of serum ELISA and faecal culture for diagnosis of paratuberculosis in Greek dairy sheep and goats

Latent class models were used to estimate the sensitivity (Se) and the specificity (Sp) of a serum ELISA and a faecal culture (FC) method for the diagnosis of paratuberculosis separately, in sheep and goats. The estimates were obtained by a Bayesian method. Possible dependence of diagnostic errors was investigated by comparing models where independence was assumed to models allowing for conditional dependence given the true disease status. ROC analysis for the serum ELISA was also performed and optimized cut-off values based on the misclassification cost term were determined. No evidence of conditional dependence was found. Assuming independence, posterior medians and 95% credible intervals for the Se(ELISA), Sp(ELISA), Se(FC) and Sp(FC), were 63% (42, 93%), 95% (90, 98%), 8% (2, 17%) and 98% (95, 100%) in goats and 37% (10, 80%), 97% (93, 99%), 16% (2, 48%) and 97% (95, 99%) in sheep. AUC was calculated 0.702 for sheep and 0.847 for goats. For the serum ELISA, there is need of species- and purpose-specific cut-off selection. For instance, with 20% prevalence situation and assuming equal and five-fold cost of a false negative to a false positive test result, the optimal cut-off is 0.3 and 0.05 in sheep, respectively, while it is 0.6 and 0.1 in goats, respectively. Serum ELISA performed better in goats than in sheep. Lowering the cut-off, in relation to the one recommended by the manufacturer, improved Se(ELISA) without seriously compromising Sp(ELISA), in either species.

Comparison of IS900 tissue PCR, bacterial culture, johnin and serological tests for diagnosis of naturally occurring paratuberculosis in goats

Comparative efficacy of an IS900 tissue PCR, bacterial culture, johnin, agar-gel immunodiffusion (AGID) and absorbed-ELISA tests was investigated in 43 goats naturally infected with paratuberculosis. On histological examination, tissue sections from all animals showed typical granulomatous inflammatory changes. The lesions were classified as multibacillary (MB) (n=30), which had diffuse granulomatous lesions with abundant acid-fast bacilli (AFB), and paucibacillary (PB) (n=13), which had focal or multifocal granulomatous lesions with few AFB. The sensitivities of johnin test, tissue culture, faecal culture, tissue PCR, AGID and ELISA were 68% (17/25), 100% (30/30), 84.6% (22/26), 100% (30/30), 96.2% (25/26) and 100% (26/26) in MB goats, and 88.8 (8/9), 46.1% (8/13), 40% (4/10), 61.5% (8/13), 50% (5/10), and 70% (7/10) in PB goats, respectively. Except for the johnin test, which showed higher sensitivity in PB goats, all other tests displayed significantly higher sensitivities in MB goats. The results indicate the usefulness of tissue PCR, culture and serological tests in the diagnosis of clinically affected paratuberculous goats, especially with multibacillary pathology.

A long-term study in Angora goats experimentally infected with Mycobacterium avium subsp. paratuberculosis: Clinical disease, faecal culture and immunological studies

Two longitudinal experiments involving Angora goats challenged with either bovine or ovine strains of Mycobacterium avium subspecies paratuberculosis (Map) have been conducted over a period of 54 and 35 months, respectively. Blood samples for the interferon-gamma (IFN-gamma) test and the absorbed ELISA and faecal samples for bacteriological culture were taken pre-challenge and monthly post-challenge. Persistent shedding, IFN-gamma production, seroconversion and clinical disease occurred earlier with the bovine Map gut mucosal tissue challenge inoculum than with cultured bacteria. The IFN-gamma responses of the gut mucosal tissue and bacterial challenge groups were substantially and consistently higher than those of the control group. The in vivo and cultured cattle strains were much more pathogenic for goats than the sheep strains with persistent faecal shedding, seroconversion and clinical disease occurring in the majority of bovine Map challenged goats. With the ovine Map, 3 goats developed persistent antibody responses but only one of these goats developed persistent faecal shedding and clinical disease. However, there was no significant difference between the IFN-gamma responses of the tissue challenged, bacterial challenged and control groups. Compared with sheep, the ELISA appeared to have higher sensitivity and the IFN-gamma test lower specificity.

The association of sub-clinical paratuberculosis with the fertility of Greek dairy ewes and goats varies with parity

Our cross-sectional study investigated the association of sub-clinical Mycobacterium avium subsp. paratuberculosis (MAP) infection with failing to produce a live offspring the season of lambing/kidding (November 2001 to January 2002) before testing (in April-May 2002), in four dairy-sheep and/or goat flocks in Greece (369 animals >or=1.5-year-old). From each selected animal 10 ml of blood and 10 g of feces from the rectum were obtained. The harvested sera were tested for antibodies to MAP with a commercial ELISA test kit; the feces were cultured on Herrold's egg-yolk medium supplemented with mycobactin J and antibiotics. An animal was considered sub-clinically infected when found either seropositive or culture positive. The true prevalence of sub-clinically infected animals, adjusted for the sensitivity and specificity of the parallel testing, was 14% (0.1-28%) and 35.9% (9.2-62.7%) in sheep and goats, respectively. The association of fertility of sheep and goats with sub-clinical paratuberculosis was investigated in random-effects logistic models. Sub-clinically infected animals (compared to uninfected) had OR for live offspring the previous year of 5.4 for parity <4, OR=0.05 for parity >6, and a non-significant OR for the middle parity category.

Progressive immunopathological changes during early stages of experimental infection of goats with Mycobacterium avium subspecies paratuberculosis

A dose of 10(10) Mycobacterium avium subspecies paratuberculosis was administered orally on seven occasions to produce experimental paratuberculosis infection in 10 5-8-week-old goat kids. Bacteriological, immunological, and histopathological changes, their relationships, and the efficacy of the commonly used diagnostic methods were studied during the progressive disease up to 270 days postinfection (DPI). Significant lymphocyte proliferative responses in the peripheral blood of five goats were detected as early as 60 DPI. A lymphoproliferative test was also performed on lymphocytes purified from different compartments of the guts of five infected and five control goats. Significant proliferative responses were observed in lymphocytes of jejunal compartments of all five goats, of which four had also significant lymphocyte proliferation in the blood. The ileal lymphocytes from two goats, one each at 120 and 270 DPI, had significant proliferation. The histological lesions were mainly observed in the gut-associated lymphoid tissues of the ileocecal valve, the ileum, and the terminal jejunum. Acid-fast bacilli were demonstrated in the lesions of two goats at 60 and 210 DPI. Bacterial culture showed poor sensitivity, detecting positive results for only one goat in the fecal and tissue samples at 210 DPI, whereas polymerase chain reaction (PCR) detected one goat in fecal sample at 210 DPI and two goats in tissue samples at 60 and 210 DPIs, respectively. Enzyme-linked immunosorbent assay and agar gel immunodiffusion test were found to be 100% sensitive from 180 and 210 DPI onwards, respectively.

Evaluation of a LAM ELISA for diagnosis of paratuberculosis in sheep and goats

A milk and serum ELISA containing lipoarabinomanan (LAM) antigen was evaluated in sheep and goats versus agar gel immunodiffusion (AGID) test and polymerase chain reaction (PCR) using milk and lymph nodes. Milk and serum samples were obtained from six, two, and four flocks with unknown, negative and positive status of infection, respectively. By comparison of serum ELISA activity and PCR results, the positive and negative predictive values were calculated. Receiver operation characteristic (ROC) analysis was used for calculating the specificity and sensitivity at different cut-offs.