Transmission of Rickettsia tsutsugamushi strains among humans, wild rodents, and trombiculid mites in an area of Japan in which tsutsugamushi disease is newly endemic

Abstract

Thirty-two newly isolated strains ofRickettsia tsutsugamushi, 14 from patients with tsutsugamushi disease, 12 from wild rodents, and 6 from trombiculid mites parasitizing rodents in Gifu Prefecture, Japan, were examined for reactivities to 12 monoclonal antibodies by an indirect fluorescent-antibody test to classify their antigenicities. All of the isolates could be classified into one of six groups (KN-1, KN-2, KN-3, GJ-1, R158, and R161) according to their reactivities to the monoclonal antibodies. The KN-1 and GJ-1 strains that are prevalent among patients from Gifu Prefecture had the same reactivities as the Kawasaki and Kuroki strains, respectively, which have been isolated and are prevalent in the Miyazaki and Kagoshima prefectures in southwest Japan. The isolates from patients were different in serotype from those from rodents and mites (Leptotrombidium paUlidum). The KN-2 and KN-3 strains were most prevalent among patients and among rodents and mites, respectively. No close similarity between KN-2 and other strains tested was observed. KN-3 is only a minor contributor to diseases in patients in Gifu Prefecture; however, it was proven that the same strain was prevalent in Niigata Prefecture in northern Japan. Thus, Gifu Prefecture is an area where southern, northern, and local strains are found. We hypothesize that humans are prone to infection with KN-2, GJ-1 (very similar to Kuroki), and KN-1 (very similar to Kawasaki), probably by infestation with Leptotrombidium scuteUare. While both L. scuteUlare and L. paUlidum parasitize wild rodents and may carry any rickettsial strain, the most virulent strain, KN-3, is predominant among wild rodents. Antigenic analysis using monoclonal antibodies to R. tsutsugamushi should be useful for epidemiological studies of infection with this organism.

Demonstration of Antigenic and Genotypic Variation in Orientia tsutsugamushi Which Were Isolated in Japan, and Their Classification into Type and Subtype

“…Antigenic variety among the strains of O. tsutsugamushi has been detected by immunological methods with polyclonal hyperimmune sera (4,10) and MAbs (31,36). In the present study, 40 strains of O. tsutsugamushi were analyzed by immunological and genotypic methods targeting the variation of type-specific antigen of 56-kDa protein which is located on the surface of this microorganism.…”

“…Several investigators in Japan characterized the antigenic types of O. tsutsugamushi isolated from patients, wild rodents and trombiculid mites in different endemic areas with strain-specific and cross-reactive monoclonal antibodies (MAbs) (7,14,31,34,36), and they found *Address correspondence to Dr . Akira Tamura, Department of Microbiology, Niigata College of Pharmacy, 5-13-2 Kamishin'eicho, Niigata, Niigata 950-21, Japan.…”

“…Abbreviations: bp, base pair; CY, cyclophosphamide; EDTA, ethylenediaminetetraacetic acid; ICU, infected cell counting unit; IF, immunofluorescence; kDa, kilodalton; MAbs, monoclonal antibodies; MEM, Eagle's minimum essential medium; MLD50, 50% mouse lethal doses; PCR, polymerase chain reaction; RFLP, restriction fragment length polymorphism; rRNA, ribosomal RNA; Tris, tris(hydroxymethyl)aminomethane; VD, variable domain. that most strains were antigenically identical but some were different from the prototype strains (31,36). However, the MAbs used were prepared independently by the respective workers, and therefore the results obtained could not be combined for comparison.…”

“…These prototype strains were provided by A. Shishido, National Institute of Health, Japan in 1978, and were cloned by triple plaque-purification in L929 cell cultures in our laboratory. Most of the other strains were isolated in our previous studies (7,8,28,(34)(35)(36) from patients with tsutsugamushi disease through cyclophosphamide (CY)-treated or -untreated ddY mice, ICI nude mice, or cultures of BS-C40 or L929 cells. Strain hie (12) was provided by Y. Kobayashi, Ehime University.…”

Antigenic Relationship among the Eight Prototype and New Serotype Strains of Orientia tsutsugamushi Revealed by Monoclonal Antibodies

“…The usefulness of MAbs to O. tsutsugamushi strains for classifying their antigenicities has been suggested in several studies and several new isolates which are distinguished from prototype strains have been identified based on the IFA test with MAbs (2,(22)(23)(24).…”