复发性疏螺旋体是虱子传播的复发性发热的病原体,是唯一由昆虫而不是tick媒介传播的疏螺旋体。虽然臭虫(CimexlectulariusL.)不是任何人类病原体的确定载体,最近的一项研究报告说,它们可能是B.然而,在这种可能的次要媒介中,感染和传播的许多方面仍不清楚.这里,我们进行了几项定量实验室研究,以更好地了解臭虫相对于已建立的体虱媒介的宿主适用性,以及可能影响臭虫传播病原体能力的因素。我们喂食了臭虫B.recurrentis,并使用实时成像估计了血淋巴感染的水平和持续时间。我们进行了定量PCR(qPCR)来检查全身螺旋体水平和垂直传播到后代的发生。我们还开发了一种测定法,以比较从最近充血的臭虫和体虱中释放感染性血淋巴所需的力量。最后,我们分析了血淋巴的体液抗菌活性,血淋巴pH值,和两种昆虫的血细胞活性。我们的结果证实,在摄入后24小时内,B.复发可以穿透臭虫的中肠上皮并进入血淋巴,克服一个主要的宿主障碍,就像身体虱子一样。一旦进入血淋巴,螺旋体保持可见至少4天。此外,我们发现臭虫比体虱更容易被压碎,这表明压碎是从臭虫血淋巴自然传播复发芽孢杆菌的可行途径,至于身体虱子。尽管如此,我们的数据还表明,臭虫是复发芽孢杆菌的次优宿主,因为细菌似乎没有增殖到高水平或稳定定植在血淋巴中,并且在这种环境中表现出多态性。特别是,我们的数据表明血淋巴pH值和独特的细胞免疫反应,而不是体液效应,可能参与限制螺旋体在臭虫中的存活。值得注意的是,我们首次记录了臭虫血细胞形成的细胞外DNA陷阱。由于这些原因,虽然臭虫的传播能力有限,但鉴于它们的生态,相对于体虱,矢量能力可能很小。对臭虫的人类病原体感染的其他机制研究可能为限制其作为载体的能力的生物因素提供急需的见解,并可能揭示新的免疫机制。
Borrelia recurrentis is the causative agent of louse-borne relapsing fever and the only Borrelia species transmitted by an insect rather than a tick vector. While bed bugs (Cimex lectularius L.) are not established vectors of any human pathogens, a recent
study reported that they may be competent vectors of B. recurrentis. However, many aspects of infection and transmission remain unclear in this possible secondary vector. Here, we carried out several quantitative laboratory studies to gain a better understanding of the host suitability of bed bugs relative to the established body louse vector as well as the factors that may affect the ability of bed bugs to transmit the pathogen. We fed bed bugs B. recurrentis and estimated the level and duration of infection in the hemolymph using live imaging. We performed quantitative PCR (qPCR) to examine whole-body spirochete levels and the occurrence of vertical transmission to progeny. We also developed an assay to compare the amounts of force required to release infectious hemolymph from recently engorged bed bugs and body lice. Finally, we analyzed humoral antibacterial activity in the hemolymph, hemolymph pH, and hemocyte activity in both insect species. Our results confirm that within 24 h of ingestion, B. recurrentis can penetrate the midgut epithelium of bed bugs and enter the hemolymph, overcoming a major host barrier, as in body lice. Once in the hemolymph, spirochetes remain visible for at least 4 days. Moreover, we show that bed bugs are more physically susceptible to crushing than body lice, suggesting that crushing is a feasible route for the natural dissemination of B. recurrentis from the hemolymph of bed bugs, as for body lice. Nonetheless, our data also indicate that bed bugs are suboptimal hosts for B. recurrentis, as the bacterium does not appear to proliferate to high levels or stably colonize the hemolymph and exhibits pleomorphism in this environment. In particular, our data suggest that hemolymph pH and unique cellular immune responses, rather than humoral effectors, may be involved in limiting spirochete survival in bed bugs. Notably, we document the formation of extracellular DNA traps by bed bug hemocytes for the first time. For these reasons, while bed bugs may be capable of limited transmission given their ecology, vector competence is probably minimal relative to body lice. Additional mechanistic studies of human pathogen infection of bed bugs may provide much-needed insight into the biological factors that restrict their ability to act as vectors and may reveal novel mechanisms of immunity.