Direct isolation in vitro of Trypanosoma brucei from man and other animals, and its potential value for the diagnosis of gambian trypanosomiasis

A protocol to improve genotyping of problematic microsatellite loci of Trypanosoma brucei gambiense from body fluids

Microsatellite genotyping of Trypanosoma brucei gambiense, the causative agent of human African trypanosomiasis or sleeping sickness, and population genetics tools, are useful for inferring population parameters such as population size and dispersal. Amplifying parasite DNA directly from body fluids (i.e., blood, lymph or cerebrospinal fluid) allows avoiding costly and tedious isolation phases. It is however associated to increased frequencies of amplification failures (allelic dropouts and/or null alleles) at some loci. In this paper, we present a study focused on three T. brucei gambiense microsatellite loci suspected to present amplification problems when amplified from body fluids sampled in Guinean sleeping sickness foci. We checked for the real nature of blank and apparent homozygous genotypes of parasite DNA directly amplified from body fluids and tested the effect of three different DNA quantities of trypanosomes. Our results show that some initially blank and homozygous genotypes happen to be actual heterozygous genotypes. In Guinea, lymph from the cervical nymph nodes, known to contain the highest concentrations of parasites, appeared to provide the best amplification results. Simply repeating the PCR may be enough to retrieve the correct genotype, but we also show that increasing initial DNA content provides better results while undertaking first amplification. We finally propose an optimal protocol for amplifying trypanosome's DNA directly from body fluids that should be adapted to local characteristics and/or constraints.

Molecular epidemiology of African sleeping sickness

Human sleeping sickness in Africa, caused by Trypanosoma brucei spp. raises a number of questions. Despite the widespread distribution of the tsetse vectors and animal trypanosomiasis, human disease is only found in discrete foci which periodically give rise to epidemics followed by periods of endemicity A key to unravelling this puzzle is a detailed knowledge of the aetiological agents responsible for different patterns of disease – knowledge that is difficult to achieve using traditional microscopy. The science of molecular epidemiology has developed a range of tools which have enabled us to accurately identify taxonomic groups at all levels (species, subspecies, populations, strains and isolates). Using these tools, we can now investigate the genetic interactions within and between populations of Trypanosoma brucei and gain an understanding of the distinction between human- and nonhuman-infective subspecies. In this review, we discuss the development of these tools, their advantages and disadvantages and describe how they have been used to understand parasite genetic diversity, the origin of epidemics, the role of reservoir hosts and the population structure. Using the specific case of T.b. rhodesiense in Uganda, we illustrate how molecular epidemiology has enabled us to construct a more detailed understanding of the origins, generation and dynamics of sleeping sickness epidemics.

Cryopreservation of Trypanosoma brucei gambiense in a commercial cryomedium developed for bull semen

There have been major advances in the formulation of cryomedia for spermatozoa owing to their economic importance. In this study, the suitability of the commercial cryomedium Triladyl developed for bull semen was evaluated for the cryopreservation of Trypanosoma brucei gambiense. Cryopreservation efficacy was determined by direct counting of motile trypanosomes and by viability assessment using in vitro and in vivo methods. Culture medium containing 10% glycerol was used as the control. Trypanosomes cryopreserved in Triladyl demonstrated a higher in vitro viability than those in culture medium with 10% glycerol. Similar results were obtained in vivo in immunosuppressed Mastomys natalensis. Trypanosomes cryopreserved in Triladyl showed better growth characteristics than those in culture medium with glycerol. It can be concluded that the use of Triladyl in the cryopreservation of T. b. gambiense leads to a better survival of the trypanosomes which could lead to an improved isolation of T. b. gambiense from sleeping sickness patients.

