Trachoma

In tropical countries 25 million people are blind from preventable causes and of those, trachoma is the most important. Trachoma is a very common chronic conjunctival infection caused by Chlamydia trachomatis, which is transmitted by flies or through close personal contact.

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.

• Trachoma is the second commonest cause of blindness in the world and the commonest infective cause.
• 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.¹
• There is an estimate of 84 million people affected worldwide with 8 million visually impaired and 3.4 million blind.²
• 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.
• In hyperendemic areas active disease is most common in pre-school children with prevalence rates as high as 60-90% although blindness does not occur until early adulthood or middle age.
• 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.

The infectious organism is Chlamydia trachomatis. Transmission is mostly between children and the women who care for them but blindness does not ensue until middle age. This accounts for the higher prevalence in women. Repeated episodes of infection cause chronic follicular conjunctival inflammation (active trachoma), leading on to the cicatrical stage of tarsal conjunctival scarring.

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

• Follicular trachoma (Grade TF) produces active follicles on the upper tarsal conjunctiva. The peak age is in children age 3 to 5.³
• 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. ⁴
• Trachomatous scarring (Grade TS) produces easily visible scarring in the upper tarsal conjunctiva.⁵
• Trichiasis (Grade TT) is when eyelashes touch the globe causing fibrosis and corneal opacification. Some vision can be restored with successful correction of trichiasis.⁶
• Corneal opacity (Grade CO) is defined as one that is easily visible and obscures at least part of the pupillary margin.⁷

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.

The World Health Organisation (WHO) has implemented a policy of prevention known by the mnemonic SAFE:⁸

• Surgery for trichiasis
• Antibiotics, especially azithromycin to eradicate infection
• Facial cleansing and attention to hygiene
• Environmental improvement

To turn to each:

• Eyelid surgery can prevent corneal scarring and blindness.
• Oral azithromycin 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 but the latter is a shorter course.⁹ Even a single dose of azithromycin causes a marked fall in prevalance and intensity of the disease in a mass programme and it was sustained for 2 years.¹⁰ A single dose of azithromycin is as effective as 6 weeks of topical tetracycline.
• Community based health promotion about facial cleansing and hygiene reduce the risk and severity of trachoma.¹¹ 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.

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