|
KMID : 0371919880010010137
|
|
Journal of Wonju College of Medicine
1988 Volume.1 No. 1 p.137 ~ p.152
|
|
|
Development and Cercarial Shedding of Echinostoma kortense in the Snail Host, Radix auricularia coreana
|
|
|
|
|
Abstract
|
|
|
It has been proven in the laboratory and according to the field survey that Radix auricularia coreana, a freshwater snail, plays a main role as the first intermediate host of Echinostoma hortense in Korea.
This study aimed to observe 1) the developmental stages of E. hortense larvae in R. auricularia coreana rearing in the laboratory, with live and histological specimens, 2) cercarial shedding from infected snails and 3) the vitality of the host snails infeted with different numbers of miracidia which were hatched out from the parasite´s eggs in the laboratory.
The results obtained from this study are summarized as follows:
1. Larval development in the snails.
a) Miracidia were experimentally placed together with the snails in a beaker containing conditioned tapwater. Miracidia wandering around the snails attacked at the tentacles, head, foot or mantle cavity within 1 to 2 hours. It took approximately more than 5 hours until the parasites have completed invading inside the snails.
b) Miracidia penetrated into the snails were surrounded by host tissues, and developed as sporocysts. Larval development was obviously retarded by complicated host-parasite relationship. However, miracidia penetrated into the soft tissues where body fluid circulated smoothly, easily moved into the host hemocele, ovotestis or digestive glands called liver, and caused damages to the host snails.
c) Thirty one snails were experimentally infected with 5 miracidia each per snail. Of the thirty one snails, 22 (77.4%) were shedding cercariae.
d) According to the repeated redial development, the rediae gradually degenerated, and the numbers of cercariae in the rediae as well as cercarial shedding from the snails were also decreased.
2. Vitality of the infected snails
There showed differences in the vitality according to the number of parasites exposed to the hosts. The more miracidia were exposed to the snails, the earlier snails have died.
The vitality of the snails exposed with 2 to 5 miracidia per snail was 45% to 50% and 12.5% in the snails exposed with 10 miracidia until 60 days after exposure. In the snails exposed with 20 miracidia, 18.2% of the snails were survived 30 days after exposure, and all the snails were dead 45 days after exposure.
3. Number of shedding cercariae
Cercarial shedding is deeply related to the larval development in the snails, and affected with water temperature. The range of water temperature was 13~32℃ and the optimal temperature was 23℃ in the summer season.
Three snail groups were exposed to 2 miracidia (M₂), 10 miracidia (M_(10)) and 20 miracidia (M_(20)), respectively at 18℃ and observed for cercarial shedding at 21~28℃ of water temperature. The initial sheddings of cercariae were on the 26th day after miracidial exposure in M₂ group, and on 15th day in M_(10) and M_(20) groups. It meant that the period of initial shedding of cercariae was delayed in snails infected with smaller numbers of miracidia as compared with the snails infected with larger numbers of miracidia.
A total shedding number of cercariae until death of infected snails was 1,847 per snail in M₂ group, 2,015 in M_(10) group and 1,900 in M_(20) group. Also, the period of days of cercarial shedding from the snails were 48 in M₂ group, 34 in M_(10) group and 16 iin M_(20) group. It general figures, the period of cercarial shedding from the snails infected with more miracidia was remarkably shorter than the snails infected with lesser miracidia, although similar numbers of cercariae were shed among the snail groups infected with different numbers of miradicia.
On the other hand, although there appeared a little differences in cercarial shedding numbers according to the rearing time of the snails among the experimental groups, maximum shedding dates (2~3 days) periodically appeared 3 to 4 times in all the groups.
|
|
|
KEYWORD
|
|
|
|
|
|
FullTexts / Linksout information
|
|
|
|
|
|
Listed journal information
|
|
|
|
|