Trachoma

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Trachoma
Classification and external resources
DiseasesDB 29100
MeSH D014141


Introduction

Trachoma is the most common infectious cause of blindness in the world and is due to recurrent ocular infection with Chlamydia trachomatis. Repeat infection with this organism leads to conjunctival inflammation and scarring, trichiasis, and ultimately blinding corneal opacification.

Epidemiology

The World Health Organization (WHO) reports trachoma is endemic to more than 50 countries, with most blinding trachoma in Africa. An estimated 21 million people are living with active trachoma and another 2.2 million people are blind or severely visually impaired. Furthermore, 7.3 million people suffer from trichiasis and are at risk for developing blindness.

Epidemiologic studies have shown active trachoma is most common in young children with the prevalence of active trachoma decreasing with age. The long-term sequelae of trachoma infection, including scarring, trichiasis and corneal opacification in adults relates to their exposure to active trachoma when they were young. The gender distrubtion of active trachoma is similar; however, scarring and trichiasis are more common in women than men because women are more likely to care for young children and have longer exposure to the disease.

Pathogenesis

The Organism:

Trachoma is caused by four ocular serotypes of Chalmydia trachomatis: A, B, Ba and C. Infection with genital serotypes D to K can cause isolated episodes of ophthalmia neonatorum in infants or inclusion conjunctivitis in adults and do not generally lead to blindness.

Pathophysiology:

Blindness from trachoma is due to recurrent episodes of active infection. The initial infection is confined to the conjunctival epithelium and triggers an immune response. Repeat infections with subsequent inflammatory responses results in tissue destruction, scarring, cicatricial entropion with trichiasis, and corneal opacification from lashes rubbing against the cornea.

Risk Factors

Risk factors for trachoma include things that favor transmission of the organism. Examples include:

  1. Inadequate Water Supply: less water availabe to use for facial cleansing
  2. Poor Facial Hygiene: secretions around the eye attracts flies that are physical vectors for C. trachomatis tranmission
  3. Latrine Access: limited latrine access leads to increased fecal contamination of the environment which provides a breeding environment for the fly.
  4. Overcrowded Living Conditiosn: close contact, especially between children sleeping in same bed, enables exchange of secretions

Grading

The WHO grading system: [1]

Trachomatous Inflammation (TF) The presence of 5 or more follicles (>0.5 mm) in the upper tarsal conjunctiva
Trachomatous Inflammation (TI) Inflammatory thickening of the tarsal conjunctiva that obscures more than half of the deep normal vessels
Trachomatous Scarring (TS) The presence of scarring in the tarsal conjunctiva
Trachomatous Trichiasis (TT) At least one lash rubs on the eyeball
Corneal Opacity Easily visible corneal opacity over the pupil

Clinical Findings

The clinical manifestations of trachoma can be divided into findings associated with active disease and those associated with repeat infections.

Active Disease:

  • Follicular Conjunctivitis: Follicles are dome-shaped collections of lympoid cells. The center of the follicle is avascular and has blood vessels that surround the round base. These appear as yellow-white elevations and are prominent on the everted upper eyelid in trachoma. Large conjunctival follicles located at the upper margin of the cornea may leave depressions known as 'Herbert's pits' which are pathognomonic for trachoma.
  • Papillary Hypertrophy: engorgement of small vessels with edema that can obscure deep tarsal vessels
  • Corneal Pannus: vascularization of the upper cornea.


Repeat Infection and Inflammation:

  • Conjunctival Scarring: White bands or lines that represent fibrosis
  • Cicatricial Entropion and Trichiasis: Fibrotic scar tissue contraction causes the eyelid turning inward and lashes touching the eyeball.
  • Corneal Opacification: secondary to repeat corneal irritation from inward turning eyelashes

Symptoms

Most individuals are asymptomatic or have mild symptoms depending on the level of inflammation. Symptoms, if present, are similar to those seen in any chronic conjunctivitis and include redness, discomfort, tearing, photophobia and muco-purulent discharge.

Diagnosis

Trachoma is a clinical diagnosis based on the above mentioned clinical findings. PCR testing developed for urogenital infection is available but typically utilized for research purposes only.

Management

The World Health Organization recommends the 'SAFE' strategy for the management of trachoma. This strategy was developed in 1997 by The Alliance for the Global Elimination of Blinding Trachoma by the year 2020 (GET 2020) and utilizes a 4 step approach:

  • S: Surgery for Trichiasis
  • A: Antibiotics for C. trachomatis infection
  • F: Facial cleanliness
  • E: Environmental change to improve sanitation and increase access to clean water

Additional Resources

References

  1. WHO/Department of control of neglected tropical diseases. Trachoma simplified grading card SAFE documents. World Health Organization (WHO), 1987. http://www.who.int/trachoma/resources/SAFE_documents/en/ Accessed 10 October 2017