Trachoma

Background

In tropical countries, it is estimated that 25 million people are blind from preventable causes and of those, trachoma is the most important, contributing to approximately 4% of global blindness.^[1] Trachoma is a very common chronic conjunctival infection caused by Chlamydia trachomatis, which is transmitted by flies or through close personal contact. (Note that the organism involved is C. trachomatis serotype A-C; C. trachomatis serotypes D-K are associated with genital infections and only occasionally cause a chronic follicular conjunctivitis that is clinically indistinguishable from trachoma^[2]).
Other causes of preventable blindness include:

• Xerophthalmia, due to lack of vitamin A in the diet.
• Onchocerciasis, or river blindness, an infection of the skin by filarial larvae that may also affect the conjunctiva of the eye.

Epidemiology

• Trachoma is the second most common cause of blindness in the world and the most common infective cause. The World Health Organisation (WHO) is aiming to eliminate trachoma as a blinding disease by 2020.^{[1, 3]}
• It was once endemic in most countries but now is confined to Africa, Asia, the Middle East and Aboriginal communities in Australia, as shown on the WHO map.^[4]
• There are an estimated 84 million people affected worldwide with 8 million visually impaired and 3.4 million blind.^[5]
• There is no racial predilection, only a predilection for poverty and poor personal hygiene.
• Women are affected 2 to 4 times as often as men but pre-school children of both genders are equally affected.
• In hyperendemic areas active disease is most common in pre-school children with prevalence rates as high as 60-90%, most commonly aged 3-5 years old.^[6]
• Where community prevalence decreases to around 20%, active disease is clearly seen to cluster in families.^[2]
• It is currently responsible for more than 3% of the world's blindness but the number keeps changing due to the effect of socio-economic development and current control programmes for this disease.

Pathophysiology

Transmission is mostly between children and the women who care for them (disease of the crèche); this accounts for the higher prevalence in women. Blindness does not ensue until middle age: repeated episodes of infection cause chronic follicular conjunctival inflammation (active trachoma), leading on to the cicatricial stage of tarsal conjunctival scarring, entropion, trichiasis (in-turning of the eyelashes) which leads to corneal scarring and opacity.

There are various stages of the disease that are described below; the references in this section link to pictures provided by the WHO:

• Follicular trachoma (Grade TF) produces active follicles on the upper tarsal conjunctiva. This phase of the disease is relatively asymptomatic.
• Inflammatory trachoma (Grade TI) causes thickening of the upper tarsal conjunctiva, which obscures more than half of the normal tarsal vessels and can produce significant conjunctival scarring and blindness. ^[7]
• Trachomatous scarring (Grade TS) produces easily visible scarring in the upper tarsal conjunctiva.^[8] Although this may not cause direct symptoms per se,
• Trichiasis (Grade TT) is when eyelashes touch the globe causing fibrosis and corneal opacification. Some vision can be restored with successful correction of trichiasis.^[9]
• Corneal opacity (Grade CO) is defined as one that is easily visible and obscures at least part of the pupillary margin.^[10]

Diagnosis

Laboratory tests are not used in endemic areas where the clinical appearance is enough.

• Cell culture used to be the standard test but has been superseded by newer tests.
• In other areas, polymerase chain reaction (PCR) and ligase chain reaction (LCR) have high sensitivity and specificity.
• Another new test is direct fluorescein-labeled monoclonal antibody (DFA) and enzyme immunoassay (EIA) of conjunctival smears.
• Giemsa cytology (the finding of intracytoplasmic inclusions) is technically demanding, has a high specificity but low sensitivity.

Management and prevention

The World Health Organisation (WHO) has implemented a policy of prevention known by the mnemonic SAFE:^[11]

• S urgery for trichiasis
• A ntibiotics, especially azithromycin to eradicate infection
• F acial cleansing and attention to hygiene
• E nvironmental improvement

To turn to each:

• Eyelid surgery can prevent corneal scarring and blindness. As an interim to prevent entropion, double-sided sticking plaster has been used to good effect.^[12]
• Oral azithromycin (1 gm po or 20 mg/kg in children, stat^[3] then repeated every 6-12 months^[1]) is the antibiotic of choice and if a child is infected the whole family should be treated. Topical tetracycline and polymixin is as effective as oral azithromycin.^[13] The latter is a shorter course and associated with few side-effects (which are mild) but is more expensive (although large donation programmes are in place^[1]). Even a single dose of azithromycin causes a marked fall in prevalence and intensity of the disease in a mass programme and it was sustained for 2 years.^[14] A single dose of azithromycin is as effective as 6 weeks of topical tetracycline. Topical antibiotics are less useful long-term as C. trachomatis occurs in the oropharynx and patients may re-infect themselves.^[2] Mass treatment programmes of entire communities may be necessary where the prevalence in 1-9 year old children exceeds 10%^[2] but this has to be balanced with the possibility of antimicrobial resistance (not a problem to date).^[15]
• Community-based health promotion about facial cleansing and hygiene reduces the risk and severity of trachoma.^[16] Do not let flies walk over children's eyes.
• Environmental health involves personal hygiene as well as clean water and safe sewage disposal along with a reduction in flies.

This SAFE approach has been shown to be successful in a number of countries.^[17] Researchers have highlighted the need to focus management on children in order to tackle the problem in its early stages.^[18]

Prognosis

Appropriate treatment of early disease gives an excellent prognosis. Severe disease may be stabilised but vision may not improve. Re-infection worsens the prognosis.