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A geographical approach to identify sleeping sickness risk factors in a mangrove ecosystem
Tropical Medicine & International Health
Abstract
To provide a better understanding of sleeping sickness transmission and spread in mangrove areas to optimize its control.
In the Forecariah mangrove area, Guinea, 19 sleeping sickness cases and 19 matched controls were followed up in their living areas (at home, in fields and at water points). All occupational sites and pathways were mapped and then placed in their environmental context.
The sleeping sickness cases displayed a significantly broader and more diverse spatial occupation than the controls. They covered double the daily walking distances of controls and had on average two more occupational sites, most of which were located in mangrove forests. Activities with a higher transmission risk (rice culture, attendance of pirogue jetties) were identified as well as high-risk areas and pathways.
An entomological control strategy targeting transmission risk areas is proposed. Its implementation in a control programme would reduce by 86% the efforts needed for a classical vector control programme throughout the area. Medical surveys set up at specific locations, such as pirogue jetties and high-risk paths, should also enable better targeting of the population at highest risk.
... An increased risk of Rhodesian HAT in areas close to 'long vegetation swamp' habitats has been detected in two recent studies [4,5]. Several other studies have examined tsetse populations and risk of Gambian HAT (caused by Trypanosoma brucei gambiense) in relation to the presence of particular crop types (such as coffee or cocoa) [6,7], the level of human land use, disturbance of vegetation and also human movement patterns [8][9][10]. ...
... However, the entomological surveys required for this risk index can be costly and time consuming. More recently, the identification of high risk areas for T. b. gambiense transmission, to allow the implementation of targeted tsetse control, was carried out by Courtin et al. [10] by tracking the movements of individuals (HAT cases and controls) and characterising the epidemiological risk of different sites and activities. Another recent study (focusing on Rhodesian HAT in Uganda) investigated the significance of the proportion of different sized buffer zones (circular zones, of defined radius, centred on a point of interest) surrounding homesteads that intersected with areas of wetland for HAT acquisition. ...
... The location of a HAT patient's village of residence or homestead does not provide sufficient information to identify the areas in which an elevated epidemiological risk occurs or the landscape features contributing to this increased infection risk. The methods which have previously been used to identify high transmission risk areas (e.g. the use of entomological sampling or the tracking of human movements) are time consuming and can be costly [10,18]. Here, a novel method has been explored, utilising knowledge of the distance outside of the village of residence travelled by village inhabitants on an average day to identify the areas which are likely to support elevated HAT transmission. ...
Tsetse-transmitted human and animal trypanosomiasis are constraints to both human and animal health in sub-Saharan Africa, and although these diseases have been known for over a century, there is little recent evidence demonstrating how the parasites circulate in natural hosts and ecosystems. The spread of Rhodesian sleeping sickness (caused by Trypanosoma brucei rhodesiense) within Uganda over the past 15 years has been linked to the movement of infected, untreated livestock (the predominant reservoir) from endemic areas. However, despite an understanding of the environmental dependencies of sleeping sickness, little research has focused on the environmental factors controlling transmission establishment or the spatially heterogeneous dispersal of disease following a new introduction. In the current study, an annually stratified case-control study of Rhodesian sleeping sickness cases from Serere District, Uganda was used to allow the temporal assessment of correlations between the spatial distribution of sleeping sickness and landscape factors. Significant relationships were detected between Rhodesian sleeping sickness and selected factors, including elevation and the proportion of land which was “seasonally flooding grassland” or “woodlands and dense savannah.” Temporal trends in these relationships were detected, illustrating the dispersal of Rhodesian sleeping sickness into more ‘suitable’ areas over time, with diminishing dependence on the point of introduction in concurrence with an increasing dependence on environmental and landscape factors. These results provide a novel insight into the ecology of Rhodesian sleeping sickness dispersal and may contribute towards the implementation of evidence-based control measures to prevent its further spread.
... An increased risk of Rhodesian HAT in areas close to 'long vegetation swamp' habitats has been detected in two recent studies [4,5]. Several other studies have examined tsetse populations and risk of Gambian HAT (caused by Trypanosoma brucei gambiense) in relation to the presence of particular crop types (such as coffee or cocoa) [6,7], the level of human land use, disturbance of vegetation and also human movement patterns [8][9][10]. ...
... However, the entomological surveys required for this risk index can be costly and time consuming. More recently, the identification of high risk areas for T. b. gambiense transmission, to allow the implementation of targeted tsetse control, was carried out by Courtin et al. [10] by tracking the movements of individuals (HAT cases and controls) and characterising the epidemiological risk of different sites and activities. Another recent study (focusing on Rhodesian HAT in Uganda) investigated the significance of the proportion of different sized buffer zones (circular zones, of defined radius, centred on a point of interest) surrounding homesteads that intersected with areas of wetland for HAT acquisition. ...
... The location of a HAT patient's village of residence or homestead does not provide sufficient information to identify the areas in which an elevated epidemiological risk occurs or the landscape features contributing to this increased infection risk. The methods which have previously been used to identify high transmission risk areas (e.g. the use of entomological sampling or the tracking of human movements) are time consuming and can be costly [10,18]. Here, a novel method has been explored, utilising knowledge of the distance outside of the village of residence travelled by village inhabitants on an average day to identify the areas which are likely to support elevated HAT transmission. ...
Background
Specific land cover types and activities have been correlated with Trypanosoma brucei rhodesiense distributions, indicating the importance of landscape for epidemiological risk. However, methods proposed to identify specific areas with elevated epidemiological risk (i.e. where transmission is more likely to occur) tend to be costly and time consuming. This paper proposes an exploratory spatial analysis using geo-referenced human African trypanosomiasis (HAT) cases and matched controls from Serere hospital, Uganda (December 1998 to November 2002) to identify areas with an elevated epidemiological risk of HAT.
Methods
Buffers 3 km from each case and control were used to represent areas in which village inhabitants would carry out their daily activities. It was hypothesised that the selection of areas where several case village buffers overlapped would enable the identification of locations with increased risk of HAT transmission, as these areas were more likely to be frequented by HAT cases in several surrounding villages. The landscape within these overlap areas should more closely relate to the environment in which transmission occurs as opposed to using the full buffer areas. The analysis was carried out for each of four annual periods, for both cases and controls, using a series of threshold values (number of overlapping buffers), including a threshold of one, which represented the benchmark (e.g. use of the full buffer area as opposed to the overlap areas).
Results
A greater proportion of the overlap areas for cases consisted of seasonally flooding grassland and lake fringe swamp, than the control overlap areas, correlating well with the preferred habitat of the predominant tsetse species within the study area (Glossina fuscipes fuscipes). The use of overlap areas also resulted in a greater difference between case and control landscapes, when compared with the benchmark (using the full buffer area).
Conclusions
These results indicate that the overlap analysis has enabled the selection of areas more likely to represent epidemiological risk zones than similar analyses using full buffer areas. The identification of potential epidemiological risk zones using this method requires fewer data than other proposed methods and further development may provide vital information for the targeting of control measures.
... Following some more recent case detections, targeted active screening strategies were put in place. These included door-to-door [8] and spatial follow-up of cases [19] by which it is possible to screen the family and most-at-risk populations that share the same daily spaces as the gHAT cases and unconfirmed serosuspects. The diagnostic algorithm is shown in Fig 2a. ...
... IndividualHD fits (or subprefecture fits in the case of Bouaflé HD) can be found in the S1 Text. Much of the case reporting dynamics appear to be driven by Bonon subprefecture of Bouaflé HD which accounted for between19 and 100% of all actively reported cases and 11-62% of passively ...
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) is being achieved. 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 surveillance strategies 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) between 2000-2021 in two endemic and two hypo-endemic health districts.
Results: Between 2015 and 2019, nine gHAT cases were detected in two health districts in which the number of cases/10,000 inhabitants was far below 1, a necessary condition for validating the EPHP. Modelling estimated a slow but steady decline in transmission across the four 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.
... The medical teams target the most at risk people, e.g., in "boat landing points" in Guinea, coffee/ cocoa plantations in Côte d'Ivoire, or market places in Chad. A spatial follow-up of HAT cases and mapping of areas where they are likely to have been infected is used to orient medical and vector activities [14]. In addition, a geographical method called "Identification of Villages at Risk" (IVR) is implemented in historical foci and areas at risk, where the situation of g-HAT is not well known, in order to update the epidemiological situation [15]. ...
