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.

Conclusion: 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.

Figure 1

Figure 1

Simple model for the progression...

Figure 1

Simple model for the progression of untreated HAT.

Figure 2

Figure 2

Expected shapes of the observed...

Figure 2

Expected shapes of the observed distribution of survival times after detection . Shaded...

Figure 3

Figure 3

Fitted interval-censored stage 1 survival...

Figure 3

Fitted interval-censored stage 1 survival models . For comparison purposes, the figure also...

Figure 4

Figure 4

Timing of actual follow-up visits...

Figure 4

Timing of actual follow-up visits with respect to the scheduled date . Data...