Trypanosomoses are parasitic diseases caused by Trypanosoma protozoa transmitted by tsetse flies (Glossina spp.) to humans and animals. These diseases cause major health and economic disruptions in sub-Saharan Africa. Despite the development and wide implementation of control strategies, the disease burden remains high and complementary tools are needed. Ivermectin is an endectocide toxic to arthropods, including Glossina. The aim of this study was to test the efficacy of different doses of ivermectin administered to cattle on the survival and fecundity of Glossina palpalis gambiensis Vanderplank, 1949 in Burkina Faso. This study compared the survival and fecundity of tsetse flies exposed to cattle treated with ivermectin–clorsulon (onefold veterinary therapeutic dose [TD; 0.2 mg/kg], twofold TD [2TD; 0.4 mg/kg], and fourfold TD [4TD; 0.8 mg/kg]) with those of flies exposed to control cattle (no treatment). Direct-skin blood-feeding experiments were performed at different days post-injection (DPI) (DPI: 1, 8, 15, 22, 29, and 36). The 30-day fly survival was analyzed using Kaplan–Meier curves and Cox proportional hazards models. Fecundity parameters were compared among treatments using generalized linear modeling (GLM). Time to first pupation was also measured. Fly mortality differed significantly between treatments (χ2 = 353.63, df = 3, P < 0.001), with 30-day mortality rates at 1 DPI of 24.0

African animal trypanosomosis (AAT) is one of the major diseases of livestock in Côte d'Ivoire. However, the lack of comprehensive, nationally aggregated data hinders the rational planning of control measures and the estimation of their impacts on disease transmission. To address this shortcoming, the Institut Pierre Richet (IPR, Ministry of Health) and the Directorate of Veterinary Services (Ministry of Livestock) embarked on the development of a national tsetse flies and AAT in Côte d'Ivoire. The atlas is a dynamic, georeferenced database on the distribution of disease and its vectors, and this article focuses on the tsetse component of the initiative.All data on tsetse flies collected by the IPR between 2005 and 2024 were retrospectively compiled, georeferenced and harmonised. The data originate from 20 of the 31 regions of the country, and from 3164 sites, corresponding to 5696 trapping events and an overall trapping intensity of 13,181 trap days. Monoconical and, to a lesser extent, biconical traps were used. A total of 27,493 tsetse flies belonging to eight species from the three groups of Glossina were captured. In addition to being the most abundant species, G. palpalis (84.36% of the captures), was also the one with the widest distribution across the country (i.e. 19 of the 20 study regions). The atlas produced provides important evidence for planning tsetse surveillance and monitoring control activities at the national level. However, as next steps, it will be crucial to include also data collected by other stakeholders, to extend surveys to areas of the country not yet covered, and to enhance, finalize and publish the already developed AAT component of the atlas.

The Republic of Guinea has faced an important challenge with human African trypanosomiasis (HAT), which was endemic over the last century. After initial control in the 1960s-1970s, HAT resurged in the 1990s along the Guinean coast, driven by economic and demographic pressures on the mangrove ecosystem. In response, the Guinean government established a national control program in 2002, focusing on medical mass screenings. In 2012, vector control using tiny targets was introduced in the East Boffa focus to reduce fly density and human-vector contact. However, the Ebola epidemic from 2013 to 2016 disrupted these efforts, leading to a reliance on passive screening. Resuming screenings in 2016-2017 revealed increased cases in all foci except the East Boffa area, where vector control had been effective. Vector control continued during the SARS-CoV2 pandemic and at the same time targeted door-to-door screenings were introduced to target high-risk individuals. Since 2018, around 30,000 at-risk individuals have been screened annually. These strategies reduced the total number of new cases below 1 per 10,000 inhabitants in endemic areas over the period 2019-2023, allowing to validate the elimination of HAT as a public health problem. The Guinean team and partners then focused on systematic spatial monitoring of patients and community engagement in vector control. The program also integrates control of other neglected tropical diseases and addresses new research questions, especially about anatomical and animal reservoirs for parasites. These efforts, combined with implementation of improved diagnostic tests and new oral treatments, through active involvement in multiple clinical trials and studies, now aim to interrupt HAT transmission by 2030.

