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Strategies for Trypanosoma brucei gambiense elimination
Comment
Strategies for Trypanosoma brucei gambiense elimination Human African trypanosomiasis, a disease caused by Trypanosoma brucei (T b) gambiense, is endemic in 24 countries across sub-Saharan Africa, affecting disproportionately the most impoverished regions, including the Democratic Republic of Congo and Central African Republic.1 Since the early 1990s, concerted control efforts have achieved a steady decline in incidence. This success has spurred WHO’s goal to eliminate human African trypanosomiasis caused by T b gambiense as a public health problem by 2020, defined as reducing reported cases to fewer than one per 10 000 inhabitants in at least 90% of settings, with fewer than 2000 cases annually in Africa.2 The subsequent goal of WHO is to eliminate any reported cases of human African trypanosomiasis caused by T b gambiense in endemic countries by 2030, thereby terminating transmission of the disease globally. To facilitate WHO’s goals, it is important to assess the cost-effectiveness of interventions that incorporate emerging technologies for case detection, treatment, and vector control in the context of economic constraints and logistical barriers. In an elegant modelling study in The Lancet Global Health, Simone Sutherland and colleagues evaluated the cost-effectiveness of synergistic and progressively available approaches.3 To account for heterogeneity in tsetse exposure and the role of animal reservoirs, strategies were investigated in the context of varying disease dynamics and transmission intensities that characterise a range of settings. Their analyses indicated that, although several strategy combinations have the potential to achieve elimination goals, only approaches that incorporate emerging diagnostic, treatment, and vector control technologies are cost-effective. More specifically, their findings suggested that current control methods comprised exclusively of passive and active case-finding followed by treatment are not costeffective options relative to strategies that include vector control with improved insecticide-impregnated screens, mobile teams with rapid diagnostic methods, and next-generation treatment regimens. Over the past decade, the incidence of human African trypanosomiasis caused by T b gambiense has dropped by more than 75%, down to fewer than 4000 reported cases a year. Nonetheless, an estimated
70 million people across 35 countries remain at risk of T b gambiense infection, and incidence is thought to be widely under-reported. Among regions at risk of human African trypanosomiasis caused by T b gambiense, 62% are currently low transmission areas.4 Sutherland and colleagues found that strategies most likely to meet elimination goals are not cost-effective in areas of low transmission, highlighting the effect of variations in transmission intensities across settings on the costeffectiveness of control efforts. Heterogeneity in incidence between settings arises from variable tsetse density, distributions in human exposure to tsetse, animal reservoirs, compliance with active screening, and under-reporting. The effect of variation in these factors should be considered with respect to the optimality of alternative strategies in specific settings. For example, strategies most likely to achieve elimination in areas such as Bipindi, Cameroon, where livestock are an important disease reservoir,5 might be different in settings including Boffa, Guinea, where livestock have a small role.6 As a result, the cost-effectiveness of tailored and localised recommendations will have greater use in facilitating elimination than will broad guidance. We should also bear in mind that, as incidence declines, handling of remaining cases becomes disproportionately costly and challenging. Further studies that capture the long-term benefits of eradication, including the reduced monetary commitment and, most importantly, averted health burden for future generations, will be fundamental to assessing the indirect benefits and the positive externalities of achieving and sustaining elimination. Progress towards WHO’s goals for 2020 and 2030 must be paralleled with a shift in focus towards identifying optimum control strategies to maintain elimination, as shown by the history of control efforts for human African trypanosomiasis caused by T b gambiense. Through a combination of vector control and active and passive case-finding for early detection and rapid treatment of cases, human African trypanosomiasis caused by T b gambiense was near eradicated in the early 1960s. Unfortunately, a collapse of surveillance and monitoring activities in endemic countries, primarily originating from political instability, led to re-emergence of the disease in the early
www.thelancet.com/lancetgh Published online November 21, 2016 http://dx.doi.org/10.1016/S2214-109X(16)30284-4
Lancet Glob Health 2016 Published Online November 21, 2016 http://dx.doi.org/10.1016/ S2214-109X(16)30284-4 See Online/Articles http://dx.doi.org/10.1016/ S2214-109X(16)30237-6
1
Comment
1990s.7 The cost-effectiveness framework developed by Sutherland and colleagues for human African trypanosomiasis is a powerful method for informing a more effective endgame strategy. For example, to mitigate the possibility of resurgence, evaluation of the cost-effectiveness of surveillance methods to maintain elimination status across settings and assessment of the value of dedicating resources for post-elimination efforts will be important. Despite impressive progress towards elimination, social unrest, gaps in the coverage of populations at risk, competing health interests, and possible donor fatigue present challenges to successful elimination of human African trypanosomiasis caused by T b gambiense and subsequent maintenance of this status. The timely findings of Sutherland and colleagues show the value of adopting new control methods for diagnosis, treatment, and surveillance that are expected to accelerate elimination cost-effectively, in a range of settings. Translation of these findings into field implementation will require continued awareness and commitment among governments and key players in global public health, until 2030 and beyond.
