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.

Mycobacterium avium subspecies paratuberculosis confirmed following serological surveillance of small ruminants in Grenada, West Indies

Surveillance for Mycobacterium avium subsp. paratuberculosis ( Map) infection in small ruminants of Grenada was undertaken using a commercial enzyme-linked immunosorbent assay (ELISA). Among the 479 sheep tested, 11 (2.3%) were ELISA positive while only 1 out of 260 goats (0.3%) was ELISA positive. Five of the 12 ELISA-positive animals were also positive in a commercial agar gel immunodiffusion (AGID) assay, and 4 of these showed acid-fast rods consistent with Map in fecal smears. Two sheep that were test-positive by ELISA, AGID, and fecal smears were euthanized and necropsied. Both had gross and histological lesions of paratuberculosis affecting the ileocecal area of small intestines and adjacent lymph nodes. These tissues were successfully cultured in 2 of 3 variants of Middlebrook 7H10 medium. The identity of acid-fast organisms isolated from the tissues was confirmed as Map by multiplex conventional polymerase chain reaction. Using IS 1311 amplification and Hinf I restriction digest analysis, isolates were identified as cattle (C) strains of Map. The current study describes Map infection in Grenada and confirms the presence of C type in sheep on the island of Carriacou. The low seroprevalence in clinically normal animals on the islands of Grenada and Carriacou suggests that control measures implemented in the near future may have a good chance of preventing spread of the infection.

Paratuberculosis in captive and free-ranging wildlife

All ruminant species, exotic or domestic, captive or free-ranging, are susceptible to disease and death due to Mycobacterium avium subsp. paratuberculosis (MAP) infection. Young ruminants are the most prone to infection through fecal-oral transmission. Fatal Johne’s disease cases have occurred in numerous zoologic hoofstock collections and thus MAP infection is of concern for an industry focused on conserving rare individual animals and their genetics. Diagnosis is best based on MAP detection by PCR or culture in non-domestic species. True nonruminant wildlife reservoirs (ie, a population capable of sustaining the infection independently of reinfection from the initial source and transmitting the pathogen to other species) are rare.

Successful control of Johne's disease in nine dairy herds: results of a six-year field trial

The objective was to evaluate if a standardized Johne's disease control program significantly reduced the prevalence of cattle infected with Mycobacterium avium ssp. paratuberculosis in dairy herds with a moderate to high initial infection prevalence of >or=10% ELISA-positive adult cattle. Nine Wisconsin dairy herds of diverse sizes and management styles completed the 6-yr study. The control program involved changes to heifer rearing practices in combination with a routine testing program. For heifers, the program specifically required 1) segregated maternity pens for ELISA-positive and ELISA-negative cattle; 2) removal of calves from the maternity pen in <2h; 3) use of colostrum only from individual ELISA-negative cows (no colostrum pooling); 4) hygienic collection of colostrum; 5) feeding of pasteurized milk as milk replacer or on-farm pasteurized milk until weaning; and 6) minimizing contact with manure from the adult cattle until weaning. The testing program was designed to detect the most infectious cattle by using a commercial ELISA once on every adult during each lactation. Producers were required to cull cows with strong-positive ELISA results before the next calving and to label cows with low- to medium-level ELISA results and manage them to limit infection transmission. Outcomes were measured by comparing the apparent prevalence based on ELISA or fecal culture in the whole herd and in first-lactation cohorts at 2 time points: before implementation of the control program and at the end of the trial. The combined results from the 9 herds showed a significant reduction in ELISA-positive cows, from 11.6% at the start of the trial to 5.6% at conclusion of the trial. The apparent prevalence decline among first-lactation cows was greater and was evident by ELISA (10.4 vs. 3.0%) and by fecal culture (17.0 vs. 9.5%). Although variations among farms were observed, the collective results demonstrated that bovine paratuberculosis can be controlled in dairy herds through effective heifer husbandry practices in combination with diagnostic testing to identify, for culling or management, cows most likely infectious.

