Transmission of Rickettsia orientalis to man by Leptotrombidium akamushi at a scrub typhus endemic area in Akita Prefecture, Japan
Kitaoka, M.; Asanuma, K.; Otsuji, J.
American Journal of Tropical Medicine and Hygiene 23(5): 993-999
1974
ISSN/ISBN: 0002-9637 PMID: 4451238 Document Number: 80304
During the summers of 1956 to 1970 93 larvae of Trombiculids were removed from 386 people who had been bitten by Trombiculids in Jumonji, Akita Prefecture, Japan, where scrub typhus caused by Rickettsia orientalis is endemic. All 87 larvae that were available for examination were identified as Leptotrombidium akamushi (Brumpt). Infestation of man occurred from June to November, but mainly during July and August. The duration of attachment was approximately 1-3 days. Usually only one larva was found on each person, but on occasion as many as 7 were present. Scrub typhus developed in 45 of the 386 farmers bitten by larvae. Although patients with scrub typhus may have sustained multiple bites, only one eschar was found. However, 76% of the patients did not recognise a bite either at the site where an eschar subsequently appeared or elsewhere prior to the onset of the disease. If it is assumed that workers who did not subsequently become ill were unaware of Trombiculid bites, then the probable incidence of disease in those bitten by mites was 3.1%. The minimum infectivity rate of larvae of L. akamushi in Akita Prefecture was estimated to be 2.3%. Based on the assumption that infection was transmitted as the result of a single bite, the infection rate of larvae attacking man was calculated to be 2.5%.