After 3 years of research from 2015 to 2017, the Taiwan Centers for Disease Control (Taiwan CDC) has developed a new diagnostic kit to detect scrub typhus antibodies rapidly. This achievement has been published in The American Journal of Tropical Medicine and Hygiene in March 2019, and was granted a patent in Taiwan in July 2019. Currently, this new kit is commonly used in Taiwan CDC laboratories for the detection of scrub typhus infection. Traditional diagnostic kits with immunofluorescence assay (IFA) used to be considered as the gold standard method for the serological diagnosis of scrub typhus. The results indicated that the sensitivity of the new diagnostic kit (80.7%) is significantly higher than that of IFA (68.8%). In addition, the new kit can be used for screening large numbers of samples automatically.
The new diagnostic kit is composed of 3 prototypes (Karp, Gilliam, and Kato) and 4 local antigens (TW-1, TW-10, TW-19, and TW-22). Among them, TW-1 is the most prevalent strain in Taiwan, TW-10 and TW-19 strains are closely related to East Asian and Southeast Asian strains, and TW-22 is a unique strain in Taiwan. The diagnostic kit had been sent to the US Naval Medical Research Center to evaluate its efficacy in June 2019. Results showed that this kit can not only detect scrub typhus infection in Taiwan, but also can be used to detect patients in Thailand, Sri Lanka, Malaysia, and Australia.
Scrub typhus is endemic in the Asia-Pacific region, especially in rural areas in Southeast Asia. A total of 270 cases of scrub typhus have been identified in Taiwan thus far this year (2019). The numbers of confirmed cases annually were between 350 and 500 in the last 5 years. Most cases were from eastern Taiwan and offshore islands. The number of scrub typhus cases peaked from May to October, with male cases outnumbering female cases, and peak incidence is found between 50 and 60 years of age.
Scrub typhus is caused by the intracellular bacterium Orientia tsutsugamushi following the bite of an infected larval-stage trombiculid mite (chigger). Chiggers normally stay in the grass and wait for the opportunity to climb onto humans or animals. The incubation period of the disease varies from 9 to 12 days. Clinical symptoms include persistent high fever, headache, swollen lymph nodes, and red punctate papule on the skin. Eschar is also a clinical feature, but it is an often ignored aspect in patients. Case fatality rate can be up to 60%, if being misdiagnosed or delayed for treatment. Therefore, people engaging in outdoor activities should wear protective clothing such as light-colored clothing, long sleeves and long pants, apply government-approved mosquito repellent to exposed skin, take a bath and change all clothes promptly after returning home from outdoor activities. Please seek immediate medical attention and inform the doctor of any recent travel and activity history to facilitate prompt diagnosis, case reporting, and treatment. For more information, please visit the Taiwan CDC’s website at https://www.cdc.gov.tw or call the toll-free Communicable Disease Reporting and Consultation Hotline, 1922 (or 0800-001922).