Identification of seroreactive proteins in the culture filtrate antigen of Mycobacterium avium ssp. paratuberculosis human isolates to sera from Crohn's disease patients

The etiology of Crohn's disease (CD) is unresolved, but it is likely that an interplay of host genetic factors and environmental triggers is relevant. Mycobacterium paratuberculosis (MAP) has been focused upon as one of these triggers because it causes a similar chronic inflammatory bowel disease in animals. However, the differences among MAP antigens isolated from humans (H-MAP) and cattle (B-MAP) have not been well characterized. In this study, culture filtrate (CF) proteins from MAP isolates were tested with sera from CD patients and healthy controls in enzyme-linked immunosorbent assay (ELISA). Antibody produced by seven CD patients reacted differently according to the antigen source: strong reactivity was seen to H-MAP CF, but not to B-MAP CF. Six proteins, ModD, PepA, transaldolase, EchA9, MAP2120c, and MAP2950c, in H-MAP CF reacting specifically with CD patient sera were identified by liquid chromatography-electrospray ionization-MS. Bioinformatic analysis revealed that ModD and PepA were the same proteins reacting with sera from cattle infected with MAP. The elevated antibody responses of CD patients to rModD and rPepA were confirmed by ELISA (P<0.001). These results support previous studies showing ModD and PepA as key antigens for the diagnosis of MAP infections. The study also identified additional proteins potentially useful in the design of assays for human MAP infections.

Effects of interactions of antibacterial drugs with each other and with 6-mercaptopurine on in vitro growth of Mycobacterium avium subspecies paratuberculosis

OBJECTIVES

Mycobacterium avium subspecies paratuberculosis (MAP) has been targeted for treatment with clarithromycin and rifamycin derivatives in numerous cases of Crohn's disease (CD). 6-Mercaptopurine and its pro-drug azathioprine are widely used as immunomodulators in the treatment of CD and have recently been shown to have anti-MAP activity in vitro. The objectives of the study were to evaluate the in vitro effects on MAP of (i) 6-mercaptopurine when combined with each of eight conventional antibacterial agents with in vitro anti-MAP activity and (ii) antibacterial combinations consisting of two drugs (clarithromycin combined with amikacin, rifampicin, ciprofloxacin or ethambutol) and three drugs (clarithromycin, rifabutin and clofazimine).

METHODS

The drug interaction effects on nine human isolates of MAP were determined by the chequerboard method adapted for the BACTECMGIT960 culture system and by calculation of the fractional inhibitory concentration index (FICI) for drug combinations.

RESULTS

Synergism (FICI < or = 0.5) was observed between 6-mercaptopurine and azithromycin (seven isolates), clarithromycin, rifampicin, rifabutin (four isolates each) and ethambutol (two isolates). 6-Mercaptopurine was not antagonistic with any of the antibacterial agents tested. Among the combinations of two and three antibacterials tested, the clarithromycin/rifampicin combination was synergistic against four isolates, while all other combinations showed no interaction.

CONCLUSIONS

This in vitro study suggests that 6-mercaptopurine may be synergistic with macrolides and rifamycin derivatives against MAP. The activity of clarithromycin against MAP seems to be enhanced by rifampicin.

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.

Mycobacterium avium subspecies paratuberculosis and Mycobacterium avium subsp. avium infections in a tule elk (Cervus elaphus nannodes) herd

Between 2 August and 22 September 2000, 37 hunter-killed tule elk (Cervus elaphus nannodes) were evaluated at the Grizzly Island Wildlife Area, California, USA, for evidence of paratuberculosis. Elk were examined post-mortem, and tissue and fecal samples were submitted for radiometric mycobacterial culture. Acid-fast isolates were identified by a multiplex polymerase chain reaction (PCR) that discriminates among members of the Mycobacterium avium complex (MAC). Histopathologic evaluations were completed, and animals were tested for antibodies using a Johne's enzyme-linked immunosorbent assay (ELISA) and agar gel immunodiffusion. In addition, 104 fecal samples from tule elk remaining in the herd were collected from the ground and submitted for radiometric mycobacterial culture. No gross lesions were detected in any of the hunter-killed animals. Mycobacterium avium subsp. paratuberculosis (MAP) was cultured once from ileocecal tissue of one adult elk and was determined to be a strain (A18) found commonly in infected cattle. One or more isolates of Mycobacterium avium subsp. avium (MAA) were isolated from tissues of five additional adult elk. Gastrointestinal tract and lymph node tissues from 17 of the 37 elk (46%) examined had histopathologic lesions commonly seen with mycobacterial infection; however, acid-fast bacteria were not observed. All MAC infections were detected from adult elk (P = 0.023). In adult elk, a statistically significant association was found between MAA infection and ELISA sample-to-positive ratio (S/P) > or = 0.25 (P=0.021); four of five MAA culture-positive elk tested positive by ELISA. Sensitivity and specificity of ELISA S/P > or = 0.25 for detection of MAA in adult elk were 50% and 93%, respectively. No significant associations were found between MAC infection and sex or histopathologic lesions. Bacteriologic culture confirmed infection with MAP and MAA in this asymptomatic tule elk herd. The Johne's ELISA was useful in signaling mycobacterial infection on a population basis but could not discriminate between MAA and MAP antibodies. The multiplex PCR was useful in discriminating among the closely related species belonging to MAC.

