Medical Malacology Laboratory, Theodor Bilharz Research Institute, Giza, 12411, Egypt.
National Institute of Parasitic Diseases, Chinese Center for Diseases Control and Prevention; Key Laboratory of Parasite and Vector Biology, Ministry of Health, Shanghai, 200025, China.
Infect Dis Poverty. 2018 Dec 8;7(1):120. doi: 10.1186/s40249-018-0505-5.
Schistosomiasis is a common parasitic disease designated as a neglected tropical disease by the World Health Organization. Schistosomiasis mansoni is a form of the disease that is caused by the digenean trematode Schistosoma mansoni, transmitted through Biomphalaria spp. as an intermediate host. Biomphalaria was introduced to Hong Kong, China in aquatic plants shipments coming from Brazil and the snail rapidly established its habitats in southern China. Earlier studies of Biomphalaria spp. introduced to southern China identified the snails as Biomphalaria straminea, one of the susceptible species implicated in S. mansoni transmission in South America. However, recent molecular investigations also indicated the presence of another South American species, B. kuhniana, which is refractory to infection. As such, it is important to identify accurately the species currently distributed in southern China, especially with emerging reports of active S. mansoni infections in Chinese workers returning from Africa.
We combined morphological and molecular taxonomy tools to precisely identify Biomphalaria spp. distributed in Guangdong Province, southern China. In order to clearly understand the molecular profile of the species, we constructed a phylogeny using mtDNA data (COI and 16S rRNA sequences) from six populations of Biomphalaria spp. from Shenzhen City in Guangdong Province. In addition, we examined the external morphology of the shell and internal anatomy of the reproductive organs.
Both morphological and molecular evidences indicated a close affinity between Biomphalaria spp. populations from Guangdong and B. straminea from Brazil. The shell morphology was roughly identical in all the populations collected with rounded whorls on one side and subangulated on the other, a smooth periphery, an egg-shaped aperture bowed to one side, and a deep umbilicus. The shape and number of prostate diverticula (ranged from 11.67 to 17.67) in Guangdong populations supports its close affinity to B. straminea rather than B. kuhniana. Molecular analysis did not conflict with morphological analysis. Little genetic differentiation was observed within Biomphalaria populations collected. Phylogenetic analysis of COI and 16S rRNA haplotypes from snails collected and B. straminea sequences from Brazil and China using Bayesian inference revealed that Guangdong populations were clustered in one clade with B. straminea from Hong Kong of China and B. straminea from Brazil indicating their close affinity to each other.
Data obtained in the current study clearly show that the populations of Biomphalaria spp. investigated are B. straminea, and we assume that those snails were either introduced via passive dispersal from Hong Kong of China or as a result of multiple introduction routes from Brazil.
血吸虫病是一种常见的寄生虫病，被世界卫生组织列为被忽视的热带病。曼氏血吸虫病是由曼氏血吸虫寄生引起的一种疾病，通过中间宿主双脐螺属传播。双脐螺属于 20 世纪初被引入中国香港，在南方迅速建立了栖息地。早期对引入中国南方的双脐螺属的研究表明，这些蜗牛是一种易感染物种，与南美洲的曼氏血吸虫传播有关。然而，最近的分子研究也表明存在另一种南美洲物种，即 B. kuhniana，它不易感染。因此，准确识别目前分布在中国南方的物种非常重要，特别是随着越来越多的报道称从非洲返回的中国工人中出现了曼氏血吸虫感染。
我们结合形态学和分子分类学工具，精确鉴定了分布在中国广东省的双脐螺属。为了清楚地了解该物种的分子特征，我们利用来自广东省深圳市的六个双脐螺属种群的 mtDNA 数据（COI 和 16S rRNA 序列）构建了系统发育树。此外，我们还检查了贝壳的外部形态和生殖器官的内部解剖结构。
形态学和分子证据都表明，来自广东的双脐螺属与来自巴西的 B. straminea 密切相关。收集到的所有种群的贝壳形态大致相同，一侧有圆形螺层，另一侧有亚角形螺层，边缘光滑，卵形口向一侧弯曲，脐孔很深。广东种群前列腺憩室的形状和数量（范围为 11.67 至 17.67）支持其与 B. straminea 的密切关系，而不是与 B. kuhniana 的关系。分子分析与形态分析没有冲突。在收集到的双脐螺属种群中，观察到的遗传分化很小。利用贝叶斯推断对从蜗牛中收集到的 COI 和 16S rRNA 单倍型以及从巴西和中国收集到的 B. straminea 序列进行分析表明，广东种群与来自中国香港的 B. straminea 和来自巴西的 B. straminea 聚类在一个分支中，表明它们彼此密切相关。
本研究获得的数据清楚地表明，所研究的双脐螺属种群是 B. straminea，我们假设这些蜗牛是通过中国香港的被动扩散或从巴西的多种途径引入的。
