Parasites as biological models

Abstract

The value of metazoan parasites as models for the investigation of fundamental biological phenomena is discussed. The fields in which they are of particular value include: immunology, neuromuscular physiology, nucleo-cytoplasmic relationships, genetics, cyto-differentiation, comparative biochemistry.After reviewing some examples of experimental organisms in trematodes and nematodes, the cestode, Echinococcus granulosus, in particular, is examined as a model.Problems of particular interest in this organism are: the function of the rostellar gland, whose cells release a secretion which has its origin in the nuclei of these cells; the mode of action of the suckers, which in vivo are thought to remain in a state of sustained contraction; the mode of digestion at the host–parasite interface—membrane digestion appears to be involved; the various modes of membrane transport through the tegument; factors controlling cystic or strobilar differentiation, a problem viewed in the light of the Jacob–Monad model of gene action.A hypothetical control circuit for differentiation of the stages in parasite life-cycles in general is also put forward.Some preliminary experiments on the in vitro culture of Taenia serialis, are described. The factors controlling differentiation into cystic or strobilar directions appear to be generally similar to those which operate for Echinococcus granulosus.It was stressed that many other species of parasites could also serve as models for investigating similar or related problems.Some of the studies described here were supported by grants from the Australian Wool Board, the U.S. Public Health Service (Grant no. A 107452–02) and the Rural Credits Development Fund.I am grateful to Mr D. Heath for the provision of the micrographs of Taenia pisiformis and T. serialis in P1. 2, figs. 2, 3.