The villus architecture of the small intestine in the tropics: a necropsy study

Campylobacter vaccination reduces diarrheal disease and infant growth stunting among rhesus macaques

Campylobacter-associated enteric disease is estimated to be responsible for more than 160 million cases of gastroenteritis each year and is linked to growth stunting of infants living under conditions of poor sanitation and hygiene. Here, we examine naturally occurring Campylobacter-associated diarrhea among rhesus macaques as a model to determine if vaccination could reduce severe diarrheal disease and infant growth stunting. Compared to unvaccinated controls, there are no Campylobacter diarrhea-associated deaths observed among vaccinated infant macaques and all-cause diarrhea-associated infant mortality is decreased by 76% (P = 0.03). By 9 months of age, there is a 1.3 cm increase in dorsal length that equaled a significant 1.28 LAZ (Length-for-Age Z score) improvement in linear growth among vaccinated infants compared to their unvaccinated counterparts (P = 0.001). In this work, we show that Campylobacter vaccination not only reduces diarrheal disease but also potentially serves as an effective intervention that improves infant growth trajectories.

Toll-Like Receptor-Induced Immune Responses During Early Childhood and Their Associations With Clinical Outcomes Following Acute Illness Among Infants in Sub-Saharan Africa

Severely ill children in low- and middle-income countries (LMICs) experience high rates of mortality from a broad range of infectious diseases, with the risk of infection-related death compounded by co-existing undernutrition. How undernutrition and acute illness impact immune responses in young children in LMICs remains understudied, and it is unclear what aspects of immunity are compromised in this highly vulnerable population. To address this knowledge gap, we profiled longitudinal whole blood cytokine responses to Toll-like receptor (TLR) ligands among severely ill children (n=63; 2-23 months old) with varied nutritional backgrounds, enrolled in the CHAIN Network cohort from Kampala, Uganda, and Kilifi, Kenya, and compared these responses to similar-aged well children in local communities (n=41). Cytokine responses to ligands for TLR-4 and TLR-7/8, as well as Staphylococcus enterotoxin B (SEB), demonstrated transient impairment in T cell function among acutely ill children, whereas innate cytokine responses were exaggerated during both acute illness and following clinical recovery. Nutritional status was associated with the magnitude of cytokine responses in all stimulated conditions. Among children who died following hospital discharge or required hospital re-admission, exaggerated production of interleukin-7 (IL-7) to all stimulation conditions, as well as leukopenia with reduced lymphocyte and monocyte counts, were observed. Overall, our findings demonstrate exaggerated innate immune responses to pathogen-associated molecules among acutely ill young children that persist during recovery. Heightened innate immune responses to TLR ligands may contribute to chronic systemic inflammation and dysregulated responses to subsequent infectious challenges. Further delineating mechanisms of innate immune dysregulation in this population should be prioritized to identify novel interventions that promote immune homeostasis and improve outcomes.

Reduced infant rhesus macaque growth rates due to environmental enteric dysfunction and association with histopathology in the large intestine

Environmental enteric dysfunction is associated with malnutrition as well as infant growth stunting and has been classically defined by villous blunting, decreased crypt-to-villus ratio, and inflammation in the small intestine. Here, we characterized environmental enteric dysfunction among infant rhesus macaques that are naturally exposed to enteric pathogens commonly linked to human growth stunting. Remarkably, despite villous atrophy and histological abnormalities observed in the small intestine, poor growth trajectories and low serum tryptophan levels were correlated with increased histopathology in the large intestine. This work provides insight into the mechanisms underlying this disease and indicates that the large intestine may be an important target for therapeutic intervention.

Environmental enteric dysfunction (EED), a subclinical disorder of intestinal function, is associated with malnutrition, infant growth stunting and pathologies in the small intestine. Here the authors report that infant rhesus macaques that are naturally exposed to enteric pathogens commonly linked to human growth stunting present with EED and growth faltering that associates with large intestine pathologies.

Minimally Invasive Postmortem Intestinal Tissue Sampling in Malnourished and Acutely Ill Children Is Feasible and Informative

BACKGROUND

Intestinal disorders such as environmental enteric dysfunction (EED) are prevalent in low- and middle-income countries (LMICs) and important contributors to childhood undernutrition and mortality. Autopsies are rarely performed in LMICs but minimally invasive tissue sampling is increasingly deployed as a more feasible and acceptable procedure, although protocols have been devoid of intestinal sampling to date. We sought to determine (1) the feasibility of postmortem intestinal sampling, (2) whether autolysis precludes enteric biopsies' utility, and (3) histopathologic features among children who died during hospitalization with acute illness or undernutrition.

