FIG 4.

SFV variants with amino acid residue differences in E2 vary in virulence, viremia, and brain titer following i.p. inoculation of adult mice. (A) Schematic representation of SFV constructs. These viruses (5,000 PFU) were i.p. inoculated into 4- to 5-week-old mice. Groups (n = 8) were monitored for survival for up to 2 weeks. Virulence (indicated by + or −) was defined as described in Materials and Methods. Virus titers in groups (n = 6) in the blood (B and C) and brain (D and E) were determined by plaque assay at PID 1 and 3. Each symbol represents an individual mouse. The line depicts the mean titers for each group. The dotted line depicts the limit of detection. In panels B to E, blood and brain virus titers for viruses c, h, i, and j were compared to those for SFV4 (a); results for c and h were statistically significantly different (P ≤ 0.05 by Mann-Whitney test). In addition, blood and brain virus titers for viruses h, i, and j were compared to those for SFV6 (b); results for i and j were statistically significantly different (P ≤ 0.05 by Mann-Whitney test).