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A matrix model is used to describe the dynamics of a population of female tsetse flies structured by parity (i.e., by the number of larvae laid). For typical parameter values, the intrinsic growth rate of the population is zero when the adult daily survival rate is 0.970, corresponding to an adult life expectancy of 1/0.030 = 33.3 days. This value is plausible and consistent with results found earlier by others. The intrinsic growth rate is insensitive to the variance of the interlarval period. Temperature being a function of the time of the year, a known relationship between temperature and mean pupal and interlarval times was used to produce a time-varying version of the model which was fitted to temperature and (estimated) population data. With well-chosen parameter values, the modeled population replicated at least roughly the population data. This illustrates dynamically the abiotic effect of temperature on population growth. Given that tsetse flies are the vectors of trypanosomiasis ("sleeping sickness") the model provides a framework within which future transmission models can be developed in order to study the impact of altered temperatures on the spread of this deadly disease.

An agent-based model (AMB) used to simulate the spread of Human African Trypanosomiasis is presented together with the results of simulations of a focus of the disease. This model is a completely spatialized approach taking into account a series of often overlooked parameters such as human behaviour (activity-related movements), the density and mobility of the disease vectors – tsetse flies (Glossina spp.) – and the influence of other tsetse feeding hosts (livestock and wild animal populations). The agents that represent humans and tsetse flies move in a spatially structured environment managed by specialized location agents. Existing compartmental mathematical models governed by differential equations fail to incorporate the spatial dimension of the disease transmission. Furthermore, on a small scale, transmission is unrealistically represented by entities less than one. This ABM was tested with data from one village of the Bipindi sleeping sickness focus (southern Cameroon) and with obtained realistic simulations of stable transmission involving an animal reservoir. In varying different spatial configurations, we observe that the stability of spread is linked to the spatial complexity (number of heterogeneous locations). The prevalence is very sensitive to the human densities and to the number of tsetse flies initially infected in a given location. A relatively low and durable prevalence is obtained with shortening the phase I. In addition, we discuss some upgrading possibilities, in particular the linkage to a Geographical Information System (GIS). The agent-based approach offers new ways to understanding the spread of the disease and a tool to evaluate risk and test control strategies. To cite this article: G. Muller et al., C. R. Biologies 327 (2004).

A compartmental model of Gambian sleeping sickness is described that takes into account density-dependent migratory flows of infected flies. Equilibrium and stability theorems are given which show that with a basic reproduction number R0 below unity, then in the absence of reinvasion the disease goes to extinction. However, even a low prevalence rate among reinvading flies can then bring about significant equilibrium prevalence rates among humans. For a set of realistic parameter values we show that even in the case of a virulent parasite that keeps infected individuals in the first stage for as little as 4 or 8 months (durations for which there would be extinction with no infected reinvading flies) there is a prevalence rate in the range 13.0-36.9%, depending on whether 1 or 2% of reinvading flies are infected. A rate of convergence of the population dynamics is introduced and is interpreted in terms of a halving time of the infected population. It is argued that the persistence and/or extension of Gambian sleeping sickness foci could be due either to a continuous reinvasion of infected flies or to slow dynamics.

A microsimulation model of the spread of Gambian sleeping sickness is described. The model focuses on the randomness of epidemic trajectories brought about merely by the random nature of fly bites on humans. There is a high level of variability in the trajectories, primarily due to the small sizes of the populations involved. There is an inverse relationship between the probability of initial extinction and the size of an epidemic flare-up when the disease takes hold. When a stream of one infected fly enters the focus every 3 days, a low-level endemic can be sustained with less variability. Implications and further subjects of study are briefly discussed.

Les films de polyethylene utilises pour la fabrication du piege bipyramidal a mouches tse-tse en Republique Centrafricaine presentent des variations aleatoires dans leur coloration. Des experiences conduites sur Glossina fuscipes fuscipes a l’aide d’un nouveau protocole, combinant dans la meme experience, le carre latin et la competition de deux pieges en vis-a-vis, revelent qu’une coloration legerement moins intense du bleu diminuait significativement l’attractivite du piege. L’utilisation de polyethylene pour la fabrication de piege a mouches tse-tse presente de nombreux avantages mais demande de verifier l’homogeneite de sa coloration.

