Host exchange of Lyme disease borreliae during tick feeding

莱姆病是一种新近发现的由疏螺旋体属螺旋体引起的全身性感染。本研究以卡氏疏螺旋体、全沟硬蜱和小鼠为实验材料，对蜱取食过程中疏螺旋体的宿主交换进行了组织学研究。在感染的小鼠皮肤中，疏螺旋体的数量极低，但它们似乎包裹在真皮中的胶原纤维周围。通过使用基于鞭毛蛋白基因的引物的巢式PCR分析，鼠皮肤中疏螺旋体的数量估计为<1000/10 mg。在蜱的取食过程中，小鼠皮肤上的疏螺旋体被蜱幼虫吸入体内，并通过蜕皮过程经口传播给蜱若虫。在未进食的受感染的蜱虫中，疏螺旋体局限于它们的中肠腔。疏螺旋体在进食蜱中迁移的动力学尚不清楚;然而，疏螺旋体在唾液腺中逐渐增加，支持疏螺旋体唾液传播的假设。通过荧光抗体技术估计48小时喂养的蜱的唾液腺中疏螺旋体的数量为<10个细胞/蜱。这少量的疏螺旋体足以诱导小鼠感染。疏螺旋体在蜱中的中肠穿透和唾液侵入机制仍有待阐明。今后，应研究蜱取食过程中疏螺旋体从沉默型向感染型的转化。

Lyme disease is a newly recognized systemic infection caused by spirochetes of the genus Borrelia. In this study, the host exchange of borreliae during tick feeding process was examined histologically by using Borrelia garinii, Ixodes persulcatus ticks, and mice. In infected murine skin, the number of borreliae was extremely low ; however, they seemed to be wrapped around collagen fibers in dermis. The number of borreliae in the murine skin was estimated at<1000 per 10 mg by the nested PCR analysis using flagellin gene-based primers. During tick feeding process, borreliae in murine skin were sucked into larval ticks and transstadially transmitted to nymphal ticks through the molting process. In unfed infected nymphs, borreliae were localized in their midgut lumen. The dynamics of borrelial migration in feeding ticks was unclear ; however, borreliae gradually increased in the salivary glands, supporting a hypothesis of salivary transmission of borreliae. The number of borreliae in salivary glands of 48 hours-fed nymphs was estimated at<10 cells per tick by the fluorescent antibody technique. This small number of borreliae was sufficient to induce the murine infection. The mechanism of midgut penetration and salivary invasion of borreliae in ticks still remains to be elucidated. In the future, the transformation of borreliae from the silent form to the infective form during the feeding process of ticks should be examined.