Mixed infections of trypanosomes in tsetse and pigs and their epidemiological significance in a sleeping sickness focus of Côte d'Ivoire

In a sleeping sickness focus of Côte d'Ivoire, trypanosomes were characterized in humans, pigs and tsetse using various techniques. Out of 74 patients, all the 43 stocks isolated by KIVI (Kit for In Vitro Isolation) appeared to belong to only one zymodeme of Trypanosoma brucei gambiense group 1 (the major zymodeme Z3). The only stock isolated on rodents belonged to a different, new, zymodeme (Z50), of T. b. gambiense group 1. From 18 pigs sampled in the same locations as the patients, PCR showed a high proportion of mixed infections of T. brucei s. l. and T. congolense riverine-forest. Zymodemes of T. brucei s. l. from these pigs were different from those found in humans. From a total of 16 260 captured tsetse (Glossina palpalis palpalis), 1701 were dissected and 28% were found to be infected by trypanosomes. The most prevalent trypanosome was T. congolense riverine-forest type, followed by T. vivax, T. bruceis. l. and T. congolense savannah type, this latter being associated to the forest type of T. congolense in most cases. Mixed infections by 2 or 3 of these trypanosomes were also found. Use of a microsatellite marker allowed us to distinguish T. b. gambiense group 1 in some of the mature infections in tsetse. Differences in infection rates and in trypanosome genotypes according to the host might indicate that the pig may not be an active animal reservoir for humans in this focus.

African trypanosomiasis: Changing epidemiology and consequences

Human African trypanosomiasis has re-emerged as a serious public health threat after near-elimination because of diminished investment in previously successful control programs. The continued, occasional importation of African trypanosomiasis to the United States can be expected as tourists and immigrants travel from high-risk areas. No vaccine or chemoprophylaxis is available for this disease, and travelers to affected areas should be counseled on tsetse fly avoidance. New diagnostic and staging tests are promising but have not replaced the classical method of examining body fluids for trypanosomes. Prompt diagnosis and staging is essential because if untreated, East African and West African sleeping sickness are fatal. Drug regimens are toxic and cumbersome, and short-term prospects for therapeutic advances are limited.

Options for field diagnosis of human african trypanosomiasis

Human African trypanosomiasis (HAT) due to Trypanosoma brucei gambiense or T. b. rhodesiense remains highly prevalent in several rural areas of sub-Saharan Africa and is lethal if left untreated. Therefore, accurate tools are absolutely required for field diagnosis. For T. b. gambiense HAT, highly sensitive tests are available for serological screening but the sensitivity of parasitological confirmatory tests remains insufficient and needs to be improved. Screening for T. b. rhodesiense infection still relies on clinical features in the absence of serological tests available for field use. Ongoing research is opening perspectives for a new generation of field diagnostics. Also essential for both forms of HAT is accurate determination of the disease stage because of the high toxicity of melarsoprol, the drug most widely used during the neurological stage of the illness. Recent studies have confirmed the high accuracy of raised immunoglobulin M levels in the cerebrospinal fluid for the staging of T. b. gambiense HAT, and a promising simple assay (LATEX/IgM) is being tested in the field. Apart from the urgent need for better tools for the field diagnosis of this neglected disease, improved access to diagnosis and treatment for the population at risk remains the greatest challenge for the coming years.

An isoenzyme survey ofTrypanosoma bruceis.l. from the Central African subregion: population structure, taxonomic and epidemiological considerations

In order to improve our knowledge about the taxonomic status and the population structure of the causative agent of Human African Trypanosomiasis in the Central African subregion, 169 newly isolated stocks, of which 16 came from pigs, and 5 reference stocks, were characterized by multilocus enzyme electrophoresis, for 17 genetic loci. We identified 22 different isoenzyme profiles or zymodemes, many of which showed limited differences between them. These zymodemes were equated to multilocus genotypes. UPGMA dendrograms revealed one main group:Trypanosoma brucei gambiensegroup I and 3T. brucei‘non-gambiense’ stocks.T. b. gambiensegroup I zymodemes were very homogenous, grouping all the human stocks and 31% of the pig stocks. Two main zymodemes (Z1 and Z3) grouping 74% of the stocks were found in different remote countries. The genetic distances were relatively high inT. brucei‘non-gambiense’ zymodemes, regrouping 69% of pig stocks. The analysis of linkage disequilibrium was in favour of a predominantly clonal population structure. This was supported by the ubiquitous occurrence of the main zymodemes, suggesting genetic stability in time and space of this parasite's natural clones. However, in some cases an epidemic population structure could not be ruled out. Our study also suggested that the domestic pig was a probable reservoir host forT. b. gambiensegroup I in Cameroon.

