La trypanosomose est une maladie qui affecte à la fois l’homme et les animaux. Elle est provoquée par Trypanosoma sp. et cycliquement transmise par un vecteur, la glossine. Bien que cette maladie soit essentiellement endémique dans l’aire de distribution de son vecteur, les zones endémiques qui présentent une transmission active des deux types de la maladie ont rarement été décrites. Dans la présente étude, des enquêtes épidémiologique et entomologique ont été menées, puis les échantillons obtenus ont été analysés par la technique d’amplification en chaîne par polymérase (PCR). Au total, 13 410 personnes ont été examinées et 132 cas diagnostiqués. L’examen de 144 bovins par PCR a révélé l’infection de 33 d’entre eux, soit par Trypanosoma brucei (39 p. 100 des infections), soit par T. vivax (55 p. 100 des infections), soit par une coïnfection (deux animaux). Trois familles d’insectes (Glossinidae, Stomoxyinae et Tabanidae) ont été capturées à des densités variables. Glossina fuscipes fuscipes a été capturée uniquement dans la partie sud du foyer et la plus forte densité apparente (DAP = 0,56 glossine/piège/jour) a été observée dans la forêt galerie bordant les villages où a été diagnostiqué le plus grand nombre de malades. Les Tabanidae ont été présentes dans toutes les zones prospectées mais la plus forte densité (DAP =  15,55 tabanidés/piège/jour) a été observée dans la partie nord du foyer. Les stomoxes ont été absents de la zone prospectée la plus éloignée de la rivière. L’identification des trypanosomes chez l’homme et le bétail, et la présence du vecteur cyclique et des vecteurs mécaniques potentiels ont confirmé l’endémie de trypanosomose animale et humaine dans ce foyer. Seule une stratégie globale d’élimination permettrait de la contrôler durablement.

BackgroundIn Chad, several species of tsetse flies (Genus: Glossina ) transmit African animal trypanosomoses (AAT), which represents a major obstacle to cattle rearing, and sleeping sickness, which impacts public health. After the failure of past interventions to eradicate tsetse, the government of Chad is now looking for other approaches that integrate cost-effective intervention techniques, which can be applied by the stake holders to control tsetse-transmitted trypanosomoses in a sustainable manner. The present study thus attempted to assess the efficacy of restricted application of insecticides to cattle leg extremities using footbaths for controlling Glossina m. submorsitans, G . tachinoides and G . f . fuscipes in southern Chad.Methodology/Principal FindingsTwo sites were included, one close to the historical human African trypanosomiasis (HAT) focus of Moundou and the other to the active foci of Bodo and Moissala. At both sites, a treated and an untreated herd were compared. In the treatment sites, cattle were treated on a regular basis using a formulation of deltamethrin 0.005% (67 to 98 cattle were treated in one of the sites and 88 to 102 in the other one). For each herd, tsetse densities were monthly monitored using 7 biconical traps set along the river and beside the cattle pen from February to December 2009. The impact of footbath treatment on tsetse populations was strong (p < 10-3) with a reduction of 80% in total tsetse catches by the end of the 6-month footbath treatment.Conclusions/SignificanceThe impact of footbath treatment as a vector control tool within an integrated strategy to manage AAT and HAT is discussed in the framework of the “One Health” concept. Like other techniques based on the treatment of cattle, this technology should be used under controlled conditions, in order to avoid the development of insecticide and acaricide resistance in tsetse and tick populations, respectively.

Transmission experiments were conducted to compare the transmissibility of genetically different Trypanosoma congolense (Savannah subgroup) strains isolated from cattle in a trypanosomiasis endemic area of eastern Zambia. A total of 17 strains were compared. Three strains were extremely virulent with a short pre-patent period, high parasitaemia and a short median survival time (between 5 and 9 days) in mice. The remainder of the strains belonged to the moderate (6 strains) or low (8 strains) virulence categories with median survival times between 10 and 30 days and >30 days, respectively. Batches of 40 teneral Glossina morsitans morsitans (Diptera: Glossinidae) were offered a single bloodmeal on mice infected with one of those strains. Flies were dissected to determine their infection status 21 days later. The proportion of flies with procyclic and metacyclic infections differed significantly between trypanosome strains and were significantly higher in flies infected with extremely virulent strains (P=0.033 and P=0.016 for the differences in the procyclic infection rate of strains with moderate and low virulence, respectively and P=0.005 and P=0.019 for the differences in the metacyclic infection rate of strains with moderate and low virulence, respectively). On the other hand, moderately virulent strains had, in general, higher procyclic and metacyclic infection rates compared to low virulent strains. But the differences were not significant (P>0.05). The outcome of those experiments shows clear differences in transmissibility of trypanosome strains associated with their virulence. This observation confirms the theory for the evolution and maintenance of virulence in a parasite population and may explain the persistence of virulent trypanosome strains in a susceptible host population.