Adaptive physiological processes in the host during gastrointestinal parasitism

Parasite infection of the gastrointestinal tract with helminths or protozoa induces detrimental effects on host tissues and host physiology, which hav e been extensively studied and reviewed. However, parasitism of the digesti ve system is also associated with adaptive, compensatory phenomena based on changes in host physiology or structures and which tend to counterbalance the negative consequences. The objective of this review is to describe thes e adaptive processes and their possible underlying mechanisms. Different pr ocesses which tend to attenuate the effect of either the loss of appetite, the intestinal malabsorption or the increased tissue losses have been asses sed. These processes have been reported both for helminth and protozoan inf ections, where they present similar characteristics The mechanisms involved in the adaptation to parasitism remain largely unidentified. The role of f eedback mechanisms based on host regulation, possibly through gastrointesti nal hormones, has been raised. On the other hand, some data support the pro posal that parasites themselves may initiate some of the adaptive processes and consequently favour their own survival. These adaptive phenomena appea r to be an essential component in the dynamic balance between host and para sites. Also, parasite infections represent unique models to study the adapt ation of the gastrointestinal tract to aggressors. (C) 2001 Australian Soci ety for Parasitology Inc. Published by Elsevier Science Ltd. All rights res erved.