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Korean J Parasitol > Volume 29(2):1991 > Article

Original Article
Korean J Parasitol. 1991 Jun;29(2):161-172. Korean.
Published online Mar 20, 1994.  http://dx.doi.org/10.3347/kjp.1991.29.2.161
Copyright © 1991 by The Korean Society for Parasitology
Experimental life history of Echinostoma hortense
S H Lee,S W Hwang,W M Sohn,*W G Kho,*S T Hong and J Y Chai
Department of Parasitology and Institute of Endemic Diseases, Seoul National University College of Medicine, Seoul 110-460, Korea.

The complete life cycle of Echinostoma hortense has been maintained in the laboratory, using Lymnaea pervia snails and Rana nigromaculata tadpoles as the first and second intermediate hosts. ICR mice was used as the definitive host. Within the egg of E. hortense, the miracidium was fully matured in 13 days of incubation at 29-30℃. The miracidium was 93.8 × 53.6 µm in average size, covered with numerous cilia of 7-11 µm length. The epidermal plates were arranged in 6-8-4-2 formula. The first generation rediae (1.19 × 0.27 mm in average size) were observed in 14 days after miracidial challenge to the snails, and the second generation rediae (1.40 × 0.26 mm in average size) in 30 days. The average size of the cercaria was 295.5 × 145.0 µm. Their head crown was poorly developed, and collar spines were not yet observed.

After a cercarial challenge to the tadpoles, all of the tadpoles became infected and the average worm recovery rate was 88.5%. The majority of the metacercariae (75.5%) were recovered from the muscle of the tadpole's posterior body and the rest (24.3%) from their gills. The metacercariae from the tadpoles were elliptical, and 167.7 × 129.9 µm in average size. The recovery rate of adults from the mice was different by the age of the metacercariae grown in the tadpoles. The metacercariae younger than 5 hrs could not infect mice whereas those older than 6 hrs could infect mice. The recovery rate became higher as the metacercaria matured, with the peak recovery rate of 90.0% at the metacercarial age of 9 days. Thereafter the recovery rate decreased to 55.0% at the age of 50 days. As shown by the above results, the whole life cycle of E. hortense has been completed in the laboratory. At least 55-58 days were required to maintain one egg-to-egg cycle of E. hortense.


Figs. 1-4
Fig. 1. A newly laid egg of Echinostoma hortense.

Fig. 2. A developing egg after 6 day of incubation.

Fig. 3. A developing egg after 8 day of incubation.

Fig. 4. An almost fully-developed egg after 13 days of incubation.

*Bar unit: µm

Fig. 5
A miracidium of E. hortense showing an eye spot and numerous cilia.

*Bar unit: µm

Fig. 6
A miracidium of E. hortense showing epidermal plates.

*Bar unit: µm

Fig. 7
Lymnaea pervia, used as the first intermediate host in this study.

*Bar unit: µm

Figs. 8-13
Fig. 8. Sporocysts of E. hortense (arrow heads) in the mantle of a snail 2 hrs after miracidial infection.

Fig. 9. Sporocysts of E. hortense (arrow heads) in the head-foot of a snail 7 days after miracidial challenge.

Fig. 10. A redia in the cephalopedal sinus of a snail, 16 days old.

Fig. 11. Rediae (arrow heads) in the digestive glands of a snail, 16 days old.

Fig. 12. A redia in the head-foot of a snail, 21 days old.

Fig. 13. A redia in the hemocele of a snail, 21 days old.

*Bar unit: µm

Figs. 14-17
Fig. 14. A first generation redia, 15 day old.

Fig. 15. A Second generation redia, 25 day old.

Fig. 16. A Second generation redia, 30 day old.

Fig. 17. A cercaria obtained from an experimental snail.

*Bar Unit: µm

Figs. 18-22
Fig. 18. Metacercariae in the gill of a tadpole.

Fig. 19. A metacercaria isolated from the gill of a tadpole.

Fig. 20. An excysted metacercaria showing the collar spines and excretory granules.

Fig. 21. A three-day old juvenile worm showing 4 end group spines (arrow heads).

Fig. 22. Adult of E. hortense from an experimental nouse 12 days after infection.

*Bar unit: µm


Table 1
Measurements of E. hortense rediae from experimentally infected snails

Table 2
Measurements* of E. hortense cercariae from experimentally infected snails (on micrometers)

Table 3
Recovery rates of E. hortense metacercariae from experimentally infected tadpoles

Table 4
Measurements of E. hortense metacercariae from experimentally infected tadpoles

Table 5
The infectivity of E. hortense metacercariae by the age of infection in tadpoles

Table 6
The period form development of E. hortense by stage

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