Abstract

The growth and development of the metacercariae of F. seoulensis cultivated in vitro or on the chick chorioallantois were assessed by comparison with the optimum process of maturation in albino rats and new born chickens. The process of maturation was divided for convenience into six stages: Stage 1; cell multiplication, Stage 2; body shaping, Stage 3; separation of genital anlagen, Stage 4; organogeny, Stage 5; gametogony, and Stage 6; oviposition. In Hank's and Tyrode's solutions, the metacercariae were alive up to 200 days or more at 4 degrees C without any development. The in vivo maturation process in rats or chicks was as follows: stage 1 from 6 hours; stage 2 from 24 hours; stage 3 from 48 to 72 hours; stage 4 from 3 to 4 days; stage 5 from 4 to 5 days; and stage 6 from 5 to 8 days. Despite unsuccessful infection of the metacercariae to 12 day old chicks, fully mature worms of stage 5 or 6 were recovered from new born chicks (1 to 2 days old). The metacercariae of F. seoulensis grown in vitro were up to stage 3 and no further maturation was observed. Of various media employed, the medium NCTC 109 (Gibco) or NCTC 135 (Gibco) supplemented with 20% egg yolk or 20% whole egg macerate or 0.5% yeast was basically required for the earlier development of the fluke. It took 16.1 days (in average) to reach the stage 3 after cultivation. The metacercariae cultivated on the chorioallantoic membranes of 6-13 day old chick embryo at 37-38 degrees C showed their full development up to stage 5 or 6. However, the worms were in general remarkably retarded, compared with those grown in rats or chickens. In the experiments of worm transplant, although the transfer was failed from in vitro culture to in vivo of rats (per os), the transplants from in vitro culture to the chorioallantois and from the chorioallantois to in vivo of rat host were successful with or without development of the transferred worms. In the present study, it was observed that the metacercariae of F. seoulensis can be maintained in vitro media with poor development as well as fully matured in 1 to 2 day-old chicks or on the chorioallantois at a very low rate.