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Abhishek Pandey, *Alison Galvani Center for Infectious Disease Modeling and Analysis, Yale School of Public Health, New Haven, CT 06520, USA [email protected] We declare no competing interests. Copyright © The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY license. 1
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WHO. Human African trypanosomiasis: number of new cases of human African trypanosomiasis (T b gambiense) reported, 2015. http://apps.who. int/neglected_diseases/ntddata/hat/hat.html (accessed Sept 13, 2016). Uniting to Combat NTDs. The London Declaration. http://unitingtocombatntds.org/resource/london-declaration (accessed Sept 14, 2016). Sutherland CS, Stone CM, Steinmann P, Tanner M, Tediosi F. Seeing beyond 2020: an economic evaluation of contemporary and emerging strategies for elimination of Trypanosoma brucei gambiense. Lancet Glob Health 2016; published online Nov 21. http://dx.doi.org/10.1016/S2214109X(16)30237-6. Simarro PP, Cecchi G, Franco JR, et al. Monitoring the progress towards the elimination of gambiense human African trypanosomiasis. PLoS Negl Trop Dis 2015; 9: e0003785. Njiokou F, Nimpaye H, Simo G, et al. Domestic animals as potential reservoir hosts of Trypanosoma brucei gambiense in sleeping sickness foci in Cameroon. Parasite 2010; 17: 61–66. Kagbadouno MS, Camara M, Rouamba J, et al. Epidemiology of sleeping sickness in Boffa (Guinea): where are the trypanosomes? PLoS Negl Trop Dis 2012; 6: e1949. Simarro PP, Diarra A, Ruiz Postigo JA, Franco JR, Jannin JG. The human African trypanosomiasis control and surveillance programme of the World Health Organization 2000–2009: the way forward. PLoS Negl Trop Dis 2011; 5: e1007.
www.thelancet.com/lancetgh Published online November 21, 2016 http://dx.doi.org/10.1016/S2214-109X(16)30284-4
Strategies for Trypanosoma brucei gambiense elimination Human African trypanosomiasis, a disease caused by Trypanosoma brucei (T b) gambiense, is endemic in 24 countries across sub-Saharan Africa, affecting disproportionately the most impoverished regions, including the Democratic Republic of Congo and Central African Republic.1 Since the early 1990s, concerted control efforts have achieved a steady decline in incidence. This success has spurred WHO’s goal to eliminate human African trypanosomiasis caused by T b gambiense as a public health problem by 2020, defined as reducing reported cases to fewer than one per 10 000 inhabitants in at least 90% of settings, with fewer than 2000 cases annually in Africa.2 The subsequent goal of WHO is to eliminate any reported cases of human African trypanosomiasis caused by T b gambiense in endemic countries by 2030, thereby terminating transmission of the disease globally. To facilitate WHO’s goals, it is important to assess the cost-effectiveness of interventions that incorporate emerging technologies for case detection, treatment, and vector control in the context of economic constraints and logistical barriers. In an elegant modelling study in The Lancet Global Health, Simone Sutherland and colleagues evaluated the cost-effectiveness of synergistic and progressively available approaches.3 To account for heterogeneity in tsetse exposure and the role of animal reservoirs, strategies were investigated in the context of varying disease dynamics and transmission intensities that characterise a range of settings. Their analyses indicated that, although several strategy combinations have the potential to achieve elimination goals, only approaches that incorporate emerging diagnostic, treatment, and vector control technologies are cost-effective. More specifically, their findings suggested that current control methods comprised exclusively of passive and active case-finding followed by treatment are not costeffective options relative to strategies that include vector control with improved insecticide-impregnated screens, mobile teams with rapid diagnostic methods, and next-generation treatment regimens. Over the past decade, the incidence of human African trypanosomiasis caused by T b gambiense has dropped by more than 75%, down to fewer than 4000 reported cases a year. Nonetheless, an estimated
