Biological characterization and molecular identification of cercaria of two fluke species
Objective To understand the characteristics of cercariae and their shedding from Parafossarulus striatulus in Jiangxi Province,providing a scientific basis for the control of trematode cercariae. Methods From September to November 2023,P. striatulus snails were collected three times from a fish pond in Xinfeng County,Jiangxi Province. Cercaria infection was identified by the cercarial shedding method. From 06:00 to 18:00 each day over two consecutive days,the number of released cercariae was recorded under constant temperature at an interval of 2 hours. Morphological characteristics of the cercariae were observed under the microscope. DNA from different cercariae was extracted,and internal transcribed spacer region 2 (ITS2) was amplified by PCR. The amplified products were sequenced,and the sequences were then compared by Blast. With Clonorchis sinensis as the outgroup,a phylogenetic tree based on the ITS2 gene sequence was constructed by the neighbor-joining method using MEGA 7.0 software to determine the species of escaped cercariae. Results A total of 1982 P. striatulus snails were collected,with two species of cercariae emerging,showing an overall positive rate of 1.21％ (24/1982). Cercaria a was oval-shaped,with a blunt front end and slightly pointed rear end. No cercaria shedded from 8:00 to 12:00,and a small amount was released after noon. The shedding rate gradually increased after 16:00,reached a peak at 18:00,and gradually declined after 20:00. Cercaria b consisted of body and tail parts,with the tail longer than the body and bifurcated at the end,displaying movement in"man"or"Y"shapes. The shedding rate of cercaria b gradually increased between 08:00 and 12:00,peaked at 12:00,decreased gradually thereafter,and almost no cercariae emerged after 16:00,with no escape at night,possibly related to light exposure. Gene sequencing and sequence comparison showed that the ITS2 gene of cercaria a had the highest homology with Lecithodendrium linstowi at 92.43％,whereas cercaria b showed the highest homology with Holostephanus dubinini at 99.35％. Conclusions P. striatulus snails in Jiangxi Province can be infected with different species of cercariae,which display significant differences in the biological characteristics and shedding pattern. Molecular analysis shows that cercaria a may belong to the genus of Lecithodendrium,and cercaria b may be H. dubinini. Understanding the biological characteristics of cercariae could be valuable for implementing corresponding control measures for different species of trematodes.
万方数据
维普
