Departamento de Medicina Veterinária Preventiva e Saúde Animal, Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo, São Paulo, SP, Brazil.
Departamento de Patologia, Programa de Pós-graduação em Ciência Animal, Universidade Estadual do Maranhão, São Luís, MA, Brazil.
J Med Entomol. 2020 Jan 9;57(1):308-311. doi: 10.1093/jme/tjz141.
The bacterium Rickettsia rickettsii is the agent of Brazilian spotted fever (BSF), a highly fatal disease that is transmitted in Brazil mainly by the tick Amblyomma sculptum Berlese, which uses capybaras (Hydrochoerus hydrochaeris Linnaeus) as major hosts. In 2015, we captured nine capybaras in a BSF-endemic area of southeastern Brazil. From each capybara, we collected blood sera that were tested through the immunofluorescence assay using Rickettsia spp. antigens, and A. sculptum ticks, processed for isolation of R. rickettsii through guinea pig inoculation. All capybaras (100%) were seroreactive to Rickettsia spp., with highest titers to R. rickettsii. A total of 166 A. sculptum ticks were macerated and inoculated into nine guinea pigs, from which only one presented high fever and seroconverted to R. rickettsii. Blood from this febrile animal was inoculated into additional guinea pigs (guinea pig passages), which also became febrile and seroconverted, or when euthanized during the fever period, their internal organs (spleen, lung) were shown to contain R. rickettsii DNA. The present rickettsial isolate has been maintained cryopreserved as infected guinea pig organs. There was at least one R. rickettsii-infected tick among the 166 macerated ticks, giving a minimal infection rate of 0.6% (1/166). This infection rate is within the range of previous studies, which reported that only 0.05% to at most 1.28% A. sculptum ticks were infected by R. rickettsii in other BSF-endemic areas. These low infection rates support the low incidence of BSF, despite of A. sculptum being the most frequent human-biting tick in southeastern Brazil.
立克次氏体细菌 Rickettsia rickettsii 是巴西斑疹热（BSF）的病原体，这种疾病在巴西主要通过 Amblyomma sculptum Berlese 传播，该蜱虫以水豚（Hydrochoerus hydrochaeris Linnaeus）为主要宿主。2015 年，我们在巴西东南部的 BSF 流行地区捕获了 9 只水豚。从每只水豚中采集了血清，并通过免疫荧光分析用立克次体 spp. 抗原和 A. sculptum 蜱虫进行了测试，然后通过豚鼠接种来分离 R. rickettsii。所有水豚（100%）对立克次体 spp. 均具有血清学反应性，对 R. rickettsii 的滴度最高。共捣碎了 166 只 A. sculptum 蜱虫并接种到 9 只豚鼠中，只有 1 只出现高热并对 R. rickettsii 血清转化。从发热动物的血液中接种到其他豚鼠（豚鼠传代）中，这些豚鼠也出现发热和血清转化，或者在发热期间安乐死时，它们的内脏（脾脏、肺）被证明含有 R. rickettsii DNA。目前已将这种立克次氏体分离株冷冻保存为感染豚鼠器官。在捣碎的 166 只蜱虫中至少有 1 只有 R. rickettsii 感染，感染率最低为 0.6%（1/166）。该感染率在以前的研究范围内，这些研究报告称，在其他 BSF 流行地区，只有 0.05%至最多 1.28%的 A. sculptum 蜱虫感染了 R. rickettsii。尽管 A. sculptum 是巴西东南部最常见的人咬蜱虫，但如此低的感染率支持了 BSF 的低发病率。