METHODS

Transabdominal needle and endoscopic forceps upper and lower intestinal sampling were conducted among children aged 1 week to 59 months who died while hospitalized in Blantyre, Malawi. Autolysis ratings were determined for each hematoxylin and eosin slide, and upper and lower intestinal scoring systems were adapted to assess histopathologic features and their severity.

RESULTS

Endoscopic and transabdominal sampling procedures were attempted in 28 and 14 cases, respectively, with >90% success obtaining targeted tissue. Varying degrees of autolysis were present in all samples and precluded histopathologic scoring of 6% of 122 biopsies. Greater autolysis in duodenal samples was seen with longer postmortem interval (Beta = 0.06, 95% confidence interval, 0.02-0.11). Histopathologic features identified included duodenal Paneth and goblet cell depletion. Acute inflammation was absent but chronic inflammation was prevalent in both upper and lower enteric samples. Severe chronic rectal inflammation was identified in children as young as 5.5 weeks.

CONCLUSIONS

Minimally invasive postmortem intestinal sampling is feasible and identifies histopathology that can inform mortality contributors.

Biomarkers of environmental enteric dysfunction are not consistently associated with linear growth velocity in rural Zimbabwean infants

BACKGROUND

Child stunting remains a poorly understood, prevalent public health problem. Environmental enteric dysfunction (EED) is hypothesized to be an important underlying cause.

OBJECTIVES

Within a subgroup of 1169 children enrolled in the SHINE (Sanitation Hygiene Infant Nutrition Efficacy) trial in rural Zimbabwe, followed longitudinally from birth to 18 mo of age, we evaluated associations between the concentration of 11 EED biomarkers and linear growth velocity.

METHODS

At infant ages 1, 3, 6, 12, and 18 mo, nurses measured child length and collected stool and blood; the lactulose-mannitol urine test was also conducted at all visits except at 1 mo. Stool neopterin, α-1 antitrypsin, myeloperoxidase, and regenerating gene 1β protein; urinary lactulose and mannitol; and plasma kynurenine, tryptophan, C-reactive protein, insulin-like growth factor-1 (IGF-1), soluble CD14, intestinal fatty acid binding protein, and citrulline were measured. We analyzed the change in relative [∆ length-for-age z score (LAZ)/mo] and absolute (∆ length/mo) growth velocity during 4 age intervals (1-3 mo; 3-6 mo; 6-12 mo; and 12-18 mo) per SD increase in biomarker concentration at the start of each age interval.

RESULTS

In fully adjusted models, we observed only 3 small, statistically significant associations: kynurenine:tryptophan ratio at 12 mo was associated with decreased mean LAZ velocity during the 12-18 mo interval (-0.015 LAZ/mo; 95% CI: -0.029, -0.001 LAZ/mo); mannitol excretion at 6 mo was associated with increased LAZ velocity during the 6-12 mo interval (0.013 LAZ/mo; 95% CI: 0.001, 0.025 LAZ/mo), and plasma IGF-1 at 1 mo was associated with increased LAZ velocity during the 1-3 mo interval (0.118 LAZ/mo; 95% CI: 0.024, 0.211 LAZ/mo). Results for absolute growth velocity were similar, except IGF-1 was also associated with growth during the 12-18 mo interval. We found no other associations between any EED biomarker and linear growth velocity.

CONCLUSIONS

None of 11 biomarkers of EED were consistently associated with linear growth among Zimbabwean children.This trial was registered at clinicaltrials.gov as NCT01824940.

Adaptation of the small intestine to microbial enteropathogens in Zambian children with stunting

