Departamento de Parasitología, Facultad de Farmacia, Universidad de Valencia, Valencia, Spain.
PLoS One. 2011;6(9):e24567. doi: 10.1371/journal.pone.0024567. Epub 2011 Sep 29.
Lymnaeid snails transmit medical and veterinary important trematodiases, mainly fascioliasis. Vector specificity of fasciolid parasites defines disease distribution and characteristics. Different lymnaeid species appear linked to different transmission and epidemiological patterns. Pronounced susceptibility differences to absolute resistance have been described among lymnaeid populations. When assessing disease characteristics in different endemic areas, unexpected results were obtained in studies on lymnaeid susceptibility to Fasciola. We undertook studies to understand this disease transmission heterogeneity.
METHODOLOGY/PRINCIPAL FINDINGS: A ten-year study in Iran, Egypt, Spain, the Dominican Republic, Mexico, Venezuela, Ecuador and Peru, demonstrated that such heterogeneity is not due to susceptibility differences, but to a hitherto overlooked cryptic species, Lymnaea schirazensis, confused with the main vector Galba truncatula and/or other Galba/Fossaria vectors. Nuclear rDNA and mtDNA sequences and phylogenetic reconstruction highlighted an old evolutionary divergence from other Galba/Fossaria species, and a low intraspecific variability suggesting a recent spread from one geographical source. Morphometry, anatomy and egg cluster analyses allowed for phenotypic differentiation. Selfing, egg laying, and habitat characteristics indicated a migration capacity by passive transport. Studies showed that it is not a vector species (n = 8572 field collected, 20 populations): snail finding and penetration by F. hepatica miracidium occur but never lead to cercarial production (n = 338 experimentally infected).
CONCLUSIONS/SIGNIFICANCE: This species has been distorting fasciolid specificity/susceptibility and fascioliasis geographical distribution data. Hence, a large body of literature on G. truncatula should be revised. Its existence has henceforth to be considered in research. Genetic data on livestock, archeology and history along the 10,000-year post-domestication period explain its wide spread from the Neolithic Fertile Crescent. It is an efficient biomarker for the follow-up of livestock movements, a crucial aspect in fascioliasis emergence. It offers an outstanding laboratory model for genetic studies on susceptibility/resistance in F. hepatica/lymnaeid interaction, a field of applied research with disease control perspectives.
圆口螺科蜗牛传播医学和兽医重要的吸虫病，主要是片形吸虫病。 片形吸虫寄生虫的媒介特异性决定了疾病的分布和特征。 不同的圆口螺科物种似乎与不同的传播和流行病学模式有关。 在圆口螺种群中，已经描述了明显的易感性差异，从绝对抗性到抗性。 在评估不同流行地区的疾病特征时，在研究圆口螺对 Fasciola 的易感性时，得到了出乎意料的结果。 我们进行了研究以了解这种疾病传播的异质性。
方法/主要发现： 在伊朗、埃及、西班牙、多米尼加共和国、墨西哥、委内瑞拉、厄瓜多尔和秘鲁进行的为期十年的研究表明，这种异质性不是由于易感性差异，而是由于一种迄今为止被忽视的隐种，即 Schirazensis 圆口螺，与主要媒介 Galba truncatula 和/或其他 Galba/Fossaria 媒介混淆。 核 rDNA 和 mtDNA 序列和系统发育重建突出了与其他 Galba/Fossaria 物种的古老进化分歧，以及低的种内变异性，表明最近从一个地理来源扩散。 形态学、解剖学和卵群分析允许进行表型分化。 自交、产卵和栖息地特征表明其具有通过被动运输进行迁移的能力。 研究表明，它不是一种媒介物种（n = 8572 个野外采集，20 个种群）：F. hepatica 尾蚴在蜗牛中的发现和穿透会发生，但从未导致尾蚴的产生（n = 338 个经实验感染）。
结论/意义： 该物种一直扭曲了片形吸虫的特异性/易感性和片形吸虫病的地理分布数据。 因此，大量关于 Galba truncatula 的文献应该被修订。 今后必须考虑到它的存在。 在 10000 年的驯化后时期，有关家畜、考古学和历史的遗传数据解释了它从新石器时代肥沃新月地带的广泛传播。 它是家畜运动监测的有效生物标志物，这是片形吸虫病出现的一个关键方面。 它为 Fasciola hepatica/lymnaeid 相互作用中的易感性/抗性的遗传研究提供了一个出色的实验室模型，这是一个具有疾病控制前景的应用研究领域。
