Human African Trypanosomosis Research Articles

Phylogeography and Taxonomy of Trypanosoma brucei

BackgroundCharacterizing the evolutionary relationships and population structure of parasites can provide important insights into the epidemiology of human disease.Methodology/Principal FindingsWe examined 142 isolates of Trypanosoma brucei from all over sub-Saharan Africa using three distinct classes of genetic markers (kinetoplast CO1 sequence, nuclear SRA gene sequence, eight nuclear microsatellites) to clarify the evolutionary history of Trypanosoma brucei rhodesiense (Tbr) and T. b. gambiense (Tbg), the causative agents of human African trypanosomosis (sleeping sickness) in sub-Saharan Africa, and to examine the relationship between Tbr and the non-human infective parasite T. b. brucei (Tbb) in eastern and southern Africa. A Bayesian phylogeny and haplotype network based on CO1 sequences confirmed the taxonomic distinctness of Tbg group 1. Limited diversity combined with a wide geographical distribution suggested that this parasite has recently and rapidly colonized hosts across its current range. The more virulent Tbg group 2 exhibited diverse origins and was more closely allied with Tbb based on COI sequence and microsatellite genotypes. Four of five COI haplotypes obtained from Tbr were shared with isolates of Tbb, suggesting a close relationship between these taxa. Bayesian clustering of microsatellite genotypes confirmed this relationship and indicated that Tbr and Tbb isolates were often more closely related to each other than they were to other members of the same subspecies. Among isolates of Tbr for which data were available, we detected just two variants of the SRA gene responsible for human infectivity. These variants exhibited distinct geographical ranges, except in Tanzania, where both types co-occurred. Here, isolates possessing distinct SRA types were associated with identical COI haplotypes, but divergent microsatellite signatures.Conclusions/SignificanceOur data provide strong evidence that Tbr is only a phenotypic variant of Tbb; while relevant from a medical perspective, Tbr is not a reproductively isolated taxon. The wide distribution of the SRA gene across diverse trypanosome genetic backgrounds suggests that a large amount of genetic diversity is potentially available with which human-infective trypanosomes may respond to selective forces such as those exerted by drugs.

Antitrypanosomal Activity of Flavonoid Extracted from Ximenia Americana Stem Bark

The resurgence of Human African Trypanosomosis and Animal African Trypanosomosis in the latter part of the 20th century after it had been brought largely under control in the 1960 has been alarming. Methanolic extract of stem bark of Ximennia americana were partitioned to obtain their major phytochemical fractions, these were evaluated for their in vitro and in vivo antitrypanosomal activities against Trypanosoma congolense. The Flavonoid fraction significantly (P<0.05) inhibited the motility of the blood stream forms with 10mg/ml. However, when the infected mice were treated at 5, 10 and 25mg/ml of the flavonoid fractions, there was a suppression of the growth of the parasites in a dose dependent manner with the 25mg/ml producing the maximum effect. The results further confirm the ethnopharmacological usage of Ximenia americana against Trypanosomosis.KEYWORD: Flavonoid , Ximenia americana, antitrypanosomal activity

Factors influencing the sero-prevalence of Trypanosoma brucei gambiense sleeping sickness in Juba District, Central Equatoria State, Southern Sudan

A surveillance of the Gambian type of Human African Trypanosomosis (HAT) conducted in Juba area using the Card Agglutination Test for Trypanosomosis (CATT) showed that 257 (11.1%) out of 2322 individuals were sero-positive. The sero-positive rate in the pooled adults was higher but not significanty different from that of the pooled children. The adult females sero-prevalence rate was significantly higher than those of adult males, male or female children. There were no significant differences in the sero-prevalence rates between adult men and male or female children. The internally-displaced group and the military personnel showed statistically higher sero-positive rates than the resident groups regardless of the presence or absence of the only extant tsetse species, Glossina fuscipesfuscipes. The proportions of sero-positives differed significantly between locations in the study area. The respondents examined along the riverine vegetation had a statistically higher encounter with the disease than those in the derived savanna and the open savanna woodland. There was no significant correlation between the density of G. fuscipes fuscipes and the incidence of Trypanosoma bruceigambiense. Key words: CATT, sero-prevalence, sleeping sickness, HAT, Gambian type.

