Persistent viral carriage of severe fever with thrombocytopenia syndrome virus in canine: A potential canine-to-human transmission event in a family cluster

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne viral disease with a substantial case-fatality rate. Here, we reported a family cluster of SFTS cases in Southeast China. The index case was a 57-year-old man, whose son and wife subsequently developed SFTS-compatible symptoms at two and three days after his onset, respectively. All three cases were laboratory-confirmed for SFTS, and retrospectively reported close care to a sick golden retriever prior to symptom onset. In contrast, the other two family members without such canine exposure remained serologically and clinically uninfected. All three cases denied a tick-biting history before illness onset. Subsequent testing confirmed SFTS virus (SFTSV) infection in the golden retriever, and SFTSV was also detected in a tick collected from the dog. Longitudinal viral screening of serial canine samples revealed persistent SFTSV shedding: viral positivity was sustained for 23 days in nasal swabs and urethral swabs, 27 days in serum samples, and at least 30 days in rectal swabs following its symptom onset. Genomic analysis showed near-identical SFTSV sequences from the index case and the infected dog, with identities of 99.94% for the small segment, 100% for the medium segment, and 99.98% for the large segment. This study reveals prolonged SFTSV shedding in infected canine, suggests a plausible risk of canine-to-human SFTSV transmission, and highlights the potential role of dogs in the spread and evolution of SFTSV.