Urban malaria in sub-Saharan Africa: dynamic of the vectorial system and the entomological inoculation rate.

Sub-Saharan Africa is registering one of the highest urban population growth across the world. It is estimated that over 75% of the population in this region will be living in urban settings by 2050. However, it is not known how this rapid urbanization will affect vector populations and disease transmission. The present study summarizes findings from studies conducted in urban settings between the 1970s and 2020 to assess the effects of urbanization on the entomological inoculation rate pattern and anopheline species distribution. Different online databases such as PubMed, ResearchGate, Google Scholar, Google were screened. A total of 90 publications were selected out of 1527. Besides, over 200 additional publications were consulted to collate information on anopheline breeding habitats and species distribution in urban settings. The study confirms high malaria transmission in rural compared to urban settings. The study also suggests that there had been an increase in malaria transmission in most cities after 2003, which could also be associated with an increase in sampling, resources and reporting. Species of the Anopheles gambiae complex were the predominant vectors in most urban settings. Anopheline larvae were reported to have adapted to different aquatic habitats. The study provides updated information on the distribution of the vector population and the dynamic of malaria transmission in urban settings. The study also highlights the need for implementing integrated control strategies in urban settings.

Bovine trypanosomiasis in tsetse-free pastoral zone of the Far-North region, Cameroon.

BACKGROUND & OBJECTIVES: The Far-North region of Cameroon has been considered free of tsetse and trypanosomiasis for the past three decades. But recent reports by pastoralists indicate its reappearance in the region. This study was aimed to confirm the existence of cattle trypanosomiasis and determine its prevalence, and to establish pastoralists knowledge and practice (KP) of the disease in Ndiyam Shinwa pastoral zone of Cameroon. METHODS: A total of 118 herds were surveyed for a descriptive, cross-sectional study in Ndiyam Shinwa pastoral zone from May to November 2014. Out of these, 110 herds were visited in the beginning of the rainy season, 22 of the 110 herds (suspect cattle) were revisited along with the remaining eight herds in the end of the season. The blood samples of 635 suspect cattle and 135 nonsuspect cattle were collected. Samples were subjected to two diagnostic tests: Buffy coat test (BCT) and packed cell volume (PCV) determination. A survey on pastoralist's (n = 118) KP about trypanosomiasis was also undertaken. RESULTS: Parasitological analyses revealed six infections by Trypanosoma vivax: Four in suspect cattle against two in nonsuspect cattle, corresponding respectively to apparent prevalence of 0.63 and 1.46% and true prevalence of (0.79-3.15%) and (1.82-7.30%). The proportion of cattle found infected in the PCV as well as BCT tests was 33.26% for suspect cattle. More than 75% of followed-up suspects showed persisting symptoms nearly three months after initial examination. The most common diagnostic signs for pastoralists were ruffled hair, lacrimation, anorexia and emaciation. INTERPRETATION & CONCLUSION: Cattle trypanosomiasis has reappeared in the Far-North region and seems to be in the inter-epizootic phase. Pastoralists have a good knowledge of the disease, but their perception of its importance seems to be influenced by the persistence of symptoms attributed to this disease in suspect cattle.

Significant population genetic structure of the Cameroonian fresh water snail, Bulinus globosus, (Gastropoda: Planorbidae) revealed by nuclear microsatellite loci analysis.

In order to characterize the demographic traits and spatial structure of Cameroonians Bulinus globosus, intermediate host of Schistosoma haematobium, genetic structure of seven different populations, collected from the tropical zone, was studied using six polymorphic microsatellites. Intrapopulation genetic diversity ranged from 0.37 to 0.55. Interpopulation genetic diversity variation clearly illustrated their significant isolation due to distance with gene flow substantially limited to neighbouring populations. The effective population sizes (Ne) were relatively low (from 3.0 to 18.6), which supposes a high rate from which populations would lose their genetic diversity by drift. Analysis of genetic temporal variability indicated fluctuations of allelic frequencies (35 of 42 locus-population combinations, P<0.05) characteristic of stochastic demography, and this is reinforced by events of bottlenecks detected in all populations. These findings demonstrated that Cameroonian B. globosus were mixed-maters with some populations showing clear preference for outcrossing. These data also suggest that genetic drift and gene flow are the main factors shaping the genetic structure of studied populations.

