A Study of Rickettsia tsutsugamushi in Russia.

为进行俄罗斯东部地区恙虫病的生态学和流行病学研究，我们从海参崴附近的野外采集恙螨和野生啮齿动物中分离出恙虫病立克次体。将278只啮齿类动物的脾脏、肝脏和血清解剖后立即在液氮中冷冻，并将冷冻样品在干冰罐中带回日本。免疫荧光试验仅在4只鼠中检出抗立克次体抗体，其中2只为阳性，2只为假阳性。另一方面，从啮齿类动物中收获12，600只饱食螨，在鉴定种属后，也将活螨用于立克次体分离。将螨和啮齿动物器官的匀浆接种到L或Vero细胞培养物中，或用或不用免疫抑制剂处理的小鼠中。根据我们的经验，这些细胞和小鼠足以分离出毒力和无毒力立克次体。通过偶尔更换培养基将细胞保存两个月，并将接种小鼠的脾匀浆盲传两次至其他小鼠。然而，立克次体既没有在细胞培养物中分离，也没有在小鼠中分离。此外，抗立克次体抗体在接种的小鼠中没有升高。这些结果表明，目前俄罗斯远东地区恙虫病立克次体感染的螨类和啮齿动物很少。然而，这项研究的同事Tarasevich报告说，该地区的啮齿动物和螨在20世纪60年代受到严重感染，立克次体很容易从这些动物中分离出来。这些证据表明，立克次体感染的恙螨显着下降，在几十年。关于这些戏剧性变化的原因，一个有趣而重要的问题有待于进一步研究

For the ecological and epidemiological study of tsutsugamushi disease in the Fdr East Russia, we attempted to isolate Rickettsia tsutsugamushi from trombiculid mites and wild rodents which were collected on the field near Vladivostok. The spleens, livers and sera of 278 rodents were frozen in liquid nitrogen immediately after dissection, and the frozen samples in a dryice jar were carried back to Japan. By immunofluorescence test, antirickettsial antibodies were found only in 4 rodents : two positive and two puedopositive.The organs from these four rodents and 21 others captured in the same areas were used for rickettsial isolation. On the other hand, 12,600 engorged mites were harvested from the rodents, and the alive mites were also used for rickettsial isolation after identification of the species. The homogenates of mites and the organs of rodents were inoculated to L or Vero cell cultures, or mice treated with or without immunosuppressive agent. In our experience, these cells and mice are adequate for isolation of both virulent and avirulent rickettsiae. The cells were kept for two months by exchanging occasionally the culture medium, and spleen-homogenates of the inoculated mice were blind-passaged twice to other mice. However, rickettsiae were isolated in neither cell cultures nor mice. Furthermore anti-rickettsial antibody did not rise in the inoculated mice. These results indicated that very few mites and rodents in the Far East Russia were infected with R.tsutsugamushi at present. However, Tarasevich, a coworker of this study, reported that the rodents and mites in this region were heavily infected in 1960s and rickettsiae were easily isolated from these animals. These lines of evidence suggest that rickettsial infection in the trombiculid mites decreased markedly during a few decades. An interesting and important question on the reason of these dramatic change is remained for further studies