Pathogens utilize different modes of transmission to maximize transmission success. In vector‐borne disease systems, both vertical and horizontal modes of transmission are common, but the relative contribution of these modes is not well understood but may be determined by host genetics, physiology, or environmental conditions. This study focuses on an emerging tick‐borne relapsing fever pathogen, Borrelia miyamotoi, that can be transmitted both vertically and horizontally. The enzootic cycle of this pathogen has not been described in the western USA where it was recently found in the tick species, Ixodes pacificus. Our field surveys found that all three life stages of I. pacificus carry the pathogen, and therefore, all stages pose some level of disease risk to humans. The prevalence of infection increases with each life stage suggesting that horizontal transmission is important in the persistence of this pathogen in the enzootic cycle. In support of this finding, we found that small mammal hosts that are frequently parasitized by juvenile stages of I. pacificus were infected with B. miyamotoi and may therefore function as a source of horizontal transmission and enzootic maintenance of this disease. Our data show that in the western USA B. miyamotoi is maintained in natural populations by both transovarial transmission and transmission from blood meal hosts and that synchronous phenology of juvenile stages of I. pacificus may facilitate the transmission dynamics of B. miyamotoi and other vertically transmitted, vector‐borne pathogens.

中文翻译：

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混合传播模式可促进新兴的tick传播病原体的持久性

病原体利用不同的传播方式来最大化传播成功。在媒介传播的疾病系统中，垂直和水平传播方式都是常见的，但是这些方式的相对作用尚不清楚，但可能取决于宿主的遗传学，生理学或环境条件。这项研究的重点是新兴的由tick传播的复发性发热病原体宫本疏螺旋体，该病原体可以垂直和水平传播。这种病原体的Enzootic周期尚未在美国西部描述，最近在壁虱物种Ixodes pacificus中被发现。我们的实地调查发现，太平洋大肠埃希菌的所有三个生命阶段携带病原体，因此，所有阶段对人类构成一定程度的疾病风险。感染的发生率随着每个生命阶段的增加而增加，这表明水平传播对这种病原体在整个生长期的持久性至关重要。为支持这一发现，我们发现经常被太平洋大肠埃希氏菌幼虫寄生的小型哺乳动物宿主感染了宫本芽孢杆菌，因此可以作为这种疾病的水平传播和动物维持的来源。我们的数据显示，在美国西部B. miyamotoi在自然种群由血粉主机都卵巢传播和传递和少年阶段是同步的物候保持一个pacificus可能会促进宫本芽孢杆菌和其他垂直传播的媒介传播病原体的传播动力学。