Tsetse Control and Gambian Sleeping Sickness; Implications for Control Strategy.
BACKGROUND
Gambian sleeping sickness (human African trypanosomiasis, HAT) outbreaks are brought under control by case detection and treatment although it is recognised that this typically only reaches about 75% of the population. Vector control is capable of completely interrupting HAT transmission but is not used because it is considered too expensive and difficult to organise in resource-poor settings. We conducted a full scale field trial of a refined vector control technology to determine its utility in control of Gambian HAT.


RESULTS
The major vector of Gambian HAT is the tsetse fly Glossina fuscipes which lives in the humid zone immediately adjacent to water bodies. From a series of preliminary trials we determined the number of tiny targets required to reduce G. fuscipes populations by more than 90%. Using these data for model calibration we predicted we needed a target density of 20 per linear km of river in riverine savannah to achieve >90% tsetse control. We then carried out a full scale, 500 km2 field trial covering two HAT foci in Northern Uganda to determine the efficacy of tiny targets (overall target density 5.7/km2). In 12 months, tsetse populations declined by more than 90%. As a guide we used a published HAT transmission model and calculated that a 72% reduction in tsetse population is required to stop transmission in those settings.


CONCLUSIONS
The Ugandan census suggests population density in the HAT foci is approximately 500 per km2. The estimated cost for a single round of active case detection (excluding treatment), covering 80% of the population, is US$433,333 (WHO figures). One year of vector control organised within the country, which can completely stop HAT transmission, would cost US$42,700. The case for adding this method of vector control to case detection and treatment is strong. We outline how such a component could be organised.
Liverpool School of Tropical Medicine, Liverpool, United Kingdom.
Inaki
I
Tirados
Liverpool School of Tropical Medicine, Liverpool, United Kingdom.
Johan
J
Esterhuizen
Liverpool School of Tropical Medicine, Liverpool, United Kingdom.
Vanja
V
Kovacic
Bindura University of Science Education, Department of Animal Science, Bindura, Zimbabwe.
T N Clement
TN
Mangwiro
Southern African Centre for Epidemiological Modelling and Analysis, University of Stellenbosch, Stellenbosch, South Africa.
Glyn A
GA
Vale
Liverpool School of Tropical Medicine, Liverpool, United Kingdom.
Ian
I
Hastings
Institut de Recherche pour le Developpement (IRD), UMR IRD-CIRAD 177 INTERTRYP CIRDES 01, Bobo-Dioulasso, Burkina Faso.
Philippe
P
Solano
Liverpool School of Tropical Medicine, Liverpool, United Kingdom.
Michael J
MJ
Lehane
Liverpool School of Tropical Medicine, Liverpool, United Kingdom; Warwick Medical School, University of Warwick, Coventry, United Kingdom.
Steve J
SJ
Torr
D000818:Animals; D006801:Humans; D007300:Insect Control / Q000191:economics; D007303:Insect Vectors / Q000469:parasitology / Q000502:physiology; D007630:Kenya / Q000453:epidemiology; D014347:Trypanosoma brucei gambiense / Q000502:physiology; D014353:Trypanosomiasis, African / Q000191:economics / Q000453:epidemiology / Q000469:parasitology / Q000517:prevention & control*; D014370:Tsetse Flies / Q000469:parasitology / Q000502:physiology*; D014454:Uganda / Q000453:epidemiology