FIG 1.

Selection of biologically relevant RVFV-infected samples. (A) Schematic representation of the selected animal samples. Liver and spleen samples of lambs exposed to RVFV strain 35/74 were selected from another study (34). Group 1 consists of uninfected (non-responsive) lambs necropsied at 8 days post-exposure. Group 2 and group 3 consist of infected lambs necropsied at 2 and 4 days post-infection (dpi), respectively (n = 4 samples per group). (B and C) Viral RNA copy numbers and infectious titers in the blood (B) and target organs (C). Viral RNA was quantified by M-segment-specific RT-qPCR, and infectious titers were determined by an endpoint dilution virus isolation assay (34). In panel B, graphs show the means with standard deviations (SD) at each time point. In panel C, dots represent individual replicates, and the horizontal lines represent the means. Dashed lines indicate the limits of detection (50 RNA copies/mL for RT-qPCR and 35.5 median tissue culture infectious doses [TCID₅₀]/mL for the virus isolation assay). (D) Hematoxylin and eosin (H&E) staining of liver tissue sections. Group 1 shows no histological alterations in the liver, while groups 2 and 3 show acute hepatitis with necrosis of hepatocytes and an influx of polymorphonuclear cells. Bars, 20 μm. (E) Immunohistochemical detection of RVFV antigen in liver tissue. RVFV Gn glycoprotein (brown) was detected with antibody 4-D4 (61) in combination with HRP-conjugated secondary antibodies. Bars, 200 μm. Inf., infected.