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Volume 23, Number 1—January 2017

Mathematical Modeling of Programmatic Requirements for Yaws Eradication

Michael MarksComments to Author , Oriol Mitjà, Christopher Fitzpatrick, Kingsley Asiedu, Anthony W. Solomon, David C.W. Mabey, and Sebastian Funk
Author affiliations: Hospital for Tropical Diseases, London, UK (M. Marks, A.W. Solomon, D.C.W. Mabey); London School of Hygiene and Tropical Medicine, London (M. Marks, A.W. Solomon, D.C.W. Mabey, S. Funk); ISGlobal, Barcelona, Spain (O. Mitjà); World Health Organization, Geneva, Switzerland (C. Fitzpatrick, K. Asiedu, A.W. Solomon)

Main Article

Table 1

Parameters used in modeling treatment coverage required to achieve yaws eradication

Parameter Parameter estimate Source of estimate Comments
Epidemiologic parameters
R0* 1.08–3.32 Derived from published survey data (17) The average number of new cases occurring from a single index case in a fully susceptible population
Monthly probability of progression from 
primary to secondary disease without treatment 2.78%–5.56% Derived from expert opinion and previously published models (1,14)
All untreated persons with primary disease either develop secondary or latent stage disease, and this occurs over a period of 2–6 mo. Untreated persons with latent cases might relapse for a period of >5 y and become actively infectious again.
Monthly probability of progression from 
infectious to latent disease without treatment 13.9%–27.8%
Monthly probability of relapse from latent 
disease to infectious stage without treatment
Population parameters
Susceptible at baseline 64% Derived from published survey data (17)
Data derived from multiple pre–mass drug administration surveys conducted in communities where yaws is endemic
Primary yaws at baseline 1.5%
Secondary yaws at baseline 1.5%
Latent yaws at baseline
Mass treatment parameters
Total community treatment coverage† 65%–95% Expert opinion and published data on coverage achieved in other mass treatment campaigns (18) Coverage estimates were chosen to reflect the range achieved in real-world mass drug administration programs for other neglected tropical diseases
Total targeted treatment coverage of persons 
with active cases‡ 65%–95%
Total targeted treatment coverage of persons 
with latent cases‡ 65%–95%
No. rounds of total community treatment† 1–3
No. rounds of total targeted treatment‡ 0–5

*R0 (basic reproduction number) is the number of new cases arising from a single index case in a fully susceptible population.
†Total community treatment consists of mass drug administration to all residents in a community where yaws is endemic regardless of clinical or serologic evidence of disease.
‡Total targeted treatment consists of active case finding and treatment of newly identified persons with yaws and their contacts.

Main Article

Page created: December 14, 2016
Page updated: December 14, 2016
Page reviewed: December 14, 2016
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