Identification of Trypanosoma brucei circulating in a sleeping sickness focus in Côte d'Ivoire: assessment of genotype selection by the isolation method

Genetic studies of Trypanosoma brucei have been mainly based on rodent inoculation (RI) for isolation of trypanosome strains. However, Trypanosoma brucei gambiense is difficult to grow in rodents. The development and use of the Kit for In Vitro Isolation (KIVI) of trypanosomes has led to a better isolation success. However, some authors report a genetic monomorphism in T. b. gambiense, and the extensive use of the KIVI was suspected as being responsible for this low genetic diversity. In the present work, trypanosome stocks were isolated from both humans and pigs in an active sleeping sickness focus in Côte d'Ivoire. Two methods were simultaneously used for this purpose: KIVI and rodent inoculation. None of the human stocks grew in rodents. Some of the stocks originating from pigs could be isolated with both methods. Each of these stocks (from the same pig) showed a different isoenzymatic pattern according to the isolation method used. All the human stocks identified belonged to the major zymodeme 3 of T. b. gambiense group 1, whereas the stocks isolated from pigs belonged to a new group of zymodemes even if they were genetically closely related. These observations may have significant implications when analysing the population structure of T. brucei, and also raise again the question of the importance of the animal reservoir in Human African Trypanosomiasis (HAT).

Genetic characterization of Trypanosoma brucei gambiense and clinical evolution of human African trypanosomiasis in Côte d'Ivoire

Human African trypanosomiasis is a parasitic infection caused by protozoa belonging to Trypanosoma brucei subspecies. The clinical evolution of this disease is complex and might be because of the parasite itself, as genetic diversity has been observed in T. brucei ssp. We investigated the relationship between the genetic diversity of trypanosomes and the diversity of clinical patterns in Côte d'Ivoire. We studied clinical sleeping sickness cases, and genetically analysed the trypanosomes isolated from these patients. An important genetic monomorphism among stocks isolated in Côte d'Ivoire was observed by using various markers: isoenzymes electrophoresis, random amplified polymorphism DNA and PCR of microsatellite sequences. At the same time, the diversity of clinical patterns and evolutions was confirmed by clinical analysis. The existence of an individual susceptibility to disease (human trypanotolerance) should be taken into account even if our genetic conclusions might be distorted because the isolation success rates were particularly poor. In fact, we observed that the isolation success rate varied significantly depending both on the focus of origin (P=0.0002) and on the ethnic group (P=0.0317) of the patient. Further investigations are required in order to study a possible selective impact of the use of the kit for in vitro isolation of trypanosomes as an isolation technique.

Characterization of Trypanosoma brucei s.l. subspecies by isoenzymes in domestic pigs from the Fontem sleeping sickness focus of Cameroon

Though it has been established that domestic animals (especially the pig) are potential reservoir hosts for Trypanosoma brucei gambiense in West Africa, there is little data to this effect concerning Central Africa. Instead, some previous authors report the absence of Trypanozoon type trypanosomes in domestic animals in Cameroon. Thirty-two domestic pigs were sampled by KIVI (kit for in vitro isolation) of trypanosomes in the northern region (Bechati) of the Fontem sleeping sickness focus of Cameroon. Twenty-one of these were found positive, from 15 of which 17 isolates were successfully obtained. Isoenzyme characterization revealed that isolates from 4 of the 15 pigs belonged to zymodemes associated with T. brucei gambiense group 1. The prevalence of this disease in the local human population is, however, very low. It is evident from this study that the domestic pig may be a potential reservoir host for T. brucei gambiense in the Fontem focus. There is, however, need for an extensive study on domestic animals in Cameroon and other neighbouring countries for a better comprehension of the epidemiology of sleeping sickness within the Central African region.

