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

Abstract

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 bruce i 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 1x10 4 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.

Some Biochemical Perturbations May Modify the Understanding of Trypanotolerance in the West African Dwarf Sheep Infected With Trypanosoma brucei brucei and Trypanosoma congolense

“…The prepatent period of 5 to 6 days for intraperitoneal inoculation of T brucei brucei and T congolense in our study compares well with experimental infections in mice in which the mean prepatent period was 3.8 days for T brucei brucei and 6.5 days for T congolense . 22 Also, in our study, T brucei brucei produced higher level (4.0 × 10 7 trypanosomes/mL of blood) and more fluctuating peaks of parasitaemia than T congolense (1.3 × 10 6 trypanosomes/mL of blood). The understanding of trypanotolerance includes the ability of the tolerant breeds to control parasitaemia.…”

To the Skin and Beyond: The Immune Response to African Trypanosomes as They Enter and Exit the Vertebrate Host

“…routes ( Table 1). However, a small number of comparative experiments have revealed that inoculation routes can substantially affect outcome (43,44). For example, it has been shown that the percentage of BALB/c mice with detectable parasitemia after infection by T. brucei differed between animals infected i.p.…”

“…infected mice in a dose-dependent manner (43). Moreover, the impact of infection route on infectivity also differs between trypanosome species (44). For example, T. congolense infected intramuscularly (i.m.)…”

“…administration. These observations suggest that parasites face tissue-specific challenges in the skin (e.g., resident immune cells or nutrient availability) that delineate their capacity to disseminate systemically within the vertebrate host (44).…”

“…In addition to infection route, inoculum dose has also been shown to influence the outcome of trypanosome infection (44). For example, goats infected i.d.…”