The effect of TBEV infection (TBE1) and TBEV+Bb/Ap co-infection (TBE+LD1) as well as therapy (TBE2 and TBE+LD2) on the lipid peroxidation products visible in the level of 4-HNE (A) and 8-isoPGF2α (B) assessed in plasma of patients compared to healthy subjects (control). The mean values for TBE patients (before–TBE1 and after treatment–TBE2, n = 40), patients with TBE+LD (before–TBE+LD1 and after treatment–TBE+LD2, n = 6) and control subjects (n = 20) with SD are shown as follows: x—differences vs. control group, p < 0.05; a—differences vs. TBE1 group, p < 0.05; b—differences vs. TBE+LD1 group, p < 0.05.