Blinding Trachoma: Systematic Review of Rates and Risk Factors for Progressive Disease

Abstract

BackgroundSight loss from trachoma is the end result of a scarring disease process starting in early childhood and characterised by repeated episodes of conjunctival inflammation (active trachoma). Subsequently, the conjunctiva becomes scarred, causing the eyelashes to turn inwards and scratch the cornea (trichiasis), damaging the corneal surface and leading to corneal opacification and visual impairment. It is thought that this process is initiated and driven by repeated infection with Chlamydia trachomatis. We review published longitudinal studies to re-examine the disease process, its progression rates and risk factors.Methodology/Principal FindingsWe searched PubMed for studies presenting incidence and progression data for the different stages of trachoma natural history. We only included studies reporting longitudinal data and identified 11 publications meeting this criterion. The studies were very heterogeneous in design, disease stage, duration, size and location, precluding meta-analysis. Severe conjunctival inflammation was consistently associated with incident and progressive scarring in five studies in which this was examined. One study reported an association between C. trachomatis infection and incident scarring. No studies have yet demonstrated an association between C. trachomatis infection and progressive scarring. Several studies conducted in regions with low prevalence active disease and C. trachomatis infection found evidence of on-going scarring progression.Conclusions/SignificanceOverall, there are few longitudinal studies that provide estimates of progression rates and risk factors, reflecting the challenges of conducting such studies. Our understanding of this disease process and the long-term impact of control measures is partial. Intense conjunctival inflammation was consistently associated with scarring, however, direct evidence demonstrating an association between C. trachomatis and progression is limited. This suggests that on-going chlamydial reinfection may not be mandatory for progression of established scarring, indicating that sight threatening trichiasis may continue to evolve in older people in formerly endemic populations, that will require service provision for years after active disease is controlled.

Risk factors for incidence of trachomatous scarring in a cohort of women in low endemic district

“…This rate went up with age, similar to other prevalence surveys of scarring 8–10. To our knowledge, this study was the first to report the rate of incident scarring in women in a previously hyperendemic district for trachoma, where prevalence rates of active trachoma became very low 11. The fact that new scarring was still occurring in this area, especially in older age groups, despite very low rates of trachoma suggests that factors other than concurrent exposure to trachoma were driving incident scarring in this population.…”

“…This inflammation was also associated with factors of innate immune origin 24. Interestingly, progression, unlike incidence, did not show an association with C. trachomatis , gender or age 11. We can postulate then that there are likely multiple environmental factors that may drive this episodic inflammation that leads to progression, with cooking fire exposure with its ocular inflammatory properties, possibly being one.…”

DEBS – a unification theory for dry eye and blepharitis

“…This exceedingly slow but chronic disease process with its various presentations has led to much confusion over the years in identifying and understanding the etiology and progression of dry eye disease 49. We tend to focus on the immediate presenting problem and not what preceded it.…”

The conjunctival transcriptome in Ethiopians after trichiasis surgery: associations with the development of eyelid contour abnormalities and the effect of oral doxycycline treatment

“…In 2017 over 200,000 people worldwide were managed for trichiasis; the disease is found predominantly in sub-Saharan Africa 2 . Trachomatous inflammation and scarring can progress in the absence of detectable chlamydial infection 1,3 , therefore it is expected that trichiasis surveillance and management provisions will be required for many years in formerly endemic districts.…”