Background

Scrub typhus is an important endemic disease in tropical Asia caused by Orientia tsutsugamushi for which no effective broadly protective vaccine is available. The successful evaluation of vaccine candidates requires well-characterized animal models and a better understanding of the immune response against O. tsutsugamushi. While many animal species have been used to study host immunity and vaccine responses in scrub typhus, only limited data exists in non-human primate (NHP) models.

Methodology/Principle findings

In this study we evaluated a NHP scrub typhus disease model based on intradermal inoculation of O. tsutsugamushi Karp strain in rhesus macaques (n = 7). After an intradermal inoculation with 10⁶ murine LD₅₀ of O. tsutsugamushi at the anterior thigh (n = 4) or mock inoculum (n = 3), a series of time course investigations involving hematological, biochemical, molecular and immunological assays were performed, until day 28, when tissues were collected for pathology and immunohistochemistry. In all NHPs with O. tsutsugamushi inoculation, but not with mock inoculation, the development of a classic eschar with central necrosis, regional lymphadenopathy, and elevation of body temperature was observed on days 7–21 post inoculation (pi); bacteremia was detected by qPCR on days 6–18 pi; and alteration of liver enzyme function and increase of white blood cells on day 14 pi. Immune assays demonstrated raised serum levels of soluble cell adhesion molecules, anti-O. tsutsugamushi-specific antibody responses (IgM and IgG) and pathogen-specific cell-mediated immune responses in inoculated macaques. The qPCR assays detected O. tsutsugamushi in eschar, spleen, draining and non-draining lymph nodes, and immuno-double staining demonstrated intracellular O. tsutsugamushi in antigen presenting cells of eschars and lymph nodes.

Conclusions/Significance

These data show the potential of using rhesus macaques as a scrub typhus model, for evaluation of correlates of protection in both natural and vaccine induced immunity, and support the evaluation of future vaccine candidates against scrub typhus.

中文翻译：

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恒河猴（猕猴）斑疹伤寒模型的表征：对人类病原体东方Kar虫Karp皮内攻击的敏感性

背景

斑疹伤寒是热带亚洲tsu虫病的重要地方病，东方Or虫病导致这种疾病，目前尚无有效的广泛保护性疫苗。成功评估候选疫苗需要良好表征的动物模型和对O免疫应答的更好理解。gam虫。尽管许多动物物种已被用于研究斑疹伤寒的宿主免疫力和疫苗反应，但在非人类灵长类动物（NHP）模型中只有有限的数据。

方法/原理发现

在这项研究中，我们评估了基于O的皮内接种的NHP灌木斑疹伤寒疾病模型。恒河猴中的tsutsugamushi Karp株（n = 7）。皮内接种10 ⁶鼠LD ₅₀的O后。恙虫在大腿前侧（N = 4）或模拟接种物（N = 3），一系列涉及血液学，进行生物化学，分子生物学和免疫学测定的时间过程的调查，直到第28天，当被收集的组织病理学和免疫组织化学。在所有带有O的NHP中。gam虫接种，但不是模拟接种，在接种后第7-21天观察到典型的焦with发展为中央坏死，局部淋巴结肿大和体温升高。在感染后6-18天通过qPCR检测到菌血症；感染后第14天肝酶功能改变和白细胞增加。免疫测定显示可溶性细胞粘附分子抗O的血清水平升高。mac猴中的虫特异性抗体应答（IgM和IgG）和病原体特异性细胞介导的免疫应答。的qPCR测定检测Ò。虫，脾脏，引流淋巴结和不引流淋巴结中有虫，免疫双染色证实细胞内O。虫在antigen和淋巴结的抗原呈递细胞中。

结论/意义

这些数据表明使用恒河猴作为灌木斑疹伤寒模型的潜力，可用于评估天然和疫苗诱导的免疫中保护作用的相关性，并支持评估未来候选疫苗对抗灌木斑疹伤寒。