Comparison of pathogenicity of relapsed, field and mixed isolates of Trypanosoma brucei brucei infections in rats

Objective: This study was conceived to investigate the pathogenicity of relapsed (Diminazene aceturate-resistant), field (original) and mixed (relapsed and field) isolates of Trypanosoma brucei brucei in rats. Materials and methods: Twenty eight healthy adult albino rats of both sexes weighing between 149-177 gm were used to compare the pathogenicity of relapsed, field and the mixed isolates of T. brucei brucei infections. The rats were separated into four groups (A-D); where, group A was kept as uninfected control, and group B was infected with 1x103 trypanosomes of the field isolate and 1x103 trypanosomes of the diminazene aceturate resistant isolate. The rats of groups C and D were infected with 1x106 trypanosomes of the diminazene aceturateresistant isolate and 1x106 trypanosomes of the field isolate, respectively. Results: The infected rats became parasitemic within 4 to 8 days post-infection. The mean pre-patent periods (PP) were 4.1±1.1, 6.0±2.0 and 9.1±1.1 days in groups B, C and D respectively, while the mean survival time (ST) in groups B, C and D were 21.4±10.1, 27.1±13.2 and 34.0 ±12.8 days, respectively. The PP and ST were shortest (P<0.05) in group B (mixed infections), and level of parasitemia was higher (P<0.05) in group B (mixed infections) as compared to groups C and D. The level of anemia was comparable (P>0.05) in groups C and D and more severe (P<0.05) in group B. Conclusion: Mixed infections exhibit shortest PP, ST, higher level of parasitemia and more severe anemia, and appear to be more pathogenic.