Introduction of Scrub Typhus
Table of Contents
Scrub typhus and typhoid are quite different but common thing is that both cover fever. Scrub typhus also known as bush typhus, is a disease caused by the intracellular parasite, Orientia ( formerly Rickettsia) tsutsugamushi and typhoid by Salmonella enterica serotype Typhi. Both causative agents are bacteria. Scrub typhus is transmitted by the bite of larval trombiculid mites. The most common symptoms of scrub typhus are fever, headache, body aches, and sometimes rash. Most cases of scrub typhus take place in rural areas of Southeast Asia, Indonesia, China, Japan, India, and northern Australia. Anyone living in or traveling to such areas where scrub typhus is found could get infected. It often presents as a fever with little to distinguish it clinically from co-endemic diseases such as typhoid, leptospirosis, and dengue.
The occurrence of morbilliform rash, eschar, splenomegaly, and lymphadenopathies are typical signs that support the diagnosis but it is not always present. Diagnosis, thus, depends on clinical suspicion, prompting the clinician to request an appropriate laboratory investigation, and failure to diagnose the disease will likely result in treatment with ineffective β-lactam–based regimens but also pneumonitis, encephalitis, and myocarditis occur in the late phase of illness. With proper therapy, the fever will break within 36 hours, but if left untreated, complications or death may occur.
This Scrub Typhus Rapid Test is a rapid immuno-chromatographic immunoassay for the qualitative detection of IgM antibodies to members of O. tsutsugamushi in human serum, plasma, or blood. The procedure requires no specialized equipment, takes less than 5 minutes and results are ready in 15 minutes. After the onset of symptoms, the IgM antibody titers increased gradually over 2–3 weeks, peaked at about 4 weeks, and started to decrease rapidly between 4 and 5 weeks. Over the first 2 weeks, IgG antibody titer increases sharply peaked at about 4 weeks, and decreased rather gradually thereafter.
Principle of Scrub Typhus Antibody Test
This Scrub Typhus Detect™ IgM Rapid Test is a qualitative, membrane-based immunoassay for the detection of IgM in members of O. tsutsugamushi in human serum, plasma, or blood. The membrane is pre-coated with a mixture of novel recombinants (representing several geographical isolates) on the test line region and appropriate control antigen on the control line region. During testing, the sample reacts with the dye conjugate (anti-human IgM colloidal gold conjugate) which has been pre-coated in the test device. The mixture then migrates upward on the membrane chromatographically by capillary action to react with ST-derived recombinant antigens on the membrane and generates a red band or line.
The presence of this red line indicates a positive result, while its absence indicates a negative result. Independent of the presence or absence of antibodies to scrub typhus antigens, a red line or band at the control line region will always appear when the sera-gold migrates to the immobilized control region. The presence of this red band verifies sufficient sample volume and proper flow of reagents.
Requirements for Scrub Typhus Antibody Test
- Kit contains Scrub Typhus Detect™ IgM Rapid Test Strip,
Chase Buffer Type A and test manual leaflet.
- From the outside we need-Dropper/ micropipette
- if necessary test tube
- Test specimen (whole blood/ serum)
- Centrifuge (optional for separation of serum or plasma from blood)
- Waste bin
Procedure of Scrub Typhus Rapid Test
- Open the pouch
- Put 10 µl of serum or whole blood at the sample pad ( in the area beneath the arrow) of the strip.
- Placed the test strip in a test tube or a plastic well (holds 150–
200 μL of liquid).
- After that put three drops of chase buffer.
- Read the result for up to 15 minutes.
Observe for pink or red lines or bands.
Result and interpretation of Scrub Typhus Antibody Test
- Only on the band at the control region: Test Negative
- Both bands at the control and test region: Test positive
- No band or band only at test region: Test invalid ( repeat the test with new strip)
- Our test is positive as shown above picture.
Scrub Typhus Antibody Test-Test Result, and Test Method
- This test has a sensitivity of 100 % and also a specificity of 100%.
- The SD BIOLINE Tsutsugamushi Test is a rapid, qualitative, and differential test for the detection of various antibodies like IgG, IgM, and IgA to Rickettsia Tsutsugamushi in human serum, plasma, and whole blood.
- The oldest test in current use is the Weil–Felix OX-K agglutination reaction, which is inexpensive, and easy to perform, and results are available overnight; however, it lacks specificity and sensitivity. Therefore, it is not in use.
- The indirect fluorescent antibody (IFA) test is more sensitive, and results are available in a couple of hours; however, the test is more expensive and requires considerable training.
- The PCR-based method is very useful beyond serological methods however, the high resource costs and training required make it impractical for many areas where scrub typhus is endemic.
Limitations of Scrub Typhus Rapid Test
- This rapid test device is for research use only.
- It is not for use in diagnostic procedures.
- The test should be used for the detection of antibodies to O. tsutsugamushi-derived antigens in the specimen.
- This rapid Test Device will only indicate the presence of antibodies to O. tsutsugamushi antigens in the specimen and may not imply active infection.
- Do not use serum samples containing any glycerol or other viscous materials since it will decrease the sensitivity of the assay.
- These ScrubTyphus assays have not been tested in persons with advanced HIV infection or other immunocompromised diseases that are known to have low or undetectable specific antibodies.
- Rheumatoid Factor containing (RF) sera may interfere with the result.