Gastrointestinal nematodes, nutrition and immunity: Breaking the negative spiral

Nutritionists have long understood that intestinal nematode parasites have deleterious effects on host nutritional status, but only recently has the i mportance of malnutrition as a predisposing factor to intestinal nematodes been recognized. Here we review experimental and field studies on the effec ts of protein, energy, zinc, vitamin A, and iron deficiencies on gastrointe stinal (GI) nematodes of humans, livestock, and laboratory rodents, and dra w certain conclusions about the state of our current understanding, In gene ral, malnutrition promotes the establishment. survival, and fecundity of th ese parasites, but the magnitude of the effect depends on factors such as h ost species, parasite species, particular infection protocol used, magnitud e of the infection, severity of the nutritional deficiency, and presence of single or multiple infections and single or multiple nutritional deficienc ies. We highlight the Th2 arm of the immune system as a component of primar y importance in the association between malnutrition and GI nematode infect ions. We summarize what is known about underlying mechanisms that may accou nt for the observed patterns. Finally, we suggest future research direction s.