Abstract：
For parasites, robust proliferation within hosts is crucial for establishing the infection and creating opportunities for onward transmission. While faster proliferation enhances transmission rates, it is often assumed to curtail transmission duration by killing the host (virulence), a trade-off constraining parasite evolution. Yet in many diseases, including malaria, the preponderance of infections with mild or absent symptoms suggests that host mortality is not a sufficient constraint, raising the question of what restrains evolution toward faster proliferation. In malaria infections, the maximum rate of proliferation is determined by the burst size, the number of daughter parasites produced per infected red blood cell. Larger burst sizes should expand the pool of infected red blood cells that can be used to produce the specialized transmission forms needed to infect mosquitoes. We use a within-host model parameterized for rodent malaria parasites (Plasmodium chabaudi) to project the transmission consequences of burst size, focusing on initial acute infection where resource limitation and risk of host mortality are greatest. We find that resource limitation restricts evolution toward higher burst sizes below the level predicted by host mortality alone. Our results suggest resource limitation could represent a more general constraint than virulence-transmission trade-offs, preventing evolution towards faster proliferation.
摘要：
对于寄生虫，宿主内的强健增殖对于建立感染和创造继续传播的机会至关重要。虽然更快的增殖提高了传播速率，通常认为通过杀死宿主（毒力）来缩短传播持续时间，限制寄生虫进化的权衡。然而，在许多疾病中，包括疟疾,轻度或无症状的感染占优势，表明宿主死亡率不是一个足够的约束，提出了什么限制向更快扩散发展的问题。在疟疾感染中，最大增殖速率由爆发大小决定，每个受感染的红细胞产生的子寄生虫数量。更大的爆发大小应扩大受感染的红细胞池，可用于产生感染蚊子所需的专门传播形式。我们使用针对啮齿动物疟疾寄生虫（Chabaudi疟原虫）参数化的宿主内模型来预测爆发大小的传播后果，重点关注来源限制和宿主死亡风险最大的初始急性感染。我们发现资源限制限制了向更高爆发大小的进化，低于仅宿主死亡率预测的水平。我们的结果表明，资源限制可能代表比毒力-传播权衡更普遍的约束，防止向更快的扩散进化。
