An Atlas to Support the Progressive Control of Tsetse-transmitted Animal Trypanosomosis in Burkina Faso

Background African animal trypanosomosis (AAT), transmitted by tsetse flies, is arguably the main disease constraint to integrated crop-livestock agriculture in sub-Saharan Africa, and African Heads of State and Government have adopted a resolution to rid the continent of this scourge. In order to sustainably reduce or eliminate the burden of AAT, a progressive and evidence-based approach is need, which must hinge on harmonized, spatially-explicit information on the occurrence of AAT and its vectors.MethodsA digital repository containing tsetse and AAT data collected in Burkina Faso between 1990 and 2019 was assembled. Data were collected either in the framework of control activities or for research purposes. Data were systematically verified, harmonized, georeferenced and integrated into a database (PostgreSQL). Entomological data on tsetse were mapped at the level of individual monitoring trap. When this was not possible, mapping done was at the level of site or location. Epidemiological data on AAT were mapped at the level of location/village.ResultsEntomological data showed that presence of four tsetse species in Burkina Faso. Glossina tachinoides was the most widespread and abundant species (56.35% of the catches), present from the eastern to the western part of the country. Glossina palpalis gambiensis was the second most abundant species (35.56%), and it was mainly found in the West. Glossina morsitans submorsitans was found at lower densities (6.11%), with a patchy distribution in the southern parts of the country. One only cluster of G. medicorum was detected (less than 0.1%), located in the Southwest. For the AAT component, data for 54,948 animal blood samples were assembled from 218 geographic locations. The samples were tested with a variety of diagnostic methods. AAT was found in all surveyed departments, including the tsetse-free areas in the North. Trypanosoma vivax and T. congolense infections were the dominant species 6.11±21.56% and 5.19±18.97% respectively), and to a lesser extend T. brucei infections (0.00±0.10%).Conclusions The atlas provides a synoptic view of the available information on tsetse and AAT distribution in Burkina Faso. Data are very scanty for most of the tsetse-free areas in the northern part of the country. Despite this limitation, this study generated a robust tool to aid the targeting of future surveillance and control activities. The development of the atlas also strengthened the collaboration between the different institutions involved in tsetse and AAT research and control in Burkina Faso, which will be crucial for future updates and the sustainability of the initiative.

Interactions Between Tsetse Endosymbionts and Glossina pallidipes Salivary Gland Hypertrophy Virus in Glossina Hosts

Tsetse flies are the sole cyclic vector for trypanosomosis, the causative agent for human African trypanosomosis or sleeping sickness and African animal trypanosomosis or nagana. Tsetse population control is the most efficient strategy for animal trypanosomosis control. Among all tsetse control methods, the Sterile Insect Technique (SIT) is one of the most powerful control tactics to suppress or eradicate tsetse flies. However, one of the challenges for the implementation of SIT is the mass production of target species. Tsetse flies have a highly regulated and defined microbial fauna composed of three bacterial symbionts (Wigglesworthia, Sodalis and Wolbachia) and a pathogenic Glossina pallidipes Salivary Gland Hypertrophy Virus (GpSGHV) which causes reproduction alterations such as testicular degeneration and ovarian abnormalities with reduced fertility and fecundity. Interactions between symbionts and GpSGHV might affect the performance of the insect host. In the present study, we assessed the possible impact of GpSGHV on the prevalence of tsetse endosymbionts under laboratory conditions to decipher the bidirectional interactions on six Glossina laboratory species. The results indicate that tsetse symbiont densities increased over time in tsetse colonies with no clear impact of the GpSGHV infection on symbionts density. However, a positive correlation between the GpSGHV and Sodalis density was observed in Glossina fuscipes species. In contrast, a negative correlation between the GpSGHV density and symbionts density was observed in the other taxa. It is worth noting that the lowest Wigglesworthia density was observed in G. pallidipes, the species which suffers most from GpSGHV infection. In conclusion, the interactions between GpSGHV infection and tsetse symbiont infections seems complicated and affected by the host and the infection density of the GpSGHV and tsetse symbionts.

Non-Tsetse-Transmitted Animal Trypanosomosis (NTT)

The non-tsetse-transmitted animal trypanosomoses are infections caused by three main mammalian trypanosome species, namely Trypanosoma evansi, T. equiprdum, and T. vivax. Their global distribution is much wider than tsetse-transmitted trypanosomoses and includes Africa and Latin America, Asia, and Euro-Asia. These trypanosomoses affect a very wide range of domestic animals and game and negatively impact on the development of the animal industry, thus directly affecting national economies and people's livelihoods.

