Growth and Protein Energy Malnutrition

Although clinical studies confirm that these parasites have the potential to interfere with growth and nutritional status, evidence that they are a major cause of the widespread stunting and protein-energy malnutrition seen in developing countries is not as conclusive as may be expected. This may be because most infected individuals in a community will have only low to moderate parasite loads and whether a particular disease is important in precipitating malnutrition on a community or public health scale will depend on whether or not such low level infections impact on nutritional status. Information has come from two types of study: (1) cross-sectional surveys; and (2) longitudinal, placebo controlled intervention studies in which nutritional improvements are sought following the use of antiparasite drugs.

A large number of cross-sectional community studies have associated parasitic infection with growth deficits and poor anthropometric indices. Schistoso-miasis has long been associated with poor growth, and an extreme condition, schistosomiasis dwarfism, in which physical and sexual development were severely retarded was reported to be quite common in China until the 1950s. Most recent studies of mild to moderate infection with all three schistosome species confirm an association with poor nutritional status that is more marked in girls, but the degree of impairment is variable between different regions and at best can only explain a small part of the total nutritional deficit of the subjects. Hookworm infection is similarly associated with poor appetite, slower growth, and lowered nutritional indices, all of which become more marked with increasing severity of iron deficiency anemia. Iron supplementation of hookworm-infected children has been reported to improve appetite and growth performance as well as iron status, suggesting that the lowered nutritional status may be secondary to iron deficiency rather than a direct effect of the parasite. Growth retardation seen in moderate to heavy T. trichiura infection may be similarly explained, although heavier burdens of this worm frequently cause dysentery, which can result in loss of essential trace elements such as zinc.

The impact of the protozoal parasites Giardia and Crytosporidium on nutritional status has been less well studied, but infection appears to be associated with persistent diarrheal disease and prolonged growth faltering even after apparent elimination of the parasites. Moreover, these parasites, unlike the helminths, are very common in children during the first 2 years of life when growth is at its greatest. Growth-retarding infections at this time of life, particularly in developing countries, appear to compromise growth throughout the whole growth period, thus the impact of these parasites on nutritional status may be far greater than currently appreciated. This is certainly an area requiring more research.

The results of these cross-sectional studies have been reinforced by longitudinal community-wide studies of nutritional improvement following reduction or eradication of parasite burden with anthelmintic drugs. The results of such studies have, however, been less than convincing. Successful treatment of heavily poly-parasitized Kenyan children harboring hookworm, A. lumbricoides and T. trichiura, with albendazole resulted in improvements in weight, arm circumference, and skinfold thickness and was associated with increased appetite and fitness. Statistical analysis of this data implicated hookworm as being the most important in compromising nutritional status. Weight gain above placebo-treated counterparts averaged 1.3 kg per 6 months, and added about 3% points to a weight-for-age of approximately 80%. However, similar studies in many parts of the world in subjects with lower intestinal helminth burdens have reported only small improvements, whereas others found no change at all in nutritional status indices following successful deworming. Treatment of schis-tosomiasis in Kenyan, Brazilian, and Filipino children showed only small improvements in nutritional status, e.g., in Kenya, the per cent weight-for-age only increased from 72.9 to 74.9% following eradication with praziquantel. A recent meta-analysis of these studies concluded that deworming did improve nutritional status, but that the effect was small.

Overall, both community and intervention studies do suggest that elimination of GI parasites would improve growth and anthropometric status of children in developing countries but that such improvement would be limited. This contrasts with the very substantial improvement in iron status and iron deficiency anemia that follows effective treatment of organisms causing blood loss.

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