The pathology and pathogenesis of paratuberculosis in ruminants and other species

Progressive bovine paratuberculosis is associated with local loss of CD4(+) T cells, increased frequency of gamma delta T cells, and related changes in T-cell function

Bovine paratuberculosis is caused by the infection of young calves with Mycobacterium avium subsp. paratuberculosis, resulting in a chronic granulomatous infection of predominantly the ileum. After an incubation period of 2 to 5 years, the disease becomes progressive in some of the chronically infected, but asymptomatic cows. This results in a protein-losing enteropathy that will ultimately be fatal. A loss of cell-mediated immune responses in symptomatic animals has been described, but no information is available concerning immune reactivity in the intestine. We sought to investigate putative disease status-associated lymphocyte subset distributions and antigen-specific functional characteristics of mononuclear cells isolated from blood, gut-associated lymphoid tissue, and the intestinal walls of 22 cows in different stages of disease and in control animals. The results demonstrated a significant decrease in CD4(+) T-cell frequency and a significant increase in TcR1-N12(+) gamma delta T-cell frequency in ileum lamina propria lymphocytes of symptomatic animals compared to the asymptomatic shedders. Immunohistology revealed that there was also an absolute decrease in the number of CD4(+) T cells in sections of the lesional ileum. Our findings also indicated that both peripheral and intestinal cell-mediated responses are decreased in symptomatic animals compared to asymptomatic animals. We conclude that the decrease in cell-mediated responses is likely related to a loss of antigen-specific CD4(+) T cells, which is most prominent in the lesional ileum from symptomatic animals, thus contributing to the progressive nature of bovine paratuberculosis.

The Mycobacterium avium subsp. paratuberculosis ELISA response by parity and stage of lactation

Two cross-sectional studies were carried out to determine the enzyme-linked immunosorbent assay (ELISA) response to Mycobacterium avium subsp. paratuberculosis (Map) by cow characteristics and stage of lactation. One of the studies (referred to as "milk-group") used milk samples from all lactating cows (n=7994) in 108 Danish dairy herds. The other study (referred to as "serum-group") used serum samples collected from all cows (n=5323) in a subset of 72 herds from the 108 herds. These samples were analysed using a similar ELISA for detection of antibodies. The results from the ELISAs were interpreted with two cut-off values as the optimal cut-off value is not known, and as several levels are recommended to be used in practice. The results showed that the probability of being ELISA-positive was two to three times lower for cows in parity 1 relative to cows in other parities using both milk and serum ELISA. At the beginning of the lactation the probability of being positive was highest in the milk ELISA. In the serum ELISA the odds of being positive was highest at the end of lactation. The findings are important in the interpretation of ELISA results at cow level with a subsequent tentative diagnosis and correction for parity and stage of lactation should be considered when providing a diagnosis of paratuberculosis. Some issues related to the pathogenesis are also discussed.

Paratuberculosis with special reference to cattle. A review

Paratuberculosis is a chronic, granulomatous enteritis caused by Mycobacterium avium subspecies paratuberculosis affecting domestic and wild ruminants. The symptoms of clinical paratuberculosis are chronic diarrhoea and progressive weight loss while subclinically infected animals mainly have decreased production. The infection is widespread throughout the world and causes substantial financial losses for the farming industry. One of the major obstacles in the control of this disease, is the difficulty of identifying subclinically infected animals. This review gives a summary of several aspects of paratuberculosis including clinical importance, pathology, immunology and properties of the infectious agent. Special emphasis will be on the available diagnostic methods, their use and limitations.

Effect of commercial-scale high-temperature, short-time pasteurization on the viability of Mycobacterium paratuberculosis in naturally infected cows' milk