Environmental enteropathy is a major contributor to growth faltering in millions of children in Africa and South Asia. We carried out a longitudinal, observational and interventional study in Lusaka, Zambia, of 297 children with stunting (aged 2-17 months at recruitment) and 46 control children who had good growth (aged 1-5 months at recruitment). Control children contributed data only at baseline. Children were provided with nutritional supplementation of daily cornmeal-soy blend, an egg and a micronutrient sprinkle, and were followed up to 24 months of age. Children whose growth did not improve over 4-6 months of nutritional supplementation were classified as having non-responsive stunting. We monitored microbial translocation from the gut lumen to the bloodstream in the cohort with non-responsive stunting (n = 108) by measuring circulating lipopolysaccharide (LPS), LPS-binding protein and soluble CD14 at baseline and when non-response was declared. We found that microbial translocation decreased with increasing age, such that LPS declined in 81 (75%) of 108 children with non-responsive stunting, despite sustained pathogen pressure and ongoing intestinal epithelial damage. We used confocal laser endomicroscopy and found that mucosal leakiness also declined with age. However, expression of brush border enzyme, nutrient transporter and mucosal barrier genes in intestinal biopsies did not change with age or correlate with biomarkers of microbial translocation. We propose that environmental enteropathy arises through adaptation to pathogen-mediated epithelial damage. Although environmental enteropathy reduces microbial translocation, it does so at the cost of impaired growth. The reduced epithelial surface area imposed by villus blunting may explain these findings.

Stunting Is Preceded by Intestinal Mucosal Damage and Microbiome Changes and Is Associated with Systemic Inflammation in a Cohort of Peruvian Infants

Stunting, defined as height-for-age Z score equal to or lower than -2, is associated with increased childhood mortality, cognitive impairment, and chronic diseases. The aim of the study was to investigate the relationship between linear growth, intestinal damage, and systemic inflammation in infants at risk of stunting. We followed up 78 infants aged 5-12 months living in rural areas of Peru for 6 months. Blood samples for biomarkers of intestinal damage (intestinal fatty-acid-binding protein [I-FABP] and zonulin) and systemic inflammation (interleukin-1β, interleukin-6, tumor necrosis factor α [TNF-α], soluble CD14, and lipopolysaccharide-binding protein [LBP]) and fecal samples for microbiome analysis were collected at baseline and closure of the study. The children's growth and health status were monitored through biweekly home visits by trained staff. Twenty-one percent of the children became stunted: compared with non-stunted children, they had worse nutritional parameters and higher levels of serum I-FABP at baseline. The likelihood of becoming stunted was strongly associated with an increase in sCD14 over time; LBP and TNF-α showed a trend toward increase in stunted children but not in controls. The fecal microbiota composition of stunted children had an increased beta diversity compared with that of healthy controls throughout the study. The relative abundance of Ruminococcus 1 and 2, Clostridium sensu stricto, and Collinsella increased in children becoming stunted but not in controls, whereas Providencia abundance decreased. In conclusion, stunting in our population was preceded by an increase in markers of enterocyte turnover and differences in the fecal microbiota and was associated with increasing levels of systemic inflammation markers.

Study of Environmental Enteropathy and Malnutrition (SEEM) in Pakistan: protocols for biopsy based biomarker discovery and validation

Background

Environmental Enteropathy (EE), characterized by alterations in intestinal structure, function, and immune activation, is believed to be an important contributor to childhood undernutrition and its associated morbidities, including stunting. Half of all global deaths in children < 5 years are attributable to under-nutrition, making the study of EE an area of critical priority.

Methods

Community based intervention study, divided into two sub-studies, 1) Longitudinal analyses and 2) Biopsy studies for identification of EE features via omics analyses. Birth cohorts in Matiari, Pakistan established: moderately or severely malnourished (weight for height Z score (WHZ) < − 2) children, and well-nourished (WHZ > 0) children. Blood, urine, and fecal samples, for evaluation of potential biomarkers, will be collected at various time points from all participants (longitudinal analyses). Participants will receive appropriate educational and nutritional interventions; non-responders will undergo further evaluation to determine eligibility for further workup, including upper gastrointestinal endoscopy. Histopathological changes in duodenal biopsies will be compared with duodenal biopsies obtained from USA controls who have celiac disease, Crohn’s disease, or who were found to have normal histopathology. RNA-Seq will be employed to characterize mucosal gene expression across groups. Duodenal biopsies, luminal aspirates from the duodenum, and fecal samples will be analyzed to define microbial community composition (omic analyses). The relationship between histopathology, mucosal gene expression, and community configuration will be assessed using a variety of bioinformatic tools to gain better understanding of disease pathogenesis and to identify mechanism-based biomarkers. Ethical review committees at all collaborating institutions have approved this study. All results will be made available to the scientific community.

