The interactions of malnutrition and infection are synergistic, with each modifying the other in ways that cannot be predicted from studying just one condition or the other (Scrimshaw, Taylor, and Gordon 1968). The superimposed infection is more likely to be responsible for nutritional disease than a shortage of food alone. During recovery from infectious disease, however, the quantity and quality of food available is usually the limiting factor. Moreover, the frequency and severity of infections is increased for individuals whose nutritional status is poor. Although this increase depends in part on the social and environmental circumstances frequently associated with malnutrition, more important is the reduced resistance to infection directly associated with nutrient deficiency. This chapter examines the reasons why diseases are often more common and severe in the malnourished and discusses the metabolic and other functional consequences of infections.

Nutrition and Disease Morbidity and Mortality

The high frequency of diarrheal and respiratory diseases among young children in developing countries is both a major contributor to malnutrition and a consequence of lowered immunity in a poor sanitary environment combined with unsatisfactory personal hygiene (Mata 1978; Guerrant et al. 1983; Black, Brown, and Becker 1984). Furthermore, in both developing and industrialized countries, nosocomial infections (those originating in hospitals) are responsible for worsening the nutritional status of patients and thereby increasing overall morbidity and case fatality rates (Gorse, Messner, and Stephens 1989; Scrimshaw 1989).

In children whose nutritional status is poor, episodes of any of the common communicable diseases of childhood tend to be more severe and to have more secondary complications. In Guatemala, 50 percent of children with whooping cough require more than 12 weeks, and 25 percent more than 25 weeks, to recover the weight lost because of the disease (Mata 1978). In addition, there is recent evidence for a striking reduction of mortality after vitamin A supplementation was given to populations of underprivileged children in Indonesia (Sommer, Tarwotjo, Hussaini et al. 1983, Sommer,Tarwotjo, Djunaedi et al. 1986) and India (Rahmathullah et al. 1990) and, in general, to poorly nourished children who acquire measles (Barclay, Foster, and Sommer 1987; Hussey and Klein 1990; Coutsoudis et al. 1992).