[Behavioral interactions and rhythms of activity of Glossina palpalis gambiensis and G. tachinoides (Diptera: Glossinidae) in a forest gallery in Burkina Faso]. / Interactions comportementales et rythmes d'activité de Glossina palpalis gambiensis et G. tachinoides (Diptera : Glossinidae) en galerie forestière au Burkina Faso.

Glossina palpalis gambiensis and G. tachinoides are the main vectors of human and animal trypanosomoses in West Africa. In some parts of their distribution area, they co-exist in sympatry, but little is known about their interactions. This study aimed to explore their respective flight height and daily activity when co-existing or alone. Attractive targets were used, made of a black/blue/black cloth covered with adhesive film, so that all tsetse that landed were caught. The study was conducted in two areas in South Burkina Faso: Kartasso, upstream the Mouhoun river, where G. p. gambiensis is the only tsetse occurring; and Folonzo, on the Comoé river, where both species occur. Out of more than 3,800 tsetses caught in total, in Folonzo, G. tachinoides occurred at higher densities than G. p. gambiensis (84 vs 16% of the total densities). The mean height of capture was 55 cm for G. tachinoides, and 65 cm for G. p. gambiensis. As a comparison, in Kartasso where G. p. gambiensis is alone, the mean height of capture was 46 cm, these differences being statistically significant. In average, females were caught higher in altitude than males, and the two species showed a similar activity profile in the day. These results are discussed in the light of differences in the nature of the forest gallery, or possible interspecies competition behaviour in relation with their limited energy metabolism and flight capacities, or also with species differences in landing behavior, linked to host feeding detection. These observations have consequences on control tools releasing attractive odours, which may have contrasted efficacy depending of the flight height of the species.

Trapping tsetse flies on water.

Riverine tsetse flies such as Glossina palpalis gambiensis and G. tachinoides are the vectors of human and animal trypanosomoses in West Africa. Despite intimate links between tsetse and water, to our knowledge there has never been any attempt to design trapping devices that would catch tsetse on water. In mangrove (Guinea) one challenging issue is the tide, because height above the ground for a trap is a key factor affecting tsetse catches. The trap was mounted on the remains of an old wooden dugout, and attached with rope to nearby branches, thereby allowing it to rise and fall with the tide. Catches showed a very high density of 93.9 flies/"water-trap"/day, which was significantly higher (p < 0.05) than all the catches from other habitats where the classical trap had been used. In savannah, on the Comoe river of South Burkina Faso, the biconical trap was mounted on a small wooden raft anchored to a stone, and catches were compared with the classical biconical trap put on the shores. G. p. gambiensis and G. tachinoides densities were not significantly different from those from the classical biconical one. The adaptations described here have allowed to efficiently catch tsetse on the water, which to our knowledge is reported here for the first time. This represents a great progress and opens new opportunities to undertake studies on the vectors of trypanosomoses in mangrove areas of Guinea, which are currently the areas showing the highest prevalences of sleeping sickness in West Africa. It also has huge potential for tsetse control using insecticide impregnated traps in savannah areas where traps become less efficient in rainy season. The Guinean National control programme has already expressed its willingness to use such modified traps in its control campaigns in Guinea, as has the national PATTEC programme in Burkina Faso during rainy season.

[Distribution and ecology of the Savannah human African trypanosomiasis vectors in disturbed forest zone in south Cameroon: about case in the Doumé forest]. / Distribution et écologie des vecteurs de la trypanosomose humaine africaine de type savanicole en zone de forêt dégradée au sud Cameroun: cas du foyer de Doumé.