Every year, over 700,000 people, particularly children under five, die from vector-borne diseases worldwide. Effectively controlling endemics and preventing new outbreaks requires an integrated approach that can lead to the elimination of both vectors and diseases. In the last two decades, integrating medical interventions and vector control has significantly reduced the incidence of Gambian Human African Trypanosomiasis (g-HAT), with the World Health Organization validating eight countries as having eliminated the disease as a public health problem. However, elimination of the tsetse vector has not been confirmed, leaving the possibility of re-emergence. We developed a six-step modeling framework to assess vector elimination by calculating: i) the probability of vector capture; ii) the probability of observing a series of zero catches, even without actual elimination; iii) the probability of natural elimination; iv) the probability of failing to detect a rebound; v) the reinvasion risk; and vi) the sensitivity analysis. Our case study is g-HAT in Mandoul, Chad, and the elimination of Glossina fuscipes fuscipes. We used vector control from 2014 to 2025 with no tsetse detected since 2018. We cannot yet conclude, with over 90% confidence, that tsetse has been eliminated from Mandoul, nor that any remnant population will be naturally eliminated. However, since vector control stopped in April 2025, we estimate that with continued sampling over the next 2 y, and no tsetse detected, elimination could be demonstrated with 99% confidence. Our multistep modeling framework can be applied to other vectors, providing policymakers with guidelines for ongoing and future efforts.

Background Tsetse are vectors of trypanosomes responsible for African animal trypanosomosis (AAT) and human African trypanosomiasis (HAT). While Côte d’Ivoire has successfully eliminated HAT as a public health problem and approaches elimination of transmission, AAT remains a major obstacle to agriculture and livestock production. Understanding the spatial distribution of tsetse is essential for prioritizing and sustaining disease control and elimination efforts. Methodology/Principal Findings Using 1,702 occurrence records from the national tsetse atlas we modeled the habitat suitability of the nine tsetse species present in Côte d’Ivoire. We identified suitable habitats in unsampled areas and quantified environmental constraints on tsetse distribution. Resampling the data to a 1km x 1km grid produced spatially explicit outputs at a resolution more relevant for operational planning. An ensemble modeling approach was employed integrating four algorithms—Random Forest, XGBoost, Maximum Entropy (MaxEnt), and Generalized Additive Models (GAM)— with satellite-derived environmental and anthropogenic predictors—which achieved high predictive accuracy, area under the curve and True Skill Statistics 0.80 and 0.83, respectively. Distance to waterbodies, soil moisture, distance to protected areas, maximum land surface temperature, and sheep density were key drivers of habitat suitability. Importantly, the models identified suitable habitats in 11 administrative regions not covered by the atlas, providing an improved national tsetse risk profile. Conclusions/Significance These results provide a detailed assessment of the ecological suitability of tsetse across Côte d’Ivoire and their persistence in agroecological mosaics with high human and livestock densities. We offer a high-resolution blueprint for vector and disease control, particularly in areas where field data are currently lacking. We provide a robust framework for evidence-based decision-making within the Progressive Control Pathway (PCP) for AAT by enabling the identification of priority areas and resource allocation optimization to improve livestock productivity through more effective AAT control and reduce the risk of resurgence of HAT.

The transformation of livestock production underway in Africa to support a growing population and the livelihood of farmers cannot be implemented without controlling major endemic diseases, such as vector-borne animal trypanosomosis (AT). Evidence-based decision-making is crucial for cost-effective trypanosomosis control, and through coordinated efforts, disease intelligence is being enhanced at the continental and national level. Information systems on the disease and its vectors ('atlases') have been established for Africa and in 14 high-burden countries. These initiatives underpin the progressive control pathway (PCP), a strategic approach that is being rolled out across the continent. However, information systems need continuous updates, enhanced dissemination and in-depth data analysis, including modelling, if their full potential is to be realized.

