Experimental infection of dogs with severe fever with thrombocytopenia syndrome virus: Pathogenicity and potential for intraspecies transmission

Severe fever with thrombocytopenia syndrome (SFTS) is caused by infection with Dabie bandavirus [formerly SFTS virus (SFTSV)] and is an emerging zoonotic disease. Dogs can be infected with SFTSV, but its pathogenicity and transmissibility have not been fully elucidated. In experiment 1, immunocompetent dogs were intramuscularly inoculated with SFTSV. In experiment 2, immunosuppressed dogs (immunosuppressed group; oral azathioprine 5 mg/kg/day for 30 days) were intramuscularly inoculated with SFTSV. Both immunosuppressed and immunocompetent contact dogs were co-housed with the SFTSV-inoculated dogs that had been immunosuppressed. Immunocompetent SFTSV-infected dogs did not show any clinical symptom. However, immunosuppressed SFTSV-infected dogs showed high fever and weight loss without lethality. In all SFTSV-infected dogs, viral RNA could be measured in the serum only after 3 days post infection (DPI) and neutralizing antibodies were detected in the serum beginning 9 DPI. SFTSV shedding in the urine and faeces of some infected dogs occurred between 4 and 6 DPI. The immunocompromised SFTSV-infected dogs showed thrombocytopenia beginning 3 DPI to the end of the experiment (24 DPI). We confirmed SFTSV transmission to one of three immunocompetent co-housed dogs. This dog showed a high fever, weight loss, and shed viral RNA by urine. Viral RNA and neutralizing antibodies were also detected in the serum. These results demonstrated that intramuscular inoculation with SFTSV induced minor clinical symptoms in dogs, and intraspecies SFTSV transmission in dogs can occur by contact.