... In addition, a geographical method called "Identification of Villages at Risk" (IVR) is implemented in historical foci and areas at risk, where the situation of g-HAT is not well known, in order to update the epidemiological situation [15]. In Côte d'Ivoire, these efforts are supplemented by medical teams that follow up and retest people who remain positive with screening tests but negative by microscopy, who would thus not be treated until parasites are demonstrated [14]. ...
Gambiense human African trypanosomiasis (g-HAT) is the chronic form of sleeping sickness caused by Trypanosoma brucei gambiense in West and Central Africa, while Trypanosoma brucei rhodesiense causes an acute form in eastern Africa. g-HAT is targeted for elimination as a public health problem by 2020 and 0 transmission by 2030 [1,2]. Control of g-HAT is largely based on identification and treatment of infected individuals, supplemented by control of the tsetse fly vectors [3]. There has been growing evidence that when both tsetse control and case identification activities are carried out simultaneously in the same geographies, elimination of the disease is accelerated [4–6]. Here, we describe how the Trypa-NO! Partnership is using novel and classical tools to drive g-HAT elimination in an integrated approach, progress made, lessons learnt, and future directions. The Trypa-NO! Partnership was established in September 2016 to support National Sleeping Sickness Control Programmes (NSSCP) in Chad, Coˆte d’Ivoire, Republic of Guinea, and Uganda in driving elimination of g-HAT by integrating tsetse control with screening, diagnosis, and treatment of cases. The Partnership goals are to drive to 0 the annual number of g- HAT cases reported in Coˆte d’Ivoire and Uganda by 2020 and reduce cases by 90% in the Republic of Guinea and Chad by 2022.
... It is one of the most neglected tropical diseases and, until recently, the treatment relied on ancient and toxic drugs [1]. In Western Africa, most cases of T. brucei gambiense infection are found in remote sparse active focuses such as the three major ones situated in the mangrove ecosystem of coastal Guinea [2], namely from North to South: Boffa [3][4], Dubreka [4] and Forecariah [4][5][6]. Of note, these three districts were among the most affected by the epidemic of Ebola virus disease that severely hit Guinea in 2014-2015 [7]. ...
... Our study was carried out in three districts of coastal Guinea, namely from north to south Boffa, Dubreka and Forecariah (Fig 1). The Boffa [3,4] and Dubreka [4] districts are located at the north of the capital city Conakry and Forecariah [4][5][6] district is located at the south of Conakry. All districts are situated in a mangrove ecosystem favoring the growth of the HAT vector population. ...
Background
The 2014–2015 Ebola outbreak massively hit Guinea. The coastal districts of Boffa, Dubreka and Forecariah, three major foci of Human African Trypanosomiasis (HAT), were particularly affected. We aimed to assess the impact of this epidemic on sleeping sickness screening and caring activities.
Methodology/Principal findings
We used preexisting data from the Guinean sleeping sickness control program, collected between 2012 and 2015. We described monthly: the number of persons (i) screened actively; (ii) or passively; (iii) treated for HAT; (iv) attending post-treatment follow-up visits. We compared clinical data, treatment characteristics and Disability Adjusted Life-Years (DALYs) before (February 2012 to December 2013) and during (January 2014 to October 2015) the Ebola outbreak period according to available data. Whereas 32,221 persons were actively screened from February 2012 to December 2013, before the official declaration of the first Ebola case in Guinea, no active screening campaigns could be performed during the Ebola outbreak. Following the reinforcement and extension of HAT passive surveillance system early in 2014, the number of persons tested passively by month increased from 7 to 286 between April and September 2014 and then abruptly decreased to 180 until January 2015 and to none after March 2015. 213 patients initiated HAT treatment, 154 (72%) before Ebola and 59 (28%) during the Ebola outbreak. Those initiating HAT therapy during Ebola outbreak were recruited through passive screening and diagnosed at a later stage 2 of the disease (96% vs. 55% before Ebola, p<0.0001). The proportion of patients attending the 3 months and 6 months post-treatment follow-up visits decreased from 44% to 10% (p <0.0001) and from 16% to 3% (p = 0.017) respectively. The DALYs generated before the Ebola outbreak were estimated to 48.7 (46.7–51.5) and increased up to 168.7 (162.7–174.7), 284.9 (277.1–292.8) and 466.3 (455.7–477.0) during Ebola assuming case fatality rates of 2%, 5% and 10% respectively among under-reported HAT cases.
Conclusions/Significance
The 2014–2015 Ebola outbreak deeply impacted HAT screening activities in Guinea. Active screening campaigns were stopped. Passive screening dramatically decreased during the Ebola period, but trends could not be compared with pre-Ebola period (data not available). Few patients were diagnosed with more advanced HAT during the Ebola period and retention rates in follow-up were lowered. The drop in newly diagnosed HAT cases during Ebola epidemic is unlikely due to a fall in HAT incidence. Even if we were unable to demonstrate it directly, it is much more probably the consequence of hampered screening activities and of the fear of the population on subsequent confirmation and linkage to care. Reinforced program monitoring, alternative control strategies and sustainable financial and human resources allocation are mandatory during post Ebola period to reduce HAT burden in Guinea.
... Individuals from 3 foci were included. Although these foci were close to each other and similar in terms of environment, the distribution of the disease and of the age and sex ratios varied between foci owing to differences in human exposure to tsetse flies and intensity of transmission [25][26][27]. The 3 foci are very similar in terms of microbial exposure (tuberculosis, leprosy, and cholera remain present) and are highly endemic for malaria. ...
... We also found other variables to be associated with the distribution of the disease, such as focus, sex, and age. These associations are mainly due to differences in bite exposure profiles between and within foci and individual recruitments during the medical survey [25][26][27]. ...
Background:
Human African trypanosomiasis (HAT) caused by Trypanosoma brucei gambiense (Tbg) can be diagnosed in the early haemolymphatic stage (S1) or meningoencephalitic stage (S2). Importantly, individuals harbouring high and specific antibody responses to Tbg antigens but negative parasitology are also diagnosed in the field. Whereas some develop the disease in the months following their initial diagnosis (SERO/HAT), others remain parasitologically negative for long periods (SERO) and are apparently able to control infection. Human leukocyte antigen (HLA)-G, an immunosuppressive molecule, could play a critical role in this variability of progression between infection and disease.
Methods:
Soluble HLA-G (sHLA-G) was measured in plasma for SERO (n=65), SERO/HAT (n=14) and HAT patients (n=268) and in cerebrospinal fluid (CSF) for S1 (n=55), early S2 (S2E) (n=93) and late S2 (S2L) (n=110). Associations between these different statuses and the soluble level or genetic polymorphisms of HLA-G were explored.
Results:
Plasma sHLA-G levels were significantly higher in HAT (p=6 10(-7)) and SERO/HAT (p=0.007) than SERO patients. No difference was observed between the SERO/HAT and HAT groups. Within the HAT group, specific haplotypes (HG010102 and HG0103) displayed increased frequencies in S1 (p=0.013) and S2L (p=0.036), respectively.
Conclusions:
These results strongly suggest the involvement of HLA-G in HAT disease progression. Importantly, high plasma sHLA-G levels in SERO patients could be predictive of subsequent disease development and could represent a serological marker to help take the appropriate therapeutic decision. Further studies are necessary to assess the predictive nature of HLA-G and to estimate both sensitivity and specificity.
... Guinea possesses a relatively extensive freshwater system with 1161 rivers and drainage basins, ranging in size from 5 to 99,168 km 2 . The annual rainfall for this region often exceeds 2 m, but a distinct dry season extends from December to May (Courtin et al. 2010). In lower Guinea (Prefectue de Forecariah), the flood plains and tidal areas result in an elaborate estuarine system supporting extensive mangrove forests which are central to the local economy (Kasisi 2002). ...
... The two islands have a terrestrial area of approximately 134.6 km 2 , and the coast is influenced by semidiurnal tides with a range of up to 3 m (NOAA 2011). According to Courtin et al. (2010), the local population is represented primarily by the autochthonous Soussou ethnic group, who are located in small and dispersed settlements and whose main activities are agriculture, fishing, and fresh water collection. ...