Association of fecal shedding of mycobacteria with high ELISA-determined seroprevalence for paratuberculosis in beef herds

OBJECTIVE

To evaluate the seroprevalence of paratuberculosis by use of 2 commercial ELISAs in association with prevalence of fecal shedding of mycobacteria within beef cattle herds.

DESIGN

Cross-sectional field study.

ANIMALS

Six beef herds (affected herds; 522 cattle) with and 3 geographically matched herds (181 cattle) without high seroprevalence of paratuberculosis.

PROCEDURES

Blood and fecal samples were collected from adult cattle and assessed for serum anti-Mycobacterium avium subsp paratuberculosis (MAP) antibodies with 2 commercial ELISA kits and submitted for bacterial culture for MAP and environmental bacteria (termed environmental mycobacteria) via a radiometric method, respectively. Species of mycobacterial isolates were identified, and sensitivities and specificities of the 2 ELISAs were compared.

RESULTS

Compared with comparison cattle, cattle from affected herds were 9.4 times as likely to have environmental mycobacteria isolated from feces. Among the 6 affected and 3 comparison herds, the proportions of cattle shedding environmental mycobacteria were 0.225 (range, 0.1 to 0.72) and 0.04 (range, 0 to 0.06), respectively. Although relative MAP- detection specificities (compared with bacterial culture of feces) were different between the 2 ELISAs, sensitivities were not. Nine environmental mycobacterial species were identified from participating herds. All affected herds apparently had > or = 1 bovid infected with MAP, although MAP was not isolated from any cattle in comparison herds.

CONCLUSIONS AND CLINICAL RELEVANCE

In beef herds with persistently high rates of false- positive ELISA results, which may be associated with recovery of environmental myco- bacteria from feces, organism detection via bacterial culture of feces or PCR assay should direct paratuberculosis control measures.

Rapid and reliable method for quantification of Mycobacterium paratuberculosis by use of the BACTEC MGIT 960 system

A simple method for the enumeration of viable Mycobacterium paratuberculosis cells was developed and evaluated using the MGIT 960 culture system. For each of 12 M. paratuberculosis strains isolated from either cattle or humans, single-cell suspensions of M. paratuberculosis cells were adjusted to an optical density at 600 nm of 1.00 (10(7.6) to 10(8.2) cells/ml), and serial dilutions were prepared. Standard curves were established by relating the MGIT time-to-detection data to the log10 CFU for these suspensions using standard plate counting and BACTEC 460 results as reference methods. Universal and strain-specific standard quantification curves were generated. A one-phase exponential decay equation best fit the universal standard curve and strain-specific curves (R2 of 0.96 and >0.99, respectively). Two subgroups within the universal curves were distinguished: one for laboratory-adapted strains and the other for recently isolated low-passage bovine strains. The predictive errors for log(10) estimations using the universal standard curve, each subgroup's standard curve, and strain-specific curves were +/-0.87, +/-0.45, and +/-0.31 log10 units, respectively. CFU estimations by all three standard curves were highly reproducible, regardless of the M. paratuberculosis strain or inoculum volume. In comparison with the previously described BACTEC 460 M. paratuberculosis counting method, quantification with MGIT 960 was less expensive, more rapid, more accurate, and more sensitive (<10 CFU). This MGIT counting method has broad applications for studies requiring the quantification of viable M. paratuberculosis cells, such as drug susceptibility testing or environmental survival studies.

Environmental mycobacteria in soil and water on beef ranches: association between presence of cultivable mycobacteria and soil and water physicochemical characteristics

Exposure to environmental mycobacteria has been reported to be a factor contributing to false-positive results on bovine serological tests detecting antibodies to Mycobacterium avium subsp. paratuberculosis (Mptb). This study was conducted to investigate the association between recovery of mycobacteria from the environment of cattle and both (i) historically high or low seroprevalence to Mptb, and (ii) soil and water physicochemical characteristics. Eighty-two samples (soil and water) from nine beef cattle ranches in South-central and South Texas were assessed for the presence of mycobacteria. Twelve mycobacterial species were cultured from soil and water from four herds; no Mptb were detected in environmental samples. A positive culture of environmental mycobacteria from soil was significantly associated with lower pH and calcium as well as higher iron, zinc and manganese contents. Beef cattle are likely to be exposed to environmental mycobacteria that may contribute to false-positive results on ELISAs for Mptb infection. Exposure rates to these mycobacteria likely vary across small geographical areas and may be related to soil and/or water physicochemistry.

