Trachomatous Trichiasis and Predicting the End of Blinding Trachoma

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Project Abstract Trachoma remains an important global public health problem due to the millions of individuals still affected by the disease and its blinding sequelae. The development of trachomatous trichiasis (TT), in- ward turning eyelashes resulting from conjunctival scarring and/or entropion, is the point at which trachoma becomes vision threatening. Around the world 3.2 million people suffer from TT which, if uncorrected, places these individuals at high risk of blindness from corneal opacification (CO). Importantly, TT and CO can develop after the active, infectious stage of trachoma has been eliminated. The World Health Organization has targeted trachoma for elimination as a public health problem by 2020. Elimination is defined as when formerly endemic districts demonstrate: i) a prevalence of follicular trachoma (TF) of less than 5% in children ages 1-9 years, and ii) a prevalence of TT cases (not previously offered health services) of 0.2% or less in those 15 years or older. Countries are successfully achieving the TF elimination targets; however, they are having difficulty meeting the TT elimination goals, in part, because of incident TT cases after surgical intervention programs clear the current backlog. The lack of information on the time course of trachomatous conjunctival scarring (TS) progression and TT development, especially as TF prevalence declines, contributes to the difficulty programs face in allocating resources appropriately. Specifically, data are needed on the degree to which the rate of TS and TT development and TS progression are affected by declining active trachoma. The proposed study has three aims: i) to determine the rate of incident and progressive TS in a formerly trachoma endemic area, and compare the rates with similar rates under a hyperendemic state, ii) to determine the risk of incident TT when a district has eliminated TF and quantify this risk according to scarring severity, and iii) to create a risk model for developing TT. To accomplish these aims, a longitudinal follow up study will be undertaken in an established cohort of women in Kongwa district, where images of the upper eyelid have been collected at baseline and 3.5 years later; we propose a seven year follow up to determine ongoing incidence and progression of TS and new incident cases of TT. We will also create a disease model for incident TT, using existing data, and test it under assumptions of TF elimination using newly collected data. This trachoma research proposal has a high potential for impact for two reasons: i) it will create knowledge of the time course and dynamics of disease progression from mild to severe TS and from TS to TT, and the effect of TF elimination on this progression, and ii) it will result in the development of a model which can forecast future incident TT rates based on known TS severity distribution within a district. The knowledge gained from this proposal will allow trachoma elimination programs to appropriately allot limited surgical resources after TF has been eliminated.