Existing attempts to estimate the survival rate of tsetse flies from ovarian age distributions generally assume that the population is stationary. The fact that the survival rate cannot be dissociated from the growth rate by these methods poses a problem. Under the assumption of a stable age distribution, we propose a maximum likelihood method to estimate the ‘apparent survival rate’ for three categories of females: nulliparous (β0), young parous (β1) and old parous flies (β2). The rate depends both on ‘real survival rates’ a0, a1 and a2, and a growth rate λ: β0 = a0/λ, β1 = a1/λ, and β2= a2/λ. We used a matrix model, which can be parameterized if the pupal survival rate and the pupal period are known. Replacing a0, a1 and a2 by β0,λ, β1λ, and β2λin the projection matrix, the problem amounts to calculating its dominant eigen-value λ, and hence a0, a1 and a2. The application to a field population of Glossina palpalis gambiensis Vanderplank in Burkina Faso showed there was a marked difference in survival rate according to age category. The average survival rate increased with age with decreasing variability. The results suggested that sampling (by trapping) may have had an effect on the dynamics of this tsetse population by ageing it artificially. This method may be a useful tool for monitoring tsetse control.

Glossina or tsetse flies, the vectors of sleeping sickqess,.form a unique group of insects with remarkable characteristics. They are viviparous with a- slow !hytlynof reppduction (one larva approximately every 10 days) determined by the regular ovulation df alternate ovaries. This unusual physiology enables the age of the females to be estimated by examining the ovaries. The resulting ovarian age structure of tsetse fly populations has been used to develop research into the demography of $etse flies. Several authors have proposed methods of estimating population growth rates from ovarian age distribution data. However, such methods are applicable only when the growth rate (h) is equal to 1 (i.e. the intrinsic rate of increase ris equal to O). In fact, in this type of estimation, the adult survival rate a (or equivalently the mortality rate) cannot be dissociated from the growth rate. Other independently determined demographic parameters must be used to remove this lack of identifiability. We have built a matrix model of the dynamics of tsetse fly populations which enables the growth rate to be calculated from the pupal survival, rate, the pupal period,apd the adult survival rate. Assuming that the age-groups of the population studied have reached a stable distribution, it i calculate the probabilities for the obsed@ sample of belonging to each of the age-groups, to construct a likelihood function and thus to obtain an estimate of the ‘apparent survival rate’ s = a/h If the pupal survival rate and the pupal period are known, a and h can then be calculated from s. The application of this method to data collected for over two annual cycles in a savannah habitat (Burkina-Faso) showed a high overall stability in the populations of Glossinupalpalis gambiensis. Seasonal fluctuations could be easily interpreted as being the result of climatic changes between the dry and rainy seasons.

L'auteur donne la description et le mode de fabrication du piège bipyramidal. Ce piège fait actuellement l'objet d'un programme d'évaluation en vraie grandeur dans le cadre d'une lutte anti-tsé-tsé autogérée par les éleveurs semi-nomades de République centrafricaine (Mbororo). Il est démontable, facilement transportable et ne demande aucune manipulation complexe. Le prix de revient d'un piège est d'environ 30 FF au maximum (1500 francs CFA).

Les auteurs décrivent la problématique du transfert de technologie que représente l'adoption par les éleveurs Mbororo de la lutte par piégeage. Cette lutte est dirigée contre le principal vecteur des trypanosomoses du bétail, Glossina fuscipes fuscipes, et utilise le piège bipyramidal. La vulgarisation de cette technique s'appuie sur les structures mises en place pour le développement de l'élevage en République centrafricaine. Les voies et les moyens de cette vulgarisation sont décrits et commentés.

Summary. — Based on author's data, collected during various sampling experiments of Glossina in central Africa, as well as on data from published or unpublished documents, the decline of some tsetse fly species of fusca group (= s.g. Austenina) are presented and discussed., Résumé. — L'auteur fait la synthèse de ses observations et de sa documentation concernant la raréfaction de certaines espèces de tsé-tsé du groupe fusca (= s.g. Austenina). La cause et l'importance de ces régressions sont discutées., Gouteux Jean-Paul. La raréfaction de tsé-tsé du groupe fusca en Afrique centrale (Diptera, Glossinidae). In: Bulletin de la Société entomologique de France, volume 96 (5), décembre 1991. pp. 443-449.

