An epidemic of tropical sprue in southern India. II. Epidemiology

Post-infectious irritable bowel syndrome: the past, the present and the future

BACKGROUND

Irritable bowel syndrome (IBS), once thought to be a psychosomatic disease, is being considered to be more organic. Post-infectious IBS (PI-IBS), defined as acute onset IBS (by Rome criteria) after gastrointestinal infection in an individual without prior IBS with two or more of the followings: fever, vomiting, diarrhea, a positive stool culture. The recent and old literature of PI-IBS will be reviewed. Future directions for research will be presented.

METHODS

Literature on PI-IBS was reviewed by electronic search and cross references of these papers.

RESULTS

Interest in studies on PI-IBS, which was described five to six decades ago, re-surfaced recently. 3.6 to 32% patients with acute gastroenteritis develop PI-IBS during 3-12 month follow-up. PI-IBS is commonly diarrhea predominant. Factors implicated in development include nature of pathogens, duration and severity of diarrhea, younger age, female gender and psychological co-morbidities like anxiety and depression. The pathogenesis of PI-IBS is largely related to continuing gut inflammation due to inability of the host to contain the inflammatory reaction, altered gut microbiota, increased intestinal permeability, muscle hyper-contractility and visceral hypersensitivity. There could be an overlap between PI-IBS and post-infectious malabsorption syndrome (PI-MAS), popularly known as tropical sprue.

CONCLUSIONS

Development of IBS in a subset of patients with acute gastroenteritis is uncontested. This is expected to open a paradigm shift in understanding the pathogenesis of IBS. Future studies should address the issue of overlap of PI-IBS and PI-MAS. Exploring the molecular mechanisms of pathogenesis of PI-IBS may help to design preventive and therapeutic strategies.

Suboptimal performance of IgG anti-tissue transglutaminase in the diagnosis of celiac disease in a tropical country

Serological tests using human IgA-anti-tTG have been reported to have high sensitivity and specificity in diagnosis of celiac disease. There is a paucity of data on the use of human IgG-anti-tTG in diagnosis of celiac disease. Ninety-two patients with clinical suspicion of celiac disease who underwent duodenal mucosal biopsy and celiac serology using human IgG-anti-tTG were included in this retrospective study. Diagnostic accuracy of human recombinant IgG-anti-tTG serological test for celiac disease was evaluated. Indications for celiac serological testing were diarrhea (92.3%), hypoalbuminemia (39.1%), and anemia (35.9%). Eighteen patients were diagnosed with having celiac disease and 14 (77.8%) of them were IgG-anti-tTG positive. Of the remaining 74 patients, eight (10.8%) were false-positive for IgG-anti-tTG. Sensitivity, specificity, PPV, NPV, and diagnostic accuracy of IgG-anti-tTG in celiac disease were 77.8, 89.1, 63.6, 94.2, and 87%, respectively. Human IgG-anti-tTG alone does not perform well as a diagnostic tool for celiac disease. The utility of anti-endomysial antibodies in a similar clinical setting needs to be evaluated.

Bugs and irritable bowel syndrome: The good, the bad and the ugly

Recently, there has been strong interest in the therapeutic potential of probiotics for irritable bowel syndrome (IBS). At the same time, there is a rapidly growing body of evidence to support an etiological role for gastrointestinal infection and the associated immune activation in the development of post-infectious IBS. In a more controversial area, small intestinal bacterial overgrowth has been associated with a subset of patients with IBS; the issue of whether it is appropriate to treat a subset of IBS patients with antibiotics and probiotics is currently a matter for debate. Thus, it appears that the gastrointestinal microbial flora may exert beneficial effects for symptoms of IBS under some circumstances, while in other situations gut microbes could give rise to symptoms of IBS. How do we make sense of the apparently diverse roles that 'bugs' may play in IBS? To address this question, we have conducted an in-depth review, attempting where possible to draw lessons from Asian studies.

Frequency of lactose malabsorption among healthy southern and northern Indian populations by genetic analysis and lactose hydrogen breath and tolerance tests

BACKGROUND

Lactose malabsorption (LM), the inability to break down lactose into glucose and galactose, is due to a deficiency in the small intestinal lactase phlorizin hydrolase enzyme. Ethnic and geographic variations of LM are known.

OBJECTIVE

The aim of this study was to compare the frequency of LM in healthy southern and northern Indian populations.

DESIGN

A total of 153 healthy volunteers (76 from southern and 77 from northern India) were evaluated for LM by using a lactose tolerance test (LTT), a lactose hydrogen breath test (lactose HBT), and polymerase chain reaction-restriction fragment length polymorphism to identify the lactase gene C/T-13910 polymorphism (confirmed by sequencing).

RESULTS

Volunteers from southern and northern India were comparable in age and sex. The LTT result was abnormal in 88.2% of southern Indians and in 66.2% of northern Indians (P = 0.001). The lactose HBT result was abnormal in 78.9% of southern Indians and in 57.1% of northern Indians (P = 0.003). The CC genotype was present in 86.8% and 67.5% (P = 0.002), the CT genotype was present in 13.2% and 26.0% (P = 0.036), and the TT genotype was present in 0% and 6.5% (P = 0.03) of southern and northern Indians, respectively. The frequency of symptoms after the lactose load (47.4% compared with 15.6%; P < 0.001) and peak concentrations of breath hydrogen (88.5 +/- 71.9 compared with 55.4 +/- 61.9 ppm; P = 0.003), both of which might indicate the degree of lactase deficiency, were higher in southern than in northern Indians.

