Epidemiology and Ecology
The infectious process is closely linked to natural foci. The geographical distribution of the pathogen primarily covers the coastal territories of the western Pacific (Japan, Oceania).
Small rodents and arthropods serve as reservoirs and maintain the focus in the wild. A critical biological feature is the pathogen's ability to persist in vector populations through two transmission pathways:
- Transovarial transmission — from an infected female to offspring via eggs.
- Transstadial transmission — persistence of the pathogen as the tick transitions from one developmental stage to another.
The incidence exhibits a pronounced seasonal pattern directly dependent on the activity of various tick larval stages. Two main infection peaks are recognized: the spring-summer period (April–June) and the autumn period (September–November).
Pathogenesis and Clinical Presentation
The skin serves as the portal of entry. Humans are infected during attacks by tick larvae, while the bite itself remains completely painless. A specific marker, the primary affect (eschar), forms at the attachment site.
The incubation period lasts an average of 7–10 days (ranging from 5 to 21 days). The infection features a high frequency of asymptomatic (inapparent) forms—up to 2/3 of all cases—depending on the virulence of the specific strain.
When a manifest form develops, the disease debuts acutely:
- Chills, fever, intense headache, and myalgia occur.
- Hypotension is recorded in the cardiovascular system.
- The lymphatic system responds with regional lymphadenitis, which subsequently progresses to generalized lymphadenopathy.
On days 4–7 from disease onset, an exanthem (rash) appears. It is predominantly maculopapular, and less frequently hemorrhagic. The lesions localize mainly on the trunk, whereas involvement of the palms and soles is extremely rare.
Immunity and Antigenic Structure
The pathogen features pronounced antigenic variability—numerous distinct antigenic variants exist in nature.
Post-infection immunity is strictly strain-specific. This means protective antibodies do not provide cross-protection against heterologous strains of the microorganism. Consequently, a previous infection caused by one antigenic type does not protect an individual from infection by another type, making reinfection possible.
Diagnostics, Treatment, and Prevention
Laboratory verification of the diagnosis relies on serological and molecular-genetic methods:
- Molecular-genetic: detection of pathogen DNA via PCR.
- Nonspecific serology: detection of antibodies against Proteus OX19.
- Specific serology: complement fixation test (CFT), indirect immunofluorescence assay (IFA), and ELISA to detect antibodies against tick-group antigens. These methods are also suitable for retrospective diagnosis, as antibodies can persist in the blood for up to 20 years.
The basis of etiotropic therapy is tetracycline-class antibiotics. They demonstrate exceptionally high efficacy, with clinical recovery occurring in just 4–5 days.
Specific prophylaxis (vaccination) has not been developed. The main emphasis is on nonspecific measures—tick control and prevention. For risk groups (tourists, military personnel) entering endemic zones, emergency chemoprophylaxis is indicated: administration of doxycycline once weekly.