Migration can reduce parasite burdens in migratory hosts, but it connects populations and can drive disease dynamics in domestic species. Farmed salmon are infested by sea louse parasites, often carried by migratory wild salmonids, resulting in a costly problem for industry and risk to wild populations when farms amplify louse numbers. Chemical treatment can control lice, but resistance has evolved in many salmon‐farming regions. Resistance has, however, been slow to evolve in the north‐east Pacific Ocean, where large wild‐salmon populations harbour large sea louse populations. Using a mathematical model of host–macroparasite dynamics, we explored the roles of domestic, wild oceanic and connective migratory host populations in maintaining treatment susceptibility in associated sea lice. Our results show that a large wild salmon population, unexposed to direct infestation by lice from farms; high levels of on‐farm treatment; and a healthy migratory host population are all critical to slowing or stopping the evolution of treatment resistance. Our results reproduce the “high‐dose/refuge effect,” from the agricultural literature, with the added requirement of a migratory host population to maintain treatment susceptibility. This work highlights the role that migratory hosts may play in shared wildlife/livestock disease, where evolution can occur in ecological time.

中文翻译：

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迁徙宿主可以在结构化的宿主-寄生虫系统中维持高剂量/庇护效应：以海虱和鲑鱼为例


迁徙可以减少迁徙宿主的寄生虫负担，但它可以将种群联系起来，并可以推动家养物种的疾病动态。养殖鲑鱼受到海虱寄生虫的侵扰，这些寄生虫通常由迁徙的野生鲑鱼携带，这给工业带来了代价高昂的问题，而且当养殖场增加虱子数量时，也会给野生种群带来风险。化学处理可以控制虱子，但许多鲑鱼养殖地区已经产生了耐药性。然而，在东北太平洋，耐药性的发展缓慢，那里有大量野生鲑鱼，也有大量海虱。利用宿主-大型寄生虫动力学的数学模型，我们探讨了家养、野生海洋和结缔性迁徙宿主种群在维持相关海虱治疗敏感性中的作用。我们的研究结果表明，大量野生鲑鱼种群没有受到养殖场虱子的直接侵染；高水平的农场治疗；健康的迁徙宿主群体对于减缓或阻止治疗耐药性的演变都至关重要。我们的结果再现了农业文献中的“高剂量/避难效应”，并增加了迁徙宿主群体维持治疗敏感性的要求。这项工作强调了迁徙宿主在野生动物/牲畜共同疾病中可能发挥的作用，其中进化可能发生在生态时期。