Vector control through trapping in the foci of humid forest areas is rather difficult because of the wide spreading of tsetse flies and transmission sites of human African trypanosomiasis. In fact, traps should be a priori set up everywhere to stop the transmission. The identification of the disease transmission sites enables efficient trapping through localisation of dangerous tsetse flies habitats needing vector control measures. The study of adult tsetse flies and teneral tsetse flies spatial distribution and human vector contacts was conducted in Doumb to determine the transmission of human African trypanosomiasis for efficient vector control. Glossina fuscipes fuscipes was the only tsetse fly captured with a very low apparent density of 0.13 tsetse flies per trap and per day. Furthermore, the disease transmission in the focus was not found uniform. In fact, human vector contacts are high in two villages (Paki and Mendin) located in the highly disturbed forest zones. These contacts occur in humid shallows where teneral tsetse flies were only captured around streams and forest galleries. The Doumé focus presents therefore characteristics of savannah focus where river banks and nearby biotopes are the main target sites for vector control campaigns.

Wild fauna as a probable animal reservoir for Trypanosoma brucei gambiense in Cameroon.

In order to study the existence of a wild animal reservoir for Trypanosoma brucei gambiense in South Cameroon, blood was collected from wild animals in three human African trypanosomiasis foci and from a nonendemic control area. The 1142 wild animals sampled belonged to 36 different species pertaining to eight orders (407 primates, 347 artiodactyls, 265 rodents, 54 pangolins, 53 carnivores, 11 saurians and crocodilians, and five hyraxes). QBC and KIVI tests detected trypanosomes on 1.7% (13/762) and 18.4% (43/234) of animals examined, respectively. Using specific primers, T. brucei non-gambiense group 1 DNA was detected on 56 animals (4.9%). This infection rate was 5.3% in the endemic zone and 3.8% in the control zone. Of the 832 animals of the endemic zone, PCR revealed T. b. gambiense group 1 DNA in 18 (2.2%). These hosts included two rodents, two artiodactyls, two carnivores and two primates. T. b. gambiense group 1 was absent from animals from the nonendemic zone. A decrease in the prevalence of T. b. gambiense group 1 was observed in wild animals from the Bipindi sleeping sickness focus after a medical survey and vector control in this area. The epidemiological implications of these findings remain to be determined with further investigations.

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.

Measurement of risk in endemic areas of human African trypanosomiasis in Côte d'Ivoire.

An index of epidemiological risk was developed for the foci of human African trypanosomiasis (HAT) in the forest zone of Côte d'Ivoire, based on the following characteristics of Glossina palpalis palpalis populations: daily survival rate, apparent density of teneral males and females, and frequency of human-fly contact. The index agreed well with HAT prevalence. It varied according to ethnic groups and with seasonal changes in agricultural activities and fell rapidly to zero following the start of an anti-vector control campaign. Further studies in different biogeographical zones are desirable in order to substantiate the validity of the index.

Diagnosis of human trypanosomiasis, due to Trypanosoma brucei gambiense in central Africa, by the polymerase chain reaction.

During a mass screening of sleeping sickness conducted in 1998 and 1999, and involving 27,932 persons in Cameroon and the Central African Republic, we tested the polymerase chain reaction (PCR) on whole blood for the diagnosis of human African trypanosomiasis due to Trypanosoma brucei gambiense. The 1858 samples obtained were from 4 groups: 155 infected patients, 1432 serological suspects detected by the card agglutination test for trypanosomiasis (CATT), 222 negative controls living in the prospected area (negative with the CATT and parasitological methods), and 49 negative controls (CATT and parasitological methods) and unexposed to the disease (Europeans). The technique of DNA extraction used made it possible to preserve the blood samples in the field. The primers used were specific for T. brucei s.l. Only 1 patient was PCR negative, and 3 of the negative controls, exposed to the disease, were PCR positive. Among the 1432 serological suspects, only 50 were PCR positive. During the 6-month follow-up after the surveys, the 3 negative controls, who were initially positive by PCR, were found to be negative. These initial positive PCR results are unlikely to have been due to a cross-reaction with T. brucei brucei, which is non-pathogenic for man, but are more likely to have resulted from a mislabelling of sample tubes. All control individuals, exposed or not to the disease, were negative by PCR. The PCR-negative patient was possibly a registration error. Among 50 PCR positive serological suspects, 39 of them were re-examined. Five were found to be positive by the kit for in-vitro isolation of trypanosomes, representing an increase in patients of almost 13%. At the end of the study, 160 patients were diagnosed, and the PCR was positive for 159 of them (99.4%). Moreover, the PCR made it possible to reduce the number of suspects to be re-examined (50 instead of 1432; a reduction of 96.5%).