Raw cows' milk naturally infected with Mycobacterium paratuberculosis was pasteurized with an APV HXP commercial-scale pasteurizer (capacity 2,000 liters/h) on 12 separate occasions. On each processing occasion, milk was subjected to four different pasteurization treatments, viz., 73 degrees C for 15 s or 25 s with and without prior homogenization (2,500 lb/in(2) in two stages), in an APV Manton Gaulin KF6 homogenizer. Raw and pasteurized milk samples were tested for M. paratuberculosis by immunomagnetic separation (IMS)-PCR (to detect the presence of bacteria) and culture after decontamination with 0.75% (wt/vol) cetylpyridinium chloride for 5 h (to confirm bacterial viability). On 10 of the 12 processing occasions, M. paratuberculosis was detectable by IMS-PCR, culture, or both in either raw or pasteurized milk. Overall, viable M. paratuberculosis was cultured from 4 (6.7%) of 60 raw and 10 (6.9%) of 144 pasteurized milk samples. On one processing day, in particular, M. paratuberculosis appeared to have been present in greater abundance in the source raw milk (evidenced by more culture positives and stronger PCR signals), and on this occasion, surviving M. paratuberculosis bacteria were isolated from milk processed by all four heat treatments, i.e., 73 degrees C for 15 and 25 s with and without prior homogenization. On one other occasion, surviving M. paratuberculosis bacteria were isolated from an unhomogenized milk sample that had been heat treated at 73 degrees C for 25 s. Results suggested that homogenization increases the lethality of subsequent heat treatment to some extent with respect to M. paratuberculosis, but the extended 25-s holding time at 73 degrees C was found to be no more effective at killing M. paratuberculosis than the standard 15-s holding time. This study provides clear evidence that M. paratuberculosis bacteria in naturally infected milk are capable of surviving commercial high-temperature, short-time pasteurization if they are present in raw milk in sufficient numbers.

Progress towards understanding the spread, detection and control of Mycobacterium avium subsp paratuberculosis in animal populations

OBJECTIVE

To review and interpret aspects of the pathogenesis and epidemiology of paratuberculosis (Johne's disease) for veterinarians involved in current Johne's disease control programs.

PROCEDURE

An electronic and manual search was undertaken to identify published information which, together with limited unpublished data, was interpreted and summarised.

CONCLUSIONS

Paratuberculosis, a chronic enteropathy of ruminants, is caused by Mycobacterium avium subsp paratuberculosis and is transmitted mainly in faeces to young animals by infected adults, some of which may not have clinical signs. The incubation period is inversely related to the size of the challenge dose but can be extremely prolonged. Clinical cases may not be seen within the economic lifespan of farm animals, particularly when stocking rates are low, pasture is spelled, or when animals are culled at a relatively young age. Other as yet unknown influences may determine the rate of progression or recovery from infection. Paratuberculosis appears in a range of forms from a disease with high prevalence and significant mortality through to one with very low prevalence and little obvious morbidity or mortality. Detection of infected flocks and herds relies on use of laboratory tests. Bacteriological culture of faeces is the most sensitive herd-level test. The passage of time and repeated testing are the greatest allies in detecting paratuberculosis because infected animals progress in the disease process and most tests are more effective in the later stages of the disease. These factors generally cause the prevalence of paratuberculosis to be underestimated at both herd or flock and regional level. Greater understanding of the epidemiology and pathogenesis of M a paratuberculosis infection is critical in order to design improved diagnostic strategies, assess the feasibility of eradication and develop control options, particularly in small ruminants.

How does Mycobacterium avium subsp. paratuberculosis resist intracellular degradation?

Paratuberculosis is a chronic, progressive disease of mainly ruminants caused by the facultative intracellular bacterium, Mycobacterium avium subsp. paratuberculosis. Infection usually occurs in young animals through oral uptake of food contaminated with the organisms. The ingested bacteria are transcytosed through M-cells overlying the Peyer's patches and are released in the stroma, where they are taken up by macrophages. Inside the macrophage, the mycobacteria resist enzymatic and toxic degradation and multiply until the infected macrophage ruptures. The thick, lipid-rich cell envelope is mainly responsible for micobacterial resistance. In addition to its barrier effect, which provides protections, the mycobacterial cell wall also contains several biologically active components that down-regulate the bactericidal function of macrophages. The basic survival strategy of pathogenic mycobacteria can be viewed at three levels: selective use of relatively safe entry pathways that do not trigger oxidative attack, modification of the intracellular trafficking of mycobacteria-containing phagosomes, and modulation of the cooperation between the innate and specific immunity. In doing so, pathogenic mycobacteria are successful intracellular organisms that survive and multiply inside macrophages. Current understanding about the survival strategies of M. a. paratuberculosis and its implications in the epidemiology, diagnosis, and control of the disease are discussed.