CONCLUSION

The frequency and degree of LM is higher in southern than in northern Indian healthy populations because of genetic differences in these populations.

Tropical malabsorption

Malabsorption is an important clinical problem both in visitors to the tropics and in native residents of tropical countries. Infections of the small intestine are the most important cause of tropical malabsorption. Protozoal infections cause malabsorption in immunocompetent hosts, but do so more commonly in the setting of immune deficiency. Helminth infections occasionally cause malabsorption or protein-losing enteropathy. Intestinal tuberculosis, chronic pancreatitis and small-bowel bacterial overgrowth are important causes of tropical malabsorption. In recent years, inflammatory bowel disease and coeliac disease have become major causes of malabsorption in the tropics. Sporadic tropical sprue is still an important cause of malabsorption in adults and in children in South Asia. Investigations to exclude specific infective, immunological or inflammatory causes are important before considering tropical sprue as a diagnosis. This article briefly reviews the management of tropical sprue and presents an algorithm for its investigation and management.

Tropical sprue

Tropical sprue (TS) is a clinical entity of unknown etiology characterized by an acquired chronic diarrheal illness and malabsorption that affects indigenous inhabitants and expatriates, either long-term residents or short-term visitors, in the tropical countries. The exact pathogenetic sequence of TS remains incompletely characterized. Bacterial overgrowth, disturbed gut motility, and hormonal and histopathologic abnormalities contribute to the development of TS in a susceptible host. Treatment with tetracycline and folate is effective in some patients, although relapses after treatment are common. Research in the areas of microbial factors, pathogenesis, immunogenetics, and hormonal and immune regulation, using modern diagnostic techniques, may be able to settle some of the unanswered issues and open new venues for diagnosis, prevention, and treatment of tropical sprue.

A perspective on tropical sprue

A diagnosis of tropical sprue, an infrequent affliction of inhabitants and travelers in tropical regions, should be considered in patients with a compatible history, malabsorption, and chronic diarrhea. It can occur in either endemic or epidemic form and can be preceded by acute gastroenteritis. The cause of tropical sprue is still unknown, although most data support an infectious etiology. Therapeutic experience is greatest with folic acid and tetracycline. Most patients can be expected to recover with proper nutritional support, although relapses and slow responses occur.

Tropical sprue and subclinical enteropathy: a vision for the nineties

Aside from infectious intestinal diseases with known etiology, there is a group of gastrointestinal disorders mainly affecting the small intestine of individuals predominantly living in and less often visiting or returning from the Third World, usually the tropics, and ranging from asymptomatic structural and/or functional abnormalities of the gastrointestinal mucosa (subclinical enteropathy, SE) to a fully symptomatic condition highlighted by malabsorption of nutrients with associated nutritional deficiencies responsive to folate and broad spectrum antibiotic treatment (tropical sprue, TS). Mounting evidence supports an infectious cause in many instances. The exact nature of the infection, whether initiated and/or perpetuated by enterotoxigenic coliform bacteria, virus(es) or a combination of these, is not clear. Further studies, including those using molecular techniques, are needed in order to clarify various aspects of these widely prevalent disorders.

Tropical sprue

It is surprising that in the gastrointestinal tract, with a primary barrier function and a large population of immunocytes, a major role for immunological damage has been convincingly established only for a few diseases; pernicious anaemia, gluten-sensitive enteropathy and GVHD. The complexities in investigating this relatively inaccessible area and the necessity for studying appropriate controls by similar techniques are some of the reasons that explain this paucity of data.

Tropical sprue is a syndrome with an unusual geographical distribution and unknown aetiology. Alterations in gut immunocytes, especially EL, in this disease suggest that immune-mediated mechanisms may be important in the pathogenesis. However, the available data suggests that the initiating event leading to persistent damage to enterocytes in the stem cell compartment is unlikely to be immune mediated and that the immunological alterations are secondary to the loss of barrier function consequent to enterocyte damage.

Tropical sprue in southern India

Tropical sprue, a primary malabsorption syndrome affecting residents and visitors to several tropical regions, occurs in southern India in endemic and epidemic forms. The stomach, the small intestine and colon are affected and malabsorption results in nutrient deficiency. Enterocyte damage, the primary lesion in southern Indian tropical sprue, is the result of a persistent lesion of the stem cell compartment. This lesion occurs on a background of tropical enteropathy and the available evidence suggests that an immunity conferring agent may be responsible for initiating the damage.

Malabsorption in overland travellers to India

Thirty-four cases of malabsorption are described in young adults after brief periods of overland travel to India. Symptoms included diarrhoea, abdominal distension, and weight loss. Investigation revealed fat, xylose, and vitamin B(12) malabsorption with marked morphological changes in the mucosa. Lower levels of serum folate and vitamin B(12) were observed in those with protracted diarrhoea, but no anaemia developed. Malabsorption may persist for many months after return to the U.K. Most patients responded initially to antibiotics, but some subsequently relapsed. The reasons why these patients developed tropical sprue are discussed.