In the mangroves of Guinea, where the most active foci of human African trypanosomiasis in West Africa are located, vector control against tsetse flies using insecticide-impregnated Tiny Targets was first introduced in 2012. While annual deployments of Tiny Targets have resulted in an overall 90

Background Tsetse flies, (Glossina spp), are the main vectors of trypanosome parasites responsible for the the Human African Trypanosomiasis (HAT) and the African Animal Trypanosomosis (AAT), both of which remain significant obstacles to the socio-economic development of affected regions in sub-Saharan Africa. Several control strategies have been developed, among which, vector control plays a central role. To achieve the elimination of HAT and AAT, additional and integrated complementary control strategies, such as the ivermectin treatments of animals, need to be explored. Methods To assess the systemic insecticidal efficacy of ivermectin on the survival and fecundity of Glossina palpalis gambiensis , batches of tsetse flies were fed on 6 calves that were treated with three different doses of the drug: therapeutic dose (TD) of 0.2 mg/kg, two-fold TD, and four-fold TD. Two untreated calves were used as the control group. Results The TD and 2TD induced significant mortality of the tsetse flies up to 1 days post injection (DPI), with mortality rates varying from 59.82% to 90.43%. The 4TD caused a significant decrease of 55.09% of the survival of the tsetse flies up to 15 DPI (Z = -4.37; P < 0.001 ). The cattle treatments with ivermectin also resulted in a decrease of the number of pupae produced by tsetse flies, of 43.57% with the TD, and 92.47% with the 4TD. A delay from 9 to 13 days has also been observed in the deposit of the first larva, with the doses 2TD and 4TD at 1DPI and to 10 days with the dose 4TD at 8DPI. Conclusions The ivermectin treatments to animals against the common parasitosis have an additional effect against insect vectors like tsetse flies. Thus, mass treatments of farmed animals with ivermectin, may be considered in order to improve both human and animal health.

Vector control (VC) is one of the strategies employed to manage African trypanosomoses. This study aimed at assessing the effectiveness of a VC campaign against Glossina palpalis palpalis using tiny targets (TTs) impregnated with insecticide in an isolated, protected forest in Abidjan, Côte d'Ivoire, while considering ecological, genetic, and operational factors. Between January 2020 and September 2022, 2,712 TTs were deployed at 684 sites, covering a total area of 1.7 km2. VC monitoring was conducted using Vavoua traps during 12 evaluation surveys, between June 2020 and March 2023. Five months after the initial TT deployment, tsetse fly density had decreased by 98.53%. Although tsetse density remained low due to TT redeployment and reinforcement, there was a significant increase a few months after the last redeployment. VC appeared to have minimal impact on the genetic structuring of G. p. palpalis. This suggested recruitment of local surviving tsetse flies all along the VC campaign due to a low probability of tsetse coming into contact with TTs, or to the evolution of behavioral or physiological resistance to control efforts. The genetic study revealed that one of the microsatellite markers used, the GPCAG locus, exhibited a selection signature possibly in response to VC. This could partly explain the challenges encountered in eliminating a seemingly isolated tsetse population thriving in a particularly favorable habitat.

The sleeping sickness focus of Bonon was the last one still active at a low endemic level in Côte d’Ivoire. An entomological survey carried out in June 2015 during the rainy season using “Vavoua” traps guided subsequent control activities. Indeed, it improved knowledge of tsetse fly ecology. All the tsetse flies caught (i.e. 1909) belonged to the subspecies Glossina palpalis palpalis (Robineau-Desvoidy, 1830), the major vector of Human African Trypanosomiasis (HAT) in Côte d’Ivoire. In this paper, we looked at the relationship between the apparent density (AD, flies/trap/day) and biotopes. The AD significantly varied according to biotopes, with high density around villages. The trypanosomes overall infection rate (mature and immature) according to microscopic observation was 23.2%. When considering mature infections, the infection rate was 5.5 %. Polymerase chain reaction (PCR) analyses confirmed the presence of Trypanosoma brucei s.l. and Trypanosoma congolense “forest type”. Blood meals analysis using cytochrome b gene sequences revealed that tsetse flies fed on pigs. The edges of the villages seem to constitute preferred habitats for tsetse flies where they are protected from insecticide pressure in the fields, and where they can easily take bloodmeals from free-ranging pigs. The findings of this study provided a baseline in decision-making for subsequent vector control activities.

