The bacteria that cause scrub typhus, like rickettsiae, can live only inside the cells of other organisms. Scrub typhus bacteria live in mites (the host).
Scrub typhus occurs in Japan, Korea, China, India, and northern Australia. The disease is transmitted to people when they are bitten by a chigger (mite larva).
Symptoms of scrub typhus begin suddenly, about 6 to 21 days after the bacteria enter the body. They include fever, chills, a headache, and swollen lymph nodes. A black scab may develop at the site of the chigger bite. People may have a cough during the first week of fever. A rash appears about 5 to 8 days after the fever starts.
The diagnosis of scrub typhus is suggested by symptoms in people who have recently been to an area where scrub typhus is common (such as Central Asia, southeast Asia, South Asia, and northern Australia) and have participated in outdoor activities, such as camping or visiting farms, which could expose them to chigger bites.
To confirm the diagnosis, doctors may do an immunofluorescence assay, which uses a sample from the rash (biopsy). Or they may use the polymerase chain reaction (PCR) technique to enable them to detect the bacteria more rapidly.
Doctors may do blood tests that detect antibodies to the bacteria. However, doing the test once is not enough. The test must be repeated 1 to 3 weeks later to check for an increase in the antibody level. Thus, these tests do not help doctors diagnose the infection immediately after someone becomes ill but can help confirm the diagnosis later.