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 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.
Highlights
African trypanosomes are extracellular protozoan parasites that cause chronic infections in Humans and their livestock, and are predominantly transmitted by tsetse fly[1]
T. b. brucei is virulent in dogs, camels and horses, with the horse often succumbing to infection within a few months in the absence of treatment[6] The pathogenicity of these parasites has typically been determined through intraperitoneal (IP) inoculation[7,8] of Swiss white mice animal models of trypanosomiasis[9] Parasitaemia, live body weight, packed cell volume (PCV) and survivorship in the mice have been considered appropriate indicators of the pathogenicity[5] [10].The various routes of inoculation including intraperitoneal (IP),subcutaneous(SC), intramuscular (IM), intravenous (IV) and intradermal (ID) have, previously been used to infect mice with trypanosomes[11,12,13] The IP inoculation is normally administered through the abdominal wall into the peritoneal cavity of the mice
Intramuscular (IM) route has an advantage of rapid and uniform deposition of the inoculum[15] but institutes muscle necrosis or inflammation of the nerves that can lead to lameness and self-mutilation of the affected area[16,17].Administration of ID inoculation is complicated by thin skin in mice that necessitates anesthetization and the fur clipping of the mice[18] with inadvertent SC administration as a common complication [7].In this study, we the compared the impact of route of inoculation of T. congolense KETRI 2765 or T. b. brucei KETRI 2710 parasites in Swiss white mice on pathogenicity of the parasites
Summary
African trypanosomes are extracellular protozoan parasites that cause chronic infections in Humans and their livestock, and are predominantly transmitted by tsetse fly[1]. Brucei is virulent in dogs, camels and horses, with the horse often succumbing to infection within a few months in the absence of treatment[6] The pathogenicity of these parasites has typically been determined through intraperitoneal (IP) inoculation[7,8] of Swiss white mice animal models of trypanosomiasis[9] Parasitaemia, live body weight, packed cell volume (PCV) and survivorship in the mice have been considered appropriate indicators of the pathogenicity[5] [10].The various routes of inoculation including intraperitoneal (IP),subcutaneous(SC), intramuscular (IM), intravenous (IV) and intradermal (ID) have, previously been used to infect mice with trypanosomes[11,12,13] The IP inoculation is normally administered through the abdominal wall into the peritoneal cavity of the mice.
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