Rickettsia amblyommatis belongs to the spotted fever group of Rickettsia and infects Amblyomma americanum (Lone Star ticks) for transmission to offspring and mammals. Historically, the geographic range of A. americanum was restricted to the southeastern USA. However, recent tick surveys identified the progressive northward invasion of A. americanum, contributing to the increased number of patients with febrile illnesses of unknown etiology after a tick bite in the northeastern USA. While serological evidence strongly suggests that patients are infected with R. amblyommatis, the virulence potential of R. amblyommatis is not well established. Here, we performed a bioinformatic analysis of three genome sequences of R. amblyommatis and identified the presence of multiple putative virulence genes whose products are implicated for spotted fever pathogenesis. Similar to other pathogenic spotted fever rickettsiae, R. amblyommatis replicated intracellularly within the cytoplasm of tissue culture cells. Interestingly, R. amblyommatis displayed defective attachment to microvascular endothelial cells. The attachment defect and slow growth rate of R. amblyommatis required relatively high intravenous infectious doses to produce dose-dependent morbidity and mortality in C3H mice. In summary, our results corroborate clinical evidence that R. amblyommatis can cause mild disease manifestation in some patients.

中文翻译：

---

钝感立克次体对小鼠斑疹热发病机制的毒力潜力

Rickettsia amblyommatis 属于 Rickettsia 斑疹热组，感染 Amblyomma americanum（孤星蜱）并传播给后代和哺乳动物。从历史上看，A. americanum 的地理范围仅限于美国东南部。然而，最近的蜱调查发现，美洲拟南芥逐渐向北入侵，导致在美国东北部被蜱叮咬后患有不明原因发热性疾病的患者数量增加。虽然血清学证据强烈表明患者感染了 R. amblyommatis，但 R. amblyommatis 的毒力潜力尚未确定。在这里，我们对 R 的三个基因组序列进行了生物信息学分析。amblyommatis 并确定了多个推定的毒力基因的存在，其产物与斑疹热发病机制有关。与其他致病性斑点热立克次体相似，R. amblyommatis 在组织培养细胞的细胞质内进行细胞内复制。有趣的是，R. amblyommatis 对微血管内皮细胞的附着有缺陷。R. amblyommatis 的附着缺陷和缓慢的生长速度需要相对较高的静脉内感染剂量才能在 C3H 小鼠中产生剂量依赖性发病率和死亡率。总而言之，我们的结果证实了临床证据表明 R. amblyommatis 可在某些患者中引起轻度疾病表现。amblyommatis 对微血管内皮细胞的附着有缺陷。R. amblyommatis 的附着缺陷和缓慢的生长速度需要相对较高的静脉内感染剂量才能在 C3H 小鼠中产生剂量依赖性发病率和死亡率。总而言之，我们的结果证实了临床证据表明 R. amblyommatis 可在某些患者中引起轻度疾病表现。amblyommatis 对微血管内皮细胞的附着有缺陷。R. amblyommatis 的附着缺陷和缓慢的生长速度需要相对较高的静脉内感染剂量才能在 C3H 小鼠中产生剂量依赖性发病率和死亡率。总而言之，我们的结果证实了临床证据表明 R. amblyommatis 可在某些患者中引起轻度疾病表现。