Phylogenetic Analysis of Severe Fever with Thrombocytopenia Syndrome Virus in South Korea and Migratory Bird Routes Between China, South Korea, and Japan

Abstract

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne viral disease. The SFTS virus (SFTSV) has been detected in the Haemaphysalis longicornis, which acts as a transmission host between animals and humans. SFTSV was first confirmed in China in 2009 and has also been circulating in Japan and South Korea. However, it is not known if a genetic connection exists between the viruses in these regions and, if so, how SFTSV is transmitted across China, South Korea, and Japan. We therefore hypothesize that the SFTSV in South Korea share common phylogenetic origins with samples from China and Japan. Further, we postulate that migratory birds, well-known carriers of the tick H. longicornis, are a potential source of SFTSV transmission across countries. Our phylogenetic analysis results show that the SFTSV isolates in South Korea were similar to isolates from Japan and China. We connect this with previous work showing that SFTSV-infected H. longicornis were found in China, South Korea, and Japan. In addition, H. longicornis were found on migratory birds. The migratory bird routes and the distribution of H. longicornis are concurrent with the occurrence of SFTSV. Therefore, we suggest that migratory birds play an important role in dispersing H. longicornis-borne SFTSV.

Figure 1.

Severe fever with thrombocytopenia syndrome (SFTS) patient distribution map and migration route of birds between China, South Korea, and Japan. The regions where SFTS patients were reported in China, South Korea, and Japan are shown in red, in Jeju are shown by purple circles, and the estimated migration route of birds are depicted by light green lines.,– Wetland habitats for birds in the Korean peninsula are indicated by blue squares.

Figure 2.

Phylogenetic tree constructed based on the complete S segments. The tree was constructed using the maximum likelihood method with MEGA6. S sequence of 17 severe fever with thrombocytopenia syndrome (SFTS) cases in this study are shown in bold. JP01/South Korea/07-2013 to JP07/South Korea/08-2014 were amplified from SFTS patients from Jeju Island (the southern end of South Korea) from May 2013 to August 2014, CP01/South Korea/08-2013 was amplified from an SFTS patient from Chuncheon (the northern end of South Korea), AP01/South Korea/10-2013 was amplified from an SFTS patient from Andong (the central part of South Korea), and DP01/South Korea/10-2013 was amplified from an SFTS patient from Daegu (the southern end of South Korea) (GenBank accession numbers KR612072 to KR612088, respectively). The S sequence data of the viruses identified in China, South Korea, and Japan were obtained from the National Center for Biotechnology Information (NCBI)/Basic Local Alignment Search Tool (BLAST).

Figure 3.

Worldwide distribution of four wild fowl: Zoothera aurea, Turdus hortulorum, Halcyon coromanda, and Pitta nympha (A) and East Asia/Australasia Flyway (B). Distribution of Z. aurea is shown in light yellow, T. hortulorum in light green, Halcyon coromanda in light red, and P. nympha in light blue. Areas of overlapping distribution are indicated in mixed colors (A). East Asia/Australasia is depicted by the red dotted line (B).