Tsetse flies (genus Glossina) transmit deadly trypanosomes to human populations and domestic animals in sub-Saharan Africa. Some foci of Human African Trypanosomiasis due to Trypanosoma brucei gambiense (g-HAT) persist in southern Chad, where a program of tsetse control was implemented against the local vector Glossina fuscipes fuscipes in 2018 in Maro. We analyzed the population genetics of G. f. fuscipes from the Maro focus before control (T0), one year (T1), and 18 months (T2) after the beginning of control efforts. Most flies captured displayed a local genetic profile (local survivors), but a few flies displayed outlier genotypes. Moreover, disturbance of isolation by distance signature (increase of genetic distance with geographic distance) and effective population size estimates, absence of any genetic signature of a bottleneck, and an increase of genetic diversity between T0 and T2 strongly suggest gene flows from various origins, and a limited impact of the vector control efforts on this tsetse population. Continuous control and surveillance of g-HAT transmission is thus recommended in Maro. Particular attention will need to be paid to the border with the Central African Republic, a country where the entomological and epidemiological status of g-HAT is unknown.

Background:Serological screening tests play a crucial role to diagnose gambiense human African trypanosomiasis (gHAT). Presently, they preselect individuals for microscopic confirmation, but in future “screen and treat” strategies they will identify individuals for treatment. Variability in reported specificities, the development of new rapid diagnostic tests (RDT) and the hypothesis that malaria infection may decrease RDT specificity led us to evaluate the specificity of 5 gHAT screening tests. Method: During active screening, venous blood samples from 1095 individuals from Côte d’Ivoire and Guinea were tested consecutively with commercial (Bioline HAT 2.0, HAT Sero-K-SeT, CATT) and prototype (HAT Sero-K-SeT 2.0, DCN) gHAT screening tests and with a malaria RDT. Individuals with ≥ 1 positive gHAT screening test underwent microscopy and further immunological (trypanolysis, indirect ELISA) and molecular laboratory tests (conventional PCR, SHERLOCK, Trypanozoon S²-RT-qPCR, SNP RT-qPCR). Microscopic trypanosome detection confirmed gHAT, while other individuals were considered gHAT free. Results: One gHAT case was diagnosed. Overall test specificities (n=1094) were: CATT 98.9% (98.1-99.4%); HAT Sero-K-SeT 86.7% (84.5-88.5%); Bioline HAT 2.0 82.1% (79.7-84.2%); DCN HAT RDT 78.2% (75.7-80.6%); and HAT Sero-K-SeT 2.0 78.4% (75.9-80.8%). In malaria positives, gHAT screening tests appeared less specific, but the difference was significant only in Guinea for Bioline HAT 2.0 and HAT Sero-K-Set 2.0. The specificities of immunological and molecular laboratory tests in gHAT seropositives were 98.7-100% (n=399) and 93.0-100% (n=302), respectively. Among 44 laboratory test positives, only the confirmed gHAT patient and one screening test seropositive combined immunological and molecular laboratory test positivity. Conclusions:Although a minor effect of malaria cannot be excluded, gHAT RDT specificities are far below the 95% minimal specificity stipulated by the WHO target product profile for a simple diagnostic tool to identify individuals eligible for treatment. Unless specificity is improved, an RDT-based “screen and treat” strategy would result in massive overtreatment. In view of their inconsistent results, additional comparative evaluations of the diagnostic performance of laboratory tests are indicated for better identifying, among screening test positives, those at increased suspicion for gHAT. Trial registration: The trial was retrospectively registered under NCT05466630 in clinicaltrials.gov on July 15 2022.

