Molecular epidemiology of scrub typhus in Taiwan during 2006-2016

Scrub typhus is the most common endemic vector-borne disease in Taiwan. We identified a total of 4,857 laboratory-confirmed cases during 2006-2016 with hyperendemic foci on offshore islands, including Penghu (778 cases, 16.0%) and Kinmen (716 cases, 14.7%), and eastern Taiwan, including Taitung (628 cases, 12.9%) and Hualien (508 cases, 10.5%). Scrub typhus cases occur year-round throughout Taiwan, with a summer peak in June and July. A total of 545 O. tsutsugamushi isolates were successfully obtained from patients infected in diverse geographic areas, including Taiwan and three offshore islands, and the complete open reading frame of the 56 kDa type-specific antigen gene (tsa56) sequence of these isolates was examined. High phylogenetic diversity was found in these isolates, which could be grouped into 36 distinct sequence types. Most isolates belonged to the Karp (49.9%; 272/545), followed by the TW-22 (17.8%; 97/454) and Kawasaki (14.7%; 80/545) genotypes. In conclusion, our data indicate the widespread presence of tsa56 genotypes closely related to Thailand and Korean strains and the presence of the unique endemic strains TW-12, TW-22, TW-29, and TW-36 in Taiwan. Author summaryScrub typhus is a mite-borne disease and the most common rickettsial disease in the regions including Asia-Pacific, Middle East, and South America. Taiwan is located at the center of the endemic area of scrub typhus, and surveillance of scrub typhus and monitoring of genetic sequences of O. tsutsugamushi are important for disease control and prevention. In this study, we present the results of laboratory-based scrub typhus surveillance in Taiwan during 2006-2016. A total of 4,857 laboratory-confirmed scrub typhus cases were identified. Most of the cases occurred on offshore islands and in eastern Taiwan, including Penghu Island (778 cases, 16.0%), Kinmen Island (716 cases, 14.7%), Taitung County (628 cases, 12.9%) and Hualien County (508 cases, 10.5%). Phylogenetic analyses of the 56-kDa type-specific antigen gene sequence of 545 O. tsutsugamushi strains isolated from scrub typhus patients were conducted. Most isolates belonged to the Karp (49.9%; 272/545) genotype, followed by the TW-22 (17.8%; 97/454) sequence type and Kawasaki (14.7%; 80/545) genotype. Most strains were closely related to strains from Southeast and East Asia, whereas unique isolates were also found in Taiwan.