Melarsoprol refractory T. b. gambiense from Omugo, north-western Uganda

Culture adapted T. b. gambiense isolated from Northwest Uganda were exposed to 0.001-0.14 microg/ml melarsoprol or 1.56-100 microg/ml DL-alpha-difluoromethylornithine (DFMO). Minimum inhibitory concentrations (MICs) of each drug were scored for each isolate after a period of 10 days drug exposure. The results indicate that T. b. gambiense isolates from Northwest Uganda had elevated MIC values for melarsoprol ranging from 0.009 to 0.072 microg/ml as compared with T. b. gambiense isolates from Cote d'Ivoire with MIC values ranging from 0.001 to 0.018 microg/ml or with T. b. rhodesiense from Southeast Uganda with MIC values from 0.001 to 0.009 microg/ml. All MIC values obtained fell below expected peak melarsoprol concentrations in serum of treated patients. However, it may not be possible to maintain constant drug concentrations in serum of patients as was the case in our in vitro experiments. Importantly, the MIC of 0.072 microg/ml exhibited by one of the isolates from Northwest Uganda was above levels attainable in CSF indicating that this isolate would probably not be eliminated from CSF of treated patients. PCR amplification of the gene encoding the P2-like adenosine transporter followed by restriction digestion with Sfa NI enzyme revealed presence of fragments previously observed in a trypanosome clone with laboratory-induced arsenic resistance. From our findings it appears that reduced drug susceptibility may be one factor for the frequent relapses of sleeping sickness after melarsoprol treatment occurring in Northwest Uganda.

Follow-up of Card Agglutination Trypanosomiasis Test (CATT) positive but apparently aparasitaemic individuals in Côte d'Ivoire: evidence for a complex and heterogeneous population

The aetiological diagnosis of human African trypanosomiasis (HAT) is based on the detection of the parasite, but currently available parasitological tests have low sensitivity and are hampered by fluctuating parasitaemia. The identification of seropositive individuals on whom to focus parasitological examination is based on antibody detection by means of the Card Agglutination Trypanosomiasis Test (CATT/T.b.gambiense). A complicating phenomenon is the occurrence of serologically positive but parasitologically unconfirmed results (isolated CATT positivity). This work presents a two-year longitudinal serological, parasitological and molecular follow-up of CATT-positive individuals including repeated examinations of each individual, to study the evolution over time of seropositivity at both the population and the individual levels. At the population level, the rate of seropositivity decreased during the first months of the survey, and afterwards showed remarkable stability. At the individual level, the results reveal the extreme heterogeneity of this population, with subjects showing fluctuating results, others with a short transient CATT positivity, and subjects that maintain their seropositivity over time. The stability of seropositivity and the pattern of results obtained with both immunological and parasitological examinations support the view that individual factors, such as immune response to infection, might be involved in the isolated CATT positivity phenomenon.

Comparative in vitro isolation of Trypanosoma theileri from cattle in Belgium

Ten blood samples randomly collected from cows on a farm nearby Antwerp, Belgium, were inoculated into KIVI culture medium (Kit for In Vitro Isolation of trypanosomes) and RPMI 10%+feeder medium. Within 3 weeks of incubation all KIVI cultures and four RPMI 10%+feeder revealed presence of Trypanosoma theileri. Some practical implications regarding the use of KIVI for isolation of pathogenic African trypanosomes from cattle and other Bovidae are discussed.

Isolation of Trypanosoma brucei from the monitor lizard (Varanus niloticus) in an endemic focus of Rhodesian sleeping sickness in Kenya

Monitor lizards were sampled along the shores of Lake Victoria to detect natural infections of potentially human-infective trypanosomes. In an area with endemic rhodesian sleeping sickness, one of 19 lizards was infected (Busia, Kenya). Six of ten lizards also showed indirect evidence of infection with Trypanosoma brucei (antibody ELISA). In an area with no recent history of human disease (Rusinga Island), no parasites were found and no antibodies to T. brucei were detected. The isolate was identified as T. brucei through xenodiagnosis (completion of the life cycle in the salivary glands of tsetse), and through molecular techniques (positive reactions with a PCR primer and a microsatellite DNA probe characteristic of the subgenus Trypanozoon). Experimental infections of monitor lizards were also attempted with a variety of parasites and tsetse species. It was possible to infect monitor lizards with T. brucei but not with forest or savannah genotypes of Trypanosoma congolense. Parasites reached low levels of parasitaemia for a short period without generating any pathology; they also remained infective to tsetse and laboratory rats. The implications of these findings are discussed in relation to the endemicity of sleeping sickness.

