Elusive trypanosomes

Characterization ofTrypanosoma bruceis.l. infecting asymptomatic sleeping-sickness patients in Côte d'Ivoire: a new genetic group?

Six villagers in the Sinfra focus of sleeping sickness in Côte d'Ivoire who in 1995 were asymptomatic and refusing treatment, despite then being serologically and parasitologically positive for trypanosomes, were followed-up, while still refusing treatment, until 2002. In 2002, five of the six cases remained serologically positive but no trypanosomes could be found in any of them by use of the classical parasitological methods. A PCR-based assay, however, revealed that all six had the DNA of Trypanosoma brucei s.l. in their blood, so confirming the low sensitivity of the classical parasitological tests. The analysis of satellite, minisatellite and microsatellite markers indicated that, in 2002, all six cases were infected with a 'new' distinct genetic group of T. brucei s.l. and four were co-infected with T. b. gambiense group 1. The epidemiological consequences of such co-infections are discussed. The 'new' group of T. brucei had a molecular pattern that differed from those of the classical T. b. gambiense group 1 and the 'bouaflé' group.

Cyclical transmission of Trypanosoma brucei gambiense in Glossina palpalis gambiensis displays great differences among field isolates

Six sets of teneral Glossina palpalis gambiensis (Diptera: Glossinidae) were fed on mice infected with six different isolates of Trypanosoma brucei gambiense (each mouse was infected with one of the isolates), previously isolated from patients in the sleeping sickness focus of Bonon, Côte d'Ivoire and in Makoua, Congo. All the tsetse flies were dissected 42 days post-infection and midgut and salivary glands were examined for trypanosomes by microscopical examination. No infection was observed with the reference stock whereas each of the five recently isolated trypanosome isolates was able to infect tsetse flies, with rates of infection varying between 9.7 and 18.2% depending on the isolate. Three isolates displayed only immature infections with 9.7, 17.3 and 18% of the flies showing trypanosomes in their midgut. One isolate gave both immature (12.1%) and mature infections (6.1%). Finally, the last isolate involved only mature infections in 9.7% of the Glossina species examined. These substantial differences in the cyclical transmission of T. b. gambiense in the same fly species could have important implications for the epidemiology of the transmission of Human African Trypanosomiasis.

Monitoring the developmental status of Trypanosoma brucei gambiense in the tsetse fly by means of PCR analysis of anal and saliva drops

Teneral Glossina palpalis gambiensis (Diptera: Glossinidae) were infected with a culture of procyclic forms of Trypanosoma brucei gambiense using a single-bloodmeal membrane feeding technique. The infection was monitored by analysing the saliva (mature infection) and anal drop (midgut infection) of each fly at different post-infection times both by microscopic observation and polymerase chain reaction (PCR). Amplification revealed many more positive anal drops than microscopy. The monitoring showed that the installation of T. b. gambiense in Glossina took place at least 11 days after the infection and that maturation occurred after 29 days. It also reflected precisely the parasitic status of each tsetse fly as determined by the dissection, microscopic examination and PCR amplification of the midguts and salivary glands 47 days post-infection. Twice as many tsetse flies with mature salivary glands infection were revealed by PCR than by microscopic examination, but the two techniques gave exactly the same results regarding the proportion of flies with midgut infection. This study also demonstrated the ability of natural non-infective procyclic forms of T. b. gambiense, to colonise the midgut and subsequently establish in the salivary glands of G. p. gambiensis.

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).

A high prevalence of mixed trypanosome infections in tsetse flies in Sinfra, Côte d'Ivoire, detected by DNA amplification

The prevalence of various species and subgroups of trypanosomes in the Sinfra area of Côte d'Ivoire was determined using the polymerase chain reaction (PCR). Using this technique to amplify specific satellite DNA targets, it was possible to identify developmental-stage trypanosomes in the midguts and the proboscides of tsetse without expansion of parasite populations. The predominant tsetse species in the area was Glossina palpalis, while G. pallicera and G. nigrofusca were also present. Microscopical examination of 811 non-teneral flies revealed an infection rate of 14% in midguts and/or proboscides. Three subgroups of Trypanosoma congolense (Savannah, Forest & Kilifi), T. simiae, T. godfreyi, West African T. vivax and T. brucei ssp. were identified using PCR. T. congolense Forest was the most abundant of the Nannomonas trypanosomes. Approximately 40% of all infections were mixed, and there was a significantly higher prevalence of apparently mature T. brucei ssp. trypanosomes than has previously been reported. The present study demonstrates that PCR facilitates the easy identification of mature trypanosome infections in tsetse, providing a reliable estimation of trypanosomiasis challenge.

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.

Trypanosoma (Nannomonas) godfreyi sp. nov. from tsetse flies in The Gambia: biological and biochemical characterization

We provide evidence from isoenzyme analysis, hybridization with repetitive DNA probes, behavioural studies and morphometrics that 4 trypanosome isolates from Glossina morsitans submorsitans in The Gambia constitute a new species now named Trypanosoma (Nannomonas) godfreyi. The bloodstream trypomastigotes of T. (N.) godfreyi are relatively small with a mean length of 13.7 microns (range: 9.1-21.8 microns) and a mean width of 1.65 microns (range: 0.65-2.69 microns). There is no free flagellum and the marginal kinetoplast is subterminal to a rounded posterior end; the undulating membrane is usually conspicuous. As with other Nannomonas, T. godfreyi developed in the midgut and proboscis of Glossina and infections matured in 21-28 days in laboratory G.m. morsitans. In The Gambia the normal vertebrate host appears to be the warthog, Phacochoerus aethiopicus, although elsewhere other wild and domestic suids may also be implicated in the life-cycle. T. godfreyi was identified unequivocally using a 380 bp DNA probe specific for a major genomic repeat sequence; its isoenzyme profile distinguished it clearly from T. simiae and three strain groups of T. congolense: savannah, riverine-forest and kilifi.