70 million people across 35 countries remain at risk of T b gambiense infection, and incidence is thought to be widely under-reported. Among regions at risk of human African trypanosomiasis caused by T b gambiense, 62% are currently low transmission areas.4 Sutherland and colleagues found that strategies most likely to meet elimination goals are not cost-effective in areas of low transmission, highlighting the effect of variations in transmission intensities across settings on the costeffectiveness of control efforts. Heterogeneity in incidence between settings arises from variable tsetse density, distributions in human exposure to tsetse, animal reservoirs, compliance with active screening, and under-reporting. The effect of variation in these factors should be considered with respect to the optimality of alternative strategies in specific settings. For example, strategies most likely to achieve elimination in areas such as Bipindi, Cameroon, where livestock are an important disease reservoir,5 might be different in settings including Boffa, Guinea, where livestock have a small role.6 As a result, the cost-effectiveness of tailored and localised recommendations will have greater use in facilitating elimination than will broad guidance. We should also bear in mind that, as incidence declines, handling of remaining cases becomes disproportionately costly and challenging. Further studies that capture the long-term benefits of eradication, including the reduced monetary commitment and, most importantly, averted health burden for future generations, will be fundamental to assessing the indirect benefits and the positive externalities of achieving and sustaining elimination. Progress towards WHO’s goals for 2020 and 2030 must be paralleled with a shift in focus towards identifying optimum control strategies to maintain elimination, as shown by the history of control efforts for human African trypanosomiasis caused by T b gambiense. Through a combination of vector control and active and passive case-finding for early detection and rapid treatment of cases, human African trypanosomiasis caused by T b gambiense was near eradicated in the early 1960s. Unfortunately, a collapse of surveillance and monitoring activities in endemic countries, primarily originating from political instability, led to re-emergence of the disease in the early
www.thelancet.com/lancetgh Published online November 21, 2016 http://dx.doi.org/10.1016/S2214-109X(16)30284-4
Lancet Glob Health 2016 Published Online November 21, 2016 http://dx.doi.org/10.1016/ S2214-109X(16)30284-4 See Online/Articles http://dx.doi.org/10.1016/ S2214-109X(16)30237-6
1
Comment
1990s.7 The cost-effectiveness framework developed by Sutherland and colleagues for human African trypanosomiasis is a powerful method for informing a more effective endgame strategy. For example, to mitigate the possibility of resurgence, evaluation of the cost-effectiveness of surveillance methods to maintain elimination status across settings and assessment of the value of dedicating resources for post-elimination efforts will be important. Despite impressive progress towards elimination, social unrest, gaps in the coverage of populations at risk, competing health interests, and possible donor fatigue present challenges to successful elimination of human African trypanosomiasis caused by T b gambiense and subsequent maintenance of this status. The timely findings of Sutherland and colleagues show the value of adopting new control methods for diagnosis, treatment, and surveillance that are expected to accelerate elimination cost-effectively, in a range of settings. Translation of these findings into field implementation will require continued awareness and commitment among governments and key players in global public health, until 2030 and beyond.
2
Abhishek Pandey, *Alison Galvani Center for Infectious Disease Modeling and Analysis, Yale School of Public Health, New Haven, CT 06520, USA [email protected] We declare no competing interests. Copyright © The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY license. 1
2
3
4
5
6
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WHO. Human African trypanosomiasis: number of new cases of human African trypanosomiasis (T b gambiense) reported, 2015. http://apps.who. int/neglected_diseases/ntddata/hat/hat.html (accessed Sept 13, 2016). Uniting to Combat NTDs. The London Declaration. http://unitingtocombatntds.org/resource/london-declaration (accessed Sept 14, 2016). Sutherland CS, Stone CM, Steinmann P, Tanner M, Tediosi F. Seeing beyond 2020: an economic evaluation of contemporary and emerging strategies for elimination of Trypanosoma brucei gambiense. Lancet Glob Health 2016; published online Nov 21. http://dx.doi.org/10.1016/S2214109X(16)30237-6. Simarro PP, Cecchi G, Franco JR, et al. Monitoring the progress towards the elimination of gambiense human African trypanosomiasis. PLoS Negl Trop Dis 2015; 9: e0003785. Njiokou F, Nimpaye H, Simo G, et al. Domestic animals as potential reservoir hosts of Trypanosoma brucei gambiense in sleeping sickness foci in Cameroon. Parasite 2010; 17: 61–66. Kagbadouno MS, Camara M, Rouamba J, et al. Epidemiology of sleeping sickness in Boffa (Guinea): where are the trypanosomes? PLoS Negl Trop Dis 2012; 6: e1949. Simarro PP, Diarra A, Ruiz Postigo JA, Franco JR, Jannin JG. The human African trypanosomiasis control and surveillance programme of the World Health Organization 2000–2009: the way forward. PLoS Negl Trop Dis 2011; 5: e1007.
www.thelancet.com/lancetgh Published online November 21, 2016 http://dx.doi.org/10.1016/S2214-109X(16)30284-4