Monitoring the elimination of human African trypanosomiasis: Update to 2016

Abstract

Background: Human African trypanosomiasis (HAT) is a neglected tropical disease targeted for elimination 'as a public health problem' by 2020. The indicators to monitor progress towards the target are based on the number of reported cases, the related areas and populations exposed at various levels of risk, and the coverage of surveillance activities. Based on data provided by the National Sleeping Sickness Control Programmes (NSSCP), Non-Governmental Organizations (NGOs) and research institutions-and assembled in the Atlas of HAT-the World Health Organization (WHO) provides here an update to 2016 for these indicators, as well as an analysis of the epidemiological situation.

Results: Trends for the two primary indicators of elimination are on track for the 2020 goal: 2,164 cases of HAT were reported in 2016 (as compared to the milestone of 4,000 cases), and for the period 2012-2016 280,000 km2 are estimated to be at moderate risk or higher (i.e. ≥ 1 case/10,000 people/year), as compared to the milestone of 230,000 km2. These figures correspond to reductions of 92% and 61% as compared to the respective baselines (i.e. 26,550 HAT cases in the year 2000, and 709,000 km2 exposed at various levels of risk for the period 2000-2004). Among the secondary indicators, an overall improvement in the coverage of at risk populations by surveillance activities was observed. Regarding passive surveillance, the number of fixed health facilities providing gambiense HAT diagnosis or treatment expanded, with 1,338 enumerated in endemic countries in 2017 (+52% as compared to the survey completed only sixteen months earlier). Concerning rhodesiense HAT, 124 health facilities currently provide diagnosis or treatment. The broadening of passive surveillance is occurring in a context of fairly stable intensity of active case finding, with between 1.8 million and 2.4 million people screened per year over the period 2012-2016.

Discussion: Elimination of HAT as a public health problem by 2020 seems within reach, as the epidemiological trends observed in previous years are confirmed in this latest 2016 monitoring update. However, looking beyond 2020, and in particular to the 2030 goal of elimination of transmission as zero cases for the gambiense form of the disease only, there is no room for complacency. Challenges still abound, including ensuring the effective integration of HAT control activities in the health system, sustaining the commitment of donors and HAT endemic countries, and clarifying the extent of the threat posed by cryptic reservoirs (e.g. human asymptomatic carriers and the possible animal reservoirs in gambiense HAT epidemiology). WHO provides through the network for HAT elimination the essential coordination of the wide range of stakeholders to ensure synergy of efforts.

Fig 1. Total number of reported cases of HAT (gambiense and rhodesiense) per year (2000–2016).

The green line shows the milestones set in the WHO Roadmap for HAT elimination [3].

Fig 2. Number of people screened by active case-finding surveys, in countries endemic for T. b. gambiense (2000–2016).

Concerning rhodesiense HAT, 72 and 54 cases were reported in 2015 and 2016 respectively, which constitute 2.5% of the total HAT reported cases. The cases reported in 2016 represent a reduction of 92.4% compared to the year 2000.

Fig 3

(a) The distribution of human African trypanosomiasis. Period 2012–2016. (b) The areas at risk of HAT infection. Period 2012–2016. The maps were created with ArcGIS 10.0 software (http://desktop.arcgis.com/). The base layers include the Shuttle Radar Topography Mission (https://www2.jpl.nasa.gov/srtm/), the Vector Map Level 0 (http://earth-info.nga.mil/publications/vmap0.html), and the Global Administrative Unit Layers (http://www.fao.org/geonetwork/srv/en/main.home).

Fig 4. Trends in areas at risk of gambiense and rhodesiense HAT where the disease is still considered as a public health problem (2000–2004 to 2012–2016).

The green line shows the milestones set by the WHO-NTD-STAG to achieve thfood e elimination of HAT as a public health problem by 2020.