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.

Human immunodeficiency virus infection and human African trypanosomiasis: a case-control study in Côte d'Ivoire.

To assess the association between human immunodeficiency virus (HIV) infection and human African trypanosomiasis (HAT) in Côte d'Ivoire, West Africa, a cross-sectional case-control study was conducted on 301 HAT patients recruited in the main foci of the country. For each HAT patient, 3 controls, matched for sex, age and residence, were selected. Data relating to socio-demographic factors and potential risk factors for Trypanosoma brucei gambiense and HIV infections were obtained, and serum samples were collected for HIV-1 and HIV-2 tests. A positive test consisted of enzyme immunoassay reactive to HIV-1, HIV-2 or both and confirmed by a synthetic peptide test or Western blot. Data were analyzed using conditional logistic regression with EGRET software. No statistically significant difference was found between the prevalence of HIV infection in HAT patients and controls (4.3% and 3.5% respectively; crude odds ratio (OR) 1.28, 95% confidence interval (CI) 0.65-2.50). In multivariate analysis, allowance for 5 covariates did not change the association between the 2 infections (adjusted OR 1.27, 95% CI 0.64-2.52). Although this study had limited statistical power, no significant association was found between HIV infection and T.b. gambiense infection in rural Côte d'Ivoire. Studies are needed to determine whether HIV infection influences the clinical course of HAT, a question not addressed in the present study.

Multiple trypanosome infections in wild tsetse in Côte d'Ivoire detected by PCR analysis and DNA probes.

Trypanosomes were isolated from the midguts of Glossina palpalis palpalis, G. pallicera pallicera and G. nigrofusca nigrofusca captured around the village of Guediboua, South West of Daloa in Côte d'Ivoire. Seventy of the 124 isolates, obtained from 688 flies, were examined for four different kinds of trypanosome using the Polymerase Chain Reaction (PCR). Prevalences were: Trypanozoon 46%, riverine-forest T. congolense 86% and savannah T. congolense 54%. Only 29 samples were examined for T. simiae but it was not detected. Just 30% of the infections involved a single kind of trypanosome; the remainder were mixtures either of two (37%) or all three (27%) of the target organisms. 30 of the 70 isolates examined by PCR were successfully amplified to provide material for DNA probe hybridization. To a large extent, DNA probes confirmed the PCR results; all (28/28) of the riverine-forest and 82% (18/22) of the savannah T. congolense infections were identified. However, only 8% (1/13) of the PCR positives for Trypanozoon hybridized with the appropriate DNA probe. No T. simiae or T. godfreyi infections were identified using DNA probes but a large proportion (97%) (29/30) of the probed midguts were shown to contain Kilifi T. congolense. Four isolates out of 70 could not be identified by any method. There was no obvious association between the different species of flies and the infecting trypanosomes.

A new method for identifying blood meals of human origin in tsetse flies.

A new sensitive technique using the electrophoresis of superoxide dismutase to distinguish between tsetse blood meals of human and non-human origin is described. In Côte d'Ivoire, 602 blood meals were collected; 170 were from man (28.3%), 377 from animals (62.6%) and 55 were unidentified (9.1%) because no pattern was observed. When calculating the index of epidemiological risk, it is strongly correlated with the incidence of sleeping sickness cases.

Infection rate of Trypanosoma brucei s.l., T. vivax, T. congolense "forest type", and T. simiae in small wild vertebrates in south Cameroon.

