Intestinal multiplication of Mycobacterium paratuberculosis in athymic nude gnotobiotic mice

Sheep challenged with sheep-derived type II Mycobacterium avium subsp. paratuberculosis: the first experimental model of paratuberculosis in China

BACKGROUND

Paratuberculosis (PTB), caused by Mycobacterium avium subsp. paratuberculosis (MAP), is difficult to diagnose in the early stages and poses substantial challenges in prevention, control, treatment, and eradication. A well-defined animal model can help identify disease markers and serve as a platform for vaccine and drug development. This study used sheep as a ruminant model for experimental MAP infection research.

METHODS

Nine 3-month-old lambs with negative MAP antigen and antibody were divided into three groups (control group A and inoculated groups B and C). The inoculated groups were challenged with sheep-derived type II MAP. After exposure, we recorded clinical signs, assessed fecal shedding, tested blood MAP levels, and performed fecal cultures. We also measured MAP-specific antibodies and monitored IFN-γ and IL-10 responses in vivo. At 255 days after inoculation, we performed autopsy, tissue culture, pathomorphological observation, and bacterial organ burden (BOB) testing.

RESULTS

All six sheep in groups B and C were infected, regardless of the challenge dose and exhibited emaciation; two had intermittent soft stools. Intermittent MAP shedding in feces was observed from 60 to 255 days after exposure. Typical MAP colonies formed after 4-6 weeks of fecal and tissue culture, and Ziehl-Neelsen staining showed positive results. In the groups challenged with MAP, some blood samples tested positive for MAP and MAP-specific antibodies were detected in some serum samples. IFN-γ response was significantly higher in groups B and C than that in group A from day 60 post-exposure, whereas the IL-10 response was higher than that in group A from day 120 post-exposure. In the infected groups, the ileal lesions were the most severe and were classified as grade 3 PTB granulomatous inflammation (multibacillary lesions). BOB levels varied across different tissues.

CONCLUSIONS

To the best of our knowledge, this is the first experimental MAP challenge study on sheep in China. Polymerase chain reaction detection was more sensitive than MAP culture, whereas enzyme-linked immunosorbent assay was less sensitive for detecting MAP-specific antibodies. IFN-γ and IL-10 responses may serve as targets for monitoring PTB progression. The severity of ileal lesions and acid-fast bacilli grading play crucial roles in the understanding of infection dynamics. Currently, early PTB diagnosis requires a combination of multiple sample types and detection methods.

Development of an Interspecies Nested Dose-Response Model for Mycobacterium avium subspecies paratuberculosis

Mycobacterium avium subspecies paratuberculosis (MAP) causes chronic inflammation of the intestines in humans, ruminants, and other species. It is the causative agent of Johne's disease in cattle, and has been implicated as the causative agent of Crohn's disease in humans. To date, no quantitative microbial risk assessment (QMRA) for MAP utilizing a dose-response function exists. The objective of this study is to develop a nested dose-response model for infection from oral exposure to MAP utilizing data from the peer-reviewed literature. Four studies amenable to dose-response modeling were identified in the literature search and optimized to the one-parameter exponential or two-parameter beta-Poisson dose-response models. A nesting analysis was performed on all permutations of the candidate data sets to determine the acceptability of pooling data sets across host species. Three of four data sets exhibited goodness of fit to at least one model. All three data sets exhibited good fit to the beta-Poisson model, and one data set exhibited goodness of fit, and best fit, to the exponential model. Two data sets were successfully nested using the beta-Poisson model with parameters α = 0.0978 and N50 = 2.70 × 10(2) CFU. These data sets were derived from sheep and red deer host species, indicating successful interspecies nesting, and demonstrate the highly infective nature of MAP. The nested dose-response model described should be used for future QMRA research regarding oral exposure to MAP.

What Role Does Mycobacterium avium subsp. paratuberculosis Play in Crohn's Disease?

Crohn's disease (CD) is a chronic, debilitating inflammatory bowel disease with no etiological agent yet identified. Studies have demonstrated that the bacterium Mycobacterium avium subsp. paratuberculosis (MAP) is present in a high percentage of CD patients. Although MAP has been isolated from human specimens, current techniques fail to show the presence of MAP in 100 % of tissues or biopsies obtained from CD patient lesions, and thus MAP cannot meet Koch's postulate as the etiological agent of CD. In this report, the effect of genetic and immune factors as well as the presence of MAP as a potential environmental factor is analyzed.