Trypanosoma vivax, T. congolense "forest type" and T. simiae: prevalence in domestic animals of sleeping sickness foci of Cameroon.

In order to better understand the epidemiology of Human and Animal trypanosomiasis that occur together in sleeping sickness foci, a study of prevalences of animal parasites (Trypanosoma vivax, T. congolense "forest type", and T. simiae) infections was conducted on domestic animals to complete the previous work carried on T. brucei gambiense prevalence using the same animal sample. 875 domestic animals, including 307 pigs, 264 goats, 267 sheep and 37 dogs were sampled in the sleeping sickness foci of Bipindi, Campo, Doumé and Fontem in Cameroon. The polymerase chain reaction (PCR) based method was used to identify these trypanosome species. A total of 237 (27.08%) domestic animals were infected by at least one trypanosome species. The prevalence of T. vivax, T. congolense "forest type" and T. simiae were 20.91%, 11.42% and 0.34% respectively. The prevalences of 7 vivax and T. congolense "forest type" differed significantly between the animal species and between the foci (p < 0.0001); however, these two trypanosomes were found in all animal species as well as in all the foci subjected to the study. The high prevalences of 7 vivax and T congolense "forest type" in Bipindi and Fontem-Center indicate their intense transmission in these foci.

A new transmission risk index for human African trypanosomiasis and its application in the identification of sites of high transmission of sleeping sickness in the Fontem focus of southwest Cameroon.

A new index for the risk for transmission of human African trypanosomiasis was developed from an earlier index by adding terms for the proportion of tsetse infected with Trypanosoma brucei gambiense group 1 and the contribution of animals to tsetse diet. The validity of the new index was then assessed in the Fontem focus of southwest Cameroon. Averages of 0.66 and 4.85 Glossina palpalis palpalis (Diptera: Glossinidae) were caught per trap/day at the end of one rainy season (November) and the start of the next (April), respectively. Of 1596 tsetse flies examined, 4.7% were positive for Trypanosoma brucei s.l. midgut infections and 0.6% for T. b. gambiense group 1. Among 184 bloodmeals identified, 55.1% were from pigs, 25.2% from humans, 17.6% from wild animals and 1.2% from goats. Of the meals taken from humans, 81.5% were taken at sites distant from pigsties. At the end of the rainy season, catches were low and similar between biotopes distant from and close to pigsties, but the risk for transmission was greatest at sites distant from the sties, suggesting that the presence of pigs reduced the risk to humans. At the beginning of the rainy season, catches of tsetse and risk for transmission were greatest close to the sties. In all seasons, there was a strong correlation between the old and new indices, suggesting that both can be used to estimate the level of transmission, but as the new index is the more comprehensive, it may be more accurate.

Strong genetic structure in Cameroonian populations of Bulinus truncatus (Gastropoda: Planorbidae), intermediate host of Schistosoma haematobium.

In order to evaluate the snail host contribution on the variability of mollusk/schistosome compatibility, the genetic structure of seven Cameroonian populations of the schistosome vector, Bulinus truncatus, was studied using four variable microsatellite loci. A substantial polymorphism mainly distributed among populations was observed. No heterozygous genotype was scored, confirming the high level of selfing rate occurring in B. truncatus populations. Contemporaneous samples were highly and significantly differentiated with a marginally significant correlation with geographical distances (P-value=0.069). The different sites sampled seemed to rarely exchange migrants with very small Nm (∼0.22 or below). The data also suggest that B. truncatus subpopulations might be composed of very small and isolated units at much smaller surfaces than what was investigated. Even if more data (in particular more loci) will be needed to confirm these issues, they suggest that restricted gene flow plays an important role in maintaining differentiation among snail populations in the transmission foci, potentially leading to specific adaptation between each B. truncatus population and its local Schistosoma haematobium population.