In order to identify the infection rate of trypanosome species infecting wild animals in four localities (Bipindi, Campo, Fontem and Nditam) of southern Cameroon, 1,141 wild animals were sampled. These animals belonged to 36 species grouped in 8 orders including 407 primates, 347 artiodactyls, 264 rodents, 54 pangolins, 53 small carnivores, 11 saurians and crocodilians and 5 hyraxes. PCR using specific primers for Trypanosoma vivax, T. brucei s.l., T. congolense "forest type", and T. simiae showed that 18.7% of the animals were infected by at least one of these trypanosome species. A positive PCR result may not indicate absolutely an active infection because PCR can detect also transient infections. T. vivax (Duttonella) had the highest infection rate (9.5%) and was found in almost all the host orders studied. T. brucei s.l. mostly infected primates, rodents and some duikers (Cephalophus dorsalis and C. monticola). Trypanosomes of the subgenus Nannomonas had a lower infection rate of 5.5% (2.4% for T. simiae and 3.1% for T. congolense "forest type"). They were harboured mainly by primates, ungulates and rodents. Trypanosome infection rates were highest in Nditam (24.5%) and Bipindi (21%). T. brucei s.l. (Trypanozoon) had its maximum infection rate of 10.4% in Bipindi. The "Quantitative Buffy Coat" (QBC) and Kit for in vitro isolation techniques were used to identify 48 (6.1%) infected animals. 13 were positive using QBC, and 42 were positive by KIVI. However, PCR was negative on 16 of these infected animals, probably due to infections with other trypanosome species. This study showed that trypanosomes of the subgenera Duttonella, Nannomonas and Trypanozoon could infect small wild vertebrates as has been shown for large ungulates and carnivores. The presence of T. brucei s.l. in a large range of wild animals strengthens the hypothesis of the existence of a wild animal reservoir of T. b. gambiense in Cameroon.

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 distribution and bloodmeal preferences of Glossina palpalis palpalis in the forest focus of Zoukougbeu (Ivory Coast). Epidemiological consequences]. / Répartition spatiale et préférences trophiques de Glossina palpalis palpalis dans le foyer forestier de Zoukougbeu (Cote d'Ivoire). Implications épidémiologiques.

In the sleeping sickness focus of Zoukougbeu (Côte d'Ivoire), in the cropping areas which are favourable for disease transmission, more than a quarter of the flies collected were found to have fed on domestic pigs. The sites where Glossina palpalis palpalis was caught fed on these animals were concordant with the sites where the patients were present. These results might indicate that in Zoukougbeu, but perhaps also in other sleeping sickness foci, the pig could play an active role in disease transmission, allowing the parasite to spread widely via the tsetse.

[Age group distribution of Glossina palpalis palpalis females in plantations and shallow water of the forest region of Côte d'Ivoire. Relation to the prevalence of sleeping sickness]. / Répartition des groupes d'âge de Glossina palpalis palpalis femelle dans les plantations et les talwegs en zone forestière de Côte d'Ivoire. Relation avec la prévalence de la maladie du sommeil.

In epidemiologically dangerous biotopes of foci with high prevalence of Human African Trypanosomiasis (HAT), different female age groups (nulliparous, young parous, old parous) were observed in the same proportions. On the contrary, in areas without HAT or in low prevalence foci (< 0.2%), these proportions significantly differed. Female age group distribution in epidemiologically dangerous biotopes could thus be a good indication by which to guide the control of Human African Trypanosomiasis (HAT).

[The focus of human trypanosomiasis in Campo (Cameroon). History and endemic situation in 1998]. / Le foyer de trypanosomose humaine de Campo (Cameroun). Historique et situation de l'endémie en 1998.

