Elucidation of prognostic factors in the acute phase of feline severe fever with thrombocytopenia syndrome virus infection.

Severe fever with thrombocytopenia syndrome (SFTS) is a potentially fatal tick-borne zoonotic disease, endemic to Asian regions, including western Japan. Cats appear to suffer a particularly severe form of the disease; however, feline SFTS is not clinically well characterized. Accordingly, in this study, we investigated the associations of, demographic, hematological and biochemical, immunological, and virological parameters with clinical outcome (fatal cases vs. survivors) in SFTSV-positive cats. Viral genomic analysis was also performed. Viral load in blood, total bilirubin, creatine phosphokinase, serum amyloid A, interleukin-6, tumor necrotic factor-α, and virus-specific IgM and IgG differed significantly between survivors and fatal cases, and thus may have utility as prognosticators. Furthermore, survivor profiling revealed high-level of viremia with multiple parameters (white blood cells, platelet, total bilirubin, glucose, and serum amyloid A) beyond the reference range in the 7-day acute phase, and signs of clinical recovery in the post-acute phase (parameters returning to, or tending toward, the reference range). However, SFTSV was still detectable from some survived cats even 14 days after onset of disease, indicating the risk of infection posed by close-contact exposure may persist through the post-acute phase. This study provides useful information for prognostic assessments of acute feline SFTS, and may contribute to early treatment plans for cats with SFTS. Our findings also alert pet owners and animal health professionals to the need for prolonged vigilance against animal-to-human transmission when handling cats that have been diagnosed with SFTS.

Clinical and Pathological Findings in Fatal Cases of Severe Fever With Thrombocytopenia Syndrome With High Viremia in Cats.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging zoonotic disease caused by the SFTS virus (SFTSV). SFTSV causes severe symptoms both in humans and cats. In this study, we report the clinical and pathological findings of 4 fatal cases of cats with high SFTS viremia levels. These cats showed an acute onset of fever, leukopenia, thrombocytopenia, and increased serum amyloid A and pro-inflammatory cytokine levels. A high viral copy number was detected in the blood, oral swabs, rectal swabs, conjunctiva swabs, and urine. Histopathologically, necrotizing lymphadenitis, splenitis with lymphoblastoid cell proliferation, and hemophagocytosis were observed in all 4 cats. Immunohistochemistry revealed the presence of SFTSV antigen on lymphoblastoid B cells. SFTSV-RNA was detected in systemic tissues, including the brain. The present findings provide useful information for understanding the features of fatal SFTS in cats. To elucidate the mechanisms of severe progress of SFTS cats, as well as its role as a source of human infection, further research is needed.

Seroprevalence of severe fever with thrombocytopenia syndrome virus in animals in Kagoshima Prefecture, Japan, and development of Gaussia luciferase immunoprecipitation system to detect specific IgG antibodies.

We conducted a seroprevalence investigation of the healthy population of animals in Kagoshima Prefecture, an area in which severe fever with thrombocytopenia syndrome (SFTS) is endemic. Of 104 domestic cat and 114 dog samples, 2 (1.9%) and 11 (9.6%) were positive for anti-SFTS virus (SFTSV) IgG by indirect ELISA, respectively. Viral RNA was detected in one dog (0.9%) by RT-PCR. Of the 102 wild boar (Sus scrofa) and 107 deer (Cervus nippon) samples tested, 55 (53.9%) and 37 (34.7%) were positive for anti-SFTSV IgG, respectively. Only one wild boar (1.0%) was positive for viral RNA. Although symptomatic SFTSV infections in domestic cats have increased in this area, the seroprevalence of the healthy population of domestic cats tends to be lower than those of other animals. We developed a Gaussia luciferase immunoprecipitation system (GLIPS) using mammalian cells expressing a recombinant SFTSV nucleoprotein (SFTSV-rNP) for the detection of SFTSV-specific antibodies in samples from various animal species. The sensitivity of the assay was highly consistent with that of indirect ELISA, indicating that it could serve as a useful tool for a large-scale surveillance of SFTSV across multiple species of animals.

Natural severe fever with thrombocytopenia syndrome virus infection in domestic cats in Japan.

Severe fever with thrombocytopenia syndrome (SFTS) is a recently discovered emerging infectious disease. A zoonotic disease with a high fatality rate in human beings, clinical information on SFTS virus (SFTSV) infection in animals is important. Since 2017, we have diagnosed 24 client-owned cats living in western Japan with SFTS, by genetic and serological testing. In this study, we characterized the clinical features of SFTS in cats and their associated risk factors, by evaluating the clinical parameters retrospectively. A phylogenetic analysis on SFTSV was also conducted. There were no obvious tendencies in age or sex, outdoor cats were commonly at risk of SFTSV infection. All infected cats showed acute onset of clinical signs including anorexia and lethargy, while 68.2% of the cats showed fever and 41.7% showed vomiting. The case fatality rate was 62.5%. Thrombocytopenia, leukopenia, and elevated serum total bilirubin, serum amyloid A, and creatinine phosphokinase concentration were the characteristic findings in the first clinical blood examination. Phylogenic analysis revealed that regional clustered viruses infect both humans and cats. For pet owners and animal hospitals, SFTS in small animals could be an important public health issue.