Fatal severe fever with thrombocytopenia syndrome associated with multiorgan failure and unusual cutaneous manifestations: evidence of Rhipicephalus sanguineus (Brown Dog Tick) transmission.

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne viral infection endemic in East Asia and increasingly reported in Southeast Asia, including Thailand, where reports of severe and fatal disease remain limited. We describe a fatal case in a 54-year-old Thai man with fulminant multiorgan failure, secondary hemophagocytic lymphohistiocytosis, and atypical hemorrhagic vesiculobullous skin lesions. SFTSV RNA was detected by real-time RT-PCR in multiple specimens, indicating systemic viral dissemination. An epidemiological investigation collected 268 ticks from stray dogs, the patient's dog, and the bedroom environment; all were morphologically identified as Rhipicephalus sanguineus. Six ticks tested positive for SFTSV RNA, with species identity of positive ticks confirmed by 16S rRNA gene sequencing. Phylogenetic analysis of the S, M, and L coding sequences showed clustering of tick-derived viruses with the patient-derived virus and strains from Thailand and China. These findings suggest a potential role of R. sanguineus, a common domestic dog-associated tick in Thailand, as a potential vector for human infection. This case highlights an unusual cutaneous presentation with extensive vesiculobullous lesions, underscoring the need for increased clinical awareness and domestic tick surveillance.