Introduction of African Animal Trypanosomosis (AAT)/Nagana

African animal trypanosomosis (AAT), a livestock disease, also known as Nagana, tsetse fly disease, or tsetse disease, is a widespread tsetse-borne disease complex caused by unicellular protozoan parasites belonging to the genus Trypanosoma. It is one of the major constraints to the expansion of livestock rearing and livestock-based industries in Africa. It also constrains mixed farming, human health, and livelihood in tropical Africa. The tsetse fly is the major vector of the disease. Acute disease is characterized by marked depression, intermittent fever, anorexia, anemia, blood-tinged diarrhea, and adenopathy, sometimes petechiae on mucosa, abortion, and death if not treated. Diagnosis is made by observing trypanosome parasites by direct microscopic examination of blood, lymph nodes, edema fluid, or tissues. Treatment is by chemotherapy and chemoprophylaxis. Control is achieved through vector control treatment using available molecules and use of a few available trypanotolerant breeds of animals.

Mathematical modelling and control of African animal trypanosomosis with interacting populations in West Africa—Could biting flies be important in main taining the disease endemicity?

African animal trypanosomosis (AAT) is transmitted cyclically by tsetse flies and mechanically by biting flies (tabanids and stomoxyines) in West Africa. AAT caused by Trypanosoma congolense, T. vivax and T. brucei brucei is a major threat to the cattle industry. A mathematical model involving three vertebrate hosts (cattle, small ruminants and wildlife) and three vector flies (Tsetse flies, tabanids and stomoxyines) was described to identify elimination strategies. The basic reproduction number (R0) was obtained with respect to the growth rate of infected wildlife (reservoir hosts) present around the susceptible population using a next generation matrix technique. With the aid of suitable Lyapunov functions, stability analyses of disease-free and endemic equilibria were established. Simulation of the predictive model was presented by solving the system of ordinary differential equations to explore the behaviour of the model. An operational area in southwest Nigeria was simulated using generated pertinent data. The R0 < 1 in the formulated model indicates the elimination of AAT. The comprehensive use of insecticide treated targets and insecticide treated cattle (ITT/ITC) affected the feeding tsetse and other biting flies resulting in R0 < 1. The insecticide type, application timing and method, expertise and environmental conditions could affect the model stability. In areas with abundant biting flies and no tsetse flies, T. vivax showed R0 > 1 when infected wildlife hosts were present. High tsetse populations revealed R0 <1 for T. vivax when ITT and ITC were administered, either individually or together. Elimination of the transmitting vectors of AAT could cost a total of US$ 1,056,990 in southwest Nigeria. Hence, AAT in West Africa can only be controlled by strategically applying insecticides targeting all transmitting vectors, appropriate use of trypanocides, and institutionalising an appropriate barrier between the domestic and sylvatic areas.

Prevalence and impacts of animal trypanosomosis in Vogan sheep and Djallonke sheep in southern of Togo

The aim of this study was to estimate the prevalence of animal trypanosomosis and its impact on the Packed red Cell Volume (PCV) in Vogan sheep (VS) and Djallonke sheep (DS) in two administrative regions of southern-Togo (Maritime and Plateau Regions). A total of 206 samples (104 VS and 102 DS) were analysed by microscopic observation of buffy coat, PCR and indirect ELISA. Using the three diagnostic techniques, the prevalence was 24.51% in Djallonke sheep and 20.19% in Vogan sheep with a clear predominance of Trypanosoma vivax infection. Geographical location (canton) influenced significantly the prevalence of trypanosome infections and the PCV; the highest recorded prevalence was obtained in Dagbatchi and Sevagan locations, associated with the lowest PCV. No significant difference was observed between PCV of VS and those of DS in Maritime Region. We concluded that even with a phenotype of Sahelian sheep, VS is well adapted in this area and has developed a certain degree of trypanotolerance similar to DS. However, Djallonke sheep in the Maritime Region (Vo Prefecture) might have become less trypanotolerant comparatively to those originating from the Plateau Region. These results could be used to update the epidemiological situation of trypanosomosis in this region and showed that the sheep genetic improvement strategies should take into account animal trypanosomosis.