General Medical Council, St James's Buildings, 79 Oxford Street, Manchester, M1 6FQ, UK.
Mol Ecol. 2010 Jan;19(2):241-56. doi: 10.1111/j.1365-294X.2009.04463.x. Epub 2009 Dec 15.
Population genetic perturbations of intermediate hosts, often a consequence of human pressure on environmental resources, can precipitate unexpectedly severe disease outbreaks. Such disturbances are set to become increasingly common following range changes concomitant with climate shifts, dwindling natural resources and major infrastructure changes such as hydroprojects. Construction of the Diama dam in the Senegal River Basin (SRB) reduced river salinity, enabling the freshwater snail intermediate host Biomphalaria pfeifferi to rapidly expand its distribution. A serious public health problem ensued, with an epidemic of intestinal schistosomiasis occurring in the previously schistosome-free Richard-Toll region within 2 years. The current study aimed to assess the population variability of B. pfeifferi in the SRB, and speculate upon its subsequent impact on host-parasite interactions following such engineered ecological change. Genetic variation at nine polymorphic microsatellite loci revealed little population differentiation in SRB snails compared with those from natural habitats in Zimbabwe, where Schistosoma mansoni transmission is much lower. 'Open' SRB habitats are associated with greater water contact, smaller population sizes and less genetic diversity, with sites downstream of Richard-Toll showing greater inter- and intrapopulation variation, concomitant with less frequent human contact. These observations may be explained by rapid expansion into pristine habitat selecting for high fecundity genotypes at the expense of schistosome resistance, presenting S. mansoni with genetically homogenous highly fecund susceptible populations around the focal point, promoting development of a highly compatible host-parasite relationship. Longitudinal study of such systems may prove important in predicting public health risks engendered by future environmental engineering projects.
中间宿主的种群遗传扰动，通常是人类对环境资源施加压力的结果，可能会导致疾病突然爆发。随着气候变化、自然资源减少以及大型基础设施变化（如水电项目）带来的范围变化，这种干扰将变得越来越普遍。塞内加尔河流域（SRB）迪亚曼大坝的建设降低了河水的盐度，使淡水蜗牛中间宿主比目鱼 pfeifferi 能够迅速扩大其分布范围。随后，理查德-托尔地区出现了肠道血吸虫病流行，这是一个严重的公共卫生问题，而该地区以前是没有血吸虫病的。目前的研究旨在评估 SRB 中 B. pfeifferi 的种群变异性，并推测在这种工程生态变化后，对宿主-寄生虫相互作用的后续影响。在 9 个多态微卫星基因座的遗传变异与津巴布韦自然栖息地的蜗牛相比，SRB 蜗牛的种群分化很小，而在津巴布韦，曼氏血吸虫的传播要低得多。“开放”的 SRB 栖息地与更大的水接触、更小的种群规模和更少的遗传多样性有关，下游的理查德-托尔地区的种群间和种群内的变异性更大，与人类接触的频率也更低。这些观察结果可以用以下方式解释：快速扩张到原始栖息地会选择高繁殖力基因型，而牺牲对血吸虫的抵抗力，从而使曼氏血吸虫面临遗传上同质的、高度繁殖的易感种群，促进高度相容的宿主-寄生虫关系的发展。对这类系统进行纵向研究可能对预测未来环境工程项目所带来的公共卫生风险具有重要意义。
