Abstract
Three strains of the rickettsiae of Tsutsugamushi disease, Pescadores, Fuji and Niigata strains, were inoculated intracerebrally to mice and the propagation of them in the brain were quantitatively examined and pursued. The rickettsiae propagate there drawing almost a parabolic line and attain its peak approximately ten days after the inoculation. The maximum LD50 titer attained in the brain is almost as high as that which can be attained in the liver.
Serial brain to brain passage in mice with the interval of seven to ten days was made for forty generations without loss of virulence or remarkable change of properties.
The infected brains were made to microscopic preparations and the rickettsiae in them were examined with the Giemsa-staining. Meninges, ependhyms or choroid plexus are the predilections sites of the rickettsiae for their propagation, but in nerve cells or glia cells no rickettsiae can be found at all. Namely it is observed that also in the brain the rickettsiae attack and propagate in principally the cells of mesodermal origin as already known in other susceptible organs.
In the course of intraperitoneal passage of the rickettsiae in mice the irresistible contamination by intestinal bacteria proper to mice is sometimes, especially in summer season, inevitable. In consideration with the above fact, the intracerebral passage, which is much simpler and easier in manipulation than the former and absolutely free from contaminations, except those dueing to technical mistake, is certainly a preferable method for the routine preservation of the Tsutsugamushi disease rickettsiae.