Experimental paratuberculosis in calves following inoculation with a rabbit isolate of Mycobacterium avium subsp. paratuberculosis

The role of wildlife species in the epidemiology of paratuberculosis has been the subject of increased research efforts following the discovery of natural paratuberculosis in free-living rabbits from farms in east Scotland. This paper describes the experimental inoculation of young calves with an isolate of Mycobacterium avium subsp. paratuberculosis recovered from a free-living rabbit. After a 6-month incubation period, all eight calves inoculated with the rabbit isolate had developed histopathological and/or microbiological evidence of M. avium subsp. paratuberculosis infection. Similar results were obtained from a group of calves infected with a bovine isolate of M. avium subsp. paratuberculosis. The virulence of the rabbit isolate for calves demonstrated in this study suggests that rabbits are capable of passing paratuberculosis to domestic ruminants and that wildlife reservoirs of M. avium subsp. paratuberculosis should therefore be considered when formulating control plans for the disease.

Recovery of Mycobacterium avium subsp. paratuberculosis from nematode larvae cultured from the faeces of sheep with Johne's disease

A study was conducted to determine whether trichostrongylid nematode larvae become contaminated with Mycobacterium avium subsp. paratuberculosis when they develop in the faeces of sheep with Johne's disease. Nematode larvae were hatched from ova in the faecal samples of affected sheep. Larval sheaths were removed and these as well as exsheathed larvae were subjected to radiometric culture for M. paratuberculosis. The organism was recovered from washing water used to prepare the larvae, third stage larvae and larval sheaths, but not from exsheathed larvae. The recovery of M. paratuberculosis from larvae was associated with the severity of the histological lesions in affected sheep and with the results of culture of the organism from intestinal tissues and faeces. Nematode parasites of sheep might be able to act as mechanical vectors for M. paratuberculosis as the organism associates with infective third stage larvae when these develop in the faeces of sheep with Johne's disease.

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.

Characterization of the intracellular survival of Mycobacterium avium ssp. paratuberculosis: phagosomal pH and fusogenicity in J774 macrophages compared with other mycobacteria

The phagosomes containing viable pathogenic mycobacteria, such as Mycobacterium (M.) tuberculosis and Mycobacterium avium ssp. avium (M. avium), are known to be limited in their ability to both acidify and fuse with late (but not early) endocytic organelles. Here, we analysed the pH and fusogenicity of phagosomes containing M. avium ssp. paratuberculosis (M. ptb), the causative agent of paratuberculosis in ruminants. Using the murine J774 macrophage cell line, we compared viable and heat-killed M. ptb and, in addition, viable or dead M. avium, as well as two non-pathogenic mycobacteria, Mycobacterium smegmatis and Mycobacterium gordonae. Electron microscopic analysis revealed that M. ptb persisted intracellularly in phagosomes for up to 15 days. The phagosomes containing live M. ptb and M. avium were significantly reduced in their ability to acquire some markers for the endocytic pathway, such as internalized calcein, BSA-gold or the membrane protein Lamp 2. However, they were almost completely accessible to 70 kDa fluorescein isothiocyanate (FITC)-dextran and Lamp 1. Overall, the phagosomes containing dead pathogenic mycobacteria behaved similarly to the ones containing live non-pathogenic mycobacteria in all experiments. Using FITC-dextran in a novel fluorescence-activated cell sorting (FACS)-based method, we could also show that the bulk of endocytic compartments, including phagosomes, were only very mildly acidified to approximately pH 6.3 over at least 72 h in J774 cells infected with live M. ptb and M. avium. In contrast, J774 cells treated with heat-killed M. ptb or BSA-coated latex beads showed substantial acidification of the phagosome/endocytic compartments to a pH value of approximately 5.2. After infection with M. smegmatis and M. gordonae, acidification was initially (1-5 h after infection) inhibited, but increased after longer infection to levels similar to those with dead mycobacteria.

Etiology of Crohn's disease: the role of Mycobacterium avium paratuberculosis

Crohn's disease is a chronic inflammatory bowel disease characterized by transmural inflammation and granuloma formation. Several theories regarding the etiology of Crohn's disease have been proposed, one of which is infection with Mycobacterium avium subspecies paratuberculosis (M. paratuberculosis), which causes a similar disease in animals, and is present in the human food chain. Considerable evidence supports the presence of M. paratuberculosis in the intestinal tissues of many patients with Crohn's disease including culture, detection of homologous mycobacterial DNA, detection of the mycobacterial insertion sequence IS900 by both PCR and in situ hybridization in tissues, and a serologic immune response to recombinant M. paratuberculosis antigens. Despite this evidence, and our personal belief that M. paratuberculosis is a cause of Crohn's disease, widespread acceptance of this hypothesis will require evidence that specific anti-mycobacterial chemotherapy will cure the disease.

