Differential virulence of camel Trypanosoma evansi isolates in mice

Abstract

This study assessed the virulence of Trypanosoma evansi, the causative agent of camel trypanosomiasis (surra), affecting mainly camels among other hosts in Africa, Asia and South America, with high mortality and morbidity. Using Swiss white mice, we assessed virulence of 17 T. evansi isolates collected from surra endemic countries. We determined parasitaemia, live body weight, packed cell volume (PCV) and survivorship in mice, for a period of 60 days' post infection. Based on survivorship, the 17 isolates were classified into three virulence categories; low (31-60 days), moderate (11-30 days) and high (0-10 days). Differences in survivorship, PCV and bodyweights between categories were significant and correlated (P < 0.05). Of the 10 Kenyan isolates, four were of low, five moderate and one (Type B) of high virulence. These findings suggest differential virulence between T. evansi isolates. In conclusion, these results show that the virulence of T. evansi may be region specific, the phenotype of the circulating parasite should be considered in the management of surra. There is also need to collect more isolates from other surra endemic regions to confirm this observation.

Differential virulence ofTrypanosoma brucei rhodesienseisolates does not influence the outcome of treatment with anti-trypanosomal drugs in the mouse model

“…Parasitaemia progression among Tbr isolates assigned to different virulence classes on the basis of survival time were significantly different. This finding is in agreement with previous studies in which virulence of different species of trypanosomes was characterised using parasitaemia, intensity of anaemia (PCV) and weight loss experienced by the host during the infection period [24]. In our study, parasitaemia of isolates in the very-acute virulence class was represented by a single wave whereas the acute, sub-acute and chronic virulence classes were represented by two waves.…”

“…This finding is consistent with observations by [36] who reported that acute infection of mice with Trypanosoma cruzi was characterized by an exponential growth of parasites and high mortality accompanied by anemia. A similar observation was made by [24] in mice infected with Trypanosoma evansi . In contrast, anaemia in mice infected with clones in the other various classes of virulence (acute, sub-acute and chronic) stabilized or recovered characteristic of the chronic phase anaemia [37].…”

“…We used mean survival time (MST) of mice post-infection as the main indicator of virulence as previously reported [23,30]; [24] and observed that the Tbr isolates were well distributed among the four virulence classes. This finding explains why clinical syndromes in HAT patients differ significantly even in a single HAT focus, thus complicating HAT diagnosis.…”

“…In our study, we did not measure the food intake. The failure by infected mice to register a decline calls for further investigation on causes of body weight changes in trypanosomes infected animals and especially after previous studies have recorded an increase in body weight in T.evansi [24] and in T. b. brucei or T. congolense [19] infected mice with days post infection.…”

“…rhodesiense clones were placed into four classes of virulence based on the survival of 60% or more of the infected mice as follows: very-acute (0-15 days), acute (16 – 30), sub-acute (31 – 45) and chronic classes (46 – 60). Each mouse’s survival time was based on attainment of the at extremis condition which was determined on a ≥ 25% drop in PCV and consistently high parasitaemia levels of 1×10 9 /ml for at least two consecutive days, [24]. The mice were euthanized by CO 2 asphyxiation [25] and recorded as dead animal.…”