Discussion

Operational and ethical constraints for safely obtaining intestinal biopsies from children in resource-poor settings have led to a paucity of human tissue-based investigations to understand and reverse EE in vulnerable populations. Furthermore, EE biomarkers have rarely been correlated with gold standard histopathological confirmation. The Study of Environmental Enteropathy and Malnutrition (SEEM) is designed to better understand the pathophysiology, predictors, biomarkers, and potential management strategies of EE to inform strategies to eradicate this debilitating pathology and accelerate progress towards the 2030 Sustainable Development Goals.

Trial registration

Retrospectively registered; clinicaltrials.gov ID NCT03588013.

Electronic supplementary material

The online version of this article (10.1186/s12887-019-1564-x) contains supplementary material, which is available to authorized users.

Identifying the etiology and pathophysiology underlying stunting and environmental enteropathy: study protocol of the AFRIBIOTA project

BACKGROUND

Globally one out of four children under 5 years is affected by linear growth delay (stunting). This syndrome has severe long-term sequelae including increased risk of illness and mortality and delayed psychomotor development. Stunting is a syndrome that is linked to poor nutrition and repeated infections. To date, the treatment of stunted children is challenging as the underlying etiology and pathophysiological mechanisms remain elusive. We hypothesize that pediatric environmental enteropathy (PEE), a chronic inflammation of the small intestine, plays a major role in the pathophysiology of stunting, failure of nutritional interventions and diminished response to oral vaccines, potentially via changes in the composition of the pro- and eukaryotic intestinal communities. The main objective of AFRIBIOTA is to describe the intestinal dysbiosis observed in the context of stunting and to link it to PEE. Secondary objectives include the identification of the broader socio-economic environment and biological and environmental risk factors for stunting and PEE as well as the testing of a set of easy-to-use candidate biomarkers for PEE. We also assess host outcomes including mucosal and systemic immunity and psychomotor development. This article describes the rationale and study protocol of the AFRIBIOTA project.

METHODS

AFRIBIOTA is a case-control study for stunting recruiting children in Bangui, Central African Republic and in Antananarivo, Madagascar. In each country, 460 children aged 2-5 years with no overt signs of gastrointestinal disease are recruited (260 with no growth delay, 100 moderately stunted and 100 severely stunted). We compare the intestinal microbiota composition (gastric and small intestinal aspirates; feces), the mucosal and systemic immune status and the psychomotor development of children with stunting and/or PEE compared to non-stunted controls. We also perform anthropological and epidemiological investigations of the children's broader living conditions and assess risk factors using a standardized questionnaire.

DISCUSSION

To date, the pathophysiology and risk factors of stunting and PEE have been insufficiently investigated. AFRIBIOTA will add new insights into the pathophysiology underlying stunting and PEE and in doing so will enable implementation of new biomarkers and design of evidence-based treatment strategies for these two syndromes.

Exploring the relationship between environmental enteric dysfunction and oral vaccine responses

Oral vaccines significantly underperform in low-income countries. One possible contributory factor is environmental enteric dysfunction (EED), a subclinical disorder of small intestinal structure and function among children living in poverty. Here, we review studies describing oral vaccine responses and EED. We identified eight studies evaluating EED and oral vaccine responses. There was substantial heterogeneity in study design and few consistent trends emerged. Four studies reported a negative association between EED and oral vaccine responses; two showed no significant association; and two described a positive correlation. Current evidence is therefore insufficient to determine whether EED contributes to oral vaccine underperformance. We identify roadblocks in the field and future research needs, including carefully designed studies those can investigate this hypothesis further.

Environmental Enteropathy in Undernourished Pakistani Children: Clinical and Histomorphometric Analyses

Despite nutrition interventions, stunting thought to be secondary to underlying environmental enteropathy (EE) remains pervasive among infants residing in resource-poor countries and remains poorly characterized. From a birth cohort of 380 children, 65 malnourished infants received 12 weeks of nutritional supplementation with ready-to-use therapeutic food (RUTF). Eleven children with insufficient response to RUTF underwent upper endoscopy with duodenal biopsies, which were compared with U.S., age-matched specimens for healthy, celiac disease, non-celiac villous atrophy, non-celiac intraepithelial lymphocytosis, and graft-versus-host disease patients. Of the 11 children biopsied, EE was found in 10 (91%) with one subject with celiac disease. Morphometry demonstrated decreased villus-to-crypt (V:C) ratios in EE relative to healthy and non-celiac lymphocytosis patients. Environmental enteropathy villus volumes were significantly decreased relative to healthy controls. In EE, average CD3⁺ cells per 100 epithelial cells and per 1,000 µm² of lamina propria and the number of lamina propria CD20⁺ B-cell aggregates were increased relative to all other groups. Our results indicate that V:C ratios are reduced in EE but are less severe than in celiac disease. Environmental enteropathy intraepithelial and lamina propria T lymphocytosis is of greater magnitude than that in celiac disease. The increases in lamina propria B and T lymphocytes suggest that non-cytolytic lymphocytic activation may be a more prominent feature of EE relative to celiac disease. These results provide new insights into shared yet distinct histological and immunological features of EE and celiac disease in children.