Domestic animals as potential reservoir hosts of Trypanosoma brucei gambiense in sleeping sickness foci in Cameroon.

An explanation of the endemic nature and/or the resurgence of Human African Trypanosomiasis (HAT) in the historic foci in West and Central Africa may be the existence of an animal reservoir. In some HAT foci, pigs were found infected by Trypanosoma brucei gambiense but the implication of the other domestic animals was not quite evaluated. This study aims to determine the prevalence of T. b. gambiense in domestic animal species (goat, sheep, pig and dog) commonly found in the four active HAT foci in Cameroon (Bipindi, Fontem, Campo and Doumé). Blood samples were collected from 307 pigs, 264 goats, 267 sheep and 37 dogs and used for parasitological (QBC), immunological (LiTat 1.3 CATT) and molecular (PCR) analyses. QBC detected trypanosomes in 3.88% domestic animals while 22.7% were sero-positive with LiTat 1.3 CATT tests. Of the 875 animals analysed, 174 (19.88%) harboured T. brucei s.l. DNA, found in each of the four types of animal and in the four localities. The infection rate significantly differed among the animal species (p < 0.0001) and localities (p < 0.0001). The PCR also revealed T. b. gambiense group 1 DNA in 27 (3.08 %) domestic animals. The specific infection rates were as follows: sheep (6.74%), goats (3.08%), pigs (0.32%) and dogs (O%). T. b. gambiense was found in 8 (3.92%) animals from Bipindi, 15 (4.83%) from Campo, 4 (2.59%) from FontemCenter and none from Doumé. The infection rates significantly differed between the localities, and correlated with the intensity of HAT transmission in the foci.

Geographic and ecological distribution of the dengue and chikungunya virus vectors Aedes aegypti and Aedes albopictus in three major Cameroonian towns.

Aedes albopictus (Diptera: Culicidae) was first reported in Central Africa in 2000, together with the indigenous mosquito species Aedes aegypti (Diptera: Culicidae). Because Ae. albopictus can also transmit arboviruses, its introduction is a public health concern. We undertook a comparative study in three Cameroonian towns (Sahelian domain: Garoua; equatorial domain: Douala and Yaoundé) in order to document infestation by the two species and their ecological preferences. High and variable levels of pre-imaginal Ae. aegypti and Ae. albopictus infestation were detected. Only Ae. aegypti was encountered in Garoua, whereas both species were found in Douala and Yaoundé, albeit with significant differences in their relative prevalence. Peridomestic water containers were the most strongly colonized and productive larval habitats for both species. No major differences in types of larval habitat were found, but Ae. albopictus preferentially bred in containers containing plant debris or surrounded by vegetation, whereas Ae. aegypti tended to breed in containers located in environments with a high density of buildings. These findings may have important implications for vector control strategies.

[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.

Phylogenetic analysis reveals the presence of the Trypanosoma cruzi clade in African terrestrial mammals.

Despite the impact of some trypanosome species on human and livestock health, the full diversity of trypanosomes in Africa is poorly understood. A recent study examined the prevalence of trypanosomes among a wide variety of wild vertebrates in Cameroon using species-specific PCR tests, but six trypanosome isolates remained unidentified. Here they have been re-examined using fluorescent fragment length barcoding (FFLB) and phylogenetic analysis of glycosomal glyceraldehyde phosphate dehydrogenase gGAPDH and 18S ribosomal RNA (rDNA) genes. Isolates from a monkey (Cercopithecus nictitans) and a palm civet (Nandinia binotata) belonged to the Trypanosoma cruzi clade, known previously only from New World and Australian terrestrial mammals, and bats from Africa, Europe and South America. Of the four other isolates, three from antelope were identified as Trypanosoma theileri, and one from a crocodile as T. grayi. This is the first report of trypanosomes of the T. cruzi clade in African terrestrial mammals and expands the clade's known global distribution in terrestrial mammals. Previously it has been hypothesized that African and New World trypanosomes diverged after continental separation, dating the divergence to around 100 million years ago. The new evidence instead suggests that intercontinental transfer occurred well after this, possibly via bats or rodents, allowing these trypanosomes to establish and evolve in African terrestrial mammals, and questioning the validity of calibrating trypanosome molecular trees using continental separation.

