Nutritional consequences of infection

Abstract

This discussion will review current knowledge on malnutrition infection interactions, to provide a basis for justifiable interventions to curtail infectious diseases. Interventions should be implemented within the frame of primary health care (PHC). By doing so, malnutrition and mortality are expected to be reduced. The paradigm proposes that infectious diseases, including those caused by parasites, are in fact primary or secondary causes of malnutrition [1,2]. Malnutrition-infection interactions begin when weaning foods are given to breast-fed infants. While such foods may be nutritionally adequate, they are often contaminated with agents that cause diarrhea. Malnutrition, in turn, may be accompanied by alterations in immune response and its amplification [3, 4]. Thus, the negative effects of infection are enhanced, augmenting the risk of severe energy-protein malnutrition (EPM) and death. Good evidence that this paradigm is correct stems from the rapid change of health profiles of several traditional and transitional countries, after emphasizing control and prevention of infectious disease. Just 20 years ago, the role of infection in the causality of malnutrition was mostly ignored by nutrition workers, despite the impressive body of information and the pioneer work of some enlightened authors [3]. However, the relevance of infection had been obvious to those directly involved in village work; the original descriptions of kwashiorkor by Dr. Cicely Williams clearly showed the prominence of episodes of acute infections in children with the syndrome. The emphasis on food, with neglect for infection, stemmed from demonstration that kwashiorkor and marasmus get cured by a diet rich in protein and calories. Such clinical experience influenced scientific thought for more than three decades, with neglect of the other ecologic determinants of mal- nutrition. The "food paradigm" led to the belief that protein was the main limiting factor in diets of poor populations. Later, some authors convincingly demonstrated that the main deficit throughout the world was of calories more than protein [6]. Simultaneously, great skepticism arose regarding the alleged deficiency of local village diets [1, 6]. Failure to recognize the leading role of infection in the causality of malnutrition resulted in the equivocal assumption that diarrheal diseases in children were due to nutritional causes, hence the old term "nutritional diarrheas" [7]. Technological advances in the last 15 years enabled scientists to demonstrate viral and microbial entities in about 70% of diarrhea cases seen in pediatric emergency and outpatient services. It is now accepted that childhood diarrheas originate after ingestion of infectious agents present in food and water, or from direct or indirect contact with contaminated fingers, utensils or fomites [7]. Pediatricians had recognized the importance of diarrheal diseases and other infectious processes in the causality of malnutrition, thanks to their long-term as- sociation with the same children through their development. In reviewing the scientific basis of malnutrition-infection interactions, all infectious diseases deserve consideration because the human host reacts in similar fashion to them, whether they are systemic or localized, whether they affect the skin, blood or other tissues, or whether they are due to viruses, rickettsiae, chlamydia, mycoplasma, bacteria, yeasts, fungi or parasites. However, some emphasis will be given to diarrheal diseases because they are extremely common in less developed countries, and because they have a distinct negative effect on host nutrition and growth [8].