Kenya Trypanosomiasis Research Institute cryobank for human and animal trypanosome isolates to support research: opportunities and challenges

The pathogenicity of blood stream and central nervous system forms of Trypanosoma brucei rhodesiense trypanosomes in laboratory mice: a comparative study

Background: Human African trypanosomiasis (HAT) develops in two stages namely early stage when trypanosomes are found in the blood and late stage when trypanosomes are found in the central nervous system (CNS). The two environments are different with CNS environment reported as being hostile to the trypanosomes than the blood environment. The clinical symptoms manifested by the disease in the two environments are different. Information on whether blood stream are pathologically different from CNS trypanosomes is lacking. This study undertook to compare the inter-isolate pathological differences caused by bloodstream forms (BSF) and central nervous system (CNS) of five Trypanosoma brucei rhodesiense ( Tbr) isolates in Swiss white mice. Methods: Donor mice infected with each of the five isolates were euthanized at 21 days post infection (DPI) for recovery of BSF trypanosomes in heart blood and CNS trypanosomes in brain supernatants. Groups of Swiss white mice (n = 10) were then infected with BSF or CNS forms of each isolate and monitored for parasitaemia, packed cell volume (PCV), body weight, survivorship, trypanosome length, gross and histopathology characteristics. Results: Amplification of SRA gene prior to trypanosome morphology and pathogenicity studies confirmed all isolates as T. b. rhodesiense. At 21 DPI, CNS trypanosomes were predominantly long slender (LS) while BSF were a mixture of short stumpy and intermediate forms. The density of BSF trypanosomes was on average 2-3 log-scales greater than that of CNS trypanosomes with isolate KETRI 2656 having the highest CNS trypanosome density. Conclusions: The pathogenicity study revealed clear differences in the virulence/pathogenicity of the five (5) isolates but no distinct and consistent differences between CNS and BSF forms of the same isolate. We also identified KETRI 2656 as a suitable isolate for acute menigo- encephalitic studies.

Mouse experiments demonstrate differential pathogenicity and virulence of Trypanosoma brucei rhodesiense strains

Trypanosoma brucei rhodesiense is the causative agent for Rhodesian human African trypanosomiasis. The disease is considered acute, but varying clinical outcomes including chronic infections have been observed. The basis for these different clinical manifestations is thought to be associated with a combination of parasite and host factors. In the current study, Trypanosoma brucei rhodesiense strains responsible for varying infection outcomes were sought using mouse model. Clinical rHAT parasite isolates were subjected to PCR tests to confirm presence of the serum resistance associated (SRA) gene. Thereafter, four T. b. rhodesiense isolates were subjected to a comparative pathogenicity study using female Swiss white mice; the parasite strains were compared on the basis of parasitaemia, host survival time, clinical and postmortem biomarkers of infection severity. Isolates identified to cause acute and chronic disease were compared for establishment in insect vector, tsetse fly. The mouse survival time was significantly different (Log-rankp = 0.0001). With mice infected with strain KETRI 3801 exhibiting the shortest survival time (20 days) as compared to those infected with KETRI 3928 that, as controls, survived past the 60 days study period. In addition, development of anaemia was rapid in KETRI 3801 and least in KETRI 3928 infections, and followed the magnitude of survival time. Notably, hepatosplenomegaly was pronounced with longer survival. Mouse weight and feed intake reduced (KETRI 3801 > KETRI 2636 > EATRO 1762) except in KETRI 3928 infections which remained similar to controls. Comparatively, acute to chronic infection outcomes is in the order of KETRI 3801 > KETRI 2636 > EATRO 1762 > KETRI 3928, indicative of predominant role of strain dependent factors. Further, KETRI 3928 strain established better in tsetse as compared to KETRI 3801, suggesting that transmission of strains causing chronic infections could be common. In sum, we have identified Trypanosoma brucei rhodesiense strains that cause acute and chronic infections in mice, that will be valuable in investigating pathogen - host interactions responsible for varying disease outcomes and transmission in African trypanosomiasis.