Paratuberculosis in Red Deer (Cervus elaphus): an Immunohistochemical Study

In the present study, we compared the utility of immunohistochemistry with serological and histological results for the characterization of Mycobacterium avium ssp. paratuberculosis (M. paratuberculosis) in tissues of affected red deer. Bacterial isolation was considered the standard reference. Samples were taken from seven clinically affected animals with typical macroscopic lesions. The enzyme linked immunosorbent assay (ELISA) and the gel diffusion tests (GD) were used for serological determinations. Samples from intestine and mesenteric lymph nodes were processed for bacterial isolation and histology. M. paratuberculosis was isolated from all the animals. Histologically, lymph nodes displayed necrosis and mineralization at the cortical and medullar areas. Ziehl-Neelsen stained bacteria were numerous inside macrophages and Langhans-type giant cells. Giant and epithelioid cells and lymphocytes were prominent at the ileal mucous membrane. The immunostaining of M. paratuberculosis was very clear inside epithelioid and giant cells. Image analysis was carried out to determine the immunostained area. There was total agreement among the methods employed. Immunohistochemistry can be very useful when the microorganism cannot be recovered from tissues or faeces.

Antigen recognition and immunomodulation by gamma delta T cells in bovine tuberculosis

This report describes the in vitro proliferative responses of peripheral blood gammadelta T cells to defined mycobacterial protein Ags and the immunomodulatory effect of gammadelta T cells in cattle infected with Mycobacterium bovis. gammadelta T cell responses were specific to M. bovis infection because they were detected in cattle either experimentally or naturally infected with M. bovis, but were not present in uninfected controls. Proliferating gammadelta T cell cultures produced enhanced levels of IFN-gamma and TGF-beta, but not IL-2 in response to the more immunodominant mycobacterial AGS: Depletion of gammadelta T cells from PBMC resulted in an increased Ag-specific proliferation in half the animals tested, indicating a suppressive effect of gammadelta T cells upon other (alphabeta) T cell responses. Because gammadelta T cells constitute a major T cell population in the peripheral blood of cattle, the activities of gammadelta T cells described in this report could make a significant contribution to the immune response in bovine tuberculosis.

Paratuberculosis infection of nonruminant wildlife in Scotland

Recent reports of natural paratuberculosis (or Johne's disease) in rabbits, foxes, and stoats has focused debate on the presence and importance of wildlife reservoirs in the epidemiology of this disease. This paper describes an extensive study investigating 18 nonruminant wildlife species for evidence of paratuberculosis. Using both culture and histopathological analysis, fox, stoat, weasel, crow, rook, jackdaw, rat, wood mouse, hare, and badger were found to harbor Mycobacterium avium subsp. paratuberculosis, the causative organism of paratuberculosis, suggesting that the epidemiology of this disease is more complex than previously realized.

Identification and characterization of a gene encoding a 35-kDa protein from Mycobacterium avium subspecies paratuberculosis

Mycobacterium avium subspecies paratuberculosis is the causative agent of Johne's disease, a chronic enteritis in ruminants. A gene homologous to that of 35-kDa antigen of Mycobacterium leprae was cloned and sequenced from Mycobacterium paratuberculosis. The database searches revealed 82.79% and 95.67% similarities of its nucleotide sequence, with those of immunodominant 35-kDa protein of M. leprae and M. avium, respectively.

Differential changes in heat shock protein-, lipoarabinomannan-, and purified protein derivative-specific immunoglobulin G1 and G2 isotype responses during bovine Mycobacterium avium subsp. paratuberculosis infection

Bovine paratuberculosis is caused by infection of young calves with Mycobacterium avium subsp. paratuberculosis. In some of the chronically infected cows the long asymptomatic stage (2 to 4 years) is followed by a rapid progression to a clinical stage due to protein-losing enteropathy, which will ultimately be fatal. The current dogma is that in early stages of disease the cell-mediated responses predominate, whereas in the clinical stage of the disease the humoral responses prevail, possibly signaling a switch in immune reactivity related to disease progression. We developed immunoglobulin M (IgM)-, IgA-, and IgG1- and IgG2-isotype-specific enzyme-linked immunosorbent assays for M. avium subsp. paratuberculosis-derived antigens (heat shock proteins of 70 kDa [Hsp70] and 65 kDa [Hsp65], lipoarabinomannan [LAM], and M. avium subsp. paratuberculosis purified protein derivative PPD [PPDP]). The serological responses of cows in different stages of paratuberculosis were used to evaluate the putative shift in immune responsiveness. In the clinical stage the PPDP-specific IgG1 responses were increased compared to those in the asymptomatic stage. However, total IgG1 and IgG2 and the Hsp70-, Hsp65-, and LAM-specific isotype responses were decreased in the clinical stage were decreased compared to those in the asymptomatic stage of disease. Thus, the classical pattern was found only for PPDP antigens and the IgG1 isotype. For other antigens and isotypes and the total IgG levels, the response pattern is different and indicates that there is no uniform association with increased antibody responses during the progression from the asymptomatic stage to the clinical stage of bovine paratuberculosis.

