Estimates of the duration of the early and late stage of gambiense sleeping sickness.
BACKGROUND
The durations of untreated stage 1 (early stage, haemo-lymphatic) and stage 2 (late stage, meningo-encephalitic) human African trypanosomiasis (sleeping sickness) due to Trypanosoma brucei gambiense are poorly quantified, but key to predicting the impact of screening on transmission. Here, we outline a method to estimate these parameters.


METHODS
We first model the duration of stage 1 through survival analysis of untreated serological suspects detected during Médecins Sans Frontières interventions in Uganda and Sudan. We then deduce the duration of stage 2 based on the stage 1 to stage 2 ratio observed during active case detection in villages within the same sites.


RESULTS
Survival in stage 1 appears to decay exponentially (daily rate = 0.0019; mean stage 1 duration = 526 days [95%CI 357 to 833]), possibly explaining past reports of abnormally long duration. Assuming epidemiological equilibrium, we estimate a similar duration of stage 2 (500 days [95%CI 345 to 769]), for a total of nearly three years in the absence of treatment.


CONCLUSIONS
Robust estimates of these basic epidemiological parameters are essential to formulating a quantitative understanding of sleeping sickness dynamics, and will facilitate the evaluation of different possible control strategies.
Checchi
Francesco
F
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E7HT, UK. francesco.checchi@lshtm.ac.uk
Filipe
João A N
JA
Haydon
Daniel T
DT
Chandramohan
Daniel
D
Chappuis
François
F
D000293:Adolescent; D000328:Adult; D000818:Animals; D002648:Child; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D015995:Prevalence; D013397:Sudan / Q000453:epidemiology; D014347:Trypanosoma brucei gambiense; D014353:Trypanosomiasis, African / Q000175:diagnosis / Q000453:epidemiology*; D014454:Uganda / Q000453:epidemiology