Tsetse fly host preference from sleeping sickness foci in Cameroon: epidemiological implications.

To determine the tsetse fly host preferences in two sleeping sickness foci of southern Cameroon, four entomological surveys (two in each focus) were carried out. For the whole study, 4929 tsetse flies were caught: 3933 (79.8%) Glossina palpalis palpalis, 626 (12.7%) Glossina pallicera pallicera, 276 (5.6%) Glossina nigrofusca and 94 (1.9%) Glossina caliginea. One hundred and thirty-eight blood meals were collected and the origin of 118 (85.5%) meals was successfully identified: 38.4% from man, 23.9% from pig, 20.3% from sitatunga (Tragelaphus spekeii), 2.2% from sheep and 0.7% from golden cat (Profilis aurata). The number of Glossina palpalis palpalis with man blood meals is more important in the Human African Trypanosomiasis (HAT) focus showing endemic evolution (Campo) than in the focus (Bipindi) presenting a flare up of the disease. The consideration of both results of the prevalence of Trypanosoma brucei gambiense in vertebrate hosts and those of the tsetse fly host preferences indicates a wild animal reservoir of Gambian sleeping sickness and three transmission cycles (human, domestic and wild animals' cycles) in southern Cameroon HAT foci.

High prevalence of Trypanosoma brucei gambiense group 1 in pigs from the Fontem sleeping sickness focus in Cameroon.

To understand the importance of domestic pigs in the epidemiology of human trypanosomiasis, PCR was used to identify trypanosome populations in 133 pigs from the Fontem sleeping sickness focus of Cameroon. The results from this study show that 73.7% (98/133) of pigs from the Fontem area carry at least one trypanosome species. Trypanosoma vivax, T. brucei s.l. and T. congolense forest were found in 34.6% (46/133), 40.0% (53/133) and 46.0% (61/133) of the pigs respectively. T. simiae and T. congolense savannah were not identified in these animals. The use of repeated DNA sequences detected T. b. gambiense group 1 in 14.8% (15/101) of the pigs. Such pigs can be possible reservoir hosts for T. b. gambiense group 1 and contribute to the maintenance of the disease in the area. Mixed infections were revealed in 35.3% (47/133) of the pigs. Furthermore, we observed that under natural conditions, 52.4% (11/21) of the pigs from the Fontem focus carry mixed infections with T. b. gambiense group 1. No significant difference was observed between the percentage of T. b. gambiense group 1 single and mixed infections, and between the prevalence of this trypanosome in pigs from villages with and without sleeping sickness patients.

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.

Trypanosoma brucei s.l.: characterisation of stocks from Central Africa by PCR analysis of mobile genetic elements.

To better understand the epidemiology of sleeping sickness in the Central African sub-region, notably the heterogeneity of Human African Trypanosomiasis (HAT) foci, the mobile genetic element PCR (MGE-PCR) technique was used to genotype Trypanosoma brucei s.l. (T. brucei s.l.) isolates from this sub-region. Using a single primer REV B, which detects positional variation of the mobile genetic element RIME, via amplification of flanking regions, MGE-PCR revealed a micro genetic variability between Trypanosoma brucei gambiense (T. b. gambiense) isolates from Central Africa. The technique also revealed the presence of several T. b. gambiense genotypes and allowed the identification of minor and major ubiquitous genotypes in HAT foci. The presence of several T. b. gambiense genotypes in HAT foci may explain the persistence and the resurgence phenomena of the disease and also the epidemic and the endemic status of some Central African sleeping sickness foci. The MGE-PCR technique represents a simple, rapid, and specific method to differentiate Central African T. brucei s.l. isolates.