Review article: Mycobacterium avium subsp. paratuberculosis as one cause of Crohn's disease

A number of theories regarding the aetiology of Crohn's disease have been proposed. Diet, infections, other unidentified environmental factors and immune disregulation, all working under the influence of a genetic predisposition, have been viewed with suspicion. Many now believe that Crohn's disease is a syndrome caused by several aetiologies. The two leading theories are the infectious and autoimmune theories. The leading infectious candidate is Mycobacterium avium subspecies paratuberculosis (Mycobacterium paratuberculosis), the causative agent of Johne's disease, an inflammatory bowel disease in a variety of mammals including cattle, sheep, deer, bison, monkeys and chimpanzees. The evidence to support M. paratuberculosis infection as a cause of Crohn's disease is mounting rapidly. Technical advances have allowed the identification and/or isolation of M. paratuberculosis from a significantly higher proportion of Crohn's disease tissues than from controls. These methodologies include: (i) improved culture techniques; (ii) development of M. paratuberculosis-specific polymerase chain reaction assays; (iii) development of a novel in situ hybridization method; (iv) efficacy of macrolide and anti-mycobacterial drug therapies; and (v) discovery of Crohn's disease-specific seroreactivity against two specific M. paratuberculosis recombinant antigens. The causal role for M. paratuberculosis in Crohn's disease and correlation of infection with specific stratification(s) of the disorder need to be investigated. The data implicating Crohn's as an autoimmune disorder may be viewed in a manner that supports the mycobacterial theory. The mycobacterial theory and the autoimmune theory are complementary; the first deals with the aetiology of the disorder, the second deals with its pathogenesis. Combined therapies directed against a mycobacterial aetiology and inflammation may be the optimal treatment of the disease.

Regulation of expression of major histocompatibility antigens by bovine macrophages infected with Mycobacterium avium subsp. paratuberculosis or Mycobacterium avium subsp. avium

Mycobacterium avium subsp. paratuberculosis and Mycobacterium avium subsp. avium are antigenically and genetically very similar organisms; however, they differ markedly in their virulence for cattle. We evaluated the capacity of bovine macrophages infected with M. avium subsp. paratuberculosis or M. avium subsp. avium to express major histocompatibility complex (MHC) class I and class II antigens on their surface and to interact with primed autologous lymphocytes. Our results indicate that infection of bovine macrophages with M. avium subsp. paratuberculosis promoted the downregulation of MHC class I and class II molecules on the macrophage surface within 24 and 12 h, respectively. Alternatively, MHC class II expression by M. avium subsp. avium-infected macrophages was not detected until 24 h after infection, and the magnitude of the decrease was smaller. Decreased MHC class I expression by M. avium subsp. avium-infected macrophages was not detected. Unlike M. avium subsp. paratuberculosis-infected macrophages, M. avium subsp. avium-infected macrophages upregulated MHC class I and class II expression after activation by gamma interferon or tumor necrosis factor alpha. Further, M. avium subsp. avium-infected macrophages were lysed by primed autologous lymphocytes, whereas M. avium subsp. paratuberculosis-infected macrophages were not. Overall, the results support the hypothesis that the difference in the virulence of M. avium subsp. paratuberculosis and M. avium subsp. avium for cattle is dependent on a difference in the capacity of the organisms to suppress mycobacterial antigen presentation to T lymphocytes.

Modulation of gammadelta T cells and CD1 in Mycobacterium avium subsp. paratuberculosis infection

M.a. paratuberculosis is the causal agent of paratuberculosis (Johne's disease). Recent work has suggested that gammadelta T cells may play an important role in the early immunological response to mycobacterial diseases, and that CD1 may act as a non-classical MHC molecule in antigen presentation to these gammadelta T cells. Experimental infection of neonatal lambs with M.a. paratuberculosis was used to investigate the changes in gammadelta T cells and CD1 molecules in the gut associated lymphoid tissue 4 weeks after inoculation. Immunohistochemistry was used to label the gammadelta lymphocytes and CD1 molecules. An increase in the number of gammadelta T cells was noted in both the jejunal and ileal Peyer's patches in the gut of infected lambs, but no statistically significant change was found in the mesenteric lymph nodes. There were no obvious changes in the CD1 molecules in any tissue. This work suggests that gammadelta T cells may play a role in the initial immunological events of paratuberculosis infection.