Contribution of environmental mycobacteria to false-positive serum ELISA results for paratuberculosis

OBJECTIVE

To evaluate the effect of exposure to environmental mycobacteria on results of 2 commercial ELISAs for paratuberculosis in cattle.

DESIGN

Experimental trial.

ANIMALS

19 weaned crossbred beef calves.

PROCEDURES

Calves were inoculated SC with 1 of 5 mycobacterial isolates (3 calves/isolate) derived from herds with high proportions of false-positive serologic reactions for paratuberculosis, Mycobacterium avium subsp paratuberculosis (MAP; positive control inoculum; 2 calves), or mineral oil (negative control inoculum; 2 calves). Sera were assessed at intervals by use of 2 ELISAs (A and B) for paratuberculosis in cattle, and all calves underwent tuberculosis testing at the end of the study.

RESULTS

Neither mineral oil-inoculated calf had positive results with either ELISA during the study. Both MAP-inoculated calves were identified as seropositive via ELISA-A, and 1 calf was identified as seropositive via ELISA-B. By use of ELISA-A, > or = 1 false-positive reaction over time was detected in 2, 3, 3, and 1 of the 3 calves injected with Mycobacterium avium, Mycobacterium intracellulare, Mycobacterium scrofulaceum, or Mycobacterium terrae, respectively. By use of ELISA-B, only M scrofulaceum induced false-positive reactions (2/3 calves). Calves that had at least 1 positive ELISA-A result were more likely to be classified as suspect reactors via the caudal fold tuberculosis test.

CONCLUSIONS AND CLINICAL RELEVANCE

False-positive serologic reactions may occur during use of commercially available ELISAs for paratuberculosis in calves experimentally exposed to environmental mycobacteria; naturally occurring exposures with these mycobacteria may represent a cause for high proportions of false-positive serologic reactions for paratuberculosis in some cattle herds.

Invasion and persistence of Mycobacterium avium subsp. paratuberculosis during early stages of Johne's disease in calves

Infection with Mycobacterium avium subsp. paratuberculosis causes Johne's disease in cattle and is a serious problem for the dairy industry worldwide. Development of models to mimic aspects of Johne's disease remains an elusive goal because of the chronic nature of the disease. In this report, we describe a surgical approach employed to characterize the very early stages of infection of calves with M. avium subsp. paratuberculosis. To our surprise, strains of M. avium subsp. paratuberculosis were able to traverse the intestinal tissues within 1 h of infection in order to colonize distant organs, such as the liver and lymph nodes. Both the ileum and the mesenteric lymph nodes were persistently infected for months following intestinal deposition of M. avium subsp. paratuberculosis despite a lack of fecal shedding of mycobacteria. During the first 9 months of infection, humoral immune responses were not detected. Nonetheless, using flow cytometric analysis, we detected a significant change in the cells participating in the inflammatory responses of infected calves compared to cells in a control animal. Additionally, the levels of cytokines detected in both the ileum and the lymph nodes indicated that there were TH1-type-associated cellular responses but not TH2-type-associated humoral responses. Finally, surgical inoculation of a wild-type strain and a mutant M. avium subsp. paratuberculosis strain (with an inactivated gcpE gene) demonstrated the ability of the model which we developed to differentiate between the wild-type strain and a mutant strain of M. avium subsp. paratuberculosis deficient in tissue colonization and invasion. Overall, novel insights into the early stages of Johne's disease were obtained, and a practical model of mycobacterial invasiveness was developed. A similar approach can be used for other enteric bacteria.