Preliminary trials of 12 models of the pyramid trap were carried out in the Congo on Glossina palpalis palpalis (Robineau-Desvoidy) using Latin square designs. The models were compared with the standard trap with which they differed either in the shape of the pyramid, the addition of a royal blue cloth skirt, or the pattern of the blue-black screen. A decrease in height and/or volume of the pyramid significantly reduced the capture rate. The standard tetrahedral pyramid was significantly superior to both the regular tetrahedral and the trihedral pyramid. The addition of a royal blue cotton skirt modified both the attractiveness and effectiveness of the trap. However, although the attractiveness was probably increased, the skirt may have deterred the flies from entering the pyramid; the best results were obtained with the largest openings. The modification of the blue-black screen pattern may be a way to increase the attraction of flies to the trap. Although no model was found to be significantly superior to the standard, certain gave interesting results which should be investigated further.

A density-dependent model is used to describe the dynamics of an open population of tsetse flies (Diptera: Glossinidae). Immigration (or emigration) takes place when the total population is below (or above) a biologically determined threshold value. The population is also subjected to birth and death rates, as well as to the risk of being trapped (continuously or intermittently). During trapping the population decreases toward a ‘low’ equilibrium population and when trapping ceases the population starts recovering and increases toward a ‘high’ equilibrium. The model is fitted using data collected on trapped flies in four experiments. The first one was conducted with ‘intermittent trapping’ (i.e. several trapping-recovery cycles) on Glossina fuscipes fuscipes Newstead in the Central African Republic (Bangui area). In the other experiments, trapping data on Glossina palpalis palpalis (Robineau-Desvoidy) was collected in ‘aggregate’ form over several days at a time. Two of these were in Congo-Brazzaville (Bouenza area) and one in the Ivory Coast (Vavoua focus). Estimates are derived for the low and high equilibrium values as well as the trapping rate. The estimated effect of sustained trapping is to reduce the population to low equilibrium values that are 85–87% lower than the levels without trapping. The effects of the natural intrinsic growth and of the migration flows cannot be estimated separately because in the model they are mathematically indistinguishable.

Tsetse fly guilds usually comprise two or three species. However, the presence of only one species often indicates that anthropic modifications have occurred in the habitat. On the other hand, more than three species are seldom observed in the same zone and the presence of five is extremely rare. Previous detailed studies have always focused on a single species, without taking into account interactions between species. The authors present the results of observations carried out in Cote d'Ivoire on a guild consisting of Glossina palpalis, G. pallicera, G. nigrofusca, G. longipalpis and G. fusca. Glossina have unusual physiological characteristics: both sexes feed exclusively on blood, they have a highly developed larviparity associated with a slow rhythm of reproduction (one larva about every ten days) and a long life expectancy (up to nine months). The authors report on the size of the flies, the hosts, feeding habits, ecodistribution, resting-places, flying heights, circadian activity and seasonal dynamics of tsetse fly populations in order to understand the organization of this guild. Each species feeds indiscriminately on a wide spectrum of hosts without a particular preference. Different species shared habitat (ecodistribution) and time (circadian and annual cycles). Thus, during an annual cycle, there is always a slight time-lag between the density peaks of G. palpalis and G. pallicera, the peak of the dominant species immediately preceding that of the dominated species. In a village area, 77% of the variations in density of G. pallicera were accounted for by the previous variations in density of the dominant species (G. palpalis). Experiments show that G. pallicera and G. nigrofusca immediately invade anthropic areas from which G. palpalis has been partially removed by trapping. These species thus appear to confront each other in a global dynamic equilibrium. This suggests that there is a ‘conflicting coexistence’ between the cohabiting species. Whereas the reason for such a process is quite obvious, how it occurs still remains to be explained. Other observations may provide a clue. For example, the sex ratios of both the main species fluctuate in opposite phases during the annual cycle. This strongly suggests that interspecific interactions occur through sexual mediation. Finally, the authors discuss the consequences of dynamic cohabitation on disease systems (trypanosomes, tsetse flies, hosts) and on control possibilities.