Identification of cell wall deficient forms of M. avium subsp. paratuberculosis in paraffin embedded tissues from animals with Johne's disease by in situ hybridization

M. avium subsp. paratuberculosis (M. paratuberculosis) is the causative agent of Johne's disease (JD) in ruminants leading to enormous economical losses in dairy and meat industries worldwide. During the subclinical stage of the disease, the infected animals are difficult if not impossible to detect by the available diagnostic tests including the PCR based ones. Although only considered an animal pathogen, cell wall deficient (CWD) forms of M. paratuberculosis have been isolated from patients with sarcoidosis and Crohn's disease (idiopathic diseases) in humans. Hence, the CWD form of this organism has been suspected to play a role in the pathogenesis of these diseases by persisting in the affected tissues and triggering a localized immune response and pathology. Differentiating between the CWD and acid-fast forms of this organism may lead to the determination of whether the CWD form is the pathogenic form in the subclinical cases of JD in animals and/or the etiologic agent for the above human diseases. To localize such organisms in tissue sections, CWD forms of mycobacteria were prepared in vitro and injected into beef cubes which were then formalin fixed and paraffin embedded. An in situ hybridization (ISH) technique, combined with the IS900 M. paratuberculosis-specific probe labeled with digoxigenin, was developed for the detection of nucleic acids specifically from the CWD forms but not their acid-fast forms in tissue sections. Specificity was confirmed by the negative finding with an irrelevant probe and with control tissue preparations containing CWD cells of related mycobacteria and unrelated organisms. This ISH procedure provides a way to distinguish between the acid-fast and CWD forms of M. paratuberculosis and to localize them in tissue sections. ISH may prove useful to evaluate the significance of CWD forms of M. paratuberculosis in the pathogenesis of JD, Crohn's disease and sarcoidosis.

The pathology of goat paratuberculosis: gross and histopathological lesions in the intestines and mesenteric lymph nodes

From a pathological examination of the intestinal tracts of 1590 goats killed at slaughterhouses in the Fars Province of Iran, 59 cases (3.71%) were suspected, on gross examination, of having paratuberculosis. The diagnosis was confirmed by histopathological study and Ziehl-Neelsen staining of direct smears of rectal faeces. On the basis of severity of involvement of the terminal ileum and mesenteric lymph nodes, the microscopic lesions were classified to mild, moderate and severe forms. Caseous necrosis and calcification were observed only in the mesenteric lymph nodes. High numbers of acid-fast organisms were present in the epithelioid macrophages of the intestine but were inapparent or sparse in the mesenteric lymph nodes. On microscopic examination, 13.5% of the suspected animals were found to have paratuberculosis, in comparison with 3.38% by direct faecal smears. In addition, 30.5% and 15.3% of the animals were diagnosed as having eosinophilic enteritis and linguatulosis, respectively. These findings stress the importance of a careful histopathological examination of the intestines and mesenteric lymph nodes for the diagnosis of paratuberculosis in goats.

Effect of monensin sodium on histological lesions of naturally occurring bovine paratuberculosis

Of 19 adult cows naturally infected with paratuberculosis, 13 were treated with monensin sodium and six remained untreated. At the beginning of the study, the severity of the histological lesions was assessed from biopsy samples of ileum, liver, mesenteric lymph node and rectal mucosa. From the data acquired it was possible to assign the animals so that the lesions in the two groups were similar (P=0. 8323). Monensin was administered in the feed, which contained 147.5 mg/kg, and each treated cow received 450 mg of monensin daily for 120 days. At the end of this period all cows were killed and histopathological findings in the ileum, liver, mesenteric lymph node and rectal mucosa were compared with the initial findings. A scoring system showed that monensin had a beneficial effect in the ileum (P=0.077), liver (P=0.0322) and rectal mucosa (P=0.0578), but under the conditions of the experiment no such effect could be demonstrated in mesenteric lymph node (P=0.3599). There appeared to be an overall effect on all tissues taken together (P=0.1335). The effect of monensin may have been due to both a halting and a reversal of the pathological process. In all but one of the six untreated cows, the lesions worsened during the course of the experiment.