The Population Structure of Glossina palpalis gambiensis from Island and Continental Locations in Coastal Guinea

BackgroundWe undertook a population genetics analysis of the tsetse fly Glossina palpalis gambiensis, a major vector of sleeping sickness in West Africa, using microsatellite and mitochondrial DNA markers. Our aims were to estimate effective population size and the degree of isolation between coastal sites on the mainland of Guinea and Loos Islands. The sampling locations encompassed Dubréka, the area with the highest Human African Trypanosomosis (HAT) prevalence in West Africa, mangrove and savannah sites on the mainland, and two islands, Fotoba and Kassa, within the Loos archipelago. These data are discussed with respect to the feasibility and sustainability of control strategies in those sites currently experiencing, or at risk of, sleeping sickness.Principal FindingsWe found very low migration rates between sites except between those sampled around the Dubréka area that seems to contain a widely dispersed and panmictic population. In the Kassa island samples, various effective population size estimates all converged on surprisingly small values (10<Ne<30) that suggest either a recent bottleneck, and/or other biological or ecological factors such as strong variance in the reproductive success of individuals.Conclusion/SignificanceWhatever their origin, the small effective population sizes suggest high levels of inbreeding in tsetse flies within the island samples in marked contrast to the large diffuse deme in Dubréka zones. We discuss how these genetic results suggest that different tsetse control strategies should be applied on the mainland and islands.

Distribution pattern of Glossina fuscipes fuscipes (Diptera: Glossinidae) in Bahr el Jebel State, southern Sudan

A survey to establish the distribution of tsetse flies (Diptera: Glossinidae) in southern Sudan was conducted using biconical traps. Only Glossina fuscipes fuscipes was caught. The results obtained revealed a further northern advance of G. f. fuscipes of c. 29 km along River Bahr el Jebel and 48 km along River Luri, and a southern contraction of Glossina morsitans submorsitans belt from Lewis’ distribution limit. Glossina f. fuscipes was encountered in gallery forest along water courses with no significant differences in sex ratios and proportions of tenerals and non-tenerals between trap catches (P > 0.1). Flies were absent from villages and open savanna woodland forests away from water courses. Trap catches were significantly higher during wet than dry season (t = 2.681; P < 0.025), although flies could be caught in any one location during both seasons. These results are discussed in relation to the current epidemic of human African trypanosomosis (HAT) in southern Sudan.

Development of a rodent model for late stage rhodesian sleeping sickness

A mouse model of Trypanosoma brucei rhodesiense that can be used in pathogenesis and drug studies for Human African Trypanosomosis (HAT) has so far not been developed. In an attempt to develop such a model, a study was undertaken to determine the clinical and pathological changes in mice infected with stock of T. b. rhodesiense (KETRI 2357) and its clone (KETRI 3741). The infections resulted in a mean prepatent period of 3 (range 3-4) days for KETRI 2537 and 4 (range 3-5) days for KETRI 3741. The first wave of parasitaemia for both isolates reached peak (antilog 8.7) between 6-8 DPI and was followed by secondary latency. Thereafter, the parasitaemia increased and remained high, with slight fluctuations. The mean survival period was 36 (range: 7-45) and 50 (18-82) days for the mice infected with KETRI 2537 and KETRI 3741 respectively. At post mortem, the spleens were enlarged and there was generalized congestion in most organs. Histopathological changes were more severe in the parent stock compared to its clone. Meningoencephalitis was observed in mice infected with KETRI 3741 that survived up to 77 days. These studies demonstrate the development of late stage disease in mice infected with T. b. rhodesiense, with potential for use as a model of sleeping sickness.

Genetic and Morphometric Evidence for Population Isolation of &lt;I&gt;Glossina palpalis gambiensis&lt;/I&gt; (Diptera: Glossinidae) on the Loos Islands, Guinea

Allele frequencies at four microsatellite loci, and morphometric features based on 11 wing landmarks, were compared among three populations of Glossina palpalis gambiensis (Diptera: Glossinidae) in Guinea. One population originated from the Loos islands separated from the capital Conakry by 5 km of sea, and the two others originated from the continental mangrove area close to Dubreka, these two groups being separated by approximately 30 km. Microsatellites and wing geometry data both converged to the idea of a separation of the Loos island population from those of the mangrove area. Although occasional contacts cannot be excluded, our results support the hypothesis of the Loos population of tsetse flies being a completely isolated population. This situation will favor a sequenced intervention against human African trypanosomosis and the possibility of an elimination of tsetse from this island.