Vector control and the detection (followed by treatment) of infected individuals are the two methods currently available for the control of sleeping sickness. The basic reproduction rate of a compartmental model is used to analyse and compare the two strategies. The efficiency of each strategy will depend on two epidemiologic parameters; the intrinsic contamination rate Q (closely related to the index of new contaminations) that captures the potential spread of the disease, and the intrinsic removal rate from the first stage (intrinsic to the particular trypanosome strain and to the population's susceptibility). The model shows that when the intrinsic removal rate is low (that is, when there is a long first stage characteristic of an endemic situation) the detection of sick individuals is more efficient than vector control. The situation is reversed when the removal rate is high (in an epidemic situation). The conclusions of the analysis are shown to be in general agreement with results obtained in two different sleeping sickness foci of Central Africa.

(1996). Detection of infections of Trypanosoma grayi in Glossina fuscipes fuscipes in the Central African Republic. Annals of Tropical Medicine & Parasitology: Vol. 90, No. 5, pp. 555-557.

Some characteristics of tsetse fly population dynamics were investigated using a matrix model. To take into account the peculiarities of the tsetse fly life cycle, the classic Leslie model was modified. Our model integrated the physiological age group of Glossina females, the pupal and adult survival rate and the pupal life span. The limit of the growth rate was studied and the results were satisfactory when compared with data of tsetse fly mass rearing. The effect of adult and pupal survival rates on the growth rate was examined and confirmed the importance of adult survival. The sensitivity analysis showed that the growth rate was particularly sensitive to change in the survival rate of young nulliparous females. This matrix model, directly accessible to the experimenter, enhanced our understanding of tsetse population dynamics.

We present a five-variable compartmental model for the spread of Trypanosoma brucei gambiense, the parasite responsible for the transmission (through tsetse flies) of sleeping sickness in Central Africa. The model’s equilibrium points depend on two “summary parameters”: gr, the proportion removed among human infectives, and R0, the basic reproduction rate. Stability results are obtained for the origin but not for other equilibrium points. A two-variable simplified version of the model is presented and the stability of all its equilibrium points can be investigated analytically. Both models are applied to the Niari focus of Central Africa and used to test the impact of a vector control strategy. The models’ results are in agreement with the extinction of the epidemic that was brought about by a fifty percent decrease in vector density.

Le suivi d'un réseau d'élevage de 19 troupeaux zébus Mbororo a été mis en place pour évaluer l'impact d'une lutte par piégeage contre Glossina fuscipes fuscipes limitée aux abreuvoirs. Ce programme s'inscrit dans la stratégie d'une lutte intégrée contre les trypanosomoses bovines en République centrafricaine. Le piégeage permet d'abaisser les densités de G. f. fuscipes et de diminuer les prévalences trypanosomiennes. Ces effets se traduisent par l'amélioration des valeurs de l'hématocrite et par la diminution du nombre de traitements trypanocides réalisés. L'impact sur les productivités est plus difficile à mettre en évidence sur une courte période ; il apparaît cependant manifeste sur les paramètres calculés.

Search for a new trap model, in order to enable the Peul breeders to control Glossina fuscipes fuscipes was made by studying separately the capture system, the design of the trap, the building materials. The result was the development of a pyramidal trap in polyester mosquito netting and polyethylene blue and black sheets. It is not impregnated with any insecticide, but uses a dry capture device which leads to killing and keeping of the flies. Its efficiency is 3 to 4 times larger than that of the classical Roubaud cage. The trap was also more efficient than any other biconic, pyramid and monoconic traps already known or designed. Some problems linked to the latin square experimental method and the interest of an insecticidal impregnation or not of the trap are discussed.