Persistent enteric mycobacterial infection enhances sensitivity to acute mucosal injury

Antigen presenting cells such as intestinal macrophages are dynamic effector cells that play a critical role in maintaining mucosal homeostasis. However, it is not known how occult intestinal infections alter the response of the intestinal mucosa to subsequent intestinal injury. The aim of this study was to evaluate how persistent subclinical intestinal infection with Mycobacterium avium subsp. paratuberculosis ( Map) would influence acute dextran sulfate sodium (DSS)-mediated intestinal inflammation. BALB/c mice were infected intraperitoneally with Map. Following an incubation period of 90 d, mice were administered 2% DSS in the drinking water for six days. Prior to and during treatment with DSS, mice were evaluated for clinical signs of disease and body weights were recorded. At termination of the experiment, body weights, frequency of rectal blood, and gross and histological cecal lesions were evaluated, and tissues were collected for isolation of Map. Subclinical and persistent intestinal Map infection was established based on the absence of both weight loss and rectal blood and the isolation of Map from the small and large intestines in mice infected with Map only. Following treatment with DSS, Map-infected mice had increased weight loss, increased frequency of rectal blood, and exacerbation of gross lesions and increased cecal lesion scores. Also, there was a significant reduction in Map isolated from the small intestines of Map-infected and DSS-treated mice. In conclusion, subclinical Map infection sensitizes the host to enhanced acute DSS-mediated intestinal inflammation.

Peyer's patch-deficient mice demonstrate that Mycobacterium avium subsp. paratuberculosis translocates across the mucosal barrier via both M cells and enterocytes but has inefficient dissemination

Mycobacterium avium subsp. paratuberculosis, the agent of Johne's disease, infects ruminant hosts by translocation through the intestinal mucosa. A number of studies have suggested that M. avium subsp. paratuberculosis interacts with M cells in the Peyer's patches of the small intestine. The invasion of the intestinal mucosa by M. avium subsp. paratuberculosis and Mycobacterium avium subsp. hominissuis, a pathogen known to interact with intestinal cells, was compared. M. avium subsp. paratuberculosis was capable of invading the mucosa, but it was significantly less efficient at dissemination than M. avium subsp. hominissuis. B-cell knockout (KO) mice, which lack Peyer's patches, were used to demonstrate that M. avium subsp. paratuberculosis enters the intestinal mucosa through enterocytes in the absence of M cells. In addition, the results indicated that M. avium subsp. paratuberculosis had equal abilities to cross the mucosa in both Peyer's patch and non-Peyer's patch segments of normal mice. M. avium subsp. paratuberculosis was also shown to interact with epithelial cells by an alpha(5)beta(1) integrin-independent pathway. Upon translocation, dendritic cells ingest M. avium subsp. paratuberculosis, but this process does not lead to efficient dissemination of the infection. In summary, M. avium subsp. paratuberculosis interacts with the intestinal mucosa by crossing both Peyer's patches and non-Peyer's patch areas but does not translocate or disseminate efficiently.

Experimental animal infection models for Johne’s disease, an infectious enteropathy caused by Mycobacterium avium subsp. paratuberculosis