The principal objective of this study was to determine the accuracy of an object-based image analysis OBIA approach in classifying mangroves from spaceborne synthetic aperture radar SAR data, specifically Advanced Land Observation Satellite ALOS, phased array L-band synthetic aperture radar PALSAR, and single-polarized HH and dual-polarized HH + HV L-bands. The accuracy of the object parameters was examined to determine the optimal colour and shape ratios for the hierarchical classification. At the first level of classification mangroves from non-mangroves, the results indicate that it is possible to accurately separate mangrove areas from saltpan and water/shallow zones using both sets of SAR images for the Mabala and Yélitono islands of southern Guinea. The final accuracies, based on the most optimal object parameters, were 91.1% and 92.3% for the single-and dual-polarized data, respectively. At the second level of classification, separation among the three mangrove classes identified was most accurate when using the dual-polarized data, at an overall accuracy of only 63.4%. The three mangrove classes identified included tall red mangrove Rhizophora racemosa , dwarf red mangrove R. mangle and R. harisonii , and black mangrove Avicennia germinans . Using the optimal combination of parameters, the extent to which a filter could be used to improve the accuracy was examined. At this level, it was determined that the dual-polarized data, filtered with a 3 × 3 Lee speckle filter and a segmentation scale of 5, resulted in an overall accuracy of 64.9%. Consequently, it is recommended that for persistently cloud-covered regions, such as Guinea, ALOS PALSAR data using an OBIA could be useful as a quick method for mapping and monitoring mangroves.
... The settlement and the landscape of Boffa focus are very similar to those which can be found on other parts of the Guinean littoral. From the Mellacoree river mouth in the south, at the border with Sierra Leone, to the Rio Compony river mouth in the north, near the border with Guinea Bissau, the Guinean littoral is characterized by a mangrove ecosystem, except for the headlands of Conakry and Cape Verga [31] and the important HAT foci in Guinea (Boffa, Dubréka and Forécariah) are all located in or around this mangrove ecosystem [2,32]. Although the population of the littoral is multiethnic (Nalou, Baga, Temne ethnic groups), the Soussou group is clearly the most important. ...
... These populations conduct several activities in the mangrove that expose them to the bite of tsetse flies and so to the risk of getting HAT. In a recent study of Forecariah focus, in the southernmost part of the Guinean mangrove, the identified risk activities were rice cultivation, water supply at backwater and use of pirogue jetties [32]. In Boffa, high human mobility between the mainland and the islands is certainly an important factor that increases the risk of transmission from infected tsetse to humans, and that favors the spread of the disease. ...
Human African Trypanosomiasis (HAT) in West Africa is a lethal, neglected disease caused by Trypanosoma brucei gambiense transmitted by the tsetse Glossina palpalis gambiensis. Although the littoral part of Guinea with its typical mangrove habitat is the most prevalent area in West Africa, very few data are available on the epidemiology of the disease in such biotopes. As part of a HAT elimination project in Guinea, we carried a cross-sectional study of the distribution and abundance of people, livestock, tsetse and trypanosomes in the focus of Boffa. An exhaustive census of the human population was done, together with spatial mapping of the area. Entomological data were collected, a human medical survey was organized together with a survey in domestic animals. In total, 45 HAT cases were detected out of 14445 people who attended the survey, these latter representing 50.9% of the total population. Potential additional carriers of T. b. gambiense were also identified by the trypanolysis test (14 human subjects and two domestic animals). No trypanosome pathogenic to animals were found, neither in the 874 tsetse dissected nor in the 300 domestic animals sampled. High densities of tsetse were found in places frequented by humans, such as pirogue jetties, narrow mangrove channels and watering points. The prevalence of T. b. gambiense in humans, combined to low attendance of the population at risk to medical surveys, and to an additional proportion of human and animal carriers of T. b. gambiense who are not treated, highlights the limits of strategies targeting HAT patients only. In order to stop T. b. gambiense transmission, vector control should be added to the current strategy of case detection and treatment. Such an integrated strategy will combine medical surveillance to find and treat cases, and vector control activities to protect people from the infective bites of tsetse.
... By taking into account the epidemiological features of HAT, the behaviour of the tsetse vector and the mobility of people in the average rural African milieu where HAT occurs, a search radius of 30 km was chosen [14]. In particular, a few studies investigated the daily distance covered by people living in HAT foci [23,24,25] and revealed that this tends not to exceed 15 km. The distance of 30 km enabled to take into account, at least in part, also people's movements that do not occur on a daily basis. ...
... To this end, the relationships are to be explored between HAT occurrence and a range of factors, including human and livestock population movements [34], environmental, climatic and socio-economic variables, as well as disease and vector control. The potential of this type of models has been investigated in a few local contexts, for example in southeastern Uganda for T. b. rhodesiense [35,36,37,38], and coastal Guinea for T. b. gambiense [25]. Recent attempts have also tried to address risk forecasts at the regional level in relation to climate change [39]. ...
Background
Human African trypanosomiasis (HAT), also known as sleeping sickness, persists as a public health problem in several sub-Saharan countries. Evidence-based, spatially explicit estimates of population at risk are needed to inform planning and implementation of field interventions, monitor disease trends, raise awareness and support advocacy. Comprehensive, geo-referenced epidemiological records from HAT-affected countries were combined with human population layers to map five categories of risk, ranging from “very high” to “very low,” and to estimate the corresponding at-risk population.
Results
Approximately 70 million people distributed over a surface of 1.55 million km2 are estimated to be at different levels of risk of contracting HAT. Trypanosoma brucei gambiense accounts for 82.2% of the population at risk, the remaining 17.8% being at risk of infection from T. b. rhodesiense. Twenty-one million people live in areas classified as moderate to very high risk, where more than 1 HAT case per 10,000 inhabitants per annum is reported.
Discussion
Updated estimates of the population at risk of sleeping sickness were made, based on quantitative information on the reported cases and the geographic distribution of human population. Due to substantial methodological differences, it is not possible to make direct comparisons with previous figures for at-risk population. By contrast, it will be possible to explore trends in the future. The presented maps of different HAT risk levels will help to develop site-specific strategies for control and surveillance, and to monitor progress achieved by ongoing efforts aimed at the elimination of sleeping sickness.
... Taking the total surface where flies could be captured and the total surface of the survey, as the most realistic values, the corresponding dispersal distance would be between 40 and 44 km per generation. The constant shading, high humidity and wind conditions of the particular continuously favorable mangrove ecosystem probably explain such important values (Courtin et al., 2010(Courtin et al., , 2015Courtin & Kagbadouno, 2011). Within these surfaces, the effective population density could be considered to vary between 3 and 6 individuals per km², in minimax≈[0.1, 8]. ...
... To be more effective in a context of low prevalence, other targeted active screening strategies were put in place. These included door-to-door [8] and spatial follow-up [18] by which it was possible to screen the family in a more friendly fashion as well as the most-at-risk populations that share the same daily spaces as the gHAT cases and TL-seropositive. The diagnostic algorithm of this targeted active screening was the same as the exhaustive active screening (Fig 2A). ...
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) is being achieved. 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) 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 the EPHP. Modelling estimated a slow but steady decline in transmission across the four 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.
... In West Africa, HAT is caused by the former species. 33 The number of HAT cases decreased by 95% between 2000 and 2018 and the WHO has targeted to interrupt transmission of the disease (to zero cases) by 2030. 34 Guinea has the largest number of HAT cases observed among West African countries. ...
Neglected tropical diseases (NTDs) predominantly affect vulnerable and marginalized populations in tropical and subtropical areas and globally affect more than one billion people. In Guinea, the burden of NTDs is estimated to be >7.5 disability-adjusted life years per million inhabitants. Currently the Guinea NTDs master plan (2017-2020) has identified eight diseases as public health problems: onchocerciasis, lymphatic filariasis, trachoma, schistosomiasis and soil-transmitted helminthiasis, leprosy, human African trypanosomiasis and Buruli ulcer. In this review we discuss the past and the current case burden of the priority NTDs in Guinea, highlight the major milestones and discuss current and future areas of focus for achieving the 2030 target outlined by the World Health Organization.
... where people are most likely to get bitten by tsetse. However, previous studies have demonstrated that covering contact points only is not enough to maintain adequate suppression of the tsetse population because of reinvasion pressure as tsetse move in from neighbouring uncontrolled and infested areas-as the main rivers will not receive control [1,14,34]. Differing to Kovacic's conclusion, in DRC we do not believe the CB-Approach can substitute for the expert-led approach of deploying targets on the main rivers [29]. Unlike northern Uganda, villages in Kwilu are not close or accessible to the main rivers, which are difficult to reach and are not highly frequented by the community members; people prefer smaller tributaries and streams for water and washing. ...
