Figure 10.

Cervical LNs and spleen of cat No. 1 and acute necrotizing lymphadenitis of the cervical LNs and spleen of cat No. 2 with SFTSV. (A–H), Cervical LN; (I–N), Spleen. (A) Normal structure of lymphatic nodules of surviving cat No. 1 are observed. (B) This area is negative for virus antigen. (C) The construct of the dark cortex is unclear because some lymphatic nodules are absent. The subcapsular sinus is enlarged, and lymphocytes are depleted in the nodule (*). Fatal cat No. 2. (D) Some areas in the cortex without lymphatic nodules are positive for virus antigen. Many SFTSV-NP-positive cells are seen in the lesion. (E) Normal cells of lymphatic nodules are observed. Cat No. 1. (F) These cells are negative for viral antigen. (G) Necrotizing lymphatic nodule (higher magnification of a boxed section of C). Necrotic cells with pyknosis and round-shaped mononuclear cells (arrows) are seen in the sinus and nodule. (H) The round-shaped cells and cell debris are positive for SFTSV-NP (red arrowheads). (I) Normal structure of white pulp and red pulp are observed. Cat No. 1. (J) Necrotic nodules of the white pulp of spleen are observed (*). Cat No. 2. The number of erythrocytes decreased in the red pulp while red cells are accumulated in the marginal parts of the nodule (arrowheads). (K) Normal structure of red pulp of the spleen is observed. Cat No. 1. (L) There are not SFTSV-NP-positive cells. (M) The red pulp of the spleen (higher magnification of a boxed section of J). Several round-shaped mononuclear cells are present. (N) The round-shaped mononuclear cells are SFTSV-NP-positive. (A,C,E,G,I–K,M): H&E staining, (B,D,F,H,L,N): SFTSV-NP means SFTSV NP antigen stained by IHC. Bars, (A–D), 200 µm; (E–H,K–N), 20 µm; (I,J), 1 mm.