Epidemiology of Sleeping Sickness in Boffa (Guinea): Where Are the Trypanosomes?

Abstract

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.

In Silico Identification of a Candidate Synthetic Peptide (Tsgf118–43) to Monitor Human Exposure to Tsetse Flies in West Africa

“…We were not able in the framework of this study to assess the dynamics of apparition and disappearance of Glossina saliva specific antibodies and the relation between IgG responses and the individual tsetse exposure levels. To this end, anti-Tsgf1 18–43 IgG antibodies will be evaluated in sentinel villages from the Boffa focus in Guinea, before and after tsetse control intervention have been taken [7]. Noteworthy, we were able to show, that in cattle experimentally bitten by tsetse flies, Glossina saliva specific antibodies returned to pre-exposure levels within only few weeks after the stop of exposure (Somda et al, personnal communication).…”

“…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.…”

“…With the Pan African Tsetse and Trypanosomiasis Eradication Campaign (PATTEC), large scale tsetse eradication campaigns are now underway in several African countries such as in Uganda and Ethiopia in East Africa and Ghana, Burkina Faso and Senegal in West Africa in order to improve the breeding and agricultural potential of these animal African trypanosomiasis (AAT) endemic areas [6]. Vector control campaigns are now progressively extending to HAT endemic areas in combination with medical surveys such as in the Boffa focus along the Guinean coast [7].…”

“…They may thus lead to an underestimation of the true densities. Furthermore, tsetse density itself only poorly reflects the intensity of contact with human populations which is the most crucial parameter when the objective of vector control is to reduce human tsetse contacts to levels incompatible with maintenance of the parasite life cycle [7], [14], [15].…”

Is vector control needed to eliminate gambiense human African trypanosomiasis?

“…However, this approach to HAT control only works where cattle densities are high enough, which is not the case for most areas with gambiense HAT. Where cattle densities are not high enough, insecticide treated cloth targets or cloth traps are often used and have been used successfully (Lancien, 1991; Laveissière and Penchenier, 2005) and currently tsetse control operations conducted in Gambian HAT foci use this type of technology (Kagbadouno et al, 2011, 2012). In all situations, the vector control phase should be implemented after a first phase of baseline data collection that will help to precisely define the identity, density, and spatial distribution of the targeted tsetse species.…”