Tsetse distribution maps are a useful tool for both research workers studying trypanosomiasis and animal and human health authorities. They enable the potential vectors in the country to be identified and provide rapid information about their geographic distribution. Considerable work is involved in drawing up these maps, including the compilation of publications, unpublished reports and often the examination of entomological collections. These maps however require frequent up-dating. Ford and Katondo revised their first edition of tsetse distribution maps (1971, 1973) in 1975 and 1977. These maps were revised again by Katondo (1984) and subsequently by Moloo (1985). The revision by Moloo notably included the presence of Glossina nashi Potts 1955 in Gabon, where recent captures have been simultaneously recorded by Itard et al. (1984) and Leack and Jannin (1984). Until now this species had been recorded in Gabon by the observation of a single specimen only, reported by Machado (1959). The publication by Moloo (1985) includes clear synoptic tables and represents a significant event in that it is the most recent revision. We would like to contribute by up-dating records and also clarify some points which, in our opinion, raise difficulties. Recently, Gouteux et al. (1987) reported the discovery of G. calliginea in the Congo and the new species G. frezili, occurring in the Congo and Gabon (Gouteux, 1987). The presence of G . medicorum in Zaire and the Central African Republic should be investigated. Indeed, in a recent review, Makumyaviri (1986) did not mention this species in Zaire, nor did Finelle et al. (1963) in the Central African Republic. The presence of G. medicorum in Gabon, recorded originally by Maillot (1956, 1961), refers in fact to G. frezili (Gouteux, 1987). On the other hand, Moloo (1985) did not record G. medicorum in Togo or Guinea (Conakry) although it had been reported in Togo by Rickenbach (1961) and in Guinea by Maillot (1961). The presence of G . calliginea in Ghana and the Central African Republic should, according to

The card agglutination test for trypanosomiasis (CATT) was evaluated and compared to the classical immunofluorescent antibody test (IFAT) in the immunological diagnosis of Gambian trypanosomiasis. Tests were performed on serum and whole blood. Cross-reactions were found in the CATT with sera from patients suffering from parasitic infections other than sleeping sickness, but could be largely overcome by selecting 1/10 as the specific threshold dilution. At 1/40 dilution no false positive result was observed in the IFAT. At the specific threshold dilution, the sensitivity of IFAT was 94.7%, compared with 91.6% for the CATT. On whole blood, a more convenient sample in the field, IFAT specificity (100%) was greater than that of the CATT (94.3%), as was its sensitivity (92% compared with 82.5%). In view of its simplicity and rapidity of execution, the CATT is an efficient serological test to detect new foci. When greater sensitivity is required, IFAT should be preferred to CATT.

1934 Bantus and 379 Pygmies were investigated for Loa loa and Mansonella perstans filariasis in 7 villages in the Chaillu forest of the Congo. Bantus were more frequently infected with L. loa than Pygmies (18·9% of microfilariae carriers compared with 10·6%). In individuals over 30 years of age, males were more frequently infected than females. Microfilarial densities increased until the age of 20 years and then remained stable. Parasite load was not significantly different in the two ethnic groups. For mansonelliasis, the microfilarial rate was higher in the Pygmies (67·5% compared with 22·0%) and males of the 2 groups were more frequently infected than females. Microfilarial load was also higher in Pygmies than in Bantus (mean microfilarial densities (MfD 50) 13 and 2 respectively). In the Pygmy group, MfD 50 for M. perstans increased with age whereas it remained stable in the Bantus. 53·8% of the 249 questioned persons had experienced worm migration under the conjunctiva. Both ethnic groups were equally exposed to the vectors of L. loa and reasons for the difference in prevalence of microfilaria carriers are discussed. For mansonelliasis increased contact with vectors may explain the higher degree of infestation observed in Pygmies. Other filariases were infrequent in ( Mansonella streptocerca ), or absent from ( Onchocerca volvulus and Wuchereria bancrofti ), the study area.

