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Causative agent of spotted fever group rickettsiosis in Japan
T Okada1, Y Tange, Y Kobayashi
1First Department of Internal Medicine, School of Medicine, Ehime University, Japan.
Abstract:
Since 1984, it has been known that spotted fever group rickettsiosis exists in Japan. We isolated three strains of the causative rickettsiae, designated Katayama, Misaka, and Abe, from patients with the disease and studied the characteristics of the isolates. Nude mice and cyclophosphamide-treated mice died after infection with the isolates. However, infected normal mice recovered and acquired immunity. Infected adult male guinea pigs had fever, a scrotal reaction, and seroconversion. The isolates propagated well in tissue-cultured Vero cells. Analysis by the cross-immunofluorescence antibody method showed that these isolates were closely related serologically. To reveal their immunological properties in detail, we produced 21 anti-Katayama monoclonal antibodies. Seven of these antibodies reacted with all representative strains of spotted fever group rickettsiae used in this study, and five others reacted only with the homologous strain, revealing that the Katayama strain has a strain-specific antigen(s) different from those of other spotted fever group rickettsiae. Moreover, these strain-specific antibodies also reacted with the Misaka and Abe strains. These results demonstrate that the causative agent of spotted fever group rickettsiosis in Japan is a new serotype of spotted fever group rickettsiae.
Insights
Spotted fever group rickettsiosis in Japan was studied using three new bacterial isolates. These isolates represent a new serotype of spotted fever group rickettsiae, distinct from other known strains.
Area of Science:
- * Microbiology
- * Immunology
- * Infectious Diseases
Background:
- * Spotted fever group rickettsiosis has been endemic in Japan since 1984.
- * The specific causative agent and its antigenic properties remained largely uncharacterized.
Purpose of the Study:
- * To isolate and characterize rickettsial strains causing spotted fever group rickettsiosis in Japan.
- * To determine the antigenic and serological properties of these isolates.
- * To identify if these isolates represent a new serotype.
Main Methods:
- * Isolation and propagation of rickettsial strains (Katayama, Misaka, Abe) in Vero cells.
- * Infection studies in immunocompromised and normal mice, and guinea pigs.
- * Serological analysis using cross-immunofluorescence antibody tests.
- * Production and characterization of anti-Katayama monoclonal antibodies.
Main Results:
- * Isolated strains (Katayama, Misaka, Abe) caused disease in susceptible animal models but were cleared by immunocompetent hosts, indicating acquired immunity.
- * Cross-immunofluorescence assays revealed close serological relationships among the isolates.
- * Monoclonal antibody analysis identified a strain-specific antigen in the Katayama strain, also present in Misaka and Abe strains.
Conclusions:
- * The causative agent of spotted fever group rickettsiosis in Japan comprises isolates with distinct antigenic properties.
- * These findings demonstrate the existence of a new serotype within the spotted fever group rickettsiae endemic to Japan.