Koloski Cody W, Adam Hesham, Hurry Georgia, Foley-Eby Alexandra, Zinck Christopher B, Wei Haomiao, Hansra Satyender, Wachter Jenny, Voordouw Maarten J
Department of Veterinary Microbiology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
Department of Biology, Northeastern University, Boston, Massachusetts, USA.
Appl Environ Microbiol. 2024 Dec 18;90(12):e0129924. doi: 10.1128/aem.01299-24. Epub 2024 Nov 6.
The Lyme disease spirochete cycles between immature black-legged ticks () and vertebrate reservoir hosts, such as rodents. Larval ticks acquire spirochetes from infected hosts, and the resultant nymphs transmit the spirochetes to naïve hosts. This study investigated the impact of immunocompetence and host tissue spirochete load on host-to-tick transmission (HTT) of and the spirochete load inside immature ticks. Wild-type (WT) C57BL/6J mice and mice with severe combined immunodeficiency (SCID) were experimentally infected with . To measure HTT, WT and SCID mice were repeatedly infested with larvae, and ticks were sacrificed at three different developmental stages: engorged larvae, 1-month-old, and 12-month-old nymphs. The spirochete loads in immature ticks and mouse tissues were estimated using qPCR. In WT mice, HTT decreased from 90% to 65% over the course of the infection, whereas in the SCID mice, HTT was always 100%. Larvae that fed on SCID mice acquired a much larger dose of spirochetes compared to larvae that fed on WT mice. This difference in spirochete load persisted over tick development where nymphs that fed as larvae on SCID mice had significantly higher spirochete loads compared to their WT counterparts. HTT and the tick spirochete loads were strongly correlated with the mouse tissue spirochete loads. Our study shows that the host immune system (e.g., the presence of antibodies) influences HTT of and the spirochete load in immature ticks.IMPORTANCEThe tick-borne spirochete causes Lyme disease in humans. This pathogen is maintained in nature by cycles involving black-legged ticks and wildlife hosts. The present study investigated the host factors that influence the transmission of from infected hosts to feeding ticks. We infected immunocompetent mice and immunocompromised mice (that cannot develop antibodies) with and repeatedly infested these mice with ticks. We determined the percentage of infected ticks and their spirochete loads. This percentage was 100% for immunocompromised mice but decreased from 90% to 65% over time (8 weeks) for immunocompetent mice. The tick spirochete load was much higher in ticks fed on immunocompromised mice compared to ticks fed on immunocompetent mice. In summary, the host immune system influences the transmission of from infected hosts to ticks and the spirochete loads in those ticks, which, in turn, determines the risk of Lyme disease for people.
莱姆病螺旋体在未成熟的黑腿蜱与脊椎动物宿主（如啮齿动物）之间循环。幼虫蜱从受感染宿主获取螺旋体，随后若虫将螺旋体传播给未感染的宿主。本研究调查了免疫能力和宿主组织螺旋体载量对莱姆病螺旋体从宿主到蜱传播（HTT）以及未成熟蜱体内螺旋体载量的影响。野生型（WT）C57BL/6J小鼠和严重联合免疫缺陷（SCID）小鼠被实验性感染莱姆病螺旋体。为了测量HTT，WT和SCID小鼠被幼虫反复叮咬，蜱在三个不同发育阶段被处死：饱血幼虫、1月龄若虫和12月龄若虫。使用定量聚合酶链反应（qPCR）估计未成熟蜱和小鼠组织中的螺旋体载量。在WT小鼠中，HTT在感染过程中从90%降至65%，而在SCID小鼠中，HTT始终为100%。与以WT小鼠为食的幼虫相比，以SCID小鼠为食的幼虫获得的螺旋体剂量要大得多。这种螺旋体载量的差异在蜱的发育过程中持续存在，以SCID小鼠为幼虫宿主的若虫的螺旋体载量明显高于其WT对应物。HTT和蜱的螺旋体载量与小鼠组织螺旋体载量密切相关。我们的研究表明，宿主免疫系统（如抗体的存在）会影响莱姆病螺旋体的HTT以及未成熟蜱中的螺旋体载量。
蜱传播的螺旋体可导致人类患莱姆病。这种病原体通过涉及黑腿蜱和野生动物宿主的循环在自然界中维持。本研究调查了影响莱姆病螺旋体从受感染宿主传播到取食蜱的宿主因素。我们用莱姆病螺旋体感染有免疫能力的小鼠和免疫受损小鼠（无法产生抗体），并用蜱反复叮咬这些小鼠。我们确定了受感染蜱的百分比及其螺旋体载量。免疫受损小鼠的这一百分比为100%，但有免疫能力的小鼠在8周的时间内从90%降至65%。与以有免疫能力的小鼠为食的蜱相比，以免疫受损小鼠为食的蜱的螺旋体载量要高得多。总之，宿主免疫系统影响莱姆病螺旋体从受感染宿主传播到蜱以及这些蜱中的螺旋体载量，这反过来又决定了人类患莱姆病的风险。
