Abstract
Life cycles of intestinal parasites are complex, often involving several stages within a single host. Successful maturation depends on an orderly development of successive stages, a process that is linked inseparably to the acquisition of food from habitats within the host. To survive, parasites must have specific nutrients available in their environment as well as specific chemical and physical stimuli that control feeding behavior. These strict nutritional, chemical, and physical requirements, which may differ greatly from one stage to the next, are maintained by the host's homeo-static mechanisms.
Knowledge of how and what parasites eat may be obtained from consideration of anatomical mechanisms that have been adapted for acquisition of foodstuffs; from studies of the chemical composition and intermediary metabolism of the parasites; from in vitro cultivation experiments and from examination of the types of tissues the parasites feed upon. Intestinal parasites may compete with the host for orally ingested food, acquire nutrients from the parenteral or exocrino-enteric circulations, or receive nourishment from the solid tissues of the host. The degree to which each source is utilized has been difficult to assess experimentally because of the problems of studying one in the absence of the others.
The objective of this investigation was to determine if the helminths, Trichinella spiralis and Hymenolepis diminuta, could develop normally in rats which did not ingest food orally, i.e., animals in which all nutrients in the intestine were derived from the parenteral or exocrino-enteric circulations.
Methods and Materials. T. spiralis is a nematode that dwells in the small bowel with its head embedded in the mucosa and the remainder of its body exposed to the lumen. It is bisexual and matures within 72 hr after infection. H. diminuta is a monoecious, lumen-dwelling tapeworm that reaches maturity within 14-16 days following infection.
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