Gambiense Human African Trypanosomiasis (g-HAT) is a neglected tropical disease caused by trypanosomes transmitted by tsetse flies. 70% of cases in 2019 (604/863) occurred in the Democratic Republic of Congo (DRC). The national programme for g-HAT elimination in DRC includes a large-scale deployment of Tiny Targets which attract and kill tsetse. This intervention is directed by vector-control specialists with small teams, moving in canoes, deploying Tiny Targets along riverbanks where tsetse concentrate. While the targets are deployed in communal areas, and the method is cheap and easy-to-use, local people have little involvement. This study aimed to evaluate if a community-led vector control programme was feasible in the context of DRC's g-HAT elimination programme. In 2017, a community-led intervention was implemented in three villages in the Kwilu province of DRC. This intervention was evaluated through an Action Research with qualitative data collected through 21 focus group discussions and 289 hours of observation. Also the geographical location and quality of each Tiny Targets were collected (total number deployed = 2429). This research revealed that community-based approach largely worked: people were motivated and proactive, showed a good application of the acquired knowledge resulting in an effective deployment of Tiny Targets. In addition, our study provided evidence that acceptability of the targets by the community can improve deployment quality by reducing target loss and damage. The approach was feasible in places where canoe-based teams could not reach. Against these advantages, a community-based approach was time-consuming and had to adapt to the seasonal and daily rhythms of the community. A community-based approach for tsetse control is technically feasible and recommended but limits to the speed and scale of the approach restraints its application as a standalone strategy in a large-scale national programme aiming to eliminate g-HAT in a short timeframe.
... Les géographes se sont donc très tôt intéressés à la santé des populations, en la considérant comme une résultante des relations entre l'homme et le milieu naturel. Les grandes endémies du monde tropical telles que le paludisme (Amat-Roze, 1982), le VIH/SIDA (Amat-Roze, 2003), la fièvre jaune (Rémy, 1988), la dengue (Tran, 2004), la schistosomiase (Doumenge et al., 1982 ;Handschumacher et al., 1992), l'onchocercose (Marchal, 1978 ;Paris, 1982), la maladie du sommeil (Hervouët et Laveissière,1987 ;Courtin et al. 2010;Rouamba et al., 2009), le choléra (Roquet et al., 1998), ont fait l'objet d'études et de recherches par les géographes. Au fil du temps, la démarche géographique de la santé a abouti à la création d'une sous-discipline de la géographie, la géographie de la santé, restée longtemps méconnue. ...
... years old ) in the Forecariah and Dubreka mangrove HAT foci [23,35] that are currently the most active foci in West Africa. The Guinean mangrove ecosystem harbors high densities of G. palpalis gambiensis [7] and humans living in these areas are in close contact with tsetse flies during their daily activities [36]. Thirty six samples were from individuals diagnosed as HAT patients, and 44 were from uninfected individuals sampled in the same villages. ...
Background: The analysis of humoral responses directed against the saliva of blood-sucking arthropods was shown to provide epidemiological biomarkers of human exposure to vector-borne diseases. However, the use of whole saliva as antigen presents several limitations such as problems of mass production, reproducibility and specificity. The aim of this study was to design a specific biomarker of exposure to tsetse flies based on the in silico analysis of three Glossina salivary proteins (Ada, Ag5 and Tsgf1) previously shown to be specifically recognized by plasma from exposed individuals. Methodology/Principal Findings: Synthetic peptides were designed by combining several linear epitope prediction methods and Blast analysis. The most specific peptides were then tested by indirect ELISA on a bank of 160 plasma samples from tsetse infested areas and tsetse free areas. Anti-Tsgf1(18-43) specific IgG levels were low in all three control populations (from rural Africa, urban Africa and Europe) and were significantly higher (p < 0.0001) in the two populations exposed to tsetse flies (Guinean HAT foci, and South West Burkina Faso). A positive correlation was also found between Anti-Tsgf1(18-43) IgG levels and the risk of being infected by Trypanosoma brucei gambiense in the sleeping sickness foci of Guinea. Conclusion/Significance: The Tsgf1(18-43) peptide is a suitable and promising candidate to develop a standardize immunoassay allowing large scale monitoring of human exposure to tsetse flies in West Africa. This could provide a new surveillance indicator for tsetse control interventions by HAT control programs.
... In Côte d'Ivoire, we propose the following reactive active case-finding survey strategy, as suggested by WHO [8]: once a HAT case or a SERO TL+ is detected, a small mobile team is sent to screen the immediate neighborhood. Combined with tsetse control measures aimed at reducing human tsetse contacts in their risk environment, as was suggested by [5] in the Forecariah focus (Guinea), we believe that such measures may greatly speed up and ensure a more sustainable elimination process, especially in areas where the disease prevalence is becoming low. ...
Significant efforts to control human African trypanosomiasis (HAT) over the three past decades have resulted in drastic reductions of disease prevalence in Côte d'Ivoire. In this context, the costly and labor-intensive active mass screening strategy is no longer efficient. In addition to a more cost-effective passive surveillance system being implemented in this low-prevalence context, our aim was to develop an alternative targeted active screening strategy. In 2012, we carried out a targeted door-to-door (TDD) survey focused on the immediate vicinities of former HAT patients detected in the HAT focus of Bonon and compared the results to those obtained during classical active mass screening (AMS) surveys conducted from 2000 to 2012 in the same area. The TDD that provides a friendlier environment, inviting inhabitants to participate and gain awareness of the disease, detected significantly more HAT cases than the AMS. These results suggest that the TDD is an efficient and useful strategy in low-prevalence settings where very localized transmission cycles may persist and, in combination with passive surveillance, could help in eliminating HAT.
© M. Koffi et al., published by EDP Sciences, 2016.
... Although the decrease in tsetse density was not greater than 80%, this was enough to significantly reduce T. b. gambiense transmission within a few months, whereas in the "no vector control" area, the number of HAT cases remained stable. The need to add vector control activities to medical activities for gambiense HAT has already been pointed out [6,17,18], but the present study is the first one to accurately measure what it brings in terms of reduction of HAT transmission. The limits of the screen and treat strategy ...
Control of gambiense sleeping sickness, a neglected tropical disease targeted for elimination by 2020, relies mainly on mass screening of populations at risk and treatment of cases. This strategy is however challenged by the existence of undetected reservoirs of parasites that contribute to the maintenance of transmission. In this study, performed in the Boffa disease focus of Guinea, we evaluated the value of adding vector control to medical surveys and measured its impact on disease burden.
The focus was divided into two parts (screen and treat in the western part; screen and treat plus vector control in the eastern part) separated by the Rio Pongo river. Population census and baseline entomological data were collected from the entire focus at the beginning of the study and insecticide impregnated targets were deployed on the eastern bank only. Medical surveys were performed in both areas in 2012 and 2013.
In the vector control area, there was an 80% decrease in tsetse density, resulting in a significant decrease of human tsetse contacts, and a decrease of disease prevalence (from 0.3% to 0.1%; p=0.01), and an almost nil incidence of new infections (<0.1%). In contrast, incidence was 10 times higher in the area without vector control (>1%, p<0.0001) with a disease prevalence increasing slightly (from 0.5 to 0.7%, p=0.34).
Combining medical and vector control was decisive in reducing T. b. gambiense transmission and in speeding up progress towards elimination. Similar strategies could be applied in other foci.
... Pirogue jetties and fishing encampments are areas where humanfly contact can be intense. 102,103 • Coca, coffee, and also mango and banana plantations, where the original forest has been replaced, are also suitable habitats for tsetse flies, and these areas are related to transmission in plantation workers. 104 • Gambiense HAT is considered a rural disease, but transmission has also been occasionally observed in urban settings. ...
Human African trypanosomiasis (HAT), or sleeping sickness, is caused by Trypanosoma brucei gambiense, which is a chronic form of the disease present in western and central Africa, and by Trypanosoma brucei rhodesiense, which is an acute disease located in eastern and southern Africa. The rhodesiense form is a zoonosis, with the occasional infection of humans, but in the gambiense form, the human being is regarded as the main reservoir that plays a key role in the transmission cycle of the disease. The gambiense form currently assumes that 98% of the cases are declared; the Democratic Republic of the Congo is the most affected country, with more than 75% of the gambiense cases declared. The epidemiology of the disease is mediated by the interaction of the parasite (trypanosome) with the vectors (tsetse flies), as well as with the human and animal hosts within a particular environment. Related to these interactions, the disease is confined in spatially limited areas called "foci", which are located in Sub-Saharan Africa, mainly in remote rural areas. The risk of contracting HAT is, therefore, determined by the possibility of contact of a human being with an infected tsetse fly. Epidemics of HAT were described at the beginning of the 20th century; intensive activities have been set up to confront the disease, and it was under control in the 1960s, with fewer than 5,000 cases reported in the whole continent. The disease resurged at the end of the 1990s, but renewed efforts from endemic countries, cooperation agencies, and nongovernmental organizations led by the World Health Organization succeeded to raise awareness and resources, while reinforcing national programs, reversing the trend of the cases reported, and bringing the disease under control again. In this context, sustainable elimination of the gambiense HAT, defined as the interruption of the transmission of the disease, was considered as a feasible target for 2030. Since rhodesiense HAT is a zoonosis, where the animal reservoir plays a key role, the interruption of the disease's transmission is not deemed feasible.
