Histopathological Characterization of Cases of Spontaneous Fatal Feline Severe Fever with Thrombocytopenia Syndrome, Japan

Abstract

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tickborne infectious disease caused by SFTS virus (SFTSV). We report 7 cases of spontaneous fatal SFTS in felines. Necropsies revealed characteristic lesions, including necrotizing lymphadenitis in 5 cases and necrotizing splenitis and SFTSV-positive blastic lymphocytes in all cases. We detected hemorrhagic lesions in the gastrointestinal tract in 6 cases and lungs in 3 cases, suggesting a more severe clinical course of SFTS in felids than in humans. We noted necrotic or ulcerative foci in the gastrointestinal tract in 3 cases, the lung in 2 cases, and the liver in 4 cases. We clarified that blastic lymphocytes are predominant targets of SFTSV and involved in induction of necrotic foci. We also found that thymic epithelial cells were additional targets of SFTSV. These results provide insights for diagnosing feline SFTS during pathological examination and demonstrate the similarity of feline and human SFTS cases.

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

“…SFTSV is reportedly present in macrophages and B cell–lineage lymphocytes in fatal human infections, attacking and manipulating cells that initiate an antiviral response [ 26 ] in a way similar to the mechanisms reported for other hemorrhagic viruses, such as Ebola [ 5 , 8 ]. Histologically, SFTSV has been shown to infect B cells in lymphoid organs, including the lymph nodes, spleen and Peyer’s patches [ 24 ]. However, it cannot be completely ruled out that the cats included in this study may have had underlying diseases that could have affected their immune response to SFTS.…”

Clinical features and epidemiology of severe fever with thrombocytopenia syndrome in dogs in the Republic of Korea: an observational study (2019–2020)

“…All other dogs were managed as outpatients, and most clinical symptoms resolved within 2 weeks. Cats are highly sensitive to SFTSV, with a mortality rate of 62.5% (Matsuno et al 2018 ; Matsuu et al 2019 ; Park et al 2019 ; Sakai et al 2021 ; Seto et al 2020 ). Moreover, the mortality rate for humans is approximately 20% (Seo et al 2021 ).…”

Lethal severe fever with thrombocytopenia syndrome virus infection causes systemic germinal centre failure and massive T cell apoptosis in cats

“…This is due to the difficulty in collecting and analysing human lymph node samples. We have previously reported feline cases of SFTSV infection mimic the pathology of fatal human SFTS (Sakai et al, 2021). Furthermore, the experimental infection of cats with SFTSV reproduces severe SFTS pathology (Park et al, 2019).…”

“…As previously reported (Sakai et al, 2021), lymph nodes of cats with SFTS were histopathologically classified into three patterns: hyperplasia without SFTSV-positive cells, accumulation of SFTSV-positive cells, and necrotizing lymphadenitis. Among these three histological patterns, lymph nodes with necrotizing lymphadenitis were excluded from this study because of the massive loss of constituent cells.…”

“…In necropsy cases with clinical signs of SFTS, SFTSV infection were confirmed by conventional reverse transcription polymerase chain reaction using two primer pairs targeting the nucleoprotein region (Yoshikawa et al, 2014). The clinical information for these cases is provided in the Table 1 of our previous report (Sakai et al, 2021). The samples of systemic organs and cervical, submandibular, cervical, axillary, and mesenteric lymph nodes were collected, immersed in 10% neutral buffered formalin for fixation, and processed routinely for embedding in paraffin.…”