On the basis of epidemiological and clinical characteristics, we considered two types of diseases to be possible: rickettsial and arthropod-borne viral disease. Because of the low rates of A. phagocytophilum (rickettsial disease) detection, the research team intensified its virus search to take into account arthropod-borne viruses, including Flaviviridae (Dengue viruses [DENV] , Japanese encephalitis virus [JEV]), Togaviridae (Chikungunya virus, Eastern equine encephalitis virus [EEEV] , Western equine encephalitis virus), and Bunyaviridae (Crimean-Congo hemorrhagic fever virus, Hantaan virus, and Rift valley fever virus) [8] . Specific PCR assays for these viruses were used [9] [10] [11] [12] [13] [14] [15] [16] . However, none of the patients from 2007 to 2010 was positive for these viruses, suggesting a new infectious agent, possibly a virus, remained to be discovered. Thus, the syndrome was considered an emerging infectious disease and was named fever, thrombocytopenia and leukopenia syndrome (FTLS). To identify the etiology, the research team adopted the following strategy: 1) sequencing of randomly amplified cDNA/ DNA from FTLS patient samples using high-throughput Illumina sequencing to specifically explore viral communities present in patients suffering from FTLS, 2) PCR detection of target DNA directly from clinical specimens, 3) viral culture, 4) immunodetec-tion methods, and 5) electron microscopic study of the morphology of the cultured virus.