Causes of impaired oral vaccine efficacy in developing countries

Oral vaccines are less immunogenic when given to infants in low-income compared with high-income countries, limiting their potential public health impact. Here, we review factors that might contribute to this phenomenon, including transplacental antibodies, breastfeeding, histo blood group antigens, enteric pathogens, malnutrition, microbiota dysbiosis and environmental enteropathy. We highlight several clear risk factors for vaccine failure, such as the inhibitory effect of enteroviruses on oral poliovirus vaccine. We also highlight the ambiguous and at times contradictory nature of the available evidence, which undoubtedly reflects the complex and interconnected nature of the factors involved. Mechanisms responsible for diminished immunogenicity may be specific to each oral vaccine. Interventions aiming to improve vaccine performance may need to reflect the diversity of these mechanisms.

The Sanitation Hygiene Infant Nutrition Efficacy (SHINE) Trial: Rationale, Design, and Methods

Child stunting and anemia are intractable public health problems in developing countries and have profound short- and long-term consequences. The Sanitation Hygiene Infant Nutrition Efficacy (SHINE) trial is motivated by the premise that environmental enteric dysfunction (EED) is a major underlying cause of both stunting and anemia, that chronic inflammation is the central characteristic of EED mediating these adverse effects, and that EED is primarily caused by high fecal ingestion due to living in conditions of poor water, sanitation, and hygiene (WASH). SHINE is a proof-of-concept, 2 × 2 factorial, cluster-randomized, community-based trial in 2 rural districts of Zimbabwe that will test the independent and combined effects of protecting babies from fecal ingestion (factor 1, operationalized through a WASH intervention) and optimizing nutritional adequacy of infant diet (factor 2, operationalized through an infant and young child feeding [IYCF] intervention) on length and hemoglobin at 18 months of age. Within SHINE we will measure 2 causal pathways. The program impact pathway comprises the series of processes and behaviors linking implementation of the interventions with the 2 child health primary outcomes; it will be modeled using measures of fidelity of intervention delivery and household uptake of promoted behaviors and practices. We will also measure a range of household and individual characteristics, social interactions, and maternal capabilities for childcare, which we hypothesize will explain heterogeneity along these pathways. The biomedical pathway comprises the infant biologic responses to the WASH and IYCF interventions that ultimately result in attained stature and hemoglobin concentration at 18 months of age; it will be elucidated by measuring biomarkers of intestinal structure and function (inflammation, regeneration, absorption, and permeability); microbial translocation; systemic inflammation; and hormonal determinants of growth and anemia among a subgroup of infants enrolled in an EED substudy. This article describes the rationale, design, and methods underlying the SHINE trial.

CLINICAL TRIALS REGISTRATION

NCT01824940.

Environmental Enteric Dysfunction in Children

Diarrheal diseases are a major cause of childhood death in resource-poor countries, killing approximately 760,000 children younger than 5 years each year. Although deaths due to diarrhea have declined dramatically, high rates of stunting and malnutrition have persisted. Environmental enteric dysfunction (EED) is a subclinical condition caused by constant fecal-oral contamination with resultant intestinal inflammation and villous blunting. These histological changes were first described in the 1960s, but the clinical effect of EED is only just being recognized in the context of failure of nutritional interventions and oral vaccines in resource-poor countries. We review the existing literature regarding the underlying causes of and potential interventions for EED in children, highlighting the epidemiology, clinical and histologic classification of the entity, and discussing novel biomarkers and possible therapies. Future research priorities are also discussed.