[Dynamics of intestinal schistosomiasis in Cameroon: evolution of transmission in the mixed zone of Nkolmébanga, Lékié]. / Dynamique des schistosomoses intestinales au Cameroun: évolution de la transmission dans le foyer mixte de Nkolmébanga, Lékié.

This study was undertaken to evaluate the current status of shistosomiasis in the Nkolmébanga region (Lékié) of Cameroon, previously determined to be a mixed zone harboring both Schistosoma mansoni and S. intercalatum. Study involved both malacology with collection and identification of freshwater snails in four waterpools and parasitology with collection and analysis of stools from schoolchildren. Five species of freshwater snails were identified including two that were intermediate host of Schistosomes, i.e., Biomphalaria pfeifferi and Bulinus forskalii. Only B. pfeifferi species collected from the Momboh and Mbonsoh Rivers shed Schistosoma cercaria. A total of 347 schoolchildren were enrolled but only 200 provided stools for parasitological testing. There were 93 boys and 107 girls. Parisitology demonstrated S. intercalatum eggs in the stools of no children. S. mansoni eggs were identified in the stools of 10 children for a prevalence of 5%. Parasitic load ranged from 24 to 1104 eggs per gram of stool. In this study both malacologic and parasitological findings suggested that S. mansoni persists in Nkolmébanga region but that S. intercalatum has disappeared probably as a result of deforestation and urbanization.

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.

A study of host preference in tsetse flies using a modified heteroduplex PCR-based method.

A study of host preference in tsetse flies using a modified heteroduplex PCR-based method is described. Domestic and wild animal blood samples were collected to extract the corresponding reference DNAs. In Campo (south Cameroon), tsetse flies (mainly Glossina palpalis palpalis) were trapped and 41 bloodmeals were collected. All reference DNAs and 37 bloodmeal DNAs (90.7%) were successfully amplified and hybridised. Twelve bloodmeals (32.4%) were of human origin, 13 (35.4%) were from Sitatunga (Tragelaphus spekei) (an antelope) while 12 (32.4%) were not identified using our set of reference DNAs. The results confirmed the occurrence of frequent contacts between wild animals and this population of tsetse flies.

An isoenzyme survey of Trypanosoma brucei s.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 gambiense group I and 3 T. brucei 'non-gambiense' stocks. T. b. gambiense group 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 in T. 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 for T. b. gambiense group I in Cameroon.

[Experimental study of the compatibility between Schistosoma haematobium and two species of Bulinus in Cameroon]. / Etude expérimentale de la compatibilité entre Schistosoma haematobium et deux espèces de bulins au Cameroun.

A study on the compatibility between Schistosoma haematobium from three remote localities (Mourtourwa, Gounougou and Kékem) and four populations of Bulinus truncatus (Gounougou, Ngaoundéré, Bertoua and Kékem) and four populations of B. globosus (Mourtourwa, Ouroudoukoudje, Bafia and Yaoundé) was undertaken in order to estimate the risk of extension of urinary schistosomiasis in Cameroon. First generation of offspring from wild Bulinus was exposed to miracidia liberated by schistosome eggs extracted from patient urine. Between the 25th and the 60th day post-infestation the number of snails still alive, the number emitting cercariae and the prepatent period duration were noted. Results showed that all B. truncatus samples were susceptible to the three strains of parasite whereas only B. globosus of Mourtourwa and Ouroudoukoudje were susceptible to S. haematobium from Mourtourwa. The schistosome infection rate was then significantly higher in B. truncatus and the prepatent period significantly lower than in B. globosus. The compatibility characterised by a high infection rate and a low prepatent period was significantly better in homopatric couples than in allopatric combinations. The results suggested that B. truncatus might be potentially more implicated than B. globosus to the extension of the urinary bilharziasis 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.