Isolation of Mycobacterium avium subsp. paratuberculosis from free-ranging birds and mammals on livestock premises

Surveys for Mycobacterium avium subsp. paratuberculosis infection in free-ranging mammals and birds were conducted on nine dairy and beef cattle farms in Wisconsin and Georgia. Specimens were collected from 774 animals representing 25 mammalian and 22 avian species. Specimens of ileum, liver, intestinal lymph nodes, and feces were harvested from the larger mammals; a liver specimen and the gastrointestinal tract were harvested from birds and small mammals. Cultures were performed by using radiometric culture and acid-fast isolates were identified by 16S/IS900/IS1311 PCR and mycobactin dependency characteristics. M. avium subsp. paratuberculosis was cultured from tissues and feces from 39 samples from 30 animals representing nine mammalian and three avian species. The prevalence of infected wild animals by premises ranged from 2.7 to 8.3% in Wisconsin and from 0 to 6.0% in Georgia. Shedding was documented in seven (0.9%) animals: three raccoons, two armadillos, one opossum, and one feral cat. The use of two highly polymorphic short sequence repeat loci for analysis of 29 of the 39 strains identified 10 alleles. One allelic pattern broadly shared in domestic ruminants ("7,5") appeared in approximately one-third of the wildlife M. avium subsp. paratuberculosis isolates studied. Given the few cases of shedding by free-ranging animals compared to the volume of contaminated manure produced by infected domestic ruminant livestock, contamination of the farm environment by infected wildlife was negligible. Wildlife may, however, have epidemiological significance for farms where M. avium subsp. paratuberculosis recently has been eliminated or on farms free of M. avium subsp. paratuberculosis but located in the geographic vicinity of farms with infected livestock.

Culture and serologic survey for Mycobacterium avium subsp. paratuberculosis infection among southeastern white-tailed deer (Odocoileus virginianus)

From July 1998 through October 2002, radiometric culture (ileocecal lymph node, mesenteric lymph node, and feces) and serologic testing by enzyme-linked immunosorbent assay (ELISA) were used to survey white-tailed deer (Odocoilens virgianus) from the soutlheastern United States for infection by Mycobacterium avium subsp. paratuberculosis (Mptb), the causative agent of paratuberculosis (Johne's disease). Mycobacterium avium subsp. paratuberculosis was isolated from the ileocecal lymph node of one of 313 deer (0.3%) originating from 63 populations in Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, South Carolina, Tennessee, and West Virginia (USA). Six deer (2%), all from different populations, had ELISA results above a 0.25 sample-to-positive cutoff value, but none of the ELISA reactors originated from the population from which the single Mptb isolation was made. These six deer were seronegative when tested by agar gel immunodiffusion (AGID). Collectively, these data indicate that white-tailed deer currently do not constitute a broad regional reservoir for Mptb; however, further study is warranted to clarify the significance, if any, of infected deer to the epizootiology of paratuberculosis on a local scale. Adaptation and validation of an ELISA or another serologic assay for use with deer and other wildlife would markedly enhance Mptb surveillanece among wild populations and would be a powerful tool for gaining information on the role of wild species in epidemiology of paratuberculosis.

Mycobacterium avium subsp. paratuberculosis strains isolated from Crohn's disease patients and animal species exhibit similar polymorphic locus patterns

Analysis of short sequence repeats of Mycobacterium avium subsp. paratuberculosis isolated from Crohn's disease patients identified two alleles, both of which clustered with strains derived from animals with Johne's disease. Identification of a limited number of genotypes among human strains implies the existence of human disease-associated genotypes and strain sharing with animals.

Molecular epidemiology of Mycobacterium avium subsp. paratuberculosis isolates recovered from wild animal species

Mycobacterial isolates were obtained by radiometric culture from 33 different species of captive or free-ranging animals (n = 106) and environmental sources (n = 3) from six geographic zones within the United States. The identities of all 109 isolates were confirmed by using mycobactin J dependence and characterization of five well-defined molecular markers, including two integration loci of IS900 (loci L1 and L9), one Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis)-specific sequence (locus 251), and one M. avium subsp. avium-specific marker (IS1245), as well as hsp65 and IS1311 restriction endonuclease analyses. Seventy-six acid-fast isolates were identified as M. paratuberculosis, 15 were identified as belonging to the M. avium-M. intracellulare complex (but not M. paratuberculosis), and the remaining 18 were identified as mycobacteria outside the M. avium-M. intracellulare complex. Fingerprinting by multiplex PCR for IS900 integration loci clustered 67 of the 76 M. paratuberculosis strains into a single clade (designated clade A18) and had a Simpson's diversity index (D) of 0.53. In contrast, sequence-based characterization of a recently identified M. paratuberculosis short sequence repeat (SSR) region enabled the differentiation of the M. paratuberculosis isolates in clade A18 into seven distinct alleles (D = 0.75). The analysis revealed eight subtypes among the 33 species of animals, suggesting the interspecies transmission of specific strains. Taken together, the results of our analyses demonstrate that SSR analysis enables the genetic characterization of M. paratuberculosis isolates from different host species and provide evidence for the host specificity of some M. paratuberculosis strains as well as sharing of strains between wild and domesticated animal species.

