Japanese encephalitis (JE) is a mosquito-borne zoonotic disease caused by the Japanese encephalitis virus (JEV). Pigs and water birds are the main amplifying and maintenance hosts of the virus. In this study, we conducted a JEV survey in mosquitoes captured in pig farms and water bird wetland habitats in Taiwan during 2005 to 2012. A total of 102,633 mosquitoes were collected. Culex tritaeniorhynchus was the most common mosquito species found in the pig farms and wetlands. Among the 26 mosquito species collected, 11 tested positive for JEV by RT-PCR, including Cx. tritaeniorhynchus, Cx. annulus, Anopheles sinensis, Armigeres subalbatus, and Cx. fuscocephala. Among those testing positive, Cx. tritaeniorhynchus was the predominant vector species for the transmission of JEV genotypes I and III in Taiwan. The JEV infection rate was significantly higher in the mosquitoes from the pig farms than those from the wetlands. A phylogenetic analysis of the JEV envelope gene sequences isolated from the captured mosquitoes demonstrated that the predominant JEV genotype has shifted from genotype III to genotype I (GI), providing evidence for transmission cycle maintenance and multiple introductions of the GI strains in Taiwan during 2008 to 2012. This study demonstrates the intense JEV transmission activity in Taiwan, highlights the importance of JE vaccination for controlling the epidemic, and provides valuable information for the assessment of the vaccine's efficacy. Japanese encephalitis (JE) is a vector-borne zoonotic disease transmitted by the bite of a Japanese encephalitis virus (JEV) infected mosquito. Japanese encephalitis is an endemic disease in Taiwan. Before 2008, all known JEV isolates collected in Taiwan belonged to Genotype III of JEV. Genotype I JEV strains were first found in northern Taiwan in 2008. In this study, we conducted a survey of JEV in mosquitoes during 2005–2012. A total of 102,633 mosquitoes were collected from pig farms and wetlands. Among the 26 mosquito species collected, 11 tested JEV positive by RT-PCR, including Cx. tritaeniorhynchus, Cx. annulus and An. sinensis. Cx. tritaeniorhynchus was the predominant vector species for transmission of JEV in Taiwan. The JEV infection rate of the mosquitoes captured on the pig farms was significantly higher than the rate of those captured in the wetlands, indicating that pigs played an important role in amplifying JEV. A phylogenetic analysis of the envelope gene sequences of JEV isolated from the mosquitoes demonstrated that the predominant JEV genotype shifted from genotype III to genotype I (GI), providing evidence for multiple introductions and transmission cycle maintenance of GI strains in Taiwan during 2008–2012.

We present our surveillance results on imported dengue cases in Taiwan during 2008–2010. A total of 734 imported dengue patients were identified. The travelers were arriving from 18 countries, including Southeast Asia, the Indian subcontinent, South Pacific islands, and Latin America. Gene sequences from 358 dengue virus (DENV) isolates were used to perform phylogenetic analyses, thus, providing an updated view of the geographic distribution and dynamic transmission of DENV strains circulating in these countries. Our results suggest that the DENV-1 genotype I and DENV-2 Cosmopolitan genotype comprise the predominant DENV strains circulating in Southeast Asian countries. The DENV-3 Genotype III strain was found to be newly emerging in several Southeast Asian countries, however, the Asian genotype 2 and the Asian/American genotype of DENV-2 strains appeared to be less prevalent in Southeast Asia. Furthermore, imported dengue viruses are representative of the overall patterns of serotype/genotype frequencies of dengue outbreaks that occurred in Taiwan.

Human Case of Severe Fever with Thrombocytopenia Syndrome Virus Infection, Taiwan, 2019

Scrub typhus is a rickettsial disease transmitted to humans through the bite of chigger mites infected with Orientia tsutsugamushi, and is an endemic disease in Taiwan. To elucidate the molecular epidemiology of O. tsutsugamushi, the complete open reading frame of the 56-kDa type-specific antigen gene sequence of strains isolated from scrub typhus patients were determined and analyzed. A total of 116 isolates of O. tsutsugamushi were successfully isolated from patients infected in diverse geographic origins including Taiwan and three offshore islets, Kinmen, Matsu, and Penghu between May 2006 and December 2007. Sequence analysis revealed that 22 distinct sequence types could be identified that were broadly distributed in different clusters of the phylogenetic tree. Most of the isolates belong to Karp, Kawasaki, and Kuroki genotypes and are closely related to strains from Thailand, Japan, and Korea, whereas unique isolates different from other countries were also found in Taiwan. Distinct seasonal distributions were found in different sequence types. Some sequence types caused disease in the cold season, whereas others caused disease in the warm season.