Johnson Pieter T J, Lund Peder J, Hartson Richard B, Yoshino Timothy P
Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309, USA.
Proc Biol Sci. 2009 May 7;276(1662):1657-63. doi: 10.1098/rspb.2008.1718. Epub 2009 Jan 20.
Global biodiversity loss and disease emergence are two of the most challenging issues confronting science and society. Recently, observed linkages between species-loss and vector-borne infections suggest that biodiversity may help reduce pathogenic infections in humans and wildlife, but the mechanisms underlying this relationship and its applicability to a broader range of pathogens have remained speculative. Here, we experimentally evaluated the effects of host community structure on transmission of the human pathogen, Schistosoma mansoni, which alternates between snail intermediate hosts and vertebrate definitive hosts. By manipulating parasite exposure and community diversity, we show that heterospecific communities cause a 25-50 per cent reduction in infection among snail hosts (Biomphalaria glabrata). Infected snails raised alongside non-host snails (Lymnaea or Helisoma sp.) also produced 60-80 per cent fewer cercariae, suggesting that diverse communities could reduce human infection risk. Because focal host density was held constant during experiments, decreases in transmission resulted entirely from diversity-mediated pathways. Finally, the decrease in infection in mixed-species communities led to an increase in reproductive output by hosts, representing a novel example of parasite-mediated facilitation. Our results underscore the significance of community structure on transmission of complex life-cycle pathogens, and we emphasize enhanced integration between ecological and parasitological research on the diversity-disease relationship.
全球生物多样性丧失和疾病出现是科学和社会面临的两个最具挑战性的问题。最近，观察到的物种丧失与媒介传播感染之间的联系表明，生物多样性可能有助于减少人类和野生动物中的致病性感染，但这种关系背后的机制及其对更广泛病原体的适用性仍属推测。在这里，我们通过实验评估了宿主群落结构对人类病原体曼氏血吸虫传播的影响，曼氏血吸虫在蜗牛中间宿主和脊椎动物终宿主之间交替传播。通过控制寄生虫暴露和群落多样性，我们发现异种群落可使蜗牛宿主（光滑双脐螺）中的感染减少25%至50%。与非宿主蜗牛（椎实螺或黄斑螺属）一起饲养的受感染蜗牛产生的尾蚴也减少了60%至80%，这表明多样化的群落可以降低人类感染风险。由于在实验过程中焦点宿主密度保持不变，传播的减少完全是由多样性介导的途径导致的。最后，混合物种群落中感染的减少导致宿主繁殖输出增加，这是寄生虫介导的促进作用的一个新例子。我们的结果强调了群落结构对复杂生命周期病原体传播的重要性，并且我们强调在生态和寄生虫学研究中加强对多样性与疾病关系的整合。