Environmental enteric dysfunction: pathogenesis, diagnosis, and clinical consequences

Stunting is common in young children in developing countries, and is associated with increased morbidity, developmental delays, and mortality. Its complex pathogenesis likely involves poor intrauterine and postnatal nutrition, exposure to microbes, and the metabolic consequences of repeated infections. Acquired enteropathy affecting both gut structure and function likely plays a significant role in this outcome, especially in the first few months of life, and serve as a precursor to later interactions of infection and malnutrition. However, the lack of validated clinical diagnostic criteria has limited the ability to study its role, identify causative factors, and determine cost-effective interventions. This review addresses these issues through a historical approach, and provides recommendations to define and validate a working clinical diagnosis and to guide critical research in this area to effectively proceed. Prevention of early gut functional changes and inflammation may preclude or mitigate the later adverse vicious cycle of malnutrition and infection.

Implications of acquired environmental enteric dysfunction for growth and stunting in infants and children living in low- and middle-income countries

Changes in small bowel function early in infancy in developing countries are increasingly being demonstrated, probably accompanied by altered mucosal architecture in most individuals, including reduced enterocyte mass and evidence of immune activation and inflammation in the mucosa. These alterations appear to be the result of factors of uncertain nature in the environment, and may be a cause of growth faltering and stunting in young children. For these reasons, this constellation of findings is being referred to as environmental enteropathy, or as we propose herein, environmental enteric dysfunction. If the causes were known and effective interventions were available, strategies and policies to intervene at--or possibly before--birth could be developed and promoted in order to prevent subsequent malnutrition and recurrent infection, which are known to interact in a cyclical and synergistic manner in a downward clinical course often ending in death. Resources would be mobilized and applied differently, and the emphasis would change from treatment to prevention. In order to move in this highly desired direction, investments in research will be required to establish the criteria to assess environmental enteric dysfunction, determine its predictive value for growth faltering and stunting, identify the causes, and propose and test potential interventions. The concepts and tools are available. What is required is the decision to move forward along this pathway to better health for infants and children in low-income countries.

13C-sucrose breath test: novel use of a noninvasive biomarker of environmental gut health

OBJECTIVE

Environmental enteropathy syndrome may compromise growth and predispose to infectious diseases in children in the developing world, including Australian Aboriginal children from remote communities of the Northern Territory. In this study, we described the use of a biomarker (13)C-sucrose breath test (SBT) to measure enterocyte sucrase activity as a marker of small intestinal villus integrity and function.

METHODS

This was a hospital-based prospective case-control study of Aboriginal and non-Aboriginal children with and without acute diarrheal disease. Using the SBT, we compared 36 Aboriginal case subjects admitted to a hospital (18 diarrheal and 18 nondiarrheal disease), with 7 healthy non-Aboriginal control subjects. Intestinal permeability using the lactulose/rhamnose (L/R) ratio on a timed 90-minute blood test was performed simultaneously with the SBT. The SBT results are expressed as a cumulative percentage of the dose recovered at 90 minutes.

RESULTS

Aboriginal children with acute diarrheal disease have a significantly decreased absorptive capacity, as determined by the SBT, with a mean of 1.9% compared with either Aboriginal children without diarrhea (4.1%) or non-Aboriginal (6.1%) control subjects. The mean L/R ratio in the diarrhea group was 31.8 compared with 11.4 in Aboriginal children without diarrhea. There was a significant inverse correlation between the SBT and the L/R ratio.

CONCLUSIONS

The SBT was able to discriminate among Aboriginal children with diarrhea, asymptomatic Aboriginal children with an underlying environmental enteropathy, and healthy non-Aboriginal controls. This test provides a noninvasive, easy-to-use, integrated marker of the absorptive capacity and integrity of the small intestine and could be a valuable tool in evaluating the efficacy of interventions aimed at improving gut health.

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.

Critical appraisal of the management of severe malnutrition: 3. Complications

The high case-fatality of severe malnutrition is due to infections, dehydration, electrolyte disturbances and heart failure. We focus on the evidence about managing these complications of severe malnutrition. Signs of circulatory collapse in severely malnourished children should be treated with intravenous or bone marrow infusion of Ringer's lactate with additional dextrose and potassium at a rate 20-40 mL/kg fast with close monitoring of vital signs. Recommendations for slow or restricted fluids in the face of shock are unsafe, and hypotonic or maintenance solutions must be avoided to prevent hyponatraemia. However, the evidence that severely malnourished children do not tolerate excessive fluid administration is good, so caution must be exercised with regards to fluids in the initial phase of treatment. There is also good evidence that wide spectrum antibiotics need to be given empirically for severe malnutrition to prevent the otherwise unavoidable early mortality. There is a need for improved protocols for tuberculosis diagnosis, HIV management and treatment of infants under 6 months with severe malnutrition. The contribution of environmental enteropathy to poor growth and nutrition during the weaning period means that there should be more priority on improving environmental health, particularly better hygiene and less overcrowding. A T-cell mediated enteropathy contributes to growth failure and malnutrition, and it is related to environmental contamination of enteric organisms in the weaning period rather than allergic responses.