A critical literature review of experimental infection models for Johne's disease in farm and laboratory animals was conducted. A total of 73 references were admitted. They were published between 1938 and 2006 and covered species as diverse as cattle, sheep, goats, deer, mice, pigs and others. The factors that appeared to influence the outcome of experimental infections with Mycobacterium avium subsp. paratuberculosis (Mptb) were the species, breed and age of subject used for the infection, the route of infection, and the strain, dose and number of doses of Mptb used to inoculate the subjects. Natural paratuberculosis infection passes through stages, generally over a period measured in years. However, the endpoints chosen by researchers using experimental infections have been determined by the need for immunological, microbiological, pathological or clinical outcomes, and these were the likely factors determining the duration of the trials. Studies have been lacking in the use of a defined type strain of Mptb in pure culture prepared from an archived seed stock of Mptb that can be used at the same passage level in a later trial. Replication of experimental groups has been very uncommon, temporal replication equally rare, as have sufficiently long time scales so as to be able to observe a full range of immunological and pathological changes at different stages of the disease process. While it may be difficult to develop a satisfactory experimental infection model, there is room for improvement in the way experiments have been designed and carried out to date. Choice of animal species/breed of host and strain of Mptb used in an experimental model should be based on the purpose of the study (for example, vaccine efficacy trial, diagnostic test evaluation, pathogenesis study) and local needs. The strain of Mptb used should be typed using IS900 RFLP analysis, IS1311 sequence analysis and other genotypic methods, and preferably be from an archived low passage pure culture with viable bacteria enumerated using a sensitive method rather than from an uncharacterised and unrepeatable tissue homogenate. It is generally agreed that the faecal-oral route is the most important natural route of exposure and the oral route is therefore the preferred route of experimental inoculation to achieve Johne's disease that closely resembles natural infection.

Vaccination of sheep against M. paratuberculosis: immune parameters and protective efficacy

Johne's disease in ruminants is caused by the pathogenic bacterium Mycobacterium avium subspecies paratuberculosis (Map). Currently available Map commercial vaccines protect against clinical disease but not infection. In this study, the proprietary Johne's vaccine Neoparasec and an aqueous formulation of Map 316F (AquaVax) were tested in sheep. Detailed immunological examination of blood and gut-associated lymphoid tissues was carried out on animals after vaccination and challenge with virulent Map to identify markers of protective immunity. Neoparasec vaccination provided significant protection against disease while AquaVax did not. Immune animals had stronger cell-mediated responses and altered proportions of CD4+, CD8+, CD25+ and B cells in blood, spleen and the gut lymphatics, than diseased animals.

Development of a Johne's disease infection model in laboratory rabbits following oral administration of Mycobacterium avium subspecies paratuberculosis

To assess the rabbit as a model for the study of Johne's disease pathogenesis, a breeding group of adult and juvenile New Zealand white rabbits were orally challenged with three doses of the Mycobacterium avium subspecies paratuberculosis wildtype bovine strain, CLIJ623, on three occasions. Faecal culture, post-mortem tissue bacteriological culture and histopathology were used to monitor the disease progression in the rabbits for more than 2 years. Of 4 adult and 16 juvenile orally dosed rabbits M. paratuberculosis organisms were recovered bacteriologically from two and three animals, respectively, using the BACTECtrade mark radiometric culture system. Tissue sites from which the bacteria were recovered included the mesenteric lymph nodes, ileocaecal valve, vermiform appendix, caecum, proximal colon and jejunum. Body weight loss, reduced abdominal fat and mild lesions were observed at necropsy in four infected rabbits. Diarrhoea and persistent faecal shedding of bacteria were not observed. Faecal culture did not yield any cultivable mycobacterial organisms on solid media.

Johne's disease, inflammatory bowel disease, and Mycobacterium paratuberculosis

Johne's disease is a chronic diarrhea affecting all ruminants. Mycobacterium avium subsp. paratuberculosis (MAP), a slowly growing mycobacteria, is the etiologic agent. There is also a concern that MAP might be a causative agent of some cases of inflammatory bowel disease in humans, especially Crohn's disease. Food products including pasteurized bovine milk have been suggested as potential sources of human infection. This review addresses microbial factors that may contribute to its pathogenicity. In addition, the experimental evidence defining MAP as the cause of Johne's disease and the issues and controversies surrounding its potential pathogenic role in humans are discussed.

Paratuberculosis in a mandrill (Papio sphinx)

A 2.5-year-old captive female mandrill (Papio sphinx) died following a protracted course of intermittent abdominal bloat, diarrhea, and severe weight loss. Necropsy revealed emaciation and marked gastrointestinal distention with gas and ingesta. Histologic evaluation revealed severe diffuse granulomatous enterocolitis and mesenteric lymphadenitis with massive numbers of 1-2-microm acid-fast bacilli within macrophages. Additionally, there was moderate to severe multifocal myocardial and vascular amyloidosis, moderate multifocal pyogranulomatous interstitial pneumonia with no acid-fast bacteria, and moderate multifocal glossal candidiasis. Samples of feces, ileum, and colon were positive for Mycobacterium avium subsp. paratuberculosis by radiometric culture and a polymerase chain reaction-amplified DNA probe specific for the insertion sequence IS900 of this organism.

