Observations on the New Type Tsutsugamushi Disease in Akita Prefecture

The Oinono basin in Akita Prefecture is known as an endemic focus of the classical type (Summer type) tsutsugamushi disease. Recently, it was becoming clear that an epidemiologically different type of the disease which is called the new type (Spring and Autumn type) tsutsugamushi disease to differentiate from the former type was also seen anywhere in Akita Prefecture, and we found 21 cases of this type disease in a period from 1978 to 1979.The present study was conducted to determine the correlation between the place presumed of being infected, time of onset, clinical findings and the prototype of etiologic agent, Rickettsia tsutsugamushi.1) The new type disease occurred inside the classical endemic area had generally severe clinical symptoms which were essentially identical to the classical type disease occurred in that area, whereas the new type disease occurred outside that area had relatively milder than the classical type disease.2) Typing the rickettsiae isolated from human cases and wild rats trapped in both areas, it was defined that the Gilliam type was dominant in the former area and the Karp type was in the latter.3) Among 10 species of trombiculid mites collected from wild rats, Leptotrombidium pallidum which is considered as a most important vector of this type disease was dominant species in both areas.4) The above results may indicate that the differences in clinical pictures between two areas could be attributed to difference in mite vector but a difference in rickettsial virulence.