Abstract Background Serological screening tests play a crucial role to diagnose gambiense human African trypanosomiasis (gHAT). Presently, they preselect individuals for microscopic confirmation, but in future “screen and treat” strategies they will identify individuals for treatment. Variability in reported specificities, the development of new rapid diagnostic tests (RDT) and the hypothesis that malaria infection may decrease RDT specificity led us to evaluate the specificity of 5 gHAT screening tests. Methods During active screening, venous blood samples from 1095 individuals from Côte d’Ivoire and Guinea were tested consecutively with commercial (CATT, HAT Sero-K-SeT, Abbott Bioline HAT 2.0) and prototype (DCN HAT RDT, HAT Sero-K-SeT 2.0) gHAT screening tests and with a malaria RDT. Individuals with ≥ 1 positive gHAT screening test underwent microscopy and further immunological (trypanolysis with T.b. gambiense LiTat 1.3, 1.5 and 1.6; indirect ELISA/T.b. gambiense; T.b. gambiense inhibition ELISA with T.b. gambiense LiTat 1.3 and 1.5 VSG) and molecular reference laboratory tests (PCR TBRN3, 18S and TgsGP; SHERLOCK 18S Tids, 7SL Zoon, and TgsGP; Trypanozoon S2-RT-qPCR 18S2, 177T, GPI-PLC and TgsGP in multiplex; RT-qPCR DT8, DT9 and TgsGP in multiplex). Microscopic trypanosome detection confirmed gHAT, while other individuals were considered gHAT free. Differences in fractions between groups were assessed by Chi square and differences in specificity between 2 tests on the same individuals by McNemar. Results One gHAT case was diagnosed. Overall test specificities (n = 1094) were: CATT 98.9% (95% CI: 98.1–99.4%); HAT Sero-K-SeT 86.7% (95% CI: 84.5–88.5%); Bioline HAT 2.0 82.1% (95% CI: 79.7–84.2%); DCN HAT RDT 78.2% (95% CI: 75.7–80.6%); and HAT Sero-K-SeT 2.0 78.4% (95% CI: 75.9–80.8%). In malaria positives, gHAT screening tests appeared less specific, but the difference was significant only in Guinea for Abbott Bioline HAT 2.0 (P = 0.03) and HAT Sero-K-Set 2.0 (P = 0.0006). The specificities of immunological and molecular laboratory tests in gHAT seropositives were 98.7–100% (n = 399) and 93.0–100% (n = 302), respectively. Among 44 reference laboratory test positives, only the confirmed gHAT patient and one screening test seropositive combined immunological and molecular reference laboratory test positivity. Conclusions Although a minor effect of malaria cannot be excluded, gHAT RDT specificities are far below the 95% minimal specificity stipulated by the WHO target product profile for a simple diagnostic tool to identify individuals eligible for treatment. Unless specificity is improved, an RDT-based “screen and treat” strategy would result in massive overtreatment. In view of their inconsistent results, additional comparative evaluations of the diagnostic performance of reference laboratory tests are indicated for better identifying, among screening test positives, those at increased suspicion for gHAT. Trial registration The trial was retrospectively registered under NCT05466630 in clinicaltrials.gov on July 15 2022. Graphical Abstract

Background - Rationale:Tsetse flies (Diptera: Glossinidae) are obligate bloodfeeders that occur exclusively in Sub-Saharan Africa, where they are the vectors of trypanosomes causing HAT (human African trypanosomiasis) and AAT (African animal trypanosomiasis). In Chad, tsetse flies occur only in the most southern part of the country because of its favorable bioclimatic conditions. However, despite the importance of HAT and AAT in this country, very little is known about the current tsetse distribution, in particular its northern limit, which is of key importance for the surveillance of these diseases.Material and methods - Results:A total of 217 biconical traps were deployed in 2021 and 2022 from the West to the East around the formerly known northern limit, resulting in 1,024 tsetse caught belonging to three different taxa: Glossina morsitans submorsitans (57%), G. tachinoides (39%) and G. fuscipes fuscipes (4%). In addition to the information gathered on the presence/absence of each tsetse taxon, we show a strong North-South shift of the northen tsetse distribution limit as compared to the previous works from 1966 to 1996, and a growing spatial fragmentation in more and more discrete pockets of tsetse presence.Discussion - Conclusion:This North-South shift of the northern tsetse distribution limit in Chad is the likely consequence of the combined effect of severe draughts that affected the country, and increasing human pressure on land. This update of the tsetse northern limit will be of help to the national programmes in charge of HAT and AAT.