... years old ) in the Forecariah and Dubreka mangrove HAT foci [23,35] that are currently the most active foci in West Africa. The Guinean mangrove ecosystem harbors high densities of G. palpalis gambiensis [7] and humans living in these areas are in close contact with tsetse flies during their daily activities [36]. Thirty six samples were from individuals diagnosed as HAT patients, and 44 were from uninfected individuals sampled in the same villages. ...
The analysis of humoral responses directed against the saliva of blood-sucking arthropods was shown to provide epidemiological biomarkers of human exposure to vector-borne diseases. However, the use of whole saliva as antigen presents several limitations such as problems of mass production, reproducibility and specificity. The aim of this study was to design a specific biomarker of exposure to tsetse flies based on the in silico analysis of three Glossina salivary proteins (Ada, Ag5 and Tsgf1) previously shown to be specifically recognized by plasma from exposed individuals.
Synthetic peptides were designed by combining several linear epitope prediction methods and Blast analysis. The most specific peptides were then tested by indirect ELISA on a bank of 160 plasma samples from tsetse infested areas and tsetse free areas. Anti-Tsgf118-43 specific IgG levels were low in all three control populations (from rural Africa, urban Africa and Europe) and were significantly higher (p<0.0001) in the two populations exposed to tsetse flies (Guinean HAT foci, and South West Burkina Faso). A positive correlation was also found between Anti-Tsgf118-43 IgG levels and the risk of being infected by Trypanosoma brucei gambiense in the sleeping sickness foci of Guinea.
The Tsgf118-43 peptide is a suitable and promising candidate to develop a standardize immunoassay allowing large scale monitoring of human exposure to tsetse flies in West Africa. This could provide a new surveillance indicator for tsetse control interventions by HAT control programs.
... years old) in the Forecariah and Dubreka mangrove HAT foci [23,35] that are currently the most active foci in West Africa. The Guinean mangrove ecosystem harbors high densities of G. palpalis gambiensis [7] and humans living in these areas are in close contact with tsetse flies during their daily activities [36]. Thirty six samples were from individuals diagnosed as HAT patients, and 44 were from uninfected individuals sampled in the same villages. ...
Background: The analysis of humoral responses directed against the saliva of blood-sucking arthropods was shown to provide epidemiological biomarkers of human exposure to vector-borne diseases. However, the use of whole saliva as antigen presents several limitations such as problems of mass production, reproducibility and specificity. The aim of this study was to design a specific biomarker of exposure to tsetse flies based on the in silico analysis of three Glossina salivary proteins (Ada, Ag5 and Tsgf1) previously shown to be specifically recognized by plasma from exposed individuals. Methodology/Principal Findings: Synthetic peptides were designed by combining several linear epitope prediction methods and Blast analysis. The most specific peptides were then tested by indirect ELISA on a bank of 160 plasma samples from tsetse infested areas and tsetse free areas. Anti-Tsgf1 18–43 specific IgG levels were low in all three control populations (from rural Africa, urban Africa and Europe) and were significantly higher (p,0.0001) in the two populations exposed to tsetse flies (Guinean HAT foci, and South West Burkina Faso). A positive correlation was also found between Anti-Tsgf1 18–43 IgG levels and the risk of being infected by Trypanosoma brucei gambiense in the sleeping sickness foci of Guinea. Conclusion/Significance: The Tsgf1 18–43 peptide is a suitable and promising candidate to develop a standardize immunoassay allowing large scale monitoring of human exposure to tsetse flies in West Africa. This could provide a new surveillance indicator for tsetse control interventions by HAT control programs. Copyright: ß 2013 Dama et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: Medical surveys and laboratory work were supported by the French Ministry of Foreign Affairs (FSP/REFS and Aires-SUD projects), the World Health Organization (WHO) and the International Atomic Energy Agency (IAEA). ED was a recipient of an Institut de Recherche pour le Développement (IRD) PhD fellowship. We would also like to thank the Targeting Tsetse Project funded by the Bill and Melinda Gates Foundation who paid for the synthetic peptides. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist.
... In Forecariah, the disease seems to be clustered in certain restricted mangrove areas with the active population (15e49 years old) being by far the most affected by the disease, suggesting that transmission does not occur in the peridomestic space but instead during human activities taking place in the mangrove. Consistent with this view is the analysis of the population's daily mobility in the Forecariah focus, which showed that HAT patients were characterised by a higher number of occupational sites in the mangrove as compared to matched controls [34]. Interestingly, the distribution of HAT and SERO subjects was quite similar both at the geographic scale and according to age group, suggesting that some determinants are common to both classes of individuals; presumably exposure to infected tsetse flies. ...
At a time when human African trypanosomiasis (HAT) elimination again seems a reachable goal in many parts of sub-Saharan Africa, it is becoming increasingly important to characterise the factors involved in disease resurgence or maintenance to develop sustainable control strategies. In this study conducted in the Forecariah mangrove focus in Guinea, HAT patients and serological suspects (SERO) were identified through mass screening of the population with the Card Agglutination Test for Trypanosomiasis (CATT) and were followed up for up to 2 years. Analysis of the samples collected during the follow-up of HAT patients and SERO was performed with PCR (TBR1/TBR2) and the trypanolysis serological test (TL) in order to clarify the role played by these individuals in the epidemiology of HAT. PCR positivity was higher in TL⁺ than in SERO TL⁻ (50% vs. 18%, respectively). Whereas CATT plasma titres decreased both in treated HAT patients and SERO TL⁻, SERO TL⁺ maintained high CATT titres. Four out of 17 SERO TL⁺ developed HAT during the study. These results strongly suggest that SERO TL⁺ individuals are asymptomatic carriers. In the context where disease prevalence is sufficiently low, treating SERO TL⁺ individual may thus be of crucial importance in order to cut transmission.
... Trypanosome samples were taken from HAT active foci (Dubreka, Boffa and Forecariah) in the coastal mangroves area in Guinea (Camara et al., 2005;Courtin et al., 2010) between November 2007 and April 2009. All samples (0.5 ml blood, 10 ml lymph node, if presence, of enlarged cervical node and 0.5 ml CSF collected in 1.5 ml microcentrifuge tube and stored at À20 8C until use) were collected during active surveillance conducted by the national HAT control programs (NCP) according to the Guinean HAT diagnostic procedures. ...
Human African trypanosomiasis (HAT) or sleeping sickness is a major public health problem in sub-Saharan Africa and is due to the kinetoplastid parasite Trypanosoma brucei gambiense in West and Central Africa. The exact role of multiple infections, the basis of clinical diversity observed in patients and the determinism that leads trypanosomes into different body fluids of the host remain opened questions to date. In this paper we investigate, in three Guinean foci, whether strains found in blood, lymph or cerebrospinal fluid (CSF) or in patients at different phase of HAT (phase 1, early phase 2 and late phase 2) are representative of the focus they belong to. Amplifications of parasites directly from body fluids led to substantial amounts of allelic drop outs, especially so for blood and CSF samples, which required data recoding of all homozygous sites into missing data. While controlling for geography, date of sampling and patient's phase of the disease, we found no effect of body fluids in the genetic structure of T. b. gambiense despite the presence of mixed infections. On the contrary, we found that the strains found in patients in different phase of the disease differed genetically, with early phase patients being more likely to be infected with more recent strains than patients at a more advanced phase of the disease. Thus, the combination of date of sampling and patient's status represents a parameter to be controlled for in population genetic structure analyses. Additional studies will also be required to explore further the phenomenon of mixed infections and its consequences.