T cell-dependent inducible nitric oxide synthase production and ultrastructural morphology in BALB/c mice infected with Mycobacterium avium subspecies paratuberculosis

Euthymic BALB/c and athymic nude BALB/c mice aged 3-8 days were infected intraperitoneally with Mycobacterium avium subspecies paratuberculosis (ATCC strain 19698). After euthanasia at 5 months post-inoculation, hepatic granulomas were evaluated by morphometric analysis of digital images captured from light microscopy sections, by electron microscopy and by immunohistochemical methods. Euthymic mice differed from athymic mice in that (1) their hepatic granulomas were smaller, contained fewer bacteria, and produced more inducible nitric oxide synthase, and (2) their hepatic macrophages contained fewer bacteria, a higher percentage of degraded bacteria, and increased numbers of primary lysosomes. The study showed that macrophage activation was markedly less in the T cell-deficient athymic mice than in the euthymic mice.

Mycobacterium avium subsp. paratuberculosis in Veterinary Medicine

Mycobacterium avium subsp. paratuberculosis (basonym M. paratuberculosis) is the etiologic agent of a severe gastroenteritis in ruminants known as Johne's disease. Economic losses to the cattle industry in the United States are staggering, reaching $1.5 billion annually. A potential pathogenic role in humans in the etiology of Crohn's disease is under investigation. In this article, we review the epidemiology, pathogenesis, diagnostics, and disease control measures of this important veterinary pathogen. We emphasize molecular genetic aspects including the description of markers used for strain identification, diagnostics, and phylogenetic analysis. Recent important advances in the development of animal models and genetic systems to study M. paratuberculosis virulence determinants are also discussed. We conclude with proposals for the applications of these models and recombinant technology to the development of diagnostic, control, and therapeutic measures.

A study of immunological responses of sheep clinically-affected with paratuberculosis (Johne's disease). The relationship of blood, mesenteric lymph node and intestinal lymphocyte responses to gross and microscopic pathology

Nineteen adult sheep diagnosed as having clinical paratuberculosis (Johne's disease) and 16 unaffected controls were examined in this study. Animals were tested for the presence of circulating antibodies of Mycobacterium avium ssp. paratuberculosis (M. a. paratuberculosis) and lymphocytes derived from the blood, mesenteric lymph nodes and intestines were examined for cell-mediated immune (CMI) responses to Johnin pure protein derivative (Johnin-PPD: J-PPD). Bacteriological examinations were carried out on faeces and tissues and any mycobacterial isolates identified as M. a. paratuberculosis (IS900+) or M. avium ssp. silvaticum (M. a. silvaticum) (IS901+) by polymerase chain reaction (PCR). Full necropsy and histopathological studies were performed and diseased animals were categorised on the basis of having a lepromatous or tuberculoid form of intestinal pathology. Unaffected control sheep were generally antibody-negative and demonstrated varying CMI responses to J-PPD. Clinically-affected animals were almost always antibody-positive with variable CMI responses. A correlation was observed between the histological lesion type in the intestine and the cellular immune response. Tuberculoid-type lesions were associated with strong CMI responses in lymphocytes derived from the peripheral blood, mesenteric lymph node and intestine, whereas lepromatous-type lesions were associated with weak CMI responses in all tissues examined.

Histopathology of C57BL/6 mice inoculated orally with Mycobacterium paratuberculosis

The susceptibility of C57BL/6 mice to oral inoculation with Myobacterium paratuberculosis was evaluated histopathologically. Granulomatous lesions containing acid-fast bacteria developed in the mesenteric lymph nodes in over 50% of the mice by 11 months after inoculation. The results suggest that C57BL/6 mice may be useful for studying infection, pathogenesis, and other aspects of paratuberculosis.