Human African trypanosomiasis, caused by the gambiense subspecies of Trypanosoma brucei (gHAT), is a deadly parasitic disease transmitted by tsetse. Partners worldwide have stepped up efforts to eliminate the disease, and the Chadian government has focused on the previously high-prevalence setting of Mandoul. In this study, we evaluate the economic efficiency of the intensified strategy that was put in place in 2014 aimed at interrupting the transmission of gHAT, and we make recommendations on the best way forward based on both epidemiological projections and cost-effectiveness. In our analysis, we use a dynamic transmission model fit to epidemiological data from Mandoul to evaluate the cost-effectiveness of combinations of active screening, improved passive screening (defined as an expansion of the number of health posts capable of screening for gHAT), and vector control activities (the deployment of Tiny Targets to control the tsetse vector). For cost-effectiveness analyses, our primary outcome is disease burden, denominated in disability-adjusted life-years (DALYs), and costs, denominated in 2020 US$. Although active and passive screening have enabled more rapid diagnosis and accessible treatment in Mandoul, the addition of vector control provided good value-for-money (at less than $750/DALY averted) which substantially increased the probability of reaching the 2030 elimination target for gHAT as set by the World Health Organization. Our transmission modelling and economic evaluation suggest that the gains that have been made could be maintained by passive screening. Our analysis speaks to comparative efficiency, and it does not take into account all possible considerations; for instance, any cessation of ongoing active screening should first consider that substantial surveillance activities will be critical to verify the elimination of transmission and to protect against the possible importation of infection from neighbouring endemic foci.

Human African Trypanosomiasis (HAT) is caused by Trypanosoma brucei which is transmitted by the tsetse fly insect vector (Glossina spp). It is one of the 20 Neglected Tropical Diseases (NTD) listed by the WHO. These diseases affect the poorest and most vulnerable communities, for which the WHO has established a dedicated 2021-2030 roadmap. At the time of Alphonse Laveran, HAT devastated the African continent. In the 1960s, the disease was nearly under control, but it strongly re-emerged in the 1990s. A coordinated effort of all stakeholders, with national control programs as the main actors, a strong contribution of research and important donations by the private sector, allowed to decrease the HAT burden significantly. Since 2018, less than 1000 cases are detected annually. We here review new diagnostics, treatments and vector control tools that have been implemented jointly and successfully in several endemic countries.The next key challenge will be to sustain the gains. Newly emerging research questions include long-term carriage of trypanosomes and adaptation of tools to low prevalence contexts. Challenges out of the research area comprise the continued need of funding, maintenance of dedicated human resources, and the key question of access. Sustainable elimination as "interruption of transmission", which is the 2030 NTD roadmap target, can be reached, if these challenges are solved. We stress the importance of continuing to combine the efforts in the fight against the disease, because sustainable elimination of HAT is the best long-term prevention strategy against re-emergence. As such, HAT elimination can serve as an example for other infectious diseases.

