Transmission of severe fever with thrombocytopenia syndrome virus from a dog to humans and a cat in a household cluster.

The growing proximity and contact between companion animals and humans underscore the significant public health risk of zoonotic spillover, a core concern of the One Health framework. Severe fever with thrombocytopenia syndrome (SFTS), an emerging tick-borne zoonosis of increasing incidence, is capable of direct animal-to-human transmission; however, evidence detailing its transmission within households remains limited. This study documents a transmission chain involving a domestic dog, two owners, and a cohabiting cat. The owners developed symptoms approximately one week after exposure to their symptomatic dog, and the cat subsequently succumbed two weeks after the dog's death. High viral loads of SFTS virus (SFTSV) were consistently detected in samples from the patients and deceased animals. The S-fragment sequences from the patients showed 100% identity with those from the pets, confirming a common source. Phylogenetic analysis classified the virus as genotype D, and SFTSV was also detected in the shared household environment, indicating its role as a transmission hub. These findings provide clear evidence of multi-directional household transmission, demonstrating that companion animals can mediate cross-species transmission to humans and other susceptible species. Transmission likely occurred via infectious secretions, fomites, or potentially aerosols. In line with the One Health concept, our results emphasize the urgent need to implement enhanced surveillance of companion animals in SFTS-endemic regions and to establish integrated systems that disrupt transmission cycles among ticks, animals, and humans, thereby safeguarding public and animal health in tandem.