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.

Intestinal permeability in kwashiorkor

Intestinal permeability can be assessed non-invasively using the lactulose-rhamnose (L-R) test, which is a reliable measure of small intestinal integrity.

AIMS

To determine risk factors for abnormal intestinal permeability in kwashiorkor, and to measure changes in L-R ratios with inpatient rehabilitation.

DESIGN

A case-control study of 149 kwashiorkor cases and 45 hospital controls. The L-R test was adapted to study kwashiorkor in Malawi, with testing at weekly intervals during nutritional rehabilitation. Urine sugars were measured by thin layer chromatography in London.

RESULTS

The initial geometric mean L-R ratios (x100) (with 95% confidence interval) in kwashiorkor were 17.3 (15.0 to 19.8) compared with 7.0 (5.6 to 8.7) for controls. Normal ratios are < 5, so the high ratios in controls indicate tropical enteropathy syndrome. Abnormal permeability in kwashiorkor was associated with death, oliguria, sepsis, diarrhoea, wasting and young age. Diarrhoea and death were associated with both decreased L-rhamnose absorption (diminished absorptive surface area) and increased lactulose permeation (impaired barrier function) whereas nutritional wasting affected only L-rhamnose absorption. Despite, clinical recovery, mean L-R ratios improved little on treatment, with mean weekly ratios of 16.3 (14.0 to 19.0), 13.3 (11.1 to 15.9) and 14.4 (11.0 to 18.8).

CONCLUSION

Abnormal intestinal permeability in kwashiorkor correlates with disease severity, and improves only slowly with nutritional rehabilitation.

The ontogeny of the gut mucosal immune system and the susceptibility to infections in infants of developing countries

In this review we summarize data on the human gut mucosa associated lymphatic tissues as part of the common mucosal immune system. Its embryonal-fetal and post-natal ontogeny becomes severely distorted and compromised by mal-/undernutrition which is so prevalent in developing countries. Pathogenetic interdependencies exist between maternal-fetal undernutrition, the ontogeny of the immune system, constant antigenic stimulation of the mucosal immune system post-natally, and the 14 million deaths annually from infections in children below the age of 5 years in developing countries. A detailed knowledge of these interdependencies is required for effective prevention and treatment in an attempt to reduce the high morbidity and mortality rates of children in developing countries.

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.

[Effect of bulk materials on the upper intestinal tract]

Dietary fibers comprise a very heterogenous group of indigestible plant compounds. Whereas they exert only little effects on the recovery of the digestible parts of a meal they can modify various digestive processes. Most important seems to be the ability to inhibit digestion and absorption of carbohydrates, which enables better treatment of diabetics. The observation that serum cholesterol can be decreased by certain dietary fibers finds special interest also because of the possible reduction of risk for developing atherosclerosis. The various effects depend upon the physicochemical properties of the different fibers: they comprise the ability to bind water and organic substances, viscosity and cationic-exchange.

Tropical enteropathy in Rhodesia

Tropical enteropathy, which may be related to tropical sprue, has been described in many developing countries including parts of Africa. The jejunal changes of enteropathy are seen in Rhodesians of all social and racial categories. Xylose excretion, however, is related to socioeconomic status, but not race. Upper socioeconomic Africans and Europeans excrete significantly more xylose than lower socioeconomic Africans. Vitamin B12 and fat absorption are normal, suggesting predominant involvement of the proximal small intestine. Tropical enteropathy in Rhodesia is similar to that seen in Nigeria but is associated with less malabsorption than is found in the Caribbean, the Indian subcontinent, and South East Asia. The possible aetiological factors are discussed. It is postulated that the lighter exposure of upper class Africans and Europeans to repeated gastrointestinal infections may accound for their superior xylose absorption compared with Africans of low socioeconomic circumstances. It is further suggested that the milder enteropathy seen in Africa may be explained by a lower prevalence of acute gastroenteritis than in experienced elsewhere in the tropics.