Un des moyens de lutte contre les glossines est de les attirer sur des supports artificiels impregnes d'insecticide. Jusqu'a present, les supports utilises etaient de simples ecrans bidimentionnels de tissu bleu. Nous decrivons un nouveau modele a ecrans croises bleu-noir dont la tridimentionnalite augmente l'attractivite. Un toit de plastique protege les ecrans de la pluie et augmente la remanence de l'insecticide. Des rabats de tulle moustiquaire et de plastique creent un corps de piege interne dans lequel les glossines peuvent penetrer et avoir un contact prolonge avec l'insecticide. Modifie pour la capture, ce modele est au moins aussi efficace que le piege biconique. Sa grande simplicite de fabrication le rend trois fois moins couteux que ce dernier. Il a permis de reduire les populations de glossines de 98% en une semaine dans le foyer de trypanosomiase humaine de Kayes, au Congo. Avec une reimpregnation mensuelle, ces resultats sont maintenus depuis plus de 8 mois. Summary A new screen-trap for tsetse control: Description and trials in a focus of human trypanosomiasis in the Congo One method for control of tsetse flies is to attract them to artificial structures impregnated with insecticide. Up to now the structures used have been simple two dimensional screens of blue fabric. This paper reports a new model with two intersecting blue and black screens in which the three dimensional nature of the trap increases its attractiveness. A plastic roof protects the screens from rain and increases the residual life of the insecticide. Mosquito net and plastic flaps create partially enclosed spaces which the tsetse can enter and in which they have prolonged insecticidal contact. A design modified to capture the flies was at least as efficient as a bi-conical trap. The extreme simplicity of construction makes the cost of the new trap only a third of the bi-conical. In one week the new trap achieved a 98% reduction in the tsetse population in the Kayes focus of human trypanosomiasis in the People's Republic of the Congo. With monthly re-impregnation this level of control was maintained for more than 8 months.

Cet article presente les resultats acquis au cours d’un programme de recherches sur l’ecologie des glossines en secteur pre-forestier de Cote-d’Ivoire.Le principal outil d’investigation utilise est le piege biconique Challier-Laveissiere.Parmi les 5 especes de glossines presentes dans la region du foyer de Maladie du Sommeil a Trypanosoma b. gambiense de Vavoua, Glossina p. palpalis, G. pallicera et G. nigrofusca sont les plus abondantes. L’etude comparative des populations de glossines des zones de plantations et des terroirs villageois a porte sur leurs dynamiques, les relations inter-specifiques, leurs cycles d’agressivite et leurs preferences trophiques.Le contact homme-mouche est tres etroit lorsque l’habitat humain est disperse au sein des plantations. Au niveau des villages, les glossines se nourrissent surtout sur les porcs.Ces resultats permettent d’envisager des mesures preventives par modification des modes d’occupation de l’espace par l’homme, en plus des mesures de lutte antivectorielle par traitement chimique des lisieres ou utilisation d’ecrans impregnes d’insecticides.

Hypertrophied salivary glands are reported in tsetse for the first time from the Ivory Coast. Eleven cases were observed in 1,781 flies examined. Prevalence of this abnormality is given for Glossina palpalis, G. pallicera , and G. nigrofusca in Vavoua, a trypanosomiasis focus. No trypanosomal infection was detected by optical means in these enlarged glands.

Cet article presente differentes hypotheses possibles pour expliquer le phenomene connu sous le nom « d’effet de case » ou « contamination familiale ». Il s’agit : 1) de la transmission mecanique par des arthropodes hematophages contaminant des individus vivant ensemble. 2) d’une serie de repas interrompus pris sur plusieurs personnes par une glossine cycliquement infectante. 3) d’un facteur biologique familial. Ces differentes hypotheses sont discutees et presentees comme une introduction a une etude de la distribution spatiale et familiale des trypanosomes dans trois foyers congolais. Celle-ci montre une repartition aleatoire des malades dans les quartiers des villages, mais leur regroupement au niveau des habitations et des familles. Ce phenomene s’expliquerait par l’activite communautaire des membres des cellules familiales (deplacements, travaux aux champs, baignades) associee a un phenomene amplificateur, le plus probable etant les repas interrompus d’une glossine cycliquement infectante. Dans certains cas d’autres possibilites, telles que la transmission mecanique par glossines ou Aedes , ou encore un facteur biologique familial, peuvent etre envisagees.Ce phenomene, qui constitue l’une des caracteristiques epidemiologiques les plus remarquables la maladie du sommeil, a comme consequence, la surveillance etroite de l’entourage des malades.

Ecological surveys were carried out to assess the population characteristics and epidemiological importance of Glossina palpalis palpalis (Rob-Desv.), 1830 in the human trypanosomiasis focus of Vavoua in the forest zone of Ivory Coast. G. p. palpalis was widespread in all components of the ecosystem: forest, interstitial savannahs, coffee plantations, tracks and villages. Most flies were caught at the forest edge. Sex ratio and age composition of populations varied in relation to trapping sites. Open areas were dispersal places. Plantations provided resting, feeding and breeding sites giving rise to close man–fly contact. Here, teneral flies could become infected and later on transmit trypanosomes to plantation workers and their families. The role of man and domestic pigs together with that of fly behaviour and genetic factors in the transmission of the disease are discussed. Methods of tsetse control are suggested in the light of the findings.

