藐小棘隙吸虫尾蚴生物学研究

STUDIES ON BIOLOGY OF ECHINOCHASMUS LILIPUTANUS CERCARIAE

本研究在室内及自然条件下对藐小棘隙吸虫尾蚴在其第一中间宿主铜锈环棱螺体内形成、逸出节律及影响因素以及尾蚴的行为进行了系列观察。在露天实验池 4～ 5月份投放虫卵感染阴性铜锈环棱螺 ,经 10 3～ 140 d尾蚴从宿主螺体内逸出 ;9～ 10月份投放虫卵 ,直到第 2年 8月前后才有尾蚴逸出 ,需 30 0多天。在现场对铜锈环棱螺逐月检查结果表明 ,螺体内尾蚴检出率呈明显的年周期变化 :每年 7月底尾蚴出现 ,12月初消失 ,检出高峰在 9～11月。 10月份 (平均气温为 2 3.2℃ ) ,每只螺平均每天逸蚴 2 0 92 0 0条。在自然条件下 ,尾蚴逸出数量呈日周期变化 :尾蚴逸出时间主要集中在 8:0 0～ 16 :0 0 ,逸出高峰在 10 :0 0～ 12 :0 0 ,夜晚几乎无逸出。 4× 4拉丁方实验和 2× 2析因实验显示 ,温度、光照强度是影响尾蚴逸出的主要因素 ,但两者无交互作用。当温度、光照强度恒定时 ,尾蚴原先的逸出节律 (日周期变化 )消失。尾蚴具趋光性 ,新近 (12 h内 )逸出的尾蚴主要分布在水体的上表层 6 cm以内。对尾蚴寿命的观察显示 ,在 6℃、15℃、2 0℃、2 5℃、30℃和 37℃恒温条件下尾蚴的半数死亡时间分别为 2 5 9h、139.7h、10 5 .9h、83.7h、6 9.2 h和 12 .3h;尾蚴寿命与水温呈负相关关系 (r=- 0 .96 8,P<0 .0 1)。尾蚴?

Echinochasmus liliputanus cercariae formation in and emergence from the snail host, Bellamya aeruginosa , and its behavior in natural and experimental conditions were studied. The eggs of E. liliputanus collected from the feces of experimentally infected dogs were directly delivered into outdoors experimental pools that contain B. aeruginosa snails. The snails were then examined regularly for emergence of the cercariae. The cercariae were detected from the snails 103-140 days after the egg delivery when the eggs were delivered between the 7th of April and the 25th of May, however when the eggs were delivered during the period from the 3rd of September to the 5th of October it took much longer time for the cercariae to be detected from the snails (more than 300 days). Natural infection of B. aeruginosa was investigated in Chenqiaozhou Village, Hexian County, Anhui Province. The results showed a typical cirannual rhythm in infection rate of the snails, i.e. the cercariae first appeared in late July and disappeared in early December with a peak between October and November. The cercariae emerge regularly from the epitaenial fold of the positive snails. During October with a mean temperature of 23.2℃, the daughter radiae within the snails were able to constantly reproduce and release a large number of cercariae with a average number of 209 200 cercariae daily per snail. In the natural conditions, the release of cercariae from the snails showed a typical diurnal pattern, i.e. cercariae being released mainly between 8:00 and 16:00 with a significant peak between 10:00 and 12:00, and no cercariae being released during night. It was proven that the main factors affecting the emerging of cercariae were temperature and light. When temperature and light were stable and constant, the peak shedding of cercariae during the day became less apparent. The cercariae were phototactic and the newly shed cercariae tended to distribute within the surface water(maximum 6 cm deep from the surface). It was also showed that the time of 50% mortality of the newly released cercariae at 6℃, 15℃, 20℃, 25℃, 30℃ or 37℃ was 259 h, 139.7 h, 105.9 h, 83.7 h, 69.2 h or 12.3 h respectively. There was a negative correlation between temperature and cercarial survival (r=-0.968, P <0.01). The infectivity of cercariae was cercarial age dependent. At 25℃ the infectivity was only 35% immediately after emergence. It increased to over 64% 9 h after emergence, but then declined steadily to below 1% by 72 h post emergence. The cercariae longevity exceeded the period of infectivity at the same temperature.