Differential virulence of Trypanosoma brucei rhodesiense isolates does not influence the outcome of treatment with anti-trypanosomal drugs in the mouse model.

We assessed the virulence and anti-trypanosomal drug sensitivity patterns of Trypanosoma brucei rhodesiense (Tbr) isolates in the Kenya Agricultural and Livestock Research Organization-Biotechnology Research Institute (KALRO-BioRI) cryobank. Specifically, the study focused on Tbr clones originally isolated from the western Kenya/eastern Uganda focus of human African Trypanosomiasis (HAT). Twelve (12) Tbr clones were assessed for virulence using groups(n = 10) of Swiss White Mice monitored for 60 days post infection (dpi). Based on survival time, four classes of virulence were identified: (a) very-acute: 0-15, (b) acute: 16-30, (c) sub-acute: 31-45 and (d) chronic: 46-60 dpi. Other virulence biomarkers identified included: pre-patent period (pp), parasitaemia progression, packed cell volume (PCV) and body weight changes. The test Tbr clones together with KALRO-BioRi reference drug-resistant and drug sensitive isolates were then tested for sensitivity to melarsoprol (mel B), pentamidine, diminazene aceturate and suramin, using mice groups (n = 5) treated with single doses of each drug at 24 hours post infection. Our results showed that the clones were distributed among four classes of virulence as follows: 3/12 (very-acute), 3/12 (acute), 2/12 (sub-acute) and 4/12 (chronic) isolates. Differences in survivorship, parasitaemia progression and PCV were significant (P<0.001) and correlated. The isolate considered to be drug resistant at KALRO-BioRI, KETRI 2538, was confirmed to be resistant to melarsoprol, pentamidine and diminazene aceturate but it was not resistant to suramin. A cure rate of at least 80% was achieved for all test isolates with melarsoprol (1mg/Kg and 20 mg/kg), pentamidine (5 and 20 mg/kg), diminazene aceturate (5 mg/kg) and suramin (5 mg/kg) indicating that the isolates were not resistant to any of the drugs despite the differences in virulence. This study provides evidence of variations in virulence of Tbr clones from a single HAT focus and confirms that this variations is not a significant determinant of isolate sensitivity to anti-trypanosomal drugs.

Route of inoculation influences Trypanosoma congolense and Trypanosoma brucei brucei virulence in Swiss white mice.

Experiments on infections caused by trypanosomes are widely performed in Swiss white mice through various inoculation routes. To better understand the effect of route of trypanosome inoculation on disease outcomes in this model, we characterised the virulence of two isolates, Trypanosoma brucei KETRI 2710 and T. congolense KETRI 2765 in Swiss white mice. For each of the isolates, five routes of parasite inoculation, namely intraperitoneal (IP), subcutaneous (SC), intramuscular (IM) intradermal (ID) and intravenous (IV) were compared using groups (n = 6) of mice, with each mouse receiving 1x104 trypanosomes. We subsequently assessed impact of the routes on disease indices that included pre-patent period (PP), parasitaemia levels, Packed Cell Volume (PCV), bodyweight changes and survival time. Pre-patent period for IP inoculated mice was a mean ± SE of 3.8 ± 0.2 and 6.5 ± 0.0 for the T brucei and T. congolense isolates respectively; the PP for mice groups inoculated using other routes were not significantly different(p> 0.05) irrespective of route of inoculation and species of trypanosomes. With ID and IP routes, parasitaemia was significantly higher in T. brucei and significantly lower in T. congolense infected mice and the progression to peak parasitaemia routes showed no significant different between the routes of either species of trypanosome. The IM and ID routes in T. congolense inoculations, and IP and IV in T. b. brucei induced the fastest and slowest parasitaemia progressions respectively. There were significant differences in rates of reduction of PCV with time post infection in mice infected by the two species and which was more pronounced in sc and ip injected mice. No significant differences in mice body weight changes and survivorship was observed between the routes of inoculation. Inoculation route therefore appears to be a critical determinant of pathogenicity of Trypanosoma congolense and Trypanosoma brucei brucei in murine mouse model of African trypanosomiasis.

Infection with the secondary tsetse-endosymbiont Sodalis glossinidius (Enterobacteriales: Enterobacteriaceae) influences parasitism in Glossina pallidipes (Diptera: Glossinidae).

The establishment of infection with three Trypanosoma spp (Gruby) (Kinetoplastida: Trypanosomatidae), specifically Trypanosoma brucei brucei (Plimmer and Bradford), T. b. rhodesiense (Stephen and Fatham) and T. congolense (Broden) was evaluated in Glossina pallidipes (Austen) (Diptera: Glossinidae) that either harbored or were uninfected by the endosymbiont Sodalis glossinidius (Dale and Maudlin) (Enterobacteriales: Enterobacteriaceae). Temporal variation of co-infection with T. b. rhodesiense and S. glossinidius was also assessed. The results show that both S. glossinidius infection (χ(2)= 1.134, df = 2, P = 0.567) and trypanosome infection rate (χ(2)= 1.85, df = 2, P = 0.397) were comparable across the three infection groups. A significant association was observed between the presence of S. glossinidius and concurrent trypanosome infection with T. b. rhodesiense (P = 0.0009) and T. congolense (P = 0.0074) but not with T. b. brucei (P = 0.5491). The time-series experiment revealed a slight decrease in the incidence of S. glossinidius infection with increasing fly age, which may infer a fitness cost associated with Sodalis infection. The present findings contribute to research on the feasibility of S. glossinidius-based paratransgenic approaches in tsetse and trypanosomiasis control, in particular relating to G. pallidipes control.