Classification of lesions observed in natural cases of paratuberculosis in goats

Sixty-eight adult goats with clinical or sub-clinical paratuberculosis, from naturally infected flocks, were subjected post mortem to a pathological examination that focused on the intestinal lymphoid tissue. The lesions were divided into four categories. Focal lesions, found in 16 goats, consisted of small granulomata in the ileocaecal Peyer's patches or related lamina propria. Diffuse multibacillary lesions (34 goats) consisted of a granulomatous enteritis, affecting different intestinal sites. Numerous macrophages containing many mycobacteria were present, resulting in macroscopical changes in the normal gut morphology; in the ileum of nine of the 34 animals, however, these changes were confined to the apex of the villi and the intestinal wall was not thickened. In diffuse lymphocytic lesions (10 goats), the lymphocyte was the main inflammatory cell, with some macrophages (containing few if any mycobacteria). In diffuse mixed lesions (eight goats) the infiltrate consisted of numerous lymphocytes and macrophages, with small numbers of mycobacteria. The three types of diffuse lesion were often associated with necrosis in the lymph vessels of the mucosa, mesentery and lymph nodes, and with greater thickening of the jejunum than of the ileum. Mycobacterium avium subspecies paratuberculosis was cultured from 69% of goats with diffuse lesions and from 44.4% of those with focal lesions.

Diagnosis of enteric disease in small ruminants

Diagnosis of gastrointestinal disease in small ruminants requires integration of information obtained in the signalment, history, physical or necropsy examination, and ancillary diagnostic tests. The purpose of this article is to provide the practitioner with a review of the clinical features of several common gastrointestinal diseases of sheep and goats. Rumen acidosis, enterotoxemia, gastrointestinal parasitism, neonatal diarrhea, and salmonellosis are discussed, and where appropriate, reviews of the pathophysiology, prevention, and control of these diseases are cited for further reading.

Pathogenesis of Mycobacterium avium subspecies paratuberculosis infections in ruminants: still more questions than answers

Mycobacterium avium subspecies paratuberculosis is the etiologic agent of paratuberculosis (Johnes disease), a chronic enteritis in ruminants, which is one of the most widespread bacterial diseases of domestic animals, causing enormous economic losses worldwide. Though the disease was first described more than a century ago, the biology of the infecting organism and the mechanisms of its interactions with the host still remain a mystery. In this review, recent advances made on pathogenesis of paratuberculosis are summarized and future challenges are discussed.

Bacterial isolation, immunological response, and histopathological lesions during the early subclinical phase of experimental infection of goat kids with Mycobacterium avium subsp. paratuberculosis

The diagnosis of Mycobacterium avium subsp. paratuberculosis infection is difficult, especially in the early stages of disease. This is due to the long incubation period, the variable lag phase associated with bacterial proliferation, and the multifocal distribution of slowly developing lesions. There are few previous studies of the early stages of experimental paratuberculosis in goats. In the present study, the ability of conventional diagnostic methods to detect M. a. paratuberculosis infection during the early stages of infection was assessed. Eight goat kids were experimentally infected with M. a. paratuberculosis and subjected to a series of immunological and bacteriological tests before being euthanatized at various times postinfection. At postmortem examination, the ages of the kids ranged from 1 1/2 to 12 months. Of the eight goats infected, three had histopathological evidence of paratuberculosis. Two of these goats were positive with bacteriology, but only one was also positive with all immunological tests. One animal had a positive immunological response, but infection could not be demonstrated by bacteriologic or histopathologic examination. Histopathologic lesions were found in the jejunum, in the ileum, and in one mesenteric lymph node, but only the mesenteric lymph nodes and one retropharyngeal lymph node gave positive results following bacteriologic culture. The disparity between the localization of histopathologic lesions and bacteriologic results emphasizes the need for exhaustive sampling to confirm a diagnosis during the early phase of an infection. It also highlights the need for a better understanding of the biology of M. a. paratuberculosis and its interaction with the immune system of the host.

Mucosa-associated lymphoid tissues as sites for uptake, carriage and excretion of tubercle bacilli and other pathogenic mycobacteria

Pathogenic mycobacteria, including those that cause tuberculosis and paratuberculosis, cross mucosal barriers by endocytosis within mucosal lymphoepithelial sites. These entry sites commonly include oropharyngeal and nasopharyngeal tonsils and Peyer's patches. Bacilli discharged at the basolateral surfaces of engulfing epithelial M cells are taken up by professional antigen-presenting cells associated with T lymphocytes of the parafollicular area. Dendritic cells and macrophages in these sites allow mycobacterial replication, due to the permissive immunological environment in lymphoepithelial tissues. Abrogation of local delayed-type hypersensitivity reactions generally ensures continuing integrity and function of these tissues. Phagocytes containing intracellular mycobacteria disseminate infection to other parts of the body and also probably migrate back onto the mucosal surface to shed bacilli.