Paratuberculosis

Paratuberculosis (Johne's disease) is a chronic, wasting, widespread mycobacteriosis of ruminants. It involves extensive mycobacterial shedding, which accounts for the high contagiousness, and ends with a fatal enteritis. Decreases in weight, milk production, and fertility produce severe economic loss. The DNA of the etiological agent (Mycobacterium paratuberculosis) has a base composition (66 to 67% G+C) within the range of that of mycobacteria (62 to 70% G+C), a size (4.4 x 10(6) to 4.7 x 10(6) bp) larger than that of most pathogenic mycobacteria (2.0 x 10(6) to 4.2 x 10(6) bp), and a high relatedness (> 90%) to Mycobacterium avium DNA. However, the DNAs of the two organisms can be distinguished by restriction fragment length polymorphism analysis. M. paratuberculosis genes coding for a transposase, a cell wall-associated protein (P34), and two heat shock proteins have been cloned and sequenced. Nucleic acid probes (two of which are species specific) are used, after PCR amplification, for M. paratuberculosis identification in stools and milk. As in leprosy, with disease progression, cellular immune reactions decrease and humoral immune reactions increase. Cutaneous testing with sensitins, lymphocyte proliferation assays, and cytokine tests are used to monitor cellular immune reactions in paratuberculosis, but these tests lack specificity. Complement fixation, immunodiffusion, and enzymometric tests based on antibodies to M. paratuberculosis extracts, to mycobacterial antigen complex A36, to glycolipids, and to proteins help identify affected cattle but are not species specific. The carboxyl-terminal portion of the 34-kDa cell wall-associated A36 protein (P34) carries species-specific B-cell epitopes and is the basis for an enzyme-linked immunosorbent assay. Diagnostic tests for paratuberculosis are also used in Crohn's disease, a chronic human ileitis mimicking Johne's disease, in which isolates identified as M. paratuberculosis have been found.

Susceptibility of Balb/c, C57/B6 and C57/B10 mice to infection with Mycobacterium paratuberculosis

Balb/C, C57/B10 and C57/B6 mice were examined for their susceptibility to disseminated Mycobacterium paratuberculosis infection after intraperitoneal inoculation with a suspension of organisms containing mineral oil. Animals were examined monthly by histopathology and bacterial tissue counts of liver and spleen over a 6-month period. Only Balb/c mice maintained a steady infection with an average of 4.1 x 10(5) +/- 7.8 x 10(3) and 8.1 x 10(5) +/- 2.6 x 10(4) colony forming units (cfu) per gram of liver and spleen, respectively, during the course of the study. In contrast, C57/B10 mice reduced the bacterial counts in the liver and spleen from 6.8 x 10(4) and 1.3 x 10(5) to 7.1 x 10(2) and 4.3 x 10(3), respectively during the first 120-150 days after infection. The reduction in cfu was associated with the development of caseous necrotic lesions. C57/B10 mice were of intermediate resistance, slowly reducing cfu in the liver, but not the spleen, during the 6-month period. Balb/c was found to be a suitable mouse strain for the study of chronic M. paratuberculosis infection.

Effects of administration of anti-CD4 and anti-CD8 monoclonal antibodies on Mycobacterium paratuberculosis infection in intragastrically challenged mice

In this study, we examined the roles of CD4+ and CD8+ cells in resistance to experimental paratuberculosis. Mice received purified anti-CD4 or anti-CD8 monoclonal antibodies before intragastric challenge with Mycobacterium paratuberculosis and on a biweekly basis for six months. This resulted in sustained depletion of CD4+ and CD8+ cells as verified by flow cytometry analysis of spleen cells from M. paratuberculosis infected mice. Depletion of CD4+ or CD8+ cells did not enhance fecal shedding of M. paratuberculosis, bacillary multiplication in the liver and ceca, nor histopathologic damage to the intestinal tract, mesenteric lymph nodes, spleen and liver. These data suggest that cells other than CD4+ or CD8+ cells are important for host defense in experimental paratuberculosis.

