Retrospective study on the possibility of an SFTS outbreak associated with undiagnosed febrile illness in veterinary professionals and a family with sick dogs in 2003

Introduction: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-born disease and its animal-to-human transmission has come to attention recently. During our sero-survey of SFTS virus (SFTSV) among veterinary professionals in 2018, a veterinarian and his assistant working in an animal hospital were tested positive by enzyme-linked immunosorbent assay (ELISA). An additional survey implied a cluster of SFTS cases in which four more people, a family who brought two sick dogs to the animal hospital in 2003, were involved. This study aimed at assessing the possibility of animal-to-human transmission of SFTSV in this cluster.Methods: Retrospective interviews were performed with the owner family of the dogs and their clinical records were obtained from each hospital. SFTSV-IgG were tested by ELISA and virus neutralization test using the sera collected from them in 2018. Results: The interviews revealed that a total of six people, the two veterinary professionals and the owner family who took care of the sick dogs, suffered from SFTS-like symptoms in the same period of time in 2003. All patients did not have tick bite before the onset and all suspected causative agents were excluded by laboratory tests. The serological tests in this study revealed the four owner family members were all positive for SFTSV antibodies.Conclusions: Considering the extremely low seroprevalence of SFTSV antibodies among inhabitants of the region, the existence of SFTSV antibodies in all these six people presents a possibility that they were involved in an SFTS outbreak originated in the sick dogs in 2003.