Kinetics of Parasitemia and IFN-γ/IL-4 Responses during Co-Infection with Trypanosoma brucei rhodesiense and Plasmodium berghei ANKA in BALB/c Mice

Abstract

Introduction: Concurrent infections with Trypanosoma brucei rhodesiense and Plasmodium spp. may affect parasite progression and host immune responses, but little is known about the timing of this interaction. Aim: This study therefore determined the kinetics of parasitaemia and serum interferon-gamma (IFN-γ) and interleukin-4 (IL-4) responses in BALB/c mice during mono-infection and concurrent co-infection. Materials and Methods: We allocated 160 BALB/c mice to four groups: naïve controls, Trypanosoma brucei rhodesiense-infected, Plasmodium berghei ANKA-infected, and co-infected mice (n = 40 per group). T. b. rhodesiense bloodstream forms (1 × 10⁶ parasites) were administered intraperitoneally on Day 0, followed by P. berghei ANKA-infected erythrocytes (1 × 10⁶ pRBCs) on Day 4 in the P. berghei-only and co-infected groups. We performed terminal sampling on Days 0, 5, 7, 9, 10, 11, 12, and 13, with five mice per group at each time point. We quantified parasitaemia from Giemsa-stained blood smears and determined serum IFN-γ and IL-4 concentrations using enzyme-linked immunosorbent assays. We assessed differences between infection groups and sampling times using two-way analysis of variance with group, time, and group-by-time interaction effects, followed by appropriate post hoc or pairwise tests. We also summarised parasite burden over time using the trapezoidal area under the curve (AUC). We set statistical significance at p < 0.05. Results: During the early phase (Days 5–7), T. b. rhodesiense parasitaemia was lower in co-infected mice than in T. b. rhodesiense-only mice, with the difference reaching statistical significance on Day 7. In contrast, P. berghei parasitaemia was higher in co-infected mice at selected intermediate time points. IFN-γ concentrations peaked early on Day 7, at 470 ± 42 pg/mL in co-infected mice and 420 ± 38 pg/mL in P. berghei -only mice, and then declined. IL-4 followed a different trajectory, with T. b. rhodesiense-only mice showing a progressive increase to 395 ± 35 pg/mL on Day 13, and co-infected mice showing a biphasic response pattern with a peak at 290 ± 25 pg/mL on Day 13. Conclusions: These observations indicate that co-infection is associated with time-dependent changes in parasite burden and cytokine responses. During the early phase, higher IFN-γ concentrations coincided with lower T. b. rhodesiense parasitaemia and were accompanied by increased P. berghei parasitaemia. During the later phase, declining IFN-γ and increasing IL-4 concentrations coincided with convergence of parasite burdens between the infection groups.