Identification of trypanosomes isolated by KIVI from wild mammals in Côte d'Ivoire: diagnostic, taxonomic and epidemiological considerations

In Côte d'Ivoire, a comparative study was carried out on 122 wild mammals by parasitological and serological examination and by in vitro isolation of trypanosomes from fresh blood (KIVI). Thirteen isolated stocks were studied by isoenzymes and compared with Trypanosoma congolense and T. brucei bouaflé group reference stocks. Of the 122 animals, only 22 were positive on blood smears while 88 were KIVI positive and 92 were CATT/T. b. gambiense positive. For six stocks identified by isoenzymes as T. congolense, the agreement between ELISA and CATT was good (75%). As compared with CATT, antigen detection ELISA was not satisfactory for T. brucei (20%). Out of 18, 16 stocks represented a separate zymodeme (seven T. congolense and nine T. brucei) and a high genetic heterogeneity was observed. For T. congolense, savanna, kilifi and forest groups were represented by one zymodeme each. The four remaining zymodemes while put into this T. congolense group, were strongly independent of each other. Morphology indicated that those new zymodemes correspond to T. congolense. In the other hand, five new zymodemes fit into T. brucei classification.

Sleeping sickness in Zaire: a nested polymerase chain reaction improves the identification of Trypanosoma (Trypanozoon) brucei gambiense by specific kinetoplast DNA probes

Blood samples collected in the sleeping sickness focus of Boma, Zaire, from human patients and domestic animals were analysed by polymerase chain reaction (PCR) for the presence of trypanosome DNA. The comparison of PCR and miniature anion exchange centrifugation technique (m-AECT) results clearly shows that in domestic animals mixed infections (Trypanozoon/Trypanosoma [Nannomonas] congolense) are more frequently diagnosed by PCR than by m-AECT. Trypanozoon positive blood samples were further analysed for Trypanosoma (Trypanozoon) brucei gambiense. For that purpose amplified minicircle kinetoplast DNA (minicircle kDNA) was differentiated in gambiense and non-gambiense by hybridization with DNA probes. To analyse blood samples, especially those with low parasite numbers, the amplification step had to be improved by a nested PCR. Subsequent hybridization was done with kDNA probes generated by PCR from blood samples which had been obtained from a human patient infected with T.(T.) b. gambiense and a pig infected with Trypanozoon. The hybridization results clearly show that at least two genotypes of Trypanozoon parasites occur in the sleeping sickness focus of Boma, Baz-Zaire. One obviously corresponds to T.(T.) b. gambiense and was present in humans and two domestic animals (pig, dog). The other genotype seems to be associated with T.(T.) b. brucei and could be detected only in the blood of domestic animals. This is the first time that field samples could be analysed by a technique which facilitates the molecular identification of T.(T.) b. gambiense without prior cloning, propagation, and/or isolation of the parasites. Therefore, this technique seems to be a promising tool to elucidate the significance of the animal reservoir for the epidemiology of the gambiense sleeping sickness in Africa.

Isolation of Trypanosoma brucei gambiense from northern Uganda: evaluation of the kit for in vitro isolation (KIVI) in an epidemic focus

867 individuals from 3 sites near the town of Adjumani in the East Moyo region of north-west Uganda were investigated clinically and serologically for evidence of current trypanosome infections. Blood samples were taken from 94 persons with a positive card agglutination test for trypanosomiasis (CATT) and clinical suspects and inoculated into the kit for in vitro isolation of Trypanosoma brucei gambiense (KIVI). Amongst this group, 30 parasitaemic individuals were identified by microhaematocrit centrifugation and the quantitative buffy coat technique (QBC). Only 80% of these isolates, and one isolate from an aparasitaemic individual, grew in culture. The success or failure of cultures from parasitaemic patients was unrelated to the size of the trypanosome inoculum. The implications of these results and possible reasons for the failure of KIVI are discussed.