In Subsaharan Africa, tsetse flies (genus Glossina) are vectors of trypanosomes causing Human African Trypanosomiasis (HAT) and Animal African Trypanosomosis (AAT). Some foci of HAT persist in Southern Chad, where a program of tsetse control was started against the local vector Glossina fuscipes fuscipes in the Mandoul focus in 2014, and in Maro in 2018. Flies were also sampled in 2018 in Timb & eacute;ri and Dokoutou. We analyzed the population genetics of G. fuscipes fuscipes from the four tsetse-infested zones. The trapping samples were characterized by a strong female biased sex-ratio, except in Timb & eacute;ri and Dokoutou that had high tsetse densities. Apparent density and effective population density appeared smaller in the main foci of Mandoul and Maro and the average dispersal distance (within the spatial scale of each zone) was as large as or larger than the total length of each respective zone. The genetic signature of a population bottleneck was found in the Mandoul and Timb & eacute;ri area, suggesting a large ancient interconnected metapopulation that underwent genetic subdivision into small, isolated pockets due to adverse environmental conditions. The long-range dispersal and the existence of genetic outliers suggest a possibility of migration from remote sites such as the Central African Republic in the south (although the fly situation remains unknown there) and/or a genetic signature of recent exchanges. Due to likely isolation, an eradication strategy may be considered for sustainable HAT control in Mandoul focus. Another strategy will probably be required in Maro focus, which probably experiences much more exchanges with its neighbors.

Background Human African trypanosomiasis is a parasitic disease caused by trypanosomes among which Trypanosoma brucei gambiense is responsible for a chronic form (gHAT) in West and Central Africa. Its elimination as a public health problem (EPHP) was targeted for 2020. Côte d’Ivoire was one of the first countries to be validated by WHO in 2020 and this was particularly challenging as the country still reported around a hundred cases a year in the early 2000s. This article describes the strategies implemented including a mathematical model to evaluate the reporting results and infer progress towards sustainable elimination. Methods The control methods used combined both exhaustive and targeted medical screening strategies including the follow-up of seropositive subjects– considered as potential asymptomatic carriers to diagnose and treat cases– as well as vector control to reduce the risk of transmission in the most at-risk areas. A mechanistic model was used to estimate the number of underlying infections and the probability of elimination of transmission (EoT) was met between 2000–2021 in two endemic and two hypo-endemic health districts. Results Between 2015 and 2019, nine gHAT cases were detected in the two endemic health districts of Bouaflé and Sinfra in which the number of cases/10,000 inhabitants was far below 1, a necessary condition for validating EPHP. Modelling estimated a slow but steady decline in transmission across the health districts, bolstered in the two endemic health districts by the introduction of vector control. The decrease in underlying transmission in all health districts corresponds to a high probability that EoT has already occurred in Côte d’Ivoire. Conclusion This success was achieved through a multi-stakeholder and multidisciplinary one health approach where research has played a major role in adapting tools and strategies to this large epidemiological transition to a very low prevalence. This integrated approach will need to continue to reach the verification of EoT in Côte d’Ivoire targeted by 2025.

Abstract Background Human African trypanosomiasis (HAT) is a neglected tropical disease caused by Trypanosoma brucei gambiense transmitted by tsetse flies in sub-Saharan West Africa. In southern Chad the most active and persistent focus is the Mandoul focus, with 98% of the reported human cases, and where African animal trypanosomosis (AAT) is also present. Recently, a control project to eliminate tsetse flies (Glossina fuscipes fuscipes) in this focus using the sterile insect technique (SIT) was initiated. However, the release of large numbers of sterile males of G. f. fuscipes might result in a potential temporary increase in transmission of trypanosomes since male tsetse flies are also able to transmit the parasite. The objective of this work was therefore to experimentally assess the vector competence of sterile males treated with isometamidium for Trypanosoma brucei brucei. Methods An experimental infection was set up in the laboratory, mimicking field conditions: the same tsetse species that is present in Mandoul was used. A T. b. brucei strain close to T. b. gambiense was used, and the ability of the sterile male tsetse flies fed on blood with and without a trypanocide to acquire and transmit trypanosomes was measured. Results Only 2% of the experimentally infected flies developed an immature infection (midgut) while none of the flies developed a metacyclic infection of T. b. brucei in the salivary glands. We did not observe any effect of the trypanocide used (isometamidium chloride at 100 mg/l) on the development of infection in the flies. Conclusions Our results indicate that sterile males of the tested strain of G. f. fuscipes were unable to cyclically transmit T. b. brucei and might even be refractory to the infection. The data of the research indicate that the risk of cyclical transmission of T. brucei by sterile male G. f. fuscipes of the strain colonized at IAEA for almost 40 years appears to be small. Graphical Abstract