椎实螺个体大小对淮河水系毛毕吸虫感染影响的研究

Study on effects of Lymnaeidae size on infection of Trichobil-harzia living in Huaihe River system

目的探讨椎实螺个体大小对淮河水系毛毕吸虫感染的影响。方法采集椎实螺科耳萝卜螺按大小分组逸毛毕吸虫尾蚴并计数,测定不同大小螺体自然感染率和感染强度;在实验室内饲养阴性成螺产卵,收集同日产卵块孵育同一螺龄不同大小螺体;采集阳性鸭粪便孵毛蚴,分别感染前述子螺并测量螺高;24d后逸尾蚴,计数尾蚴量并测量螺高,观察不同大小螺体人工感染率、感染强度以及感染螺与未感染螺壳高差异。结果野外小螺体的毛毕吸虫感染率和感染强度均较低,较大螺体则感染率和感染强度均较高(x感染率2=35.909,P<0.01;F感染强度=65.55>F0.01(1,5)=16.30,P<0.01);在实验室条件下,同一螺龄的大、小螺体间毛毕吸虫感染率差异无显著性,而毛毕吸虫感染强度的差异具有显著性(x感染率2=0.347,P>0.05;F感染强度=25.16>F0.01(1,5)=16.30,P<0.01);感染螺与未感染螺壳高间差异无显著性(x2=0.023,P>0.05)。结论毛毕吸虫感染强度受耳萝卜螺本身大小影响,而毛毕吸虫自然感染率受螺龄关联的螺体大小影响。感染螺不大于未感染螺,野外大型感染螺不能归因于毛毕吸虫诱导效应。

Objective To study the effect of Lymnaeidae size on infection of Trichobilharzia living in the Huaihe River system. Methods Lymnaeidae snails (Radix auricularia) were collected and grouped by size. The cercariae from them were separated, and counted to determine natural prevalence and intensity of infection. The negative adult snails were fed for oviposition, and the same-day egg masses were collected, hatched for the same-aged snails of different sizes. The feces of the ducks infected with Trichobilharzia in Yaohe Fishery were collected, and the miracidia of Trichobilharzia from the feces were obtained by the glass tube top method. The Radix auricularia were infected with one miracidium each, and measured for the shell high with vernier calipers respectively. After 24 days, the cercariae from the infected snails were separated and counted for prevalence and intensity of infection of the same-aged snails of different sizes, the shell high were measured to assess the difference between infected and uninfected snails. Results In field populations , the prevalence and intensity of infection of large snails were higher than those of small snails, which was significantly different(xInfection rate 2=35. 909,P<0. 01; FInfection intensity=65. 55,P<0. 01). A-mong laboratory-same-aged snails, the prevalence of infection was unaffected by snail size class (xInfection rate 2= 0.347, P>0. 05), and the intensity of infection increased with the snail size (FInfection intensity=25. 16>F0.01(1,5)=16. 30,P<0. 01). The size of infected snails did not differ from that of uninfected snails significantly(x2 = 0. 023,P>0. 05). Conclusion Laboratory results thus suggest that infection intensity is related to snail size per se, whereas prevalence in the field is related to snail size only through the correlation between size and age. In addition, under these experimental conditions, infected snails were no larger than uninfected snails, so the gigantism snails observed in the field might not be attributable to Trichobilharzia-induced effect.