Malabsorption in Africa

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.

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.

Aetiology and pathogenesis of postinfective tropical malabsorption (tropical sprue)

Postinfective tropical malabsorption (TM; tropical sprue) starts with an acute intestinal infection (bacterial, viral, or parasitic) which can affect predominantly the small or the large intestine. Miscellaneous invasive pathogens cause subsequent enterocyte damage affecting the entire small intestine and, to a lesser extent, the colon. Enteroglucagon, a tropic hormone, is then liberated and reaches a high plasma concentration. Small-intestinal stasis results. Further bacterial colonisation (in the lumen and also at the enterocyte surface) is encouraged. Continuing enterocyte damage is worsened by coexistent folate depletion, which is initiated at the onset of disease; body stores of folate reach a low concentration by 3 or 4 months. The cycle continues until the bacterial overgrowth is eliminated with an antibiotic (eg, tetracycline), or mucosal integrity recovers (hastened by oral folic-acid supplements), or both.

Intestinal absorption in Saudi Arabia: an evaluation of the one hour blood xylose test

The screening value of the one-hour blood xylose test, corrected for body surface area, was prospectively studied in Saudi Arabian adults and children under investigation for suspected intestinal malabsorption. Sensitivity of discrimination between patients with and without upper small bowel disease was 91%, compared to 85% for the five-hour urine xylose test. Primary small bowel disorder was rare. In a three-year review, no cases of adult coeliac disease or tropical sprue were found. The most common causes of malabsorption were intestinal tuberculosis, abdominal lymphoma and immunoproliferative small intestinal disease. Despite its acceptability as an index of proximal small bowel function, the blood xylose test alone is an inadequate screening test for any of these conditions.

Jejunal absorption rates of glucose and glycine in post-infective tropical malabsorption

In a prospective study jejunal absorption rates of glucose (from a 200 mmol 1-1 solution) and glycine (from a 100 mmol 1-1 solution) were measured, using a perfusion technique, in nine patients with clinical evidence of post-infective tropical malabsorption (TM group) and in 10 others with trivial symptoms who had also visited the tropics (control group); all were of northern European origin. Seven and one in the two groups, respectively, had Giardia lamblia infections. Mean glucose absorption rate was significantly impaired by TM (P less than 0.01); mean rate for glycine was also depressed but not significantly. Presence of G. lamblia did not affect the severity of malabsorption although numbers studied were small.

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.

Endemic tropical sprue in Rhodesia

The existence of tropical sprue in Africa is controversial. In this paper we present 31 cases seen in Rhodesia over a 15 month period. They have the clinical features, small intestinal morphology, malabsorption pattern, and treatment response of tropical sprue. Other causes of malabsorption, and primary malnutrition, have been excluded. The severity of the clinical state and intestinal malabsorption distinguish these patients from those we have described with tropical enteropathy. The previous work on tropical sprue in Africa is reviewed and it is apparent that, when it has been adequately looked for, it has been found. It is clear that the question of tropical sprue in Africa must be re-examined and that it existence may have hitherto been concealed by the assumption that primary malnutrition is responsible for the high prevalence of deficiency states.

D-xylose absorption and jejunal morphology in African patients with pellagra (niacin tryptophan deficiency)

D-xylose absorption tests and jejunal morphology have been shown to be unaltered in 12 African patients with pellagra when compared with normal values for Zambian Africa adults; that result is contrary to two previous investigations in India and Egypt respectively. A significant inverse association has been shown, however, between D-xylose absorption and serum immunoglobulin IgG and IgA concentrations; that is consistent with previous studies and probably reflects malabsorption of xylose in the presence of systemic infections. It is concluded that pellagra per se does not alter intestinal structure or monosaccharide absorption.

High intestinal lactase concentrations in adult Arbs in Saudi Arabia

The maximum rise in blood glucose after 50 g lactose by mouth was determined in 40 adult Arabs. Out of 30 Bedouin, urban Saudi, and Yemeni and 9 of mixed ancestry (usually partly African), 25 (83%) and 2 (22%) respectively showed an increase of over 1-1 mmol/1 (20 mg/100 ml). In common with most northern Europeans and Hamitic people of northern Africa, Arabs in Saudi Arabia usually have high intestinal lactase concentrations in adult life. This persistence of high levels probably originated in the Arabian peninsula. Its selective advantage may have been associated with the fluid and calorie content of camels' milk, which is important for survival in desert nomads.