Trypanosoma simiae in the white rhinoceros (Ceratotherium simum) and the dromedary camel (Camelus dromedarius)

Trypanosoma simiae was identified as the cause of a disease outbreak in dromedary camels (Camelus dromedarius) introduced to Tsavo East National Park, confirming the susceptibility of camels to this pathogen. T. simiae was also isolated from a new host, the white rhinoceros (Ceratotherium simum) through xenodiagnosis with a susceptible tsetse species (Glossina morsitans centralis). A white rhinoceros showed some evidence of anaemia and lymphopaenia when harbouring T. simiae, but did not suffer any long-term health effects.

Detection of trypanosome infections in the saliva of tsetse flies and buffy-coat samples from antigenaemic but aparasitaemic cattle

Relatively simple protocols employing non-radioactive DNA probes have been used for the detection of African trypanosomes in the blood of mammalian hosts and the saliva of live tsetse flies. In combination with the polymerase chain reaction (PCR), the protocols revealed trypanosomes in buffy-coat samples from antigenaemic but aparasitaemic cattle and in the saliva of live, infected tsetse flies. Furthermore, the protocols were used to demonstrate concurrent natural infections of single tsetse flies with different species of African trypanosomes.

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.

In vitro assays to determine drug sensitivities of African trypanosomes: a review

In vitro test methods have been developed both for determining the sensitivity of isolates of pathogenic African trypanosomes and for evaluating new compounds for antitrypanosomal activity. The principles of the assays and their main advantages or drawbacks are presented and discussed. In vitro assays which do not require trypanosomes pre-adapted to culture conditions are the Drug Incubation Infectivity Test (DIIT) and the [3H]Hypoxanthine Incorporation Assay. Chemosensitivity tests which do require continuous growth of trypanosomes in vitro include photometric, fluorescence, growth inhibition, long-term viability and metacyclic incubation assays. Evidence is presented to use metacyclic or bloodstream forms in such assays but to avoid procyclic trypanosomes. The drug sensitivity of a homogeneous trypanosome population can be quantified by using photometric, fluorescence or growth inhibition assays lasting 1-3 days. Small numbers of resistant organisms hidden in a sensitive population can be detected employing long-term viability assays (7-10 days). Final selection of the assay to be employed will depend on the parameter to be investigated, and the equipment available.

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.

Trypanosoma (Nannomonas) congolense: molecular characterization of a new genotype from Tsavo, Kenya

Trypanosoma (Nannomonas) congolense comprises morphologically identical but genetically heterogeneous parasites infective to livestock and other mammalian hosts; three different genotypes of this parasite have been described previously. Restriction enzyme fragment length polymorphisms (RFLPs) in both kinetoplast DNA minicircle and nuclear DNA sequences, and randomly amplified polymorphic deoxyribonucleic acid (RAPD) patterns have been used here to demonstrate the existence of another type of T. (N.) congolense that is genotypically distinct from those that have so far been characterized at the molecular level. A highly repetitive, tandemly arranged DNA sequence and oligonucleotide primers, for use in polymerase chain reaction (PCR) amplification are described, which can be used for specific identification of the trypanosome and its distinction from others within the Nannomonas subgenus.

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

A recently described simple kit for isolating African trypanosomes in vitro (KIVI) was tested further with blood samples from man and other animals in Côte d'Ivoire and République du Congo. A high rate of success was achieved, with positive cultures being found 5-36 d after inoculation. The method was also of value in diagnosis. Parasitaemia was initially detected by the haematocrit method; in addition, the mini-anion exchange column was used for human blood and lymph fluid from patients with swollen glands was examined. The card agglutination test (CATT) was applied to the human blood samples. In Côte d'Ivoire, all 5 parasitaemic patients, who were also positive by CATT, yielded positive KIVI cultures. Of 15 animals, 2 parasitaemic and 10 apparently aparasitaemic individuals gave positive cultures. In the Congo, none of the 22 animals was parasitaemic and none gave a positive culture. Of 647 human subjects initially screened, 61, mostly with a positive CATT, were examined by KIVI; 20 gave positive cultures. Seven of these cultures originated from patients in whom no trypanosome had been seen in blood or lymph fluid, although blood from 2 parasitaemic patients failed to yield positive KIVI cultures. Some patients with CATT-negative whole blood and/or serum were positive by KIVI.

Sensitive detection of trypanosomes in tsetse flies by DNA amplification

African trypanosome species were identified using the Polymerase Chain Reaction (PCR) by targeting repetitive DNA for amplification. Using oligonucleotide primers designed to anneal specifically to the satellite DNA monomer of each species/subgroup, we were able to accurately identify Trypanosoma simiae, three subgroups of T. congolense, T. brucei and T. vivax. The assay was sensitive and specific, detecting one trypanosome unequivocally and showing no reaction with non-target trypanosome DNA or a huge excess of host DNA. The assay was used to identify developmental stage trypanosomes in the tsetse fly. The use of radioisotopes was not necessary and mixed infections could be detected easily by incorporating more than one set of primers in a single reaction. The use of crude preparations of template made the process very rapid. The methodology should be suitable for large-scale epidemiological studies.

The Tsetse Research Laboratory

The Tsetse Research Laboratory in Bristol was opened in December 1962, with the initial objective of developing techniques for rearing tsetse flies on a large scale outside Africa. Its work has, however, extended greatly since then. This article highlights the research undertaken at the Laboratory, not only on the breeding of tsetse flies but also on various aspects of their biology and control.