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

Abstract

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.

Fig 1. The survival times for mice (n = 10) infected with twelve T. b. rhodesiense clones.

The clones were classified as (i) very-acute (0–15 dpi), (ii) acute (16–30 dpi), (iii) sub-acute (31–45 dpi), (iv) and chronic Tbr (46–60 dpi) all classes of virulence grouped together.

Fig 2. Parasitaemia progression in mice (n = 10) infected with the four classes of T. b. rhodesiense clones.

(i) Very-acute, (ii) acute, (iii) sub-acute and (iv) chronic clones all classes of virulence grouped together.

Fig 3

Mean ± SE PCV decline in mice (n = 10) infected with T.b. rhodesiense (i) very-acute isolates, (ii) acute isolates, (iii) sub-acute isolates and (iv) chronic isolates clones all classes of virulence grouped together.

Fig 4. Mean ± SE body weight changes in mice (n = 10) infected with T.b. rhodesiense.

(i) very-acute isolates, (ii) acute isolates, (iii) sub-acute isolates and (iv) chronic isolates all classes of virulence grouped together.