Biochemistry and Physiology of Tapeworms

Abstract

The data available show that tapeworms have many physiological modifications, some of which may be correlated with obligate parasitism. The latter include: nutritional dependence on carbohydrate for growth and reproduction coupled with the limitation effected by the capacity to use only simple sugars; limited ability to perform transamination reactions; a general incapacity to digest complex organic molecules from the surrounding medium; very active membrane transport systems associated with the outer surface and showing stereospecificity for various classes of small organic molecules such as monosaccharides and amino acids; an incapacity of many species to osmoregulate but with obvious adaptations to the osmotic pressures and ionic strengths of vertebrate body fluids; and specific reactions of oncospheres and later larval stages to physiochemical factors involved in establishment within a host. The limited information available suggests that, except for carbohydrate, the nutritional requirements of tapeworms may not be much more complicated than those of vertebrates. The physiological specializations thus far delineated in tapeworms strongly support the hypothesis that the broad determinant of obligate parasitism in this group of organisms is dependence on the chemical regulatory mechanisms posessed by their vertebrate hosts. Tapeworms seem to lack many functions usually associated with maintenance of a steady state.