Elsevier

The Lancet

Volume 384, Issue 9960, 13–19 December 2014, Pages 2142-2152
The Lancet

Seminar
Trachoma

https://doi.org/10.1016/S0140-6736(13)62182-0Get rights and content

Summary

Trachoma is the most common infectious cause of blindness. Repeated episodes of infection with Chlamydia trachomatis in childhood lead to severe conjunctival inflammation, scarring, and potentially blinding inturned eyelashes (trichiasis or entropion) in later life. Trachoma occurs in resource-poor areas with inadequate hygiene, where children with unclean faces share infected ocular secretions. Much has been learnt about the epidemiology and pathophysiology of trachoma. Integrated control programmes are implementing the SAFE Strategy: surgery for trichiasis, mass distribution of antibiotics, promotion of facial cleanliness, and environmental improvement. This strategy has successfully eliminated trachoma in several countries and global efforts are underway to eliminate blinding trachoma worldwide by 2020.

Introduction

Trachoma is a blinding infection caused by an ancient organism. Chlamydia trachomatis evolved with the dinosaurs, and all vertebrates have evolved with their own chlamydial strains.1, 2 Trachoma remains the most common infectious cause of blindness.3 The intense conjunctival inflammation with follicles recognised as active trachoma (TF) is sustained by repeated episodes of reinfection and reflects a sustained immune-mediated response to chlamydial antigens.4 This inflammation causes scarring, distortion of the lid, and inturning of the lid (entropion), with the eyelashes touching the cornea (trichiasis) that leads to blindness (figure 1). The key to trachoma is that repeated episodes of reinfection and inflammation lead to the blinding complications.4

As human beings evolved, occasional chlamydial conjunctivitis did not apparently lead to blindness. However, after the last Ice Age (about 8000 years BCE), when people were crowded in growing communities and hygiene was poor, the frequency of reinfection increased and blinding trachoma resulted.6 Crowding and poor hygiene lead to outbreaks of chlamydial infections in a range of birds, mammals, and marsupials.7 Trachoma rates increased greatly as crowding and poor living standards increased at the end of the Agricultural Revolution and the start of the Industrial Revolution, but waned in the 20th century as living standards improved.6 The disappearance of trachoma from more developed countries was hastened with the introduction of sulpha drugs in the 1930s and antibiotics in the 1940s.

However, trachoma still affects millions of people in the least developed countries. In recognition of the likelihood that spontaneous improvement in living conditions and disappearance of trachoma could take many decades, a specific global commitment has been made to eliminate trachoma. A resolution of the World Health Assembly in 1997 established the Global Alliance for the Elimination of Blinding Trachoma by the year 2020 (GET 2020) and much progress is being made to eliminate the disease. Some successes have led to increased resources and effort as set out here.

Section snippets

Epidemiology

Trachoma is still endemic in many of the poorest and more remote areas of Africa, Asia, Australia, and the Middle East (figure 2). Active trachoma affects an estimated 21 million people with about 2·2 million blind or severely visually impaired. A further 7·3 million have trichiasis3 (table 1). An intensive global trachoma mapping effort is underway at present. WHO classes 53 countries as endemic for trachoma10, 11 and estimates that 229 million people live in endemic areas, with most blinding

The causative organism

Trachoma is caused by the obligate intracellular Gram-negative bacterium C trachomatis, which has a single chromosome of about 1 Mbp and a multicopy plasmid that functions as a virulence factor.2 This unusual organism has a biphasic developmental cycle. Initially the small, hardy, metabolically inactive elementary bodies attach to and enter epithelial cells. Once inside, elementary bodies transform into the larger, metabolically active reticulate bodies within an intracytoplasmic vacuole, the

Overview

Trachoma interventions are planned at the district level, though implemented at the community or household level. They aim to eliminate blinding trachoma, partly by disrupting transmission of infection, and are implemented at the district level to minimise the reintroduction of infection into treated communities. Therefore, the district-level trachoma prevalence is used to identify where programmes are needed (appendix).11

At the start of 2012, trachoma control activities covered about half of

Overview

The GET2020 campaign uses the SAFE strategy, a four-pronged approach to stop the cycle of reinfection within the community and to correct trichiasis.11 WHO and partners aim to scale up SAFE strategy programmes in affected countries in a timely and cost-effective way to eliminate trachoma by 2020.

Surgery

Individuals with trachomatous trichiasis and entropion are at risk of corneal opacification and vision loss. To prevent these features developing, the abrasive action of lashes on the cornea must be

Conclusion

The SAFE strategy provides a targeted way to speed up the process of a general improvement in living conditions and hygiene that is needed to eliminate trachoma in the most disadvantaged areas in the developing world. Countries such as Morocco, Ghana, and Oman have eliminated blinding trachoma by use of the strategy.11 Activities at present cover at least half of the world's endemic districts, and the mapping of the remainder should be completed soon (Figure 2, Figure 4).8 As increasing

Search strategy and selection criteria

We searched the University of Melbourne Discovery Library with the subjects Medicine, Dentistry, and Health Science. Databases searched included The University of Melbourne Library Catalogue, Web of Science (ISI), Scopus version 4 (Elsevier), Medline (ISI), CINAHL (EBSCO), and PubMed from Jan 1, 2008, to Dec 31, 2012. We used the search terms “trachoma”, “epidemiology”, or “SAFE strategy” in combination with “trachomatis”. We have included older key and commonly cited publications. Several

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