Robert L. Owen

Human microsporidial infections.

Microsporidia are obligate intracellular spore-forming protozoal parasites belonging to the phylum Microspora. Their host range is extensive, including most invertebrates and all classes of vertebrates. More than 100 microsporidial genera and almost 1,000 species have now been identified. Five genera (Enterocytozoon spp., Encephalitozoon spp., Septata spp., Pleistophora sp., and Nosema spp.) and unclassified microsporidia (referred to by the collective term Microsporidium) have been associated with human disease, which appears to manifest primarily in immunocompromised persons. The clinical manifestations of microsporidiosis are diverse and include intestinal, pulmonary, ocular, muscular, and renal disease. Among persons not infected with human immunodeficiency virus, ten cases of microsporidiosis have been documented. In human immunodeficiency virus-infected patients, on the other hand, over 400 cases of microsporidiosis have been identified, the majority attributed to Enterocytozoon bieneusi, an important cause of chronic diarrhea and wasting. Diagnosis of microsporidiosis currently depends on morphological demonstration of the organisms themselves. Initial detection of microsporidia by light microscopic examination of tissue sections and of more readily obtainable specimens such as stool, duodenal aspirates, urine, sputum, nasal discharge, bronchoalveolar lavage fluid, and conjunctival smears is now becoming routine practice. Definitive species identification is made by using the specific fluorescein-tagged antibody (immunofluorescence) technique or electron microscopy. Treatment options are limited, but symptomatic improvement of Enterocytozoon bieneusi infection may be achieved with the anthelmintic-antiprotozoal drug albendazole. Preliminary observations suggest that Septata intestinalis and Encephalitozoon infections may be cured with albendazole. Progress is being made with respect to in vitro propagation of microsporidia, which is crucial for developing antimicrosporidial drugs. Furthermore, molecular techniques are being developed for diagnostic purposes, taxonomic classification, and analysis of phylogenetic relationships of microsporidia. Images

Improved Light-Microscopical Detection of Microsporidia Spores in Stool and Duodenal Aspirates

BACKGROUND The diagnosis of infection with Enterocytozoon bieneusi, a microsporidian organism that causes chronic diarrhea in patients infected with the human immunodeficiency virus (HIV), has depended on invasive procedures. We have developed a new method to detect microsporidia spores in feces and duodenal aspirates. METHODS Stool was obtained from four HIV-infected patients with biopsy-confirmed intestinal microsporidiosis. Slides prepared from unconcentrated, formalin-fixed stool specimens were stained with a new chromotrope-based technique and examined by light microscopy. Methods of stool concentration were also compared. The technique was then evaluated by examining 215 specimens from 134 HIV-infected persons with or without diarrhea. In addition, duodenal aspirates from 10 patients with unexplained chronic diarrhea were examined by light microscopy after staining according to the new and the traditional techniques. RESULTS E. bieneusi spores were found in all unconcentrated stool specimens from the four patients with microsporidiosis. The use of various methods of stool concentration did not improve the detection of microsporidia spores. In the prospective study, microsporidiosis was detected in samples from 6 of 27 patients with chronic diarrhea, but in none of those from 42 patients with acute diarrhea or 65 patients without diarrhea. The presence of microsporidia spores in stool specimens and duodenal aspirates allowed the successful prediction of the presence of microsporidia in small-bowel biopsy specimens from all four patients who subsequently underwent endoscopy. CONCLUSIONS E. bieneusi is an important cause of chronic diarrhea in HIV-infected persons. This new diagnostic technique serves as a practical, noninvasive means to detect microsporidia spores in stool specimens and is also applicable to the examination of duodenal aspirates.

Ultrastructural Observations on Giardiasis in a Murine Model: I. Intestinal Distribution, Attachment, and Relationship to the Immune System of Giardia muris

Infected immunocompetent mice were studied prospectively in a well-described murine model system with the use of ultrastructural techniques to establish normal distribution of Giardia muris trophozoites, their relationships to intestinal mucosa, particularly Peyers patches, and structural indications of the normal reaction of intestine and intestinal immune organs. Trophozoites colonized the proximal 25% of the intestine, adhered to microvilli of columnar cells near the bases of villi, wedged into furrows in the epithelial surface, or lodged in mucus within the unstirred layer. Density of trophozoite colonization of the jejunal epithelium correlated with stool cyst excretion. Over Peyers patches, Giardia adhered to columnar cells and not to M-cells, which transport soluble antigens and particulate material from the lumen into the lymphoid system. Giardia entered intestinal lymphoid structures by incursions through defects in the lymphoid follicle epithelial barrier. During clearance of parasites, lymphocytes crossed the epithelium and attached to Giardia in the lumen. Giardia produced no apparent ultrastructural damage in normal mice but elicited a previously undescribed intraluminal cellular immune response during clearance by the host.