A comparison of parasitological methods for the diagnosis of gambian trypanosomiasis in an area of low endemicity in Côte d'Ivoire

The card agglutination test for trypanosomiasis (CATT) was used to examine 8974 inhabitants in 14 village areas south-west of Daloa, Côte d'Ivoire; 114 (1.3%) were CATTT or +/-, and were further examined by one or more of 6 methods for the direct detection of trypanosomes: lymphatic gland puncture, stained thick blood film (TBF), haematocrit centrifugation technique (HCT), mini-anion exchange column (MAEC), quantitative buffy coat method (QBC), and kit for in vitro isolation of trypanosomes (KIVI). Trypanosomes were seen by at least one method in 16 (14.0%) of the CATT+ group. Blood from 356 of the 8860 CATT- group was inoculated into KIVI; trypanosomes grew from the blood of 1 person. Eleven of the 17 patients with detectable trypanosomes were screened by all 6 methods: 6 were HCT+; 7 were gland+; 10 were MAEC+; 10 were KIVI+; 11 were both TBF+ and QBC+. One CATT+ patient was KIVI+ but otherwise negative, although TBF was not done. The overall prevalence of trypanosomes was 0.2% rising to 0.8% in one village area. The results support previous evidence that a reappraisal of procedures is required in the customary system of surveillance for gambian sleeping sickness.

Isolation of Trypanosoma spp. from wild tsetse flies through procyclic expansion in Glossina morsitans centralis

Procyclic trypanosomes from wild tsetse flies were membrane-fed to Glossina morsitans centralis in order to develop an optimal technique for propagating field isolates. A 70% success rate was achieved in isolating Trypanosoma simiae and a variety of genotypes of T. congolense originating from G. pallidipes, G. brevipalpis and G. swynnertoni. Parasites matured into forms infective for mammals, and could be maintained by passage of gut forms to new groups of flies. In experiments with laboratory stocks, we also passaged immature gut infections of T. congolense and T. brucei from various tsetse species to G. m. centralis. The optimal technique was investigated for procyclic T. congolense through addition of various compounds to goat blood using G. m. centralis and G. m. morsitans as recipients. From these experiments, many approaches to procyclic expansion appeared possible. However, a simple and practical method based on the use of fresh goat blood for rapid feeding of G. m. centralis is recommended. Application of this technique should aid in the resolution of questions relating to the cryptic diversity of Nannomonas trypanosomes in diverse host and vector communities.

The isolation and genetic heterogeneity of Trypanosoma brucei gambiense from north-west Uganda

Fifty-two samples of blood were taken from sleeping sickness patients in north-west Uganda. All samples failed to infect immunosuppressed mice. Ten cryopreserved blood samples were fed to laboratory bred Glossina morsitans morsitans; eight flies developed midgut infections from which procyclic cultures were established in vitro. Isoenzyme electrophoretic analysis of 9 enzymes revealed that 7 of the 8 trypanosome isolates had a combination of enzyme patterns already described for Trypanosoma brucei gambiense. The eighth isolate had a different aspartate aminotransferase polymorphism which placed it in a new zymodeme. Analysis of polymorphisms in genes for 3 variant surface glycoproteins (VSGs) confirmed that the 8 Ugandan trypanosome isolates were T.b.gambiense and revealed further heterogeneity. The VSG 117 gene was present in all the isolates in a pattern of fragments (equivalent to AnTat 1.8) characteristic for T.b.gambiense. For two other VSG genes characteristic of T.b.gambiense, the LiTat 1.3 gene was present in all the isolates, while the AnTat 11.17 gene was present in only 2 of the 8 isolates.