Physiological and proteomic profiles of Trypanosoma brucei rhodesiense parasite isolated from suramin responsive and non-responsive HAT patients in Busoga, Uganda

Human African Trypanosomiasis (HAT) is a disease of major economic importance in Sub-Saharan Africa. The HAT is caused by Trypanosoma brucei rhodesiense (Tbr) parasite in eastern and southern Africa, with suramin as drug of choice for treatment of early stage of the disease. Suramin treatment failures has been observed among HAT patients in Tbr foci in Uganda. In this study, we assessed Tbr parasite strains isolated from HAT patients responsive (Tbr EATRO-232) and non-responsive (Tbr EATRO-734) to suramin treatment in Busoga, Uganda for 1) putative role of suramin resistance in the treatment failure 2) correlation of suramin resistance with Tbr pathogenicity and 3) proteomic pathways underpinning the potential suramin resistance phenotype in vivo. We first assessed suramin response in each isolate by infecting male Swiss white mice followed by treatment using a series of suramin doses. We then assessed relative pathogenicity of the two Tbr isolates by assessing changes pathogenicity indices (prepatent period, survival and mortality). We finally isolated proteins from mice infected by the isolates, and assessed their proteomic profiles using mass spectrometry. We established putative resistance to 2.5 mg/kg suramin in the parasite Tbr EATRO-734. We established that Tbr EATRO-734 proliferated slower and has significantly enriched pathways associated with detoxification and metabolism of energy and drugs relative to Tbr EATRO-232. The Tbr EATRO-734 also has more abundantly expressed mitochondrion proteins and enzymes than Tbr EATRO-232. The suramin treatment failure may be linked to the relatively higher resistance to suramin in Tbr EATRO-734 than Tbr EATRO-232, among other host and parasite specific factors. However, the Tbr EATRO-734 appears to be less pathogenic than Tbr EATRO-232, as evidenced by its lower rate of parasitaemia. The Tbr EATRO-734 putatively surmount suramin challenges through induction of energy metabolism pathways. These cellular and molecular processes may be involved in suramin resistance in Tbr.

Differential virulence of camel Trypanosoma evansi isolates in mice

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.

Multiple evolutionary origins of Trypanosoma evansi in Kenya

Trypanosoma evansi is the parasite causing surra, a form of trypanosomiasis in camels and other livestock, and a serious economic burden in Kenya and many other parts of the world. Trypanosoma evansi transmission can be sustained mechanically by tabanid and Stomoxys biting flies, whereas the closely related African trypanosomes T. brucei brucei and T. b. rhodesiense require cyclical development in tsetse flies (genus Glossina) for transmission. In this study, we investigated the evolutionary origins of T. evansi. We used 15 polymorphic microsatellites to quantify levels and patterns of genetic diversity among 41 T. evansi isolates and 66 isolates of T. b. brucei (n = 51) and T. b. rhodesiense (n = 15), including many from Kenya, a region where T. evansi may have evolved from T. brucei. We found that T. evansi strains belong to at least two distinct T. brucei genetic units and contain genetic diversity that is similar to that in T. brucei strains. Results indicated that the 41 T. evansi isolates originated from multiple T. brucei strains from different genetic backgrounds, implying independent origins of T. evansi from T. brucei strains. This surprising finding further suggested that the acquisition of the ability of T. evansi to be transmitted mechanically, and thus the ability to escape the obligate link with the African tsetse fly vector, has occurred repeatedly. These findings, if confirmed, have epidemiological implications, as T. brucei strains from different genetic backgrounds can become either causative agents of a dangerous, cosmopolitan livestock disease or of a lethal human disease, like for T. b. rhodesiense.

Differential virulence and tsetse fly transmissibility of <i>Trypanosoma congolense</i> and <i>Trypanosoma brucei</i> strains

African animal trypanosomiasis causes significant economic losses in sub-Saharan African countries because of livestock mortalities and reduced productivity. Trypanosomes, the causative agents, are transmitted by tsetse flies (Glossina spp.). In the current study, we compared and contrasted the virulence characteristics of five Trypanosoma congolense and Trypanosoma brucei isolates using groups of Swiss white mice (n = 6). We further determined the vectorial capacity of Glossina pallidipes, for each of the trypanosome isolates. Results showed that the overall pre-patent (PP) periods were 8.4 ± 0.9 (range, 4–11) and 4.5 ± 0.2 (range, 4–6) for T. congolense and T. brucei isolates, respectively (p < 0.01). Despite the longer mean PP, T. congolense–infected mice exhibited a significantly (p < 0.05) shorter survival time than T. brucei–infected mice, indicating greater virulence. Differences were also noted among the individual isolates with T. congolense KETRI 2909 causing the most acute infection of the entire group with a mean ± standard error survival time of 9 ± 2.1 days. Survival time of infected tsetse flies and the proportion with mature infections at 30 days post-exposure to the infective blood meals varied among isolates, with subacute infection–causing T. congolense EATRO 1829 and chronic infection–causing T. brucei EATRO 2267 isolates showing the highest mature infection rates of 38.5% and 23.1%, respectively. Therefore, our study provides further evidence of occurrence of differences in virulence and transmissibility of eastern African trypanosome strains and has identified two, T. congolense EATRO 1829 and T. brucei EATRO 2267, as suitable for tsetse infectivity and transmissibility experiments.