Why does Japan have a high incidence of gastric cancer? Comparison of gastritis between UK and Japanese patients

Background and aims: The incidence of gastric cancer in Japan is four times higher than in the UK. It usually arises in a stomach with corpus predominant or pangastritis that has undergone extensive atrophy and intestinal metaplasia. We hypothesised that a Japanese population would have a more severe gastritis with a corpus predominant or pangastritis pattern and a greater degree of atrophy and intestinal metaplasia than that found in the UK. To test this we designed a comparative trial. Methods: A total of 252 age matched consecutive patients were recruited from the endoscopy services in Leeds and Tokyo. In each centre, 21 patients were prospectively selected from each decennial, between the ages of 20–80 years. All had epigastric discomfort as their predominant symptom. Patients with peptic ulcer, cancer, and oesophagitis were excluded. Five gastric biopsies were examined by two histopathologists using the updated Sydney system. Helicobacter pylori infection was assessed by histology and culture of biopsies and enzyme linked immunosorbent assay and immunoblot of plasma. Results: Gastritis was found by both pathologists in 59 (47%) UK and 76 (60%) Japanese patients (χ2 test, p = 0.04). In those patients with gastritis, corpus predominant or pangastritis was commoner in the Japanese (63% Japan v 36% in the UK (χ2 test, p = 0.003) Atrophy and intestinal metaplasia were more extensive and severe (Mann-Whitney U test, p<0.001) and chronic inflammation and polymorph activity were also greater, especially in the corpus (Mann-Whitney U test, p<0.001). Fifty three of 59 UK gastritis patients (90%) and 67/76 (88%) (χ2 test, p = 1) Japanese gastritis patients were positive for H pylori. Using a previously described “gastric cancer risk index” among H pylori positive patients, there were significantly more Japanese than UK subjects with a “high risk” score. Conclusion: In Japanese as opposed to English patients, gastritis is more prevalent and severe with more corpus predominant atrophy and intestinal metaplasia. These differences may partially explain the higher incidence of gastric cancer in Japan.

Absence of secretory component expression by epithelial cells overlying rabbit gut-associated lymphoid tissue*

The expression of secretory component by epithelial cells overlying intestinal lymphoid aggregates was examined immunocytochemically in rabbits. Intensely labeled epithelial cells were distributed along surfaces of villi surrounding follicles in jejunal and ileal Peyers patches and along interdomal epithelium in sacculus rotundus and appendix. Secretory component labeling extended from within crypts and appendiceal crevices to the tips of villi and interdomal regions. In contrast, no immunologically detectable secretory component sites were observed in follicle-associated epithelial cells. In crypts and crevices supplying follicles, epithelial cells facing the lamina propria of villi and interdomal epithelium expressed secretory component, but cells flanking the follicle domes lacked secretory component immunostaining, with a clear demarcation between positive and negative zones at the base of the stem cell regions. These findings demonstrate a unique difference in the expression of the receptor for immunoglobulin A antibody between follicle-associated and non-follicle-associated epithelium.

Intestinal Infection with Mycobacterium avium in Acquired Immune Deficiency Syndrome (AIDS) Histological and Clinical Comparison with Whipple's Disease

At endoscopy, a 30-year-old man with acquired immune deficiency syndrome (AIDS), Kaposis sarcoma, diarrhea, and unexplained malabsorption showed erythematous macular duodenal lesions consistent with Whipples disease by histology and electron microscopy. Symptoms did not respond to tetracycline. Subsequent cultures revealed systemic Mycobacterium avium (M. avium) infection. Tissue from this patient, from patients with Whipples disease and from a macaque with M. avium were compared. All contained PAS-positive macrophages but M. avium could be distinguished by positive acid-fast stains and a difference in pattern of indirect immunofluorescence staining with bacterial typing antisera. PAS-positive macrophages in the intestinal lamina propria are no longer pathognomonic of Whipples disease. Ultrastructural and histological similarities between Whipples disease and M. avium infection suggest that both are manifestations of immune deficits limiting macrophage destruction of particular bacteria after phagocytosis. M. avium must be considered in the differential diagnosis of diarrhea in patients with AIDS and other immunosuppressed conditions.SummaryAt endoscopy, a 30-year-old man with acquired immune deficiency syndrome (AIDS), Kaposis sarcoma, diarrhea, and unexplained malabsorption showed erythematous macular duodenal lesions consistent with Whipples disease by histology and electron microscopy. Symptoms did not respond to tetracycline. Subsequent cultures revealed systemicMycobacterium avium (M. avium) infection. Tissue from this patient, from patients with Whipples disease and from a macaque withM. avium were compared. All contained PAS-positive macrophages butM. avium could be distinguished by positive acid-fast stains and a difference in pattern of indirect immunofluorescence staining with bacterial typing antisera. PAS-positive macrophages in the intestinal lamina propria are no longer pathognomonic of Whipples disease. Ultrastructural and histological similarities between Whipples disease andM. avium infection suggest that both are manifestations of immune deficits limiting macrophage destruction of particular bacteria after phagocytosis.M. avium must be considered in the differential diagnosis of diarrhea in patients with AIDS and other immunosuppressed conditions.