Antigen-specific B-cell unresponsiveness induced by chronic Mycobacterium avium subsp. paratuberculosis infection of cattle

Mycobacterium avium subsp. paratuberculosis infection of cattle results in a chronic granulomatous enteritis. Clinical disease (i.e., cachexia, diarrhea, and high fecal bacterial counts) is preceded by a lengthy subclinical stage of disease. The immunologic mechanisms associated with the progression of infected cattle from subclinical to clinical disease are unclear. In this study, a cell proliferation assay was used in combination with flow cytometry to compare peripheral blood lymphocyte responses of cattle with subclinical paratuberculosis to responses of cattle with clinical paratuberculosis. B cells from cattle with subclinical disease proliferated vigorously upon stimulation with M. avium subsp. paratuberculosis antigen, with up to 12.4% of the total B cells responding. However, B cells from cattle with clinical disease did not proliferate upon antigen stimulation despite good proliferation in response to concanavalin A stimulation. In addition, these animals had high percentages of peripheral blood B cells. B cells from noninfected animals did not proliferate upon M. avium subsp. paratuberculosis antigen stimulation. Thus, it appears that B-cell proliferation is a sensitive indicator of subclinical Johne's disease. Furthermore, the immunologic mechanisms responsible for the antigen-specific unresponsiveness of peripheral blood B cells may be significant in the eventual progression from subclinical to clinical Johne's disease in cattle.

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.

A low G+C content genetic island in Mycobacterium avium subsp. paratuberculosis and M. avium subsp. silvaticum with homologous genes in Mycobacterium tuberculosis

The technique of representation difference analysis PCR has been applied to find genes specific to Mycobacterium avium subsp. paratuberculosis. This generated a 671 bp fragment which was used to isolate a larger genetic element found in the enteric pathogens M. avium subsp. paratuberculosis and M. avium subsp. silvaticum but which was absent from the very closely related and relatively benign M. avium subsp. avium. This element, designated GS, is greater than 6.5 kbp in length and has a G+C content 9 mol% lower than other genes from this species. There is a previously uncharacterized insertion sequence associated with one end. The GS element encodes five ORFs in M. avium subsp. paratuberculosis and M. avium subsp. silvaticum, all of which have counterparts encoded in Mycobacterium tuberculosis. Database searches revealed homologues for these ORFs in a number of bacterial species, predominantly Gram-negative organisms, including a number of enteric pathogens. These homologous genes encode functions related to LPS or extracellular polysaccharide biosynthesis. This element has a number of features in common with pathogenicity islands such as its low G+C content, an association with a putative insertion sequence and a grouping of genes of related function with a possible link to virulence. No direct link to pathogenicity has been shown but GS may belong to a group of related 'genetic islands' and represents the first such element to be identified in mycobacteria.

Detection of Mycobacterium avium subsp. paratuberculosis in infected tissues by new species-specific immunohistological procedures

We have previously described the cloning and sequencing of a gene portion coding for the terminal part of a 34-kDa protein of Mycobacterium avium subsp. paratuberculosis, the etiological agent of Johne's disease (P. Gilot, M. De Kesel, L. Machtelinckx, M. Coene, and C. Cocito, J. Bacteriol. 175:4930-4935, 1993). The recombinant polypeptide (a362) carries species-specific B-cell epitopes which do not cross-react with other mycobacterial pathogens (M. De Kesel, P. Gilot, M.-C. Misonne, M. Coene, and C. Cocito, J. Clin. Microbiol. 31:947-954, 1993). The present work describes the preparation of polyclonal and monoclonal antibodies directed against a362 and the use of these immunoglobulins for histopathological diagnosis of Johne's disease. The new immunohistological procedures herewith detailed proved to be able to identify M. avium subsp. paratuberculosis antigens in the intestinal tissues and lymph nodes of cattle affected by either the paucibacillary or pluribacillary form of the disease. They yielded negative responses not only with healthy animals but also with those affected by tuberculosis (Mycobacterium bovis). Both immunohistological procedures proved to be as sensitive as or more sensitive than Ziehl-Neelsen staining and, in addition, to be endowed with species specificity.