Dissemination of enteric Mycobacterium avium infections in mice rendered immunodeficient by thymectomy and CD4 depletion or by prior infection with murine AIDS retroviruses

This study shows that infection of mice with the murine AIDS virus LP-BM5 or Du5H profoundly depressed the capacity of splenic T cells from these animals to respond to the T-cell mitogen phytohemagglutinin or concanavalin A or to alloantigens. Similar effects were also observed if mice were thymectomized and then infused with monoclonal anti-CD4 antibody (TxCD4- mice). When such mice were infected intravenously with Mycobacterium avium, growth of the infection was markedly exacerbated in the TxCD4- mice or in mice given murine AIDS virus 2 months earlier. In view of these data, we then investigated whether such treatments might cause dissemination of M. avium following enteric implantation of bacteria into the mouse cecum; this route was chosen in an attempt to model events in AIDS patients, in which the gut appears to be one of the major portals of M. avium infection. In this model, the entry and hematogenous dissemination of four clinical isolates of M. avium were monitored against time and found to be accelerated and enhanced in T-cell-deficient mice. In view of this finding, these novel approaches for enteric infection that use immunodeficient mice are presented as potential new models for the evaluation of immunotherapy and chemotherapy in a setting that bears some similarity to events believed to occur in AIDS patients.

Experimental infection of severe combined immunodeficient beige mice with Mycobacterium paratuberculosis of bovine origin

Severe combined immunodeficient beige mice were inoculated orally and intraperitoneally with a bovine strain of Mycobacterium paratuberculosis to explore their potential as laboratory animal models in the study of paratuberculosis (Johne's disease). Control animals were similarly inoculated with heat-killed M. paratuberculosis. In the mice inoculated intraperitoneally, focal lesions and acid-fast bacilli were first detected in the livers (4 weeks postinfection) and later in the spleens and intestines of the test but not the control animals. No bacteria were seen in the hearts, kidneys, or lungs. At 12 weeks postinfection, all test mice had significant losses in body weight compared with those in controls (P less than 0.05), a characteristic sign of bovine paratuberculosis. Tumor necrosis factor alpha was not detected in the serum. Histologic lesions were seen in the intestines, livers, and spleens of the animals in the orally inoculated test group after 26 weeks of infection. Our results suggest that the severe combined immunodeficient beige mouse may be a useful model for the investigation of paratuberculosis and cachexia and the evaluation of antimycobacterial drugs.

Distinctive western blot antibody patterns induced by infection of mice with individual strains of the Mycobacterium avium complex

Systemic infection of mice with organisms of the Mycobacterium avium complex (MAC) induced antibody responses, characteristic for each of the three tested individual strains. The influence of host genetic factors was reflected up to 3 months after infection by the finding of generally oligobanded and multibanded Western blot patterns in C57B1/6 and BALB/c mice, respectively. Nevertheless, more bands developed at 6 months in C57BL/6 mice. The response to three antigens of 18,000, 38,000 and 24,000 MW was analysed in greater detail. Antibodies to a protease-resistant 18,000 MW band produced only by BALB/c mice were either strain specific, following infection with M. avium, strain Maa-B2, or cross-reactive within MAC, following infection with M. avium strain Maa-A6 and M. paratuberculosis, strain Map-203. Another protease-resistant antigen of 38,000 MW was immunogenic only in Maa-B2 infected mice. This constituent was found to be related to the protease-sensitive antigen of corresponding molecular weight from M. tuberculosis. Two 24,000 MW proteins of M. paratuberculosis were separated by two-dimensional gel electrophoresis: antibodies to the anodic band were induced by Map-203 infection, whilst the cathodic band was revealed by heteroclitic antibodies from Maa-B2-infected mice. The latter antigen is apparently expressed during in vivo replication, but not during in vitro culture of Maa-B2 bacteria. We generally conclude, that the selective antibody patterns after live infection, could be attributed to differences in the release of native antigens within mycobacterial lesions. In view of a high degree of species specificity, some of the immunogenic constituents identified may also be useful for serodiagnostic application.

Effects of mycobactin J and lactoferrin supplementation of drinking water on the in vivo multiplication of Mycobacterium paratuberculosis in gnotobiotic mice

In this study the effect of supplementation of drinking water with mycobactin J or lactoferrin on the multiplication of Mycobacterium paratuberculosis in gnotobiotic mice was investigated. The results indicated that neither mycobactin J nor lactoferrin, at the doses used, appeared to have any effect on fecal shedding or tissue burdens of M. paratuberculosis.

