Reducing Human-Tsetse Contact Significantly Enhances the Efficacy of Sleeping Sickness Active Screening Campaigns: A Promising Result in the Context of Elimination

Abstract

Background

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.

Methods

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.

Findings

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).

Interpretation

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.

Author Summary

Sleeping sickness is a serious neglected tropical disease which has been targeted for elimination by 2020. Currently, control relies on mass screening populations at risk and treatment of cases. This strategy is compromised because it is often impossible to reach more than 75% of the population. An alternate method is to kill the tsetse fly which transmits the parasite causing the disease. To determine the value of adding vector control to medical interventions we undertook a vector control programme alongside a screen and treat programme in the Boffa disease focus of Guinea. We divided the focus into two parts (screen and treat in the western part; screen and treat plus vector control in the eastern part). In the vector control area, there was an 80% decrease in tsetse density and a decrease of disease prevalence from three cases per thousand to one case per thousand with almost no new cases being contracted during the control period. In contrast, incidence was 10 times higher in the area without vector control. Combining medical and vector control was decisive in reducing sleeping sickness transmission and could speed up the elimination process. Similar strategies could be applied in other foci.