Community participation in the control of tropical diseases is of major importance nowadays, particularly for sleeping sickness (Gambian trypanosomiasis). Indeed, the authoritarian measures used with success to control this disease during the colonial period are difficult to apply now. Moreover, in the Congo, cultural and financial restrictions are such that patients sometimes refuse treatment. Thus, it has become highly desirable for vector control to be carried out at the same time as the treatment of patients. Trapping tsetse flies (or Glossina) is an ingenious and effective anti-vectorial method which has been tested in 55 villages of the Congo. The blue-black pyramid trap used does not require insecticide impregnation, and is hung in the branches by means of a capture-bag containing diesel oil. These trials, conducted in the sleeping sickness focus of the Niari river, have demonstrated the feasibility of local communities taking over the responsibility for the traps, while at the same time revealing certain obstacles. Indeed, the efficacy of this method depends on the optimization of trapping. This involves the determination of strategic capture sites by periodically harvesting the flies and moving the traps in order to catch the maximum number of flies. It also involves regular maintenance of the traps (i.e. repairs, checking the capture bag, clearing vegetation...). However, although these activities would appear to be feasible at community level, they are not always carried out satisfactorily. This results in the insufficient viability of the traps and finally to the reinvasion of the treated area by the tsetse. This study presents aspects of the present-day Congolese socio-cultural environment characterized by the revitalization of traditional Bantou mysticism and religious worship. The possessors of the 'Vital Force' or Kundu (sorcerers and healers) are confronted at night in an 'over-reality' consisting of the visible reality together with innumberable beings and objects existing specifically in the invisible state. This nocturnal confrontation may modify the local balance of power and relationships, and is also thought to cause certain symptoms of sleeping sickness and other diseases. During the colonial period, Kundu was prohibited. Under the influence of the Christian church, and because of the progress of modern medicine, the power of the sorcerers and healers gradually decreased. Then, in the 1960s, the eruption of Marxism as an anti-religious theory, modified the balance of power once more.(ABSTRACT TRUNCATED AT 400 WORDS)

Human filariasis due to Loa loa is confined to the tropical rain-forest of Africa. In the same area, simian populations are infected with parasites which have no clear-cut morphological differences with human Loa and exhibit a nocturnal microfilarial periodicity (Duke and Wijers, 1958). Chrysops lungi and C. centurionis are probably responsible for their transmission among monkeys (Duke, 1955). Although it appears that human and simian strains of Loa have evolved in two separate host-vector complexes (Duke and Wijers, 1958), the possibility of a transmission of simian Loa to man cannot be ruled out. Fain et al. (1974) did observe in Zairian patients from the Mayumbe area Loa microfilariae with a nocturnal periodicity. On-the other hand, simian loiasis observations showing a marked diurnal periodicity were reported by Wanson and Rodhain (1953) and Fain (1978). It is most unlikely that C. Iangi and C. centurionis, which are strictly zoophilic, would be responsible for the transmission from monkey to man. Anthropophilic Chrysops species (C. silacea and C. dimidiata) are the only potential vectors (Duke, 1955). In our study area in the Congo, the Chaillu mountains, 5189 anthropophilic flies have been examined in one year. Of these, 3848 were C. silacea (74.2%) and 1341 were C. ditnidiata (25.8%). Host preferences of anthropophilic Chrysops were investigated with a view to identifying possibilities of transmission of Lou between simian and human hosts. To this end a total of 408 blood-meal samples from C. silacea (262 flies) and C. dimidiata (146 flies) were analysed according to a procedure described by Staak et al. (1981). 88.9% and 90.4% of the samples from C. silacea and C. dimidiata, respectively, originated from man, and the rest from hippopotamus, rodents, wild pigs, wild ruminants and monitor lizards. No bloodmeal from monkey was identified. Despite their propensity for coming into contact with monkeys at canopy level (Duke, 1955), our results show that C. silacea and C. dimidiata feed mainly on man and cannot be responsible for the transmission of parasites between simian and human hosts in that part of the Congo.