Numerous disorders go untreated owing to a lack of a suitable drug delivery technology or an appropriate therapeutic moiety, particularly when toxicities and side effects are a major concern. Treatment options for microbiological infections are not fulfilled owing to significant adverse effects or extended therapeutic options. Advanced therapy options, such as active targeting, may be preferable to traditional ways of treating infectious diseases. Niosomes can be defined as microscopic lamellar molecules formed by a mixture of cholesterol, nonionic surfactants (alkyl or dialkyl polyglycerol ethers), and sometimes charge-inducing agents. These molecules comprise both hydrophilic and hydrophobic moieties of varying solubilities. In this review, several pathogenic microbes such as Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae, Plasmodium, Leishmania, and Candida spp. have been evaluated. Also, the development of a proper niosomal formulation for the required application was discussed. This review also reviews that an optimal formulation is dependent on several aspects, including the choice of nonionic surfactant, fabrication process, and fabrication parameters. Finally, this review will give information on the effectiveness of niosomes in treating acute microbial infections, the mechanism of action of niosomes in combating microbial pathogens, and the advantages of using niosomes over other treatment modalities.
The paper evaluates inter- and intra-company risk assessment methodologies and their potential adverse effect on noise control inaction.
La trypanosomiase humaine africaine est une affection parasitaire causée par un trypanosome transmis à l'homme par la glossine ou mouche tsé-tsé. En passant en 20 ans d'un contexte épidémique à un contexte d'élimination, cette maladie a subi une transition épidémiologique sans précédent à laquelle les stratégies de lutte ont dû s'adapter. En absence de vaccin et de chimioprophylaxie, ces stratégies visent à assainir le réservoir humain et animal de parasites par des méthodes de dépistage et traitement, et à lutter contre la glossine vectrice pour limiter le contact hôte/vecteur et donc le risque de transmission. L'objectif de cette revue est de faire un état des lieux des stratégies et des outils de lutte actuellement utilisés, en mettant l'accent sur leurs intérêts et limites dans ce contexte de transition épidémiologique, toujoursen progression vers l'interruption de la transmission
La trypanosomiase humaine africaine (THA) est une maladie séculaire, successivement négligée et oubliée qui a réussi à traverser le temps, depuis le début du XXe siècle jusqu'à nos jours. Elle est responsable de plusieurs millions de morts impactant négativement la vie sociale et économique des populations rurales d'Afrique subsaharienne. Si les principales manifestations cliniques n'ont pas varié depuis sa découverte, la recherche d'un traitement plus efficace, plus spécifique et moins toxique s'est poursuivie très timidement. Depuis la découverte du premier médicament, l'Atoxyl®, il y a plus de 120 ans, plusieurs autres molécules ont été adaptées au traitement de la THA. Cependant, aucune nouvelle molécule spécifique de la THA n'a été développée. Les recherches ont porté plutôt sur de nouveaux protocoles ou la combinaison de molécules déjà existantes et prévues pour le traitement d'autres maladies. Récemment toutefois, le traitement de première intention du deuxième stade de la THA à Trypanosoma brucei gambiense est passé du mélarsoprol, dérivé arsenical très toxique, à la combinaison thérapeutique de nifurtimox et d'éflornithine (NECT), puis au fexinidazole, avec en perspective, un traitement oral à dose unique à base d'acoziborole. Pour la seconde fois après le contrôle de l'endémie des années 1960, les efforts de lutte ont permis d'atteindre le plus bas nombre de nouveaux cas déclarés de THA en 2018, au point que l'OMS, ainsi que plusieurs autres initiatives (Campagne panafricaine d'éradication de la mouche tsé-tsé et de la trypanosomiase, Déclaration de Londres sur les maladies tropicales négligées, Objectifs de développement durable, etc.), visent son élimination comme problème de santé publique en 2020 et l'arrêt de la transmission en 2030. Ce contexte de faible incidence fait perdre toute rentabilité aux prospections médicales à la Jamot et appelle à un changement de stratégie. Il faut désormais privilégier la surveillance passive en intégrant le dépistage et le traitement de la THA dans les centres de santé périphériques. Cela nécessite, pour ce personnel non averti, un rappel de la symptomatologie clinique, essentielle à la suspicion de THA, et une information sur l'actualité thérapeutique
Background:
Significant efforts to control human African trypanosomiasis (HAT) over the two past decades have resulted in drastic decrease of its prevalence in Côte d'Ivoire. In this context, passive surveillance, integrated in the national health system and based on clinical suspicion, was reinforced. We describe here the health-seeking pathway of a girl who was the first HAT patient diagnosed through this strategy in August 2017.
Methods:
After definitive diagnosis of this patient, epidemiological investigations were carried out into the clinical evolution and the health and therapeutic itinerary of the patient before diagnosis.
Results:
At the time of diagnosis, the patient was positive in both serological and molecular tests and trypanosomes were detected in blood and cerebrospinal fluid. She suffered from important neurological disorders. The first disease symptoms had appeared three years earlier, and the patient had visited several public and private peripheral health care centres and hospitals in different cities. The failure to diagnose HAT for such a long time caused significant health deterioration and was an important financial burden for the family.
Conclusion:
This description illustrates the complexity of detecting the last HAT cases due to complex diagnosis and the progressive disinterest and unawareness by both health professionals and the population. It confirms the need of implementing passive surveillance in combination with continued sensitization and health staff training.
En Afrique subsaharienne, la croissance démographique et la variabilité climatique génèrent d’importants mouvements de population en direction des espaces protégés. L’installation en périphérie ou à l’intérieur de ces espaces, exposent les populations humaines et les animaux domestiques (qu’elles élèvent) à la piqûre d’insectes-vecteurs capables de transmettre des pathogènes (fièvre jaune, leishmanioses, trypanosomoses etc.). C’est le cas des glossines (ou mouches tsé-tsé), vecteurs de la Trypanosomiase Humaine Africaine (THA ou maladie du sommeil) et de la Trypanosomose Animale Africaine (TAA). En Côte d’Ivoire, la population est passée de 2,6 millions d’habitants (8 hab/km2) en 1950 à 23,1 millions d’habitants (71,6 hab/km2) en 2015. Le processus de déforestation en faveur de l’agriculture (plantations de café, de cacao, d’hévéas, d’anacardier etc.) a provoqué une saturation foncière qui a orienté les populations agricoles en direction des espaces protégés. Cette anthropisation croissante en marge et à l’intérieur des espaces protégés, exposent les populations humaines et animales domestiques à la piqûre des glossines et au risque trypanosomien. L’objectif de cette étude est de rendre compte des processus d’exploitation de territoires situés en marges et à l’intérieur de deux espaces protégés et d’évaluer le risque trypanosomien associé. Dans un premier temps, il s’agit de caractériser les dynamiques de peuplements (création, extension et multiplication des peuplements, augmentation des densités de populations humaines) et les évolutions de l’emprise rurale (superficies cultivées et types de cultures) en périphérie du Parc National de Taï (forêt) et du Parc National de la Comoé (savane). Les activités menées par les populations riveraines en périphérie et au sein de ces espaces protégés sont également étudiées (cueillette, chasse, pêche, pâturage, orpaillage, etc.). Parallèlement, afin d’évaluer le risque, des enquêtes entomologiques (diversité des espèces, densité et infection des glossines), médicales et vétérinaires (séroprévalence, prévalence de la THA et de la TAA) ont été menées. Cette approche « One Health », permet de mesurer l’exposition au risque trypanosomien, en tenant compte de la manière dont les populations humaines exploitent les territoires situés en marge et à l’intérieur d’espaces protégés. Au vu des projections démographiques et des questions foncières à venir qui leurs sont associées, cette thématique apparaît essentielle en vue de l’élimination des trypanosomoses humaines et animales.
Objectives:
The application of GIS in health science has increased over the last decade and new innovative application areas have emerged. This study reviews the literature and builds a framework to provide a conceptual overview of the domain, and to promote strategic planning for further research of GIS in health.
Method:
The framework is based on literature from the library databases Scopus and Web of Science. The articles were identified based on keywords and initially selected for further study based on titles and abstracts. A grounded theory-inspired method was applied to categorize the selected articles in main focus areas. Subsequent frequency analysis was performed on the identified articles in areas of infectious and non-infectious diseases and continent of origin.
Results:
A total of 865 articles were included. Four conceptual domains within GIS in health sciences comprise the framework: spatial analysis of disease, spatial analysis of health service planning, public health, health technologies and tools. Frequency analysis by disease status and location show that malaria and schistosomiasis are the most commonly analyzed infectious diseases where cancer and asthma are the most frequently analyzed non-infectious diseases. Across categories, articles from North America predominate, and in the category of spatial analysis of diseases an equal number of studies concern Asia.
