目的 了解拉萨市淡水螺种类和吸虫感染现状，并分析淡水螺及吸虫的系统发育情况。方法 2024年6—7月，在拉萨市城关区、堆龙德庆区、林周县、达孜区、曲水县等5个县（区）采集淡水螺样品，分类鉴定后压片镜检观察吸虫形态及感染情况。分别提取淡水螺和吸虫总DNA，PCR扩增螺线粒体细胞色素c氧化酶1（CO1）及吸虫内转录间隔区2（ITS2）序列，对扩增产物进行测序。用DNASTAR软件将测序结果进行拼接，所获得的目的序列提交至NCBI数据库，采用BLAST进行序列比对分析。用MEGA 11.0 软件以邻接法和最大似然法分别构建系统进化树。结果 共采集淡水螺1 022只，经形态学鉴定分为8属。压片镜检观察到吸虫幼虫的毛蚴、胞蚴、雷蚴、尾蚴及囊蚴多期发育形态。PCR扩增结果显示，淡水螺CO1、吸虫ITS2片段分别约为740 bp和630 bp，与预期目的片段长度一致。基因测序及序列比对结果显示，测序得到9种淡水螺CO1序列，与尖膀胱螺、狭萝卜螺、铜锈环棱螺、小土蜗、扁蜷螺属、Orientogalba viridis、耳萝卜螺、Radix makhrovi、Tibetoradix khamensis序列一致性较高，分别为98.66%、99.23%、99.29%、100%、98.78%、98.91%、99.38%、100%、99.65%；系统发育分析形成8个分支，各属物种均单独聚为一支。测序得到10种吸虫ITS2序列，分别与默氏复口吸虫、叙利亚杯尾吸虫、异幻属吸虫、具斑斜睾吸虫、肝片形吸虫、大片形吸虫及鹿同盘吸虫的序列一致性均达100%；与土耳其斯坦东毕吸虫、卷棘口吸虫、背孔科吸虫序列一致性较高，分别为99.80%、99.84%、98.78%；系统发育分析形成9个分支，各属物种单独聚为一支，各分支均具有较高自展支持率，构成稳定的单系进化支。5个县（区）的淡水螺吸虫总感染率为59.59%（609/1 022），曲水县最高（73.80%，138/187），城关区最低（39.24%，31/79）。达孜区淡水螺种类最为丰富（7种），堆龙德庆区和林周县吸虫种类最多（各9种），曲水县检出淡水螺（1种）及吸虫（2种）种类均为最少。结论 拉萨市高海拔水域中淡水螺物种丰富，其体内寄生吸虫种类多、感染率高。

Objective To investigate the species of freshwater snails and the prevalence of trematode infections in freshwater snails in Lahsa City, and to analyze the phylogeny of freshwater snails and trematodes. Methods Freshwater snail samples were collected from Chengguan District, Duilongdeqing District, Linzhou County, Dazi District and Qushui County of Lhasa City from June to July 2024, and characterized for species, and the morphology and infection of trematodes were observed using microscopy. Genomic DNA was extracted from freshwater snails and trematodes for amplification of the mitochondrial cytochrome c oxidase subunit 1 (CO1) gene of freshwater snails and the internal transcribed spacer 2 (ITS2) of trematodes using PCR assay, and the PCR amplification products were sequenced. Raw reads were assembled using the DNASTAR software, and the obtained target sequences were submitted to the NCBI database for sequence alignment using the BLAST tool. Phylogenetic trees were constructed using the neighbor-joining and maximum likelihood methods, and genetic distances were calculated using the software MEGA 11.0. Results A total of 1 022 freshwater snails were collected and 8 genera were morphologically identified. Multiple developmental stages of trematode larvae were observed using microscopy, including miracidia, sporocysts, rediae, cercariae, and metacercariae. PCR amplification displayed the CO1 fragment from freshwater snails with approximately 740 bp in length and the ITS2 fragment from trematodes with approximately 630 bp in length, which were consistent with the expected size of target fragments. Gene sequencing and sequence alignment revealed that the CO1 sequence of freshwater snails exhibited the highest sequence identity with those of Physella acuta (98.66%), Ampullaceana lagoti (99.23%), Bellamya aeruginosa (99.29%), Galba pervia (100%), Gyraulus sp. (98.78%), Orientogalba viridis (98.91%), Radix Auricularia (99.38%), R. makhrovi (100%) and Tibetoradix khamensis (99.65%), and phylogenetic analysis revealed 8 clusters, with species of each genus clustering independently into a single clade. The ITS2 sequence of trematodes exhibited 100% sequence identity with Diplostomum mergi, Cotylurus syrius, Apatemon sp., Plagiorchis maculosus, Fasciola hepatica, F. gigantica, and Paramphistomum cervi, and showed the highest sequence identity with Schistosoma turkestanicum (99.80%), Echinostoma revolutum (99.84%), and Notocotylidae sp. (98.78%), respectively. Phylogenetic analysis revealed 9 clusters, with species of each genus clustering independently into a single clade, and all clades were supported by high bootstrap values, generating stable monophyletic clades. The overall prevalence of trematode infects was 59.59% (609/1 022) in freshwater snails across five counties (districts), with the highest prevalence in Qushui County (73.80%, 138/187), and the lowest in Chengguan District (39.24%, 31/79). Dazi District exhibited the greatest species diversity of freshwater snails (7 species), whereas Duilongdeqing District and Linzhou County harbored the highest trematode species (9 species each). In addition, Qushui County had the fewest species of both freshwater snails (1 species) and trematodes (2 species). Conclusion Freshwater snail species are abundant in the high-altitude waters of Lhasa City, with diverse trematode species and high prevalence of trematode infections.