Human Angiostrongylus cantonensis: an update

Angiostrongylus cantonensis was first discovered in 1935 and has become an important emerging pathogen causing human angiostrongyliasis. Major outbreaks of human angiostrongyliasis have been reported in endemic regions. Thousands of cases of human angiostrongyliasis have been documented worldwide. A. cantonensis has spread from its traditional endemic regions of the Pacific islands and Southeast Asia to the American continent including the USA, Caribbean islands and Brazil. Humans acquire A. cantonensis by consumption of raw or undercooked intermediate snail hosts or paratenic hosts. The main clinical manifestations of human angiostrongyliasis are eosinophilic meningitis and ocular angiostrongyliasis. The treatment of this disease includes supportive treatment, corticosteroid therapy, and combined therapy with corticosteroids and anthelminthics. The most effective method for prevention is to persuade people not to eat raw or undercooked intermediate and paratenic hosts.

Impact of aging on gastrointestinal mucosal immunity

There is considerable evidence that the mucosal or secretory immune response in the gastrointestinal tract is compromised by aging. The generation of a mucosal immune response is an extremely complex process that involves antigenic stimulation of a specific subpopulation of immunologically competent cells in the Peyers patches, differentiation and migration of these cells to the small intestinal lamina propria, initiation and regulation of local antibody production in the intestinal wall, and mucosal epithelial cell receptor-mediated transport of antibodies to the intestinal lumen. Available data suggest that gastrointestinal mucosal immunosenescence reflects deficits in: (1) the differentiation and/or migration (homing) of immunoglobulin A immunoblasts to the intestinal lamina propria, and (2) the initiation and/or regulation of local antibody production. The significant age-related increases in the incidence and severity of gastrointestinal infectious diseases, coupled with the potential for immunopharmacologic manipulation of the mucosal immune compartment, substantiate the merit of studies designed to resolve the etiology of mucosal immunodeficiency in the elderly.

AIDS and the gut

There are increasing challenges for the practising gastroenterologist in treating AIDS‐related gastrointestinal diseases. The differential diagnoses of dysphagia and odynophagia include cytomegalovirus (CMV) and herpes simplex virus (HSV) infection, non‐specific aphthous ulceration and non‐AIDS oesophageal diseases, especially reflux oesophagitis. Chronic subacute abdominal pain with nausea, vomiting, early satiety and weight loss is suggestive of an obstructive lesion caused by lymphoma or Kaposis sarcoma. Severe acute abdominal pain can indicate pancreatitis or intestinal perforation due to cytomegalovirus. Right upper quadrant pain (with or without fever, vomiting or abnormal liver function tests with a cholestatic profile) is suggestive of hepatobiliary pathology including cholecystitis, cholangitis, acalculous cholecystitis and AIDS cholangiopathy. Diarrhoea is the most common gastrointestinal symptom of AIDS, affecting 50–90% of patients. Causes of AIDS diarrhoea include protozoa (Cryptosporidium parvum, Isospora belli, Enterocytozoon bieneusi, Septata intestinalis, Cyclospora spp, Entamoeba histolytica and Giardia lamblia), bacteria (Mycobacterium avium‐intracellulare, Clostridium difficile, Salmonella, Shigella and Campylobacter jejuni), and viruses (CMV, HSV and possibly HIV). Chronic diarrhoea, malnutrition and weight loss can shorten the life‐span of patients with AIDS. Elemental diets, isotonic formulas, medium chain triglycerides and total parenteral nutrition have been tried with little success in AIDS patients with severe diarrhoea and wasting.

Structural specializations for antigen uptake and processing in the digestive tract

ConclusionsEpithelial adaptations for antigen uptake and lymphoid organ cytoarchitecture differ according to the characteristics of specific sites throughout the mucosa but all facilitate antigen uptake. Whether surrounding mucosa is stratified squamous epithelium as in the oropharynx or columnar epithelium as in the intestine, organized lymphoid tissue in each area displays surface specializations which reduce local barriers and facilitate the approach and uptake of microorganisms, particles and macromolecules. In lymphoid tissue in each of these sites cellular defense mechanisms are arrayed for local containment, antigen processing and initiation of immune responses.