Mycobacterium paratuberculosis monoassociated nude mice as a paratuberculosis model

In this study, a paratuberculosis (Johne's disease) model was developed by intragastrically dosing gnotobiotic athymic nude mice with Mycobacterium paratuberculosis. The mice infrequently shed bacilli from their intestinal tracts during the first 4 months after inoculation. Following this time, increasing numbers of M. paratuberculosis (greater than 4.0 log10 bacilli per fecal pellet by 40 weeks) were recovered from the feces of the 12 mice that remained in the isolator. A similar pattern of recovery of M. paratuberculosis was obtained from the ileum, cecum, colon, and liver. Histopathologic lesions and acid-fast bacilli were rare during the first 4 months of infection and then, with time, increased in prevalence and severity. Mice maintained for 7 months or longer exhibited severe granulomatous inflammation and large numbers of acid-fast bacilli in the gastrointestinal tract and liver (up to 10(8) log10 colony forming units per gram wet weight). Five mice maintained for 7 months or more developed clinical signs consistent with those seen in paratuberculosis (weight loss, chronic diarrhea); three of these mice eventually died or became moribund and were euthanatized. M. paratuberculosis monoassociated mice released increased levels of tumor necrosis factor activity into their sera, as compared to uninfected control mice, when they were injected with bacterial lipopolysaccharide. The clinical signs, fecal shedding of M. paratuberculosis, granuloma formation, and progressive bacillary multiplication observed with these mice are consistent with naturally occurring M. paratuberculosis infection of ruminants (Johne's disease). This model will be useful for future studies of immunoregulation and antimicrobial therapy of paratuberculosis.

Cyclophosphamide and prednisolone exacerbate the severity of intestinal paratuberculosis in Mycobacterium paratuberculosis monoassociated mice

In this study we examined the effects of continuous oral administration of the immunosuppressive agents cyclophosphamide and prednisolone on the susceptibility of gnotobiotic nu/+ BALB/c mice to intestinal paratuberculosis. Treatment with either cyclophosphamide or prednisolone led to fecal shedding of Mycobacterium paratuberculosis, and increased the numbers of M. paratuberculosis recovered from the intestinal tract and liver, to levels similar to those recovered from untreated nu/nu mice. Numerous acid-fast bacilli and granulomas were observed within the intestinal tracts and livers of cyclophosphamide and prednisolone treated nu/+ and untreated nu/nu mice. In contrast, untreated control nu/+ mice infrequently shed small numbers of bacilli, harbored low numbers of M. paratuberculosis in their intestinal tracts, and did not have visible granulomas and acid fast bacilli in their tissues. Spleen cells from cyclophosphamide and prednisolone treated nu/+ mice, and from untreated nu/nu mice, had a reduced ability to proliferate in vitro in response to mitogen and antigens. These observations are consistent with previous evidence that cellular immunity restricts the development of intestinal paratuberculosis.

A rabbit model for study of Mycobacterium paratuberculosis infection

Of 21 newborn rabbits inoculated orally with Mycobacterium paratuberculosis ATCC 19698, 13 (62%) became infected, as determined by histopathology and culture. Of the 21 inoculated rabbits, 14 (67%) experienced episodes of intermittent diarrhea, sometimes as early as 5 months after inoculation. Feces varied in consistency from soft-semisolid to watery. The organism was isolated from the sacculus rotundus, vermiform appendix of the cecum, ileum, mesenteric lymph node, and feces of 9 of 21 (43%) M. paratuberculosis-inoculated rabbits 8 to 10 months after inoculation. One infected rabbit gradually became severely emaciated; advanced paratuberculosis was confirmed by culture and histopathology. Of 21 rabbits, 9 (43%) developed multifocal, well-demarcated granulomatous enteritis in the sacculus rotundus and the vermiform appendix of the cecum. There was no significant difference in the rate of infection when the organisms were administered daily for 5 or 10 days in cow milk or broth. There was no discernible effect of pregnancy, parturition, or lactation on the severity of intestinal lesions, clinical signs, or the number of rabbits infected. Complement fixation and delayed-type hypersensitivity skin tests failed to detect infection. The results of this study suggest that newborn rabbits inoculated orally with M. paratuberculosis constitute a useful animal model for the study of paratuberculosis infection.