ABSTRACT: The magnitude of an epidemic depends on host susceptibility to the disease, a trait influenced by the genetic constitution of the host and its environment. While the genetic basis of disease susceptibility is often associated with immune capacities, environmental effects generally reflect complex physiological trade-offs. We suggest here that in the case of obligate pathogens whose proliferation depends on the cellular machinery of the host (e.g. viruses), disease susceptibility is directly influenced by host growth. To test our hypothesis, we focussed on a viral disease affecting an ecologically relevant model exploited worldwide, the Pacific oyster Crassostrea gigas. Oysters originating from 3 lines with contrasting resistance to the disease were divided into 3 groups displaying different growth rates and acclimated to 3 food levels and 2 temperatures to generate different growth rates. These oysters were then exposed to the virus, and survival and viral shedding were measured. Finally, we developed a risk model to rank the relative importance of temperature, food, genetic selection and growth on disease-induced mortality. We found that increasing growth through temperature, food level or selection of fast-growing animals all increased mortality, especially in host populations where susceptible phenotypes dominated. Food provisioning was the most influential factor associated with higher viral shedding, followed by temperature, resistance phenotype and growth rate. We suggest that growth-forcing factors may promote the development of obligate intracellular pathogens and epidemic risk, thus opening up avenues for disease management based on the manipulation of host metabolism.

中文翻译：

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增加的生长代谢促进易感牡蛎种群的病毒感染

摘要：流行病的严重程度取决于宿主对疾病的易感性，这是一种受宿主遗传构成及其环境影响的特征。虽然疾病易感性的遗传基础通常与免疫能力有关，但环境影响通常反映了复杂的生理权衡。我们在此建议，对于依赖宿主细胞机制（例如病毒）增殖的专性病原体，疾病易感性直接受宿主生长的影响。为检验我们的假设，我们关注一种病毒性疾病，该病毒性疾病影响全世界开发的一种生态相关模型，即太平洋牡蛎Crassostrea gigas. 来自 3 个对疾病具有不同抗性的品系的牡蛎被分成显示不同生长速率的 3 个组，并适应 3 个食物水平和 2 个温度以产生不同的生长速率。然后将这些牡蛎暴露于病毒，并测量存活率和病毒脱落。最后，我们开发了一个风险模型来对温度、食物、遗传选择和生长对疾病引起的死亡率的相对重要性进行排序。我们发现通过温度、食物水平或选择快速生长的动物来增加生长都会增加死亡率，特别是在易感表型占主导地位的宿主种群中。食物供应是与较高病毒脱落相关的最有影响力的因素，其次是温度、抗性表型和生长速率。