Transdisciplinarity in the study of undernutrition-infection interactions.

Interactions between undernutrition, infection, and growth and development are complex, and are reviewed in this article, giving particular emphasis on the importance of diarrheal infection in this process. The effects of diet, nutrition and infection on the nutritional status of a child can vary according to the disease ecology, the age of the child, patterns of feeding and types of food consumed. There are two possible ways in which this relationship can begin; one in which poor nutritional status leads to impaired immunocompetence and reduced resistance to infection, and the other in which exposure to infectious disease can lead to appetite loss and anorexia, malabsorption, and elevated metabolism of energy and other nutrients. Once started, the interactions between these two major environmental stressors becomes increasingly complex, with the nature of the disease ecology influencing the balance of immunoparesis and adaptive immunity and its effect on subsequent disease experience. Furthermore, the disease ecology influences the type and extent of associated physiological phenomena including anorexia, fever, and malabsorption, all of which have an impact on nutritional status. Of disease categories, diarrhea has particularly potent effects in this relationship. The predicted impact of HIV infection among newborn infants is the earlier onset of the undernutrition-infection cycle, as low CD4+ T lymphocyte counts soon after birth are likely to predispose such infants to earlier opportunistic infection.