Sleeping sickness in the historical focus of forested Guinea: update using a geographically based method

Abstract

In 2017, 1447 new cases of Human African Trypanosomiasis (HAT) were reported, which reflects considerable progress towards the World Health Organisation's target of eliminating HAT as a public health problem by 2020. However, current epidemiological data are still lacking for a number of areas, including historical HAT foci. In order to update the HAT situation in the historical focus of forested Guinea, we implemented a geographically based methodology: Identification of Villages at Risk (IVR). The methodology is based on three sequential steps: Desk-based IVR (IVR-D), which selects villages at risk of HAT on the basis of HAT archives and geographical items; Field-based IVR (IVR-F), which consists in collecting additional epidemiological and geographical information in the field in villages at risk; and to be Medically surveyed IVR (IVR-M), a field data analysis through a Geographic Information System (GIS), to compile a list of the villages most at risk of HAT, suitable to guide active screening and passive surveillance. In an area of 2385 km² with 1420,530 inhabitants distributed in 1884 settlements, 14 villages with a population of 11,236 inhabitants were identified as most at risk of HAT and selected for active screening. Although no HAT cases could be confirmed, subjects that had come into contact with Trypanosoma brucei gambiense were identified and two sentinel sites were chosen to implement passive surveillance. IVR, which could be applied to any gambiense areas where the situation needs to be clarified, could help to reach the objective of HAT elimination.

Keywords: Elimination; Geography; Guinea; Risk; Sleeping sickness; Trypanosoma brucei gambiense.

Figure 1

Location of the study area. The map displays the location of the study area, including the five main towns (Kissidougou, Guéckédou, Macenta, Yomou, and N’Zerekore) and all of the villages.

Figure 2

General procedure for IVR. The IVR strategy is structured into three main steps. The first step corresponds to IVR-D, which makes it possible to assemble an initial list of at-risk villages. The second step, IVR-F, is intended to collect field data about the main health facilities and villages on the initial list. The third step involves constructing a geo-referenced database to conduct queries, in order to select the most at-risk villages to be medically surveyed (IVR-M).

Figure 3

Medical diagnosis procedure during IVR. Clinical and environmental suspected cases are first screened by CATT. If positive, the lymph nodes of individuals are examined. CATT-positive individuals who are negative for LN and TL are considered HAT-negative. All TL-positive subjects must be checked during the active screening. CATT+ = Card Agglutination Test for Trypanosomiasis positive; CATT− = Card Agglutination Test for Trypanosomiasis negative; LN+ = Lymph Node examination positive; LN− = Lymph Node examination negative; TL+ = Trypanolysis positive; TL− = Trypanolysis negative; NCPHAT: National Control Programme of HAT. TL is performed afterwards in the laboratory with the collected filter paper.

Figure 4

Location of HAT cases diagnosed from 1962 to 1964 in the Koundou Lengo Bengo focus (Gueckedou area). The map displays the distribution of HAT cases diagnosed from 1962 to 1964 in the Koundou Lengo Bengo focus, located in the Gueckedou area. This type of information is crucial in establishing the list of villages at risk of HAT to be visited in the field. Black dots with red circles represent the number of new sleeping sickness cases diagnosed between 1962 and 1964.

Figure 5

Villages identified during the IVR-D step, villages visited in the field (IVR-F), and villages selected for the active screening (IVR-M). The map displays the 49 villages selected during the IVR-D step, and the itinerary followed by the IVR team in the field to visit 24 of the villages. Fourteen of these villages were selected for the active screening, which are primarily located in the Gueckedou and N’Zerekore areas.