For the first time in the last thirteen years, the human sleeping sickness focus at Campo, spanning the Cameroon-Equatorial Guinea border areas, has been prospected. The screening was carried out simultaneously on both sides of the border. This focus has been known since the beginning of the century but, contrary to what took place in other well-known foci in bordering countries south of Cameroon, either in the 1920s or the 1980s--there has never been an epidemic outbreak in that area. Such an epidemiological situation makes this focus particularly interesting. Though still active, trypanosomiasis is not very manifest. According to passive screening carried out in recent years, the estimated prevalence ranges between 0.2 and 0.5%. For this screening, 5,255 persons were examined on the Cameroonian side of the focus (90.6% of the census population). The serological screenings were carried out with the CATT 1.3, which is the CATT generally used in screening, and with the latex CATT which associates LiTat 1.3, 1.5 and 1.6. The search for trypanosomes was made by testing the lymph nod juice in presence of adenopathy and in the blood by Quantitative Buffy Coat (QBC), the mini anion exchange centrifugation (mAEC), as well as the in vitro culture using the kit for in vitro isolation of trypanosomes (KIVI) for individuals suspected to be serologically positive. 16 patients were identified in Cameroon but none in Equatorial Guinea. The results show that the Campo focus is active only on the Cameroonian side, centred on the village of Ipono with a limited prevalence (0.3%). The persisting epidemic is most likely to be associated with the presence of pigs carrying the Trypanosoma brucei gambiense which was identified during the study in Ipono. The strain that we isolated was studied by isoenzyme electrophoresis on cellulose acetate. Its zymodeme is the same as that of the human strain isolated in Campo. With the collected epidemiological data, a concerted medical and entomological action could be planned within the limits of the village of Ipono to eradicate the disease. This action may be organised by the existing local health structures. During this study, the latex CATT proved to be more cost-effective than the CATT 1.3 since a similar result was reached requiring eight times less work at a lower cost. This remains to be confirmed in a hyperendemic focus.

[The control of the vectors of the sleeping sickness caused by Trypanosoma gambiense Dutton (author's transl)]. / La lutte contre les vecteurs de la maladie du sommeil à Trypanosoma gambiense Dutton.

In this review on tsetse control, the authors particularly stress the methods used at the present time against riverine species vectors of "Gambian sleeping sickness". The different kinds of insecticidal treatments, the means of ground and aerial application of residual or non-residual compounds as well as the planning of control campaigns are described. Besides, the authors show the present trends of the research on tsetse flies ecology, new insecticides, methods of spraying, biological control and the impact of tsetse control operations on the environment.

[Risk factors for human African trypanosomiasis in the endemic foci of Ivory Coast]. / Les facteurs de risque de la trypanosomiase humaine africaine dans les foyers endemiques de Cote d'Ivoire.

A case-control study on risk factors of Trypanosoma brucei gambiense human african trypanosomiasis was carried out in 111 patients diagnosed in the three main foci of Ivory coast. Each case was age and sex matched with one seronegative control living in the same locality. Based upon previous epidemiological surveys conducted in similar areas, the potential risk factors were identified and assessed using a standard questionnaire. The study demonstrates that in the forest area of Ivory coast human trypanosomiasis in a behavioral disease affecting mainly coffee and cocoa farmers. The allogenous populations coming from sudano-sahelian savannah are more exposed to the disease than other ethnic groups. People sleeping at the farm (encampments) are more likely to become infected than those living at the village (ODDS-Ratio = 4.5). People fetching water in natural holes and pools have an increased risk (ODDS-Ratio = 3.6). Cases reported more often than controls that they are foodstuffs dealers from the farms to the villages (ODDS-Ratio = 13.0). These results are consistent with data from previous studies. We identified preventable risk factors, upon which interventions should be carried out to reduce the incidence of the disease. The possibility of using these findings to improve sleeping sickness control programme in the forest areas of Ivory Coast is discussed.

[Risk factors for human African trypanosomiasis in the Bipindi region of Cameroon]. / Recherche des facteurs de risque de la trypanosomose humaine africaine dans le foyer de Bipindi au Cameroun.

In the course of two surveys carried out at the end of 1998 and beginning of 1999, sleeping sickness was diagnosed in a total of 43 people in the Bipindi region of Cameroon. This observation led us to investigate the mechanisms of transmission of human African trypanosomiasis in the epicentrer of the outbreak. A case-control study showed a particularly high risk of infection associated with hunting activities (Odds-Ratio: 2.87; CI 95%: 0.96-9.52). Interpretation of this finding in the light of local geographical features and current entomological data suggests that the higher risk in hunters is linked to the presence of a perennial vector population and absence of domestic pigs.