Approach Considerations

Routine laboratory studies in patients with scrub typhus reveal early lymphopenia with late lymphocytosis. A decrease in the CD4:CD8 lymphocyte ratio may also be noted. Thrombocytopenia is also seen.^{[34, 6]}The hematologic manifestations may raise the suspicion of dengue infection.^{[32, 3]}

Elevated transaminase levels may be present in 75-95% of patients. Hypoalbuminemia occurs in about 50% of cases, whereas hyperbilirubinemia is rare. These findings may be especially prevalent in children.^{[34, 47]}In adults, elevated transaminase levels relate to severity of disease.^{[11, 6]}Transaminitis combined with other symptoms and exposure history may suggest possible leptospirosis. Coinfection with leptospirosis has been reported.^{[3, 48]}

Laboratory studies of choice are serologic tests for antibodies. The main confirmatory tests are the indirect immunoperoxidase test and the immunofluorescent assay.^[49]An infection is confirmed by a 4-fold increase in antibody titers between acute and convalescent serum specimens. A single high titer with classic clinical features is considered a probable case. Serology for all suspected subtypes should be requested.^[6]

The indirect fluorescent antibody test is sensitive and provides results in a couple of hours.^[50]It uses fluorescent antihuman antibody to detect specific antibody from patient serum bound to a smear of scrub-typhus antigen. A dot immunoassay has also been used in the serodiagnosis of scrub typhus.

A study of 2 rapid immunochromatographic tests for detection of IgM and IgG against O tsutsugamushi determined that both assays were more sensitive and specific than the standard immune immunofluorescence assay for the early diagnosis of scrub typhus.^[51]

A study by Varghese et al that included 203 patients previously confirmed to have scrub typhus reported that IgM levels gradually declined but remained elevated above the diagnostic cutoff up to 12 months post-infection.^[52]

O tsutsugamushi has been identified by means of the polymerase chain reaction (PCR) technique in clinical specimens.^{[53, 6, 54]}Performing nested PCR on the eschar might be a rapid diagnostic test for scrub typhus in the early, acute stage.^[55]

In 2007, Cao et al reported on the development of a rapid diagnostic reagent for scrub typhus.^[56]

The Weil-Felix OX-K strain agglutination reaction can be used to aid in diagnosis of scrub typhus. It may be the only serologic test available in less developed countries; unfortunately, it is not a very sensitive assay.^[3]

Chest radiography may reveal pneumonitis,^{[28, 33]}especially in the lower lung fields.^[57]

Histologically, the basic pathologic change is focal or disseminated vasculitis caused by the destruction of endothelial cells and the perivascular infiltration of leukocytes.^[58]

Treatment & Management

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Media Gallery

Transmission electron micrograph depicts peritoneal mesothelial cell of mouse that had been experimentally infected intraperitoneally with Orientia tsutsugamushi. Several organisms are visible within mesothelial cell's cytoplasm.
Eschar on neck.
Eschar on scrotum.
Typical eschar.
Maculopapular rash.
Chigger. Image taken from "Food and Environmental Hygiene Department" Web site and is reproduced under license from the Government of Hong Kong Special Administrative Region.

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Author

David J Cennimo, MD, FAAP, FACP, FIDSA, AAHIVS Associate Professor of Medicine and Pediatrics, Adult and Pediatric Infectious Diseases, Rutgers New Jersey Medical School

David J Cennimo, MD, FAAP, FACP, FIDSA, AAHIVS is a member of the following medical societies: American Academy of HIV Medicine, American Academy of Pediatrics, American College of Physicians, American Medical Association, HIV Medicine Association, Infectious Diseases Society of America, Medical Society of New Jersey, Pediatric Infectious Diseases Society

Disclosure: Nothing to disclose.

Coauthor(s)

Arry Dieudonne, MD Associate Professor of Pediatrics, Division of Pulmonology, Allergy, Immunology and Infectious Diseases, Rutgers New Jersey Medical School; Clinical Director, Francois-Xavier Bagnold Center for Children, University Hospital

Arry Dieudonne, MD is a member of the following medical societies: American Academy of Pediatrics, American Medical Association, Pediatric Infectious Diseases Society

Disclosure: Nothing to disclose.

Chief Editor

Russell W Steele, MD Clinical Professor, Tulane University School of Medicine; Staff Physician, Ochsner Clinic Foundation

Russell W Steele, MD is a member of the following medical societies: American Academy of Pediatrics, American Association of Immunologists, American Pediatric Society, American Society for Microbiology, Infectious Diseases Society of America, Louisiana State Medical Society, Pediatric Infectious Diseases Society, Society for Pediatric Research, Southern Medical Association

Disclosure: Nothing to disclose.

Acknowledgements

David F Butler, MD Professor of Dermatology, Texas A&M University College of Medicine; Chair, Department of Dermatology, Director, Dermatology Residency Training Program, Scott and White Clinic, Northside Clinic

David F Butler, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American Medical Association, American Society for Dermatologic Surgery, American Society for MOHS Surgery, Association of Military Dermatologists, and Phi Beta Kappa