BACKGROUND Understanding the drivers of Lyme disease incidence at broad spatial scales is critical for predicting and mitigating human disease risk. Previous studies have identified vector phenology and behavior, host community composition, and landscape features as drivers of variable Lyme disease risk. However, while the Lyme disease transmission cycles in the eastern and western USA involve different vector species (Ixodes scapularis and Ixodes pacificus, respectively), the role of vector-specific differences in transmission efficiency has not been directly examined. By comparing the performance of traits involved in vector competence between these two species, this study aims to identify how vector competence contributes to variable Lyme disease risk. METHODS We used a suite of laboratory experiments to compare the performance of traits related to vector competence for the two USA Lyme disease vectors. For each species, we measured the rate of attachment to a common rodent host, the engorgement weight, and the efficiency of pathogen acquisition (host to tick) and pathogen transmission (tick to host) from laboratory mice. In measuring pathogen acquisition and transmission, we used two different pathogen strains, one sympatric with I. scapularis and one sympatric with I. pacificus, to assess the importance of vector-pathogen coevolutionary history in transmission dynamics. RESULTS We found I. pacificus had significantly higher host attachment success and engorgement weights, but significantly lower pathogen transmission efficiency relative to I. scapularis. Molting success and pathogen acquisition did not differ between these two species. However, pathogen acquisition efficiency was significantly higher for both sympatric vector and pathogen strains than the allopatric pairings. CONCLUSIONS This study identified species-specific vector traits as a potential driver of broad scale variation in Lyme disease risk in the USA. In particular, the exceedingly low rates of pathogen transmission from tick to host observed for I. pacificus may limit Lyme disease transmission efficiency in the western USA. Further, observed variation in pathogen acquisition between sympatric and allopatric vector-pathogen strains indicate that vector-pathogen coevolutionary history may play a key role in transmission dynamics. These findings underscore the need to consider vector traits and vector-pathogen coevolution as important factors governing regional Lyme disease risk.

中文翻译：

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北美莱姆病载体的比较载体能力。

背景技术在广泛的空间尺度上了解莱姆病发病的驱动因素对于预测和减轻人类疾病风险至关重要。先前的研究已将媒介物候和行为，宿主群落组成和景观特征确定为可变莱姆病风险的驱动因素。但是，尽管莱姆病在美国东部和西部的传播周期涉及不同的媒介物种类（分别为肩I小and和太平洋小x），但还没有直接检查载体特异性差异在传播效率中的作用。通过比较这两个物种之间与媒介能力有关的性状的表现，本研究旨在确定媒介能力如何导致可变的莱姆病风险。方法我们使用了一套实验室实验，比较了两种美国莱姆病载体与载体能力相关性状的表现。对于每种物种，我们测量了与普通啮齿动物宿主的附着率，充盈量以及实验室小鼠的病原体获取效率（宿主对tick）和病原体传播（虱对宿主）的效率。在测量病原体的获取和传播中，我们使用了两种不同的病原体菌株，其中一种与肩cap鱼共生，另一种与太平洋I.同胞共生，以评估病原体共同进化史在传播动力学中的重要性。结果我们发现太平洋I. pacificus的寄主附着成功率和吞噬体重显着提高，但相对于肩II。的病原体传播效率却显着降低。这两个物种的蜕皮成功率和病原体获取没有差异。但是，同源载体和病原体菌株的病原体获取效率均高于异源配对。结论本研究确定了特定物种的载体性状是导致美国莱姆病风险大范围变化的潜在驱动因素。特别是，在美国西部观察到的病原体从tick到宿主的病原体传播率极低，这可能会限制莱姆病在美国西部的传播效率。此外，观察到同伴和异源媒介病原体菌株之间病原体获取的变化表明，媒介病原体共同进化史可能在传播动力学中起关键作用。