VECTOR-BORNE AND ZOONOTIC DISEASES Volume 8, Number 1, 2008 © Mary Ann Liebert, Inc. DOI: 10.1089/vbz.2006.0634 Isolation of Tick-Borne Encephalitis Viruses from Wild Rodents, South Korea SU-YEON KIM, 1 SEOK-MIN YUN, 1 MYUNG GUK HAN, 1 IN YONG LEE, 2 NA YEON LEE, 1 YOUNG EUI JEONG, 1 BYEONG CHEOL LEE, 3 and YOUNG RAN JU 1 ABSTRACT To determine whether the tick-borne encephalitis virus (TBEV) is present in vector ticks and mammalian hosts in Korea, we examined two tick species, Haemaphysalis longicornis (n  548) and Ixodes nipponensis (n  87), and the lungs or spleens of rodents Apodemus agrarius (n  24) and wild boars (n  16). Tick-borne encephalitis virus was detected in samples by reverse transcriptase (RT)-nested polymerase chain reaction (PCR), after which TBEV- positive samples were inoculated into BHK-21 cells and suckling mice. Tick-borne encephalitis virus genes were detected in 4 of 38 tick pools and 5 of 24 wild rodents. Suckling mice inoculated intracerebrally with TBEV-pos- itive rodent samples showed signs of encephalitis at six days post-inoculation. The isolation of TBEV was con- firmed by inoculating samples obtained from the brains of sick mice in cell culture. Phylogenetic analysis showed that the E genes of the TBEV isolates were clustered with the Western subtype (98% identity). This study suggests the possible occurrence of tick-borne encephalitis in Korea. Key Words: Tick-borne encephalitis virus—Isolation— Rodents—Ixodes—RT-nested PCR—Cell culture—South Korea. 7 INTRODUCTION T HE TICK-BORNE ENCEPHALITIS VIRUS (TBEV) is a member of the genus Flavivirus, and one of the major arboviruses causing thousands of cases of severe neurological disease (Chiba et al. 1999). Three genetic subtypes of TBEV, the Western, Far Eastern, and Siberian subtypes, are prevalent on the Eurasian continent (Ecker et al. 1999, Hayasaka et al. 1999, Heinz et al. 1981, Ternovoi et al. 2003). The tick vectors of the TBEV parasitize wild and domestic mam- mals, birds, and reptiles. Rodents are the main- tenance and amplifying hosts for most TBEVs, and the genera Apodemus and Clethrionomys are the main reservoir hosts (Perkins et al. 2003, Süss 2003). Although tick-borne encephalitis (TBE) has not been reported in Korea, the num- ber of patients with encephalitis caused by un- known agents is increasing each year. Tick- borne encephalitis viruses have been isolated from vectors or rodents in countries near Ko- rea, including Japan, China, and Russia (Hou et al. 1997, Takashima et al. 1997, Ternovoi et al. 2003). Ixodes ricinus and I. persulcatus, the main vectors of TBEV, have been recorded in Korea since 1940. However, I. ricinus recorded from Hamgyeongbuk-do Province, in the north part of Korea, might be misidentification of I. persulcatus, so it has been accepted that this species should not be recorded as distributed in Korea and Japan (Kang et al. 1985, Yamaguti et al. 1971). In Korea, the genus Ixodes has been known as a vector for Borrelia spp. and Bar- tonella spp. (Kim et al. 2005a, Park et al. 1994). To investigate whether the TBEVs circulate in 1 Division of Arboviruses and 3 Division of Malaria & Parasitic Diseases, Center for Immunology & Pathology, Na- tional Institute of Health, Korea Centers for Disease Control and Prevention; and 2 Department of Parasitology, Col- lege of Medicine, Yonsei University, Seoul, Republic of Korea.