1954 年 4 巻 supple 号 p. 233-251
1. The correct nomenclature of the four species of Trombicula (Leptotrombidium) described by Nagayo and others, namely pallida, palpalis, intermedia and scutellaris, was discussed together with the designation of the original paper, lectotypes and type localities of these species. 2. Morphological characterisitics of larvae of Trombicula scutellaris under the present taxonomical aspects were discussed. They are morphologically most closely related to Trombicula akamushi, the vector of the classical Tsutsugamushi disease, but are considered to be definitely of different species. 3. Out of about 200 times of collections made by the author and his colleagues for search of Tsutsugamushi covering all of the four main islands of Japan, Trombicula scutellaris was recovered from 12 regions of Izu Islands, Chiba, Shizuoka, Fukui, Kyoto and Kagoshima Prefectures. The species was also recorded by Nagayo and others from Yamagata and by Kawamura and others from Niigata in the same locality as they collected akamushi. The species was considered not so widely distributed as such species like fuji, pallida, kitasatoi or G. saduski. 4. The seasonal distribution of this species is peculiar in its appearance restricted in autumn in northern regions and longer through late autumn to early spring in southern regions like Hachijo Island. 5. Larvae of this species were readily collected from ground surface of infested area by black plates or by boots, as was observed in other human biting chiggers like akamushi. The species was also proved to take a very wide range of hosts in rodents, domestic animals or birds, suggesting that humans could not be the exception. 6. The new type of Tsutsugamushi disease defined here as "winter scrub typhus" was discussed. Through epidemiological studies and ecological observation on mites, Trombicula scutellaris was suggested as the vector of this disease in Izu Islnd, Chiba and other areas. The disease highly prevalent in Hachijo Island and possibly in other areas is characterized in its occurrence in the winter season, extremely low mortality, high morbidity rate of young children and the almost equal sex ratio. 7. The possibility that the recovery of Trombicula scutellaris from certain areas would suggest the occurrence of the disease was discussed. On the other hand, exmaples of the occurrence of the similar type of the disease from regions where no specimens of this species was recovered and certain other species like pallida was abundantly collected were given. In view of the assumption that there would be much more localities in and outside of Japan where Trombicula scutellaris occurs without being discovered, and that other more widely distributed species like pallida may also act as the accidental vector, it is highly probable that winter scrub typhus might have been very widely scattered in rural areas of Japan under the misdiagnosis with related diseases like murine typhus.
