Cultivation of helminths in chick embryos.

A total of 23 species from 14 families of the Digenea have been studied in chick embryos, mainly on the chick chorioallantoic membrane (CAM). Most species for which cultivation has produced ovigerous adults in chick embryos have been avian digeneans with progenetic metacercariae. Less success has been obtained with the hermaphroditic, non-progenetic, economically important trematodes such as fasciolids and echinostomatids, although post-metacercarial development has been achieved for Fasciola hepatica and Echinostoma trivolvis (synonym of E. revolutum) (see Fried and Butler, 1979; Fried and Pentz, 1983). Success with human or animal blood flukes has been minimal, although adults of Schistosoma mansoni and Spirorchis spp. (turtle blood flukes) have at least been maintained on the CAM (see Fried et al., 1982; Fried and Tornwall, 1969). Schistosome cercariae and in vitro transformed cercariae (schistosomules) should be tested in chick embryos. Marine avian schistosomes in the genera Austrobilharzia and Ornithobilharzia, along with the freshwater avian schistosome Trichobilharzia, would provide useful material for avian embryo studies on non-human schistosomes. Studies on trematodes in chick embryos have been done mainly to gain basic biological information on these parasites. That is, to identify species for which definitive hosts are not available; for studies on worm-intraspecific variation, growth and development; for studies on worm feeding and digestion; and for studies on worm-mediated chemoattraction and worm site location on the CAM (Fried, 1989). Sites other than the upper surface of the CAM have not been well-explored for digeneans, although Irwin and Saville (1988a,b) have examined the subchorioallantois and allantois as habitats for stigeids and microphallids. They have also studied the effects of serum supplements to the embryo on the enhancement of worm growth and development. Irwin and Saville's work should be extended to other helminths. The albumen in the hen's egg is a good site for the development of Clinostomum marginatum and Amblosoma sawaense (see Larson and Uglem, 1990; Fried et al., 1981), but the reasons for the better growth of these parasites in the albumen than on the CAM are not known. The inoculation of trematode larvae into CAM blood vessels, the yolk sac, the amnion and the embryo proper have not been explored and may provide useful avenues of research. Only a single study has been done with a monogenean trematode, Polystomoides sp. (see Fried, 1965), in which worms were grown on the CAM at 30 degrees C.(ABSTRACT TRUNCATED AT 400 WORDS)