Genetic identification of rickettsiae isolated from ticks in Japan

Area of Science:

• Microbiology
• Veterinary Entomology
• Molecular Biology

Background:

• Japanese spotted fever, caused by Rickettsia japonica, was described in Japan.
• The need to identify the disease vector prompted further investigation into tick-borne rickettsiae.

Purpose of the Study:

• To identify and characterize rickettsial species and genotypes present in various tick populations in Japan.
• To determine the relationship of these isolates to known Rickettsia species, including R. japonica and R. helvetica.

Main Methods:

• Isolation and cultivation of rickettsial strains from collected ticks.
• Polymerase chain reaction (PCR) and monoclonal antibody testing for initial characterization.
• Gene amplification and sequencing of 16S rRNA and citrate synthase genes for precise identification.

Main Results:

• Sixty-three rickettsial isolates were obtained from six tick species.
• Isolates from Dermacentor taiwanensis and Haemaphysalis flava were confirmed as Rickettsia japonica.
• Rickettsia closely related to Rickettsia helvetica were identified in Ixodes ovatus, Ixodes persulcatus, and Ixodes monospinosus.
• A novel genotype, genotype AT, closely related to a Slovakian genotype, was isolated from Amblyomma testudinarium.

Conclusions:

• The study identified Rickettsia japonica in specific tick vectors in Japan.
• The presence of Rickettsia closely related to Rickettsia helvetica in Japanese ticks suggests potential broader geographic distribution or introduction.
• A new Rickettsia genotype of unknown pathogenicity was discovered, highlighting the diversity of tick-borne agents.