Tsutsugamushi disease or scrub typhus is a parasitic infection caused by a parasite, Orientia tsutsugamushi, carried by mites. It presents with fever, headache, a macular rash, lymphadenopathy and eschar at the region of the mite bite.
Tsutsugamushi disease is transmitted through a mite bite. During the inoculation period, which typically lasts for 6 to 20 days, the patient usually remains asymptomatic. Approximately at the tenth day following the initial infection, high fever, headaches, myalgia and fatigue emerge. The non-specificity of the symptoms constitutes a diagnostic obstacle at the early disease phase. During this initial period, a papule begins to form at the region of the mite bite, gradually progressing to form a necrotic localized spot, referred to as an eschar.
Despite the diagnostic challenge due to the non-specificity of the symptoms, the existence of an eschar is pathognomonic of tsutsugamushi disease; it is observed in half of the patients with a primary infection and is well-defined by the time that an individual develops fever   . Other symptoms associated with tsutsugamushi disease are lymphadenopathy, regional or generalized, ocular pain, a productive cough and infected conjunctiva  . A characteristic symptom is also the centrifugal macular rash that appears after approximately a week following the infection. The erythema develops on the torso, may gradually assume papular characteristics and may not be observed due to its transient nature .
The complete workup for scrub typhus encompasses a multitude of tests and procedures, including routine blood tests, serology, and PCR.
More specifically, laboratory blood tests including a complete blood count and biochemical studies usually yield the following results:
Serologic tests are further carried out, as they constitute the primary diagnostic procedures. A direct immunoperoxidase test and an immunofluorescent assay are used to establish the diagnosis and are expected to yield a result displaying a 4-fold augmentation of antibody titers between acute and convalescent serum specimens . All potential O. tsutsugamushi subtypes should be considered as a possibility and should, therefore, be separately investigated serologically. A dot immunoassay can also be employed in order to diagnose tsutsugamushi disease, whereas the immunochromatographic test, aimed at the detection of immunoglobulin (Ig) M and IgG antibodies exhibit a considerably greater sensitivity for an early diagnosis when compared to the standard immunofluorescence assay.
The polymerase chain reaction tests (PCR) has proven a valuable diagnostic tool, on eschar samples, early in the course of the disease. In third world countries, the method of choice is the Weil-Felix OX-K strain agglutination reaction; when more advanced medical facilities are available, this test is not opted for due to its decreased sensitivity.