Orienta tsutsugamushi - MegaMicro

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Orienta tsutsugamushi

Microbiology > Bacteriology > Intracellular bacteria > Rickettsia
Taxonomy: Order Rickettsiales, Family Rickettsiaceae

Pathobiology: Organism is an obligate intracellular, Gram negative bacteria. It is maintained in nature by transovarial transmission in larval trombiculid mites (chiggers) or harbored in rodent reservoirs. Humans can be exposed to the bacteria through chigger bites. Chigger bites often result in a pruritic rash. The bacteria invades host cells by induced phagocytosis and escaping into the cytoplasm of the host cell, but specific virulence factors related to phagosomal membrane lysis have not been identified. It is also resistant to B-lactam antibiotics due to lack of peptidoglycan in its cell wall.

Clinical Manifestations: O. tsutsugamushi causes scrub typhus. Primary disease symptoms include acute febrile illness, headache, myalgia, sweats, conjunctival injection, lymphadenopathy, and mental changes. Eschar develops at the site of the bite.
  • Early phase of infection: Leukopenia, thrombocytopenia, and abnormal liver tests
  • Late phase of infection: Pneumonitis, endocarditis, encephalitis, hemorrhaging, and intravascular coagulation

Epidemiology: Scrub typhus is endemic across extensive parts of Asia, South Asia, Australia and the Pacific, and disease prevalence is stable in those areas. US experiences are related to exposures of military personnel during WWII, the Korean War, and the Vietnam War.

Diagnosis: Clinical presentation of the disease and serologic tests to detect antibodies are mainly used in diagnosis. However, detection of antibodies is only effective in non-endemic areas because many unaffected individuals will have antibodies in endemic areas. The organism can be isolated in cell culture, and immunofluorescence and immunoperoxidase staining can also be used to demonstrate organisms in tissue.

Treatment: Prompt treatment with tetracyclines (e.g. doxycycline) or chloramphenicol. Azythromycin is used in pregnant women and when resistance is suspected. Some evidence of antibiotic resistance is being described in South Asia.

Prevention: The best prevention measure is to avoid ticks. In mouse models, riboflavin and light have been seen to reduce infectivity.
Related concepts

Key Words
1.       Scrub typhus
2.       Rickettetsia

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