The tsetse fly Glossina palpalis palpalis is composed of several genetically differentiated small populations in the sleeping sickness focus of Bonon, Côte d’Ivoire

Glossina palpalis is the main vector of human African trypanosomosis (HAT, or sleeping sickness) that dramatically affects human health in sub-Saharan Africa. Because of the implications of genetic structuring of vector populations for the design and efficacy of control campaigns, G. palpalis palpalis in the most active focus of sleeping sickness in Côte d’Ivoire was studied to determine whether this taxon is genetically structured. High and statistically significant levels of within population heterozygote deficiencies were found at each of the five microsatellite loci in two temporally separated samples. Neither null alleles, short allele dominance, nor trap locations could fully explain these deviations from random mating, but a clustering within each of the two samples into different genetic sub-populations (Wahlund effect) was strongly suggested. These different genetic groups, which could display differences in infection rates and trypanosome identity, were composed of small numbers of individuals that were captured together, leading to the observed Wahlund effect. Implications of this population structure on tsetse control are discussed.

Towards understanding the presence/absence of Human African Trypanosomosis in a focus of Côte d'Ivoire: a spatial analysis of the pathogenic system

BackgroundThis study aimed at identifying factors influencing the development of Human African Trypanosomosis (HAT, or sleeping sickness) in the focus of Bonon, located in the mesophile forest of Côte d'Ivoire. A previous study mapping the main daytime activity sites of 96 patients revealed an important disparity between the area south of the town- where all the patients lived- and the area north of the town, apparently free of disease. In order to explain this disparity, we carried out a spatial analysis of the key components of the pathogenic system, i.e. the human host, the tsetse vector and the trypanosomes in their environment using a geographic information system (GIS).ResultsThis approach at the scale of a HAT focus enabled us to identify spatial patterns which linked to the transmission and the dissemination of this disease. The history of human settlement (with the rural northern area exploited much earlier than the southern one) appears to be a major factor which determines the land use pattern, which itself may account for differences found in vector densities (tsetse were found six times more abundant in the southern rural area than in the northern). Vector density, according to the human and environmental context in which it is found (here an intense mobility between the town of Bonon and the rural areas), may explain the observed spatial differences in HAT prevalence.ConclusionThis work demonstrates the role of GIS analyses of key components of the pathogenic system in providing a better understanding of transmission and dissemination of HAT. Moreover, following the identification of the most active transmission areas, and of an area unfavourable to HAT transmission, this study more precisely delineates the boundaries of the Bonon focus. As a follow-up, targeted tsetse control activities starting north of Bonon (with few chances of reinvasion due to very low densities) going south, and additional medical surveys in the south will be proposed to the Ivoirian HAT control program to enhance the control of the disease in this focus. This work also shows the evolution of HAT regarding time and environment, and the methodology used may be able to predict possible sleeping sickness development/extinction in areas with similar history and space organization.

Serum total proteins and creatinine levels in experimental gambian trypanosomosis of vervet monkeys

Although Human African Trypanosomosis presently constitute a major socio-economic problem in several parts of sub-Saharan Africa, conflicting reports on experiemental infections appear to be one of the factors limiting the chemotherapeutic control of the disease. Attempt was therefore made to evaluate the effect of two strains of Trypanosoma brucei gambiense on total proteins and other serum biochemical parameters using vervet monkeys as a model. The outcome of both strains in vervet monkeys was traumatic as the monkeys died from infection 12 – 15 weeks post infection while the serum total proteins increased due to increase in serum globulins with resultant fall in the albumin/globulin ratio. Similarly creatinine and fibrinogen levels increased after infection. The study confirms the existence of atypical virulent infections with a resultant early death from T . b . gambiense . African Journal of Biotechnology Vol. 4 (2), pp. 187-190, 2005

Spontaneous cure of domestic pigs experimentally infected by Trypanosoma brucei gambiense: Implications for the control of sleeping sickness

