Scrub Typhus IgM Test

The scrub-typhus IgM test is a test that is used for the detection of scrub typhus transmitted to humans through the bite of the larva of trombiculid mites or through the bacteria Orientia tsutsugamushi .The bite results in the formation of an eschar or a scab at the site. The highly infectious disease is common in areas with scrub vegetation and unavailability of immediate treatment can be fatal. The test is carried out by immunofluorescence assay (IFA) for testing IgM antibodies. A Rapid test with the help of a substrate is also often carried out before the IFA. The IFA is done to confirm the presence of the above antibody bound to the scrub-typhus antigen which is called a serological test and usually done after the Rapid test.

No special preparation is required for the test. The doctor should be informed about the prior medical history and medications being taken, for specific instructions.

In case of the Rapid test, if the level of absorbance is greater than the cutoff value ,then the Scrub typhus antigen is detected. If it is lesser than the cutoff level, the antigen is not detected. In case of the IFA, if the stain shows up under the light, it is positive. If the detection is not clear, other tests should be performed to confirm the result.

The collected human serum, blood, or plasma samples are added to the slide for testing. The slides are covered with an antigen of the disease that has been artificially created. The antibodies if present in the sample, bind to the antigen. The slide is cleaned to wash away the unbound antibodies. In case of Rapid test, a substrate is added and the level of absorbance shows the concentration of antibodies.

In case of IFA, another antibody with a fluorescent marker is added that would bind to the earlier bound antibodies and the sample is studied under a UV light. The bound antibodies, if present, show up under the UV light. The scrub typhus antigen presence is tested.