Conclusion:
Spatial analysis of diseases and health service planning are well-established research areas. The development of future technologies and new application areas for GIS and data-gathering technologies such as GPS, smartphones, remote sensing etc. will be nudging the research in GIS and health.
Spatially-explicit information is essential for planning and implementing interventions against
vector-borne diseases. This is also true for African trypanosomoses, a group of diseases of both
humans and animals caused by protozoa of the Genus Trypanosoma, and transmitted by tsetse
flies (Genus Glossina).
In this thesis the knowledge gaps and the requirements for an evidence-based decision making in
the field of tsetse and trypanosomoses are identified, with a focus on georeferenced data and
Geographic Information Systems (GIS). Datasets, tools and analyses are presented that aim to fill
some of the identified knowledge gaps.
For the human form of the disease, also known as sleeping sickness, case detection and treatment
are the mainstay of control, so that accurate knowledge of the geographic distribution of
infections is paramount. In this study, an Atlas was developed that provides village-level
information on the reported occurrence of sleeping sickness. The geodatabase underpinning the
Atlas also includes the results of active screening activities, even when no cases were detected.
The Atlas enables epidemiological maps to be generated at a range of scales, from local to global,
thus providing evidence for strategic and technical decision making.
In the field of animal trypanosomosis control, also known as nagana, much emphasis has recently
been placed on the vector. Accurate delineation of tsetse habitat appears as an essential
component of ongoing and upcoming interventions against tsetse. The present study focused on
land cover datasets and tsetse habitat. The suitability for tsetse of standardized land cover classes
was explored at continental, regional and national level, using a combination of inductive and
deductive approaches. The land cover classes most suitable for tsetse were identified and
described, and tailored datasets were derived.
The suite of datasets, methodologies and tools presented in this thesis provides evidence for
informed planning and implementation of interventions against African trypanosomoses at a range
of spatial scales.
Human movement is a key behavioral factor in many vector-borne disease systems because it influences exposure to vectors and thus the transmission of pathogens. Human movement transcends spatial and temporal scales with different influences on disease dynamics. Here we develop a conceptual model to evaluate the importance of variation in exposure due to individual human movements for pathogen transmission, focusing on mosquito-borne dengue virus.
We develop a model showing that the relevance of human movement at a particular scale depends on vector behavior. Focusing on the day-biting Aedes aegypti, we illustrate how vector biting behavior combined with fine-scale movements of individual humans engaged in their regular daily routine can influence transmission. Using a simple example, we estimate a transmission rate (R(0)) of 1.3 when exposure is assumed to occur only in the home versus 3.75 when exposure at multiple locations--e.g., market, friend's--due to movement is considered. Movement also influences for which sites and individuals risk is greatest. For the example considered, intriguingly, our model predicts little correspondence between vector abundance in a site and estimated R(0) for that site when movement is considered. This illustrates the importance of human movement for understanding and predicting the dynamics of a disease like dengue. To encourage investigation of human movement and disease, we review methods currently available to study human movement and, based on our experience studying dengue in Peru, discuss several important questions to address when designing a study.
Human movement is a critical, understudied behavioral component underlying the transmission dynamics of many vector-borne pathogens. Understanding movement will facilitate identification of key individuals and sites in the transmission of pathogens such as dengue, which then may provide targets for surveillance, intervention, and improved disease prevention.
Human population growth, climate change and economic development are causing major environmental modifications in Western Africa, which will have important repercussions on the epidemiology of sleeping sickness. A new initiative, the Atlas of human African trypanosomiasis (HAT), aims at assembling and geo-referencing all epidemiological data derived from both active screening activities and passive surveillance. A geographic database enables to generate up-to-date disease maps at a range of scales and of unprecedented spatial accuracy. We present preliminary results for seven West African countries (Benin, Burkina Faso, Côte d'Ivoire, Ghana, Guinea, Mali and Togo) and briefly discuss the relevance of the Atlas for future monitoring, control and research activities.
We undertook a population genetics analysis of the tsetse fly Glossina palpalis gambiensis, a major vector of sleeping sickness in West Africa, using microsatellite and mitochondrial DNA markers. Our aims were to estimate effective population size and the degree of isolation between coastal sites on the mainland of Guinea and Loos Islands. The sampling locations encompassed Dubréka, the area with the highest Human African Trypanosomosis (HAT) prevalence in West Africa, mangrove and savannah sites on the mainland, and two islands, Fotoba and Kassa, within the Loos archipelago. These data are discussed with respect to the feasibility and sustainability of control strategies in those sites currently experiencing, or at risk of, sleeping sickness.
We found very low migration rates between sites except between those sampled around the Dubréka area that seems to contain a widely dispersed and panmictic population. In the Kassa island samples, various effective population size estimates all converged on surprisingly small values (10<N(e)<30) that suggest either a recent bottleneck, and/or other biological or ecological factors such as strong variance in the reproductive success of individuals.
Whatever their origin, the small effective population sizes suggest high levels of inbreeding in tsetse flies within the island samples in marked contrast to the large diffuse deme in Dubréka zones. We discuss how these genetic results suggest that different tsetse control strategies should be applied on the mainland and islands.
This study aimed at identifying factors influencing the development of Human African Trypanosomosis (HAT, or sleeping sickness) in the focus of Bonon, located in the mesophile forest of Côte d'Ivoire. A previous study mapping the main daytime activity sites of 96 patients revealed an important disparity between the area south of the town- where all the patients lived- and the area north of the town, apparently free of disease. In order to explain this disparity, we carried out a spatial analysis of the key components of the pathogenic system, i.e. the human host, the tsetse vector and the trypanosomes in their environment using a geographic information system (GIS).
This approach at the scale of a HAT focus enabled us to identify spatial patterns which linked to the transmission and the dissemination of this disease. The history of human settlement (with the rural northern area exploited much earlier than the southern one) appears to be a major factor which determines the land use pattern, which itself may account for differences found in vector densities (tsetse were found six times more abundant in the southern rural area than in the northern). Vector density, according to the human and environmental context in which it is found (here an intense mobility between the town of Bonon and the rural areas), may explain the observed spatial differences in HAT prevalence.
This work demonstrates the role of GIS analyses of key components of the pathogenic system in providing a better understanding of transmission and dissemination of HAT. Moreover, following the identification of the most active transmission areas, and of an area unfavourable to HAT transmission, this study more precisely delineates the boundaries of the Bonon focus. As a follow-up, targeted tsetse control activities starting north of Bonon (with few chances of reinvasion due to very low densities) going south, and additional medical surveys in the south will be proposed to the Ivoirian HAT control program to enhance the control of the disease in this focus. This work also shows the evolution of HAT regarding time and environment, and the methodology used may be able to predict possible sleeping sickness development/extinction in areas with similar history and space organization.
Allele frequencies at four microsatellite loci, and morphometric features based on 11 wing landmarks, were compared among three populations of Glossina palpalis gambiensis (Diptera: Glossinidae) in Guinea. One population originated from the Loos islands separated from the capital Conakry by 5 km of sea, and the two others originated from the continental mangrove area close to Dubreka, these two groups being separated by approximately 30 km. Microsatellites and wing geometry data both converged to the idea of a separation of the Loos island population from those of the mangrove area. Although occasional contacts cannot be excluded, our results support the hypothesis of the Loos population of tsetse flies being a completely isolated population. This situation will favor a sequenced intervention against human African trypanosomosis and the possibility of an elimination of tsetse from this island.
Conflict and war have long been recognized as determinants of infectious disease risk. Re-emergence of epidemic sleeping sickness in sub-Saharan Africa since the 1970s has coincided with extensive civil conflict in affected regions. Sleeping sickness incidence has placed increasing pressure on the health resources of countries already burdened by malaria, HIV/AIDS, and tuberculosis. In areas of Sudan, the Democratic Republic of the Congo, and Angola, sleeping sickness occurs in epidemic proportions, and is the first or second greatest cause of mortality in some areas, ahead of HIV/AIDS. In Uganda, there is evidence of increasing spread and establishment of new foci in central districts. Conflict is an important determinant of sleeping sickness outbreaks, and has contributed to disease resurgence. This paper presents a review and characterization of the processes by which conflict has contributed to the occurrence of sleeping sickness in Africa. Conflict contributes to disease risk by affecting the transmission potential of sleeping sickness via economic impacts, degradation of health systems and services, internal displacement of populations, regional insecurity, and reduced access for humanitarian support. Particular focus is given to the case of sleeping sickness in south-eastern Uganda, where incidence increase is expected to continue. Disease intervention is constrained in regions with high insecurity; in these areas, political stabilization, localized deployment of health resources, increased administrative integration and national capacity are required to mitigate incidence. Conflict-related variables should be explicitly integrated into risk mapping and prioritization of targeted sleeping sickness research and mitigation initiatives.