The existence of a pig reservoir for human African trypanosomosis (HAT) due to Trypanosoma brucei gambiense complicates the fight against this disease. This study, reports results obtained from pigs, which were inoculated with the blood of a person, suffering from HAT in Cameroon. The pigs were reared and kept in the shelter from all contact with Glossina, and monitored for 188 days. The seroconversion was checked by agglutination assays for trypanosomosis (CATT 1.3 and LATEX/ T.b.gambiense). The parasitemia was measured by quantitative buffy coat method (QBC) and by polymerase chain reaction method (PCR). In addition, growth was recorded as well as blood counting and blood formulas. The results showed that the pigs were trypanotolerant and cure themselves in less than 6 months. It is concluded that sterilisation of this reservoir could be achieved by tsetse-control measures in 1 year. It confirms the strategy to complement screening and treatment of HAT with tsetse fly control measures.

Spatial and Temporal Patterns of Human African Trypanosomosis (HAT) Transmission Risk in the Bipindi Focus, in the Forest Zone of Southern Cameroon

Vector control is an effective and cost-efficient way to disrupt the transmission of human African trypanosomosis (HAT); it has nonetheless been little used to date in the disease's foci. With the aim to target trapping more precisely and to develop an optimized vector control system, a transmission risk index was used in the HAT focus of Bipindi, in the forest zone of southern Cameroon. The authors used a simplified version of the index originally developed by Laveissière et al. in 1994. The calculation of this new index only requires knowledge of the proportion of teneral flies and the proportion of flies with human blood meals in samples caught in different biotopes. This makes it possible to identify the biotopes displaying permanent risk, such as riverbanks, as well as biotopes displaying seasonal risk, such as marshy hollows and encampmemts. In the villages, the domestic pig, with 49% of the identified blood meals, is the favorite host of the tsetse flies during the short rainy season. The proportion of blood meals taken on human beings does not significantly increase when domestic pigs are absent. Game animals, contributing to 46% and 64% of the blood meals during the short rainy season and the long dry season, respectively, are also favored as feeding hosts in this particular HAT focus.

Spatial and Temporal Patterns of Human African Trypanosomosis (HAT) Transmission Risk in the Bipindi Focus, in the Forest Zone of Southern Cameroon

Spatial and Temporal Patterns of Human African Trypanosomosis (HAT) Transmission Risk in the Bipindi Focus, in the Forest Zone of Southern Cameroon

Comparison of different DNA preparation protocols for PCR diagnosis of Human African Trypanosomosis in Côte d'Ivoire

During a medical survey the sleeping sickness focus in Bonon, Ivory Coast, PCR with Trypanosoma brucei specific primers (TBR 1–2 from Parasitology 99 (1989) 57) was tested on DNA derived from blood samples. DNA purification using a chelating resin was performed either on whole blood or on the buffy coat prepared in two different ways. The preparation based on whole blood performed better than those using the buffy-coat. Using this first method, the sensitivity was 100% on parasitologically confirmed patients, and the specificity was 92%. However, problems of reproducibility of the technique were pointed out, particularly on samples from serologically positive but apparently aparasitemic individuals. It is suggested that the PCR could help in the diagnosis of Human African Trypanosomosis, but the use of other primers should be investigated.

Evaluation of an EDTA version of CATT/ Trypanosoma bruceigambiense for serological screening of human blood samples

CATT/ Trypanosoma brucei gambiense, a direct card agglutination test designed for field surveys on human African trypanosomosis, is currently used with freshly collected heparinized blood samples. When testing serum samples, it has been observed earlier that, at lower sample dilutions, a complement-mediated inhibition phenomenon may cause false negative test results. This can be avoided by adding an anticomplementary agent such as di-sodium ethylenediaminetetraacetate dihydrate (EDTA) to the reaction. As the sensitivity of the blood assay might be improved in the same way, this possibility has been examined under both laboratory and field conditions, by adding EDTA to the test buffer or, as an anticoagulant, to the blood samples. The CATT-EDTA versions proved up to 7% more sensitive but also 1–2% less specific than the current test. CATT buffer supplemented with EDTA remained stable for at least 2 years at +45 °C.

The use of plasma haproglobin concentrations in the assessment of cure in a murine model of late stage human African trypanosomosis

The use of plasma haproglobin concentrations in the assessment of cure in a murine model of late stage human African trypanosomosis