Diagnostic testing patterns of natural Mycobacterium paratuberculosis infection in pygmy goats

Thirteen pygmy goats (Capra hircus) from a herd naturally infected with Mycobacterium avium ss. paratuberculosis (MPTB) were monitored with 4 diagnostic assays for 2 to 15 mo. Cellular and humoral immune responses to the infection were assessed with assays of gamma interferon (IFNgamma), serum antibody [enzyme-linked immunosorbent assay (ELISA) and agar gel diffusion (AGID)], and radiometric fecal culture. Microscopic examination and radiometric culture of tissue from 12 sites were performed at necropsy. Goats were considered infected if MPTB was isolated from any tissue sample collected at necropsy. Mycobacterial isolates were confirmed as MPTB with an IS900 polymerase chain reaction assay. Ten goats whose antemortem tests indicated infection carried heavy organism burdens at necropsy, both within and beyond the gastrointestinal system. False-negative ELISA, AGID, and/or culture results were obtained in 5 of the 10 confirmed cases during the study period. In 3 goats with sporadic fecal shedding of MPTB or detectable IFNgamma response, or both, no abnormalities were detected at necropsy and no MPTB was isolated from the tissue samples; the antemortem fecal-culture and IFNgamma results were thus considered false-positive. Diagnosticians should be alert to the possibility of both false-positive and false-negative test results for Johne's disease in goats. False-positive fecal-culture results may occur when a high prevalence of infection exists in the herd and the premises are likely to be heavily contaminated. The diverse antemortem testing patterns seen in these goats underscore the importance of using varied diagnostic assays serially or in parallel to increase the likelihood of identifying all infected goats.

Protein G binding to enriched serum immunoglobulin from nondomestic hoofstock species

Quick and cost-effective serologic assays, such as those based on enzyme-linked immunosorbent assay (ELISA) technology, are useful for screening animal populations for infectious diseases. Recombinant protein G is described as an almost universal ELISA conjugate for the detection of antibodies from a wide range of animal species. However, there is limited data documenting the ability of protein G to bind immunoglobulin (Ig) from many captive and free-ranging nondomestic hoofstock (Order Artiodactyla, e.g., elk, antelope, bison). Protein G binding to Ig from 11 species within this taxonomic order (addax, antelope, bison, bontebok, elk, impala, kudu/nyala, muntjac, oryx, sheep, and white-tailed deer) and 2 control species (bovine and chicken) was assessed. A serum Ig enrichment protocol, using high-performance liquid chromatography (HPLC), was optimized in bovids (Bos taurus) and then applied to the other study species. Binding assays were performed by adding protein G to microtiter wells coated with titrated dilutions of enriched artiodactyl Ig. Optical densities were measured and binding curves generated. Differences in protein G binding were observed, both within and among species, as well as within taxonomic families. Significant intraspecies binding variation was observed for 7 species tested (antelope, oryx, sheep, muntjac, impala, bontebok, and addax). No statistically significant intraspecies differences in protein G binding were found for Ig from bison, elk, kudu/nyala, white-tailed deer, plus control species (cattle and chicken). Binding of protein G to Ig from impala, muntjac, and elk was statistically different from the positive control (cattle), with muntjac binding curves statistically comparable with the negative control (chicken). For the other 7 species tested, binding curves illustrated the ability of protein G to bind Ig as well as, or better than, the positive control. These findings expand the list of animal species whose Ig is capable of being detected using recombinant protein G, with the caveat that protein G does not bind Ig uniformly in closely related species. It is concluded that recombinant protein G conjugates may serve as useful reagents for serodiagnosis by ELISA in nondomestic hoofstock, although different assay interpretation algorithms and assay protocols may need to be developed on a per species basis for maximum diagnostic effectiveness.

Paratuberculosis in key deer (Odocoileus virginianus clavium)

Paratuberculosis was diagnosed in an endangered Key deer (Odocoileus virginianus clavium) in November 1996. Between 10 April 1997 and 28 September 2000, the Key deer population was monitored for infection with Mycobacterium avium subsp. paratuberculosis by necropsy of available carcasses (n = 170), fecal cultures, and serology. One additional clinically affected Key deer was discovered in July 1998, and M. avium subsp. paratuberculosis was cultured from the feces of one live, asymptomatic deer. The results of this study provided sufficient evidence to consider the Key deer herd infected with M. avium subsp. paratuberculosis at very low prevalence.