While the number of new detected cases of HAT is falling, say the authors, sleeping sickness could suffer the "punishment of success," receiving lower priority by public and private health institutions.
Sleeping sickness (HAT) caused by T.b. rhodesiense is a major veterinary and human public health problem in Uganda. Previous studies have investigated spatial risk factors for T.b. rhodesiense at large geographic scales, but none have properly investigated such risk factors at small scales, i.e. within affected villages. In the present work, we use a case-control methodology to analyse both behavioural and spatial risk factors for HAT in an endemic area.
The present study investigates behavioural and occupational risk factors for infection with HAT within villages using a questionnaire-based case-control study conducted in 17 villages endemic for HAT in SE Uganda, and spatial risk factors in 4 high risk villages. For the spatial analysis, the location of homesteads with one or more cases of HAT up to three years prior to the beginning of the study was compared to all non-case homesteads. Analysing spatial associations with respect to irregularly shaped geographical objects required the development of a new approach to geographical analysis in combination with a logistic regression model.
The study was able to identify, among other behavioural risk factors, having a family member with a history of HAT (p = 0.001) as well as proximity of a homestead to a nearby wetland area (p < 0.001) as strong risk factors for infection. The novel method of analysing complex spatial interactions used in the study can be applied to a range of other diseases.
Spatial risk factors for HAT are maintained across geographical scales; this consistency is useful in the design of decision support tools for intervention and prevention of the disease. Familial aggregation of cases was confirmed for T. b. rhodesiense HAT in the study and probably results from shared behavioural and spatial risk factors amongmembers of a household.
The West African trypanosomoses are mostly transmitted by riverine species of tsetse fly. In this study, we estimate the dispersal and population size of tsetse populations located along the Mouhoun river in Burkina Faso where tsetse habitats are experiencing increasing fragmentation caused by human encroachment. Dispersal estimated through direct (mark and recapture) and indirect (genetic isolation by distance) methods appeared consistent with one another. In these fragmented landscapes, tsetse flies displayed localized, small subpopulations with relatively short effective dispersal. We discuss how such information is crucial for designing optimal strategies for eliminating this threat. To estimate ecological parameters of wild animal populations, the genetic measures are both a cost- and time-effective alternative to mark-release-recapture. They can be applied to other vector-borne diseases of medical and/or economic importance.
There is much historical evidence of the spread of disease through human mobility. Today in spite of medical advances and international health measures there is still much cause for concern. There is now more mobility, facilitated by modern transport and sometimes precipitated by major natural and man-made disasters. Redistribution of population is occuring in the developing world, particularly massive rural-urban movements. Population mobility has contributed to the transmission of malaria and prejudiced programmes for control and eradication; but mobility and other human factors have not been adequately studied. Parasites and vectors receive more attention than do people. Epidemiological studies need to pay greater attention to the nature and variety of population movements and to their differing impacts upon disease and health. It is essential to distinguish between migration (involving change of residence) and circulation (movement away from residence with sebsequent return). In tropical Africa various spatial and temporal dimensions can be applied to differentiate within these two major categories of mobility. In turn there are various associated physical and psychological health hazards.
During the latter months of 1998, cases of sleeping sickness caused by Trypanosoma brucei rhodesiense presented in Soroti district, eastern Uganda, a region which had not previously experienced cases of the disease. Cattle are the main reservoir for T b rhodesiense, by contrast with sleeping sickness caused by Trypanosoma brucei gambiense in west Africa where there appears to be no epidemiologically significant animal reservoir. Several factors have been identified that interacted to produce ideal conditions for the establishment of a new disease focus. After a period of civil unrest, Soroti, which is within the tsetse belt, was repopulated by people and later, cattle. Both the cattle restocking and the subsequent trade in these cattle at a local cattle market had a role in the appearance of the disease. Recently, molecular biology techniques have become available for the detection and genotype identification of T b rhodesiense and thus it is now possible to distinguish human infective and non-infective trypanosomes in cattle. In light of these advances in identification and in both field and epidemiological techniques, successful disease control management has become an achievable goal and will require the collaboration and expertise of clinicians, veterinarians, epidemiologists and laboratory scientists.
Population mobility has long been established as a feature of life in Africa south of the Sahara. Even though it appears to be a factor in the spread of sleeping-sickness there do not seem to have been serious epidemics until the latter part of the nineteenth century and the early decades of the twentieth century. Various types of population movement of the present day and their possible relevance to trypanosomiasis are discussed. Density of population and settlement patterns are also important. Some of the changes in these which are relevant to trypanosomiasis are outlined and the need for more detailed information on these and on population mobility is emphasized.
Human African trypanosomosis (HAT) remains a major public health problem in Subsaharan Africa. The region around the town of Bonon in middle western Côte d'Ivoire is a highly endemic HAT zone. The purpose of this study was to assess the role of travelling of infected patients in transmission of HAT. The study population included a total of 96 patients in whom HAT had been diagnosed actively or passively between 1999 and 2000. Information on each patient's residence and workplaces, i.e. water site, and farm field, was used to calculate the mean distance traveled and mean number of places visited daily by each patient. Findings indicated that both parameters, i.e., distance traveled and number of places visited, were significantly higher for patients living in Bonon than those living in hamlets or homesteads. Based on analysis of patient movements the endemic zone could be divided into three subdivisions with different modes of disease transmission. This study was performed as a preliminary step for a larger investigation designed to allow specific targeting of HAT hot spots based mainly on a geographic information system.
The purpose of this study carried out in two adjacent areas of the coastal mangrove forest of Guinea (Dubreka and Boffa) was to screen the population for disease, provide information on human African trypanosomiasis (HAT, a.k.a. sleeping sickness) and compare the epidemiologic and clinical features with those of outbreak areas in the Ivory Coast where more data is currently available. Cases of HAT were confirmed by parasitological testing after active medical work-up (91 of 9637 patients examined). Five cases were confirmed in patients in treatment centers. Of the first 57 cases admitted for treatment in the Dubreka and Boffa centers, 29 were responded to a clinical and epidemiological questionnaire and underwent thorough clinical examination. Disease stage was determined by cytochemical testing of cerebrospinal fluid. As in outbreak areas of the Ivory Coast, sleeping sickness in Dubreka and Boffa is a rural disease mainly affecting the working population. Most cases identified in Guinea involved men and women working in farming, fishing, or salt extraction. However unlike Ivory Coast outbreak areas where ethnic diversity related to share cropping is considered to play a major role in maintaining endemicity, almost all patients in our study (98%) were from the native Soussou population that is self employed and lives in villages with no immigrant population. While clinical symptoms observed in these patients were not different from those reported elsewhere, there was a high frequency of cervical adenopathy (93%). This finding could provide a useful diagnostic sign for screening populations living in these mangrove forest regions and as a source for parasitological diagnosis as shown by the fact that 88.5% of patients were screened on the basis of lymph node fluid specimens. Most patients including among those identified by active work-up (5%) were in the meningo-encephalitis phase of the disease (98%). The findings of this study underline the need not only to continue surveillance in these regions but also to extend surveillance throughout the country as a means of avoiding recrudescence and extension of the disease.
To review the geography and history of sleeping sickness (Human African trypanosomiasis; HAT) over the past 100 years in West Africa, to identify priority areas for sleeping sickness surveillance and areas where HAT no longer seems active.
History and geography of HAT were summarized based on a review of old reports and recent publications and on recent results obtained from medical surveys conducted in West Africa up to 2006.
Active HAT foci seem to have moved from the North to the South. Endemic HAT presently appears to be limited to areas where annual rainfall exceeds 1200 mm, although the reasons for this remain unknown. There has also been a shift towards the south of the isohyets and of the northern distribution limit of tsetse. Currently, the most severely affected countries are Guinea and Ivory Coast, whereas the northern countries seem less affected. However, many parts of West Africa still lack information on HAT and remain to be investigated. Of particular interest are the consequences of the recent political crisis in Ivory Coast and the resulting massive population movements, given the possible consequences on HAT in neighbouring countries.
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