藐小棘隙吸虫尾蚴在体内、体外成囊与囊蚴生物学活性实验研究

目的观察藐小棘隙吸虫尾蚴在体内、体外成囊和囊蚴生物学活性以及硝酸银对尾蚴体外成囊的抑制作用。方法尾蚴经或不经硝酸银处理后,观察其在金鱼体内和 Locke's 液等实验溶液中成囊情况;囊蚴在37℃0.1%去氧胆酸钠脱囊液中孵育1h 进行脱囊;同时用两种来源的囊蚴人工感染终宿主新西兰兔,比较其新西兰兔的感染力。结果尾蚴在其第二中间宿主金鱼鱼鳃中1h 即发育为成熟的囊蚴;尾蚴在 Locke's 液、生理盐水、人胃液、人工胃液等溶液中也能发育成囊蚴,24h 成囊率分别为74.28%、44.94%、8.37%和10.79%。尾蚴在0.7×-1.2×Locke's 液和0.7%-1%NaCl 溶液中成囊率较高,但体外形成的正常囊蚴以 Locke's 液最多(正常囊蚴率>50%)。体内形成的1日龄囊蚴、体外形成的正常和异常囊蚴(1日龄)在脱囊液中1h 的脱囊率分别为88.53%、88.60%和84.95%,差异无显著性。异常囊蚴室温下一般在10d内死亡,而正常囊蚴在4℃、0.5×Locke's 液中保存3个月后70%仍能脱囊。体内、体外形成的囊蚴对西兰兔的感染力相似。尾蚴经1uM 硝酸银处理后在 Locke's 液和生理盐水中的成囊率分别为16.25%和6.69%,与对照组相比差异有高度显著性意义(P<0.01);硝酸银处理的尾蚴经多次洗涤后在很大程度上恢复体外成囊(在上述两种溶液中成囊率分别64.80%和39.36%),成囊率与对照组差异无显著性。结论尾蚴在体外能形成具有生物学活性的囊蚴,特别是在人胃液中发育成囊蚴的发现有助于阐明该尾蚴直接感染终宿主的机制。硝酸银处理能可逆地抑制尾蚴在体外成囊,因此推测尾蚴体表的感觉乳突在尾蚴成囊过程中可能起关键作用。这一发现为囊蚴形成机制的研究提供了新思路。

IN VIVO AND IN VITRO ENCYSTMENT OF ECHINOCHASMUS LILIPUTANUS CERCARIAE AND BIOLOGICAL ACTIVITY OF THE METACERCARIAE

Aim To explore if Echinochasmus liliputanus cercariae can develop into metacercariae both in vivo and in vitro and biological activity of the metacercariae, then to determine the effects of silver nitrate on cercariae encystation in vitro. Methods Cercariae of Echinochasmus liliputanus from Bellamya aeruginosa snails treated with or without silver nitrate were used to infected goldfish, the second intermediate host, or to incubated in many different solutions for 24 h to record the encystation rates. The metacercariae formed both in vivo and in vitro were then used to infected New Zealand rabbits to test their infectivity to its definitive hosts or to excyst in 0.1% sodium deoxycholate excystation medium at 37℃ for 1 h. Results In vivo encystment of cercariae occurred in the gills of goldfish. However, the cercariae were also able to encyst in vitro in Locke's solution, NaCl solution, artificial gastric juice or human gastric juice with encystation rates of 74.28 %, 44.94 %, 8.37 % and 10.79 %. 0.7 × - 1.2 × Locke' s or 0. 7 % - 1.2 % NaCl solution was shown to be appropriate for in vitro encystment to occur within 24 hour, however, full - strength Locke' s solution was shown to be optimal. The one - day - old encysted metacercariae formed in vivo showed 88.53 % excystation when treated in 0.1% sodium deoxycholate excystation medium at 37℃ for 1 h. The metacercariae formed in vitro, however, showed 88.60 % and 84.95 % excystation for normal and abnormal ones respectively. While abnormal cysts at room temperature usually die within 10 days, about 70% normal cyst, both in vivo and in vitro, can still excyst after stored in 0.5 × Locke's at 4℃ for 3 mouths. Cysts formed in vivo and in vitro were equally infective to rabbits. 1 uM silver nitrate had a dramatic effect on the cercariae encysting in vitro.When treated with silver nitrate, the cercariae encystation rates decreased to 16.25 % in Locke's solution and 6.69% in NaCl solution, however, the encystment was largely restored when the cercariae were washed to remove Ag + . Conclusion The finding of E. liliputanus cercariae encysting in vitro,especially in human gastric juice, might be helpful in elucidating mechanisms of the definitive hosts infected by the cercariae directly. The encystment of the cercariae in vitro could be inhibited when the cercariae were treated with 1 uM silver nitrate. As silver nitrate binds to the papillae, especially to the ciliated papillae, on the cercarial surface, it is suggested that papillar chemoreceptors may be involved in encystment of the cercariae.