*2.1.1 Trachoma*

Trachoma is one of the oldest diseases known. Even in the twenty-seventh century BC in China and seventeenth century BC in Egypt, there are findings about the disease [12].

It had been the leading cause of blindness in history and still is the leading cause of blindness by an infectious agent worldwide.

Trachoma is a public health problem in 44 countries and is responsible for blinding or visually impairing 1.9 million people. Of all blindness worldwide, it causes about 1.4% [14].

The number of people at risk of trachoma has decreased by 91% from 1.5 billion in 2002 to about 137 million in 2020. Besides, the number of individuals requiring surgery has reduced by 68% from 7.6 million in 2002 to 2.5 million in 2019 [15].

Based on June 2022 data, 125 million people live in trachoma-endemic areas and are at risk of trachoma blindness.

Trachoma is hyperendemic in many of the poorest and most rural areas of Central and South America, Australia, Africa, Asia, and the Middle East. Overall, Africa remains the most affected continent and the one with the most intensive control efforts.

For this most sight-threatening neglected tropical disease, World Health Organization (WHO) adopted a strategy called SAFE in 1993.

Elimination programs in endemic countries are being implemented using this WHO-recommended SAFE strategy. It consists of:


Most endemic countries have agreed to accelerate the implementation of this strategy to achieve elimination targets.

WHO's mandate is to provide leadership and coordinate the international efforts aiming to eliminate trachoma as a public health problem, and to report on progress toward that target.

In the year 1996, WHO launched the WHO Alliance for the Global Elimination of Trachoma by 2020. The Alliance is a partnership that supports the implementation of the SAFE strategy by the Member States, and the strengthening of national capacity through epidemiological surveys, project evaluation, monitoring, and resource mobilization.

The World Health Assembly adopted resolution WHA51.11 in 1998, targeting the global elimination of trachoma as a public health problem with 2020 as the target date. The neglected tropical diseases road map 2021–2030, endorsed by the World Health Assembly in 2020 through its decision 73(33), sets the date 2030 as the new target for global elimination [16].

#### *2.1.1.1 Clinical features*

The discomfort degree caused by ocular infection with *C. trachomatis* ranges from minimal to severe. Most of the infections are asymptomatic. Trachoma begins as a follicular conjunctivitis of the upper palpebral conjunctiva with associated limbal follicles. The incubation period is approximately one week. Other early findings include a mucopurulent discharge, conjunctival papillary hypertrophy, a superiorly based superficial corneal pannus (invasion of the vessels to the cornea), and a fine epithelial keratitis. Clinically, trachoma can be divided into its acute (active) and chronic or late-stage manifestations, but acute and chronic signs can occur at the same time in the same individual. As a result, the inflammation causes scarring and cicatrization of the cornea, conjunctiva, and eyelids.

The blinding complications of trachoma occur as a result of conjunctival connective tissue proliferation. Arlt's Line is the name given to a horizontal scar of the upper lid's pretarsal conjunctiva. Another sequel pathognomonic for trachoma, Herbert's pits are the delineated depressions that occur after cicatrization of the limbal follicles and the resultant clear spaces filled with epithelium. A homogenous clouding can be formed on the cornea as the superior pannus is regressed [17–19].

Resultants of conjunctival scarring, eyelid deformities as distichiasis, trichiasis, ectropion, and entropion may all occur. If sufficient transconjunctival scarring accumulates, contraction over the years will cause the upper lid to turn inward so that the eyelashes rub against the cornea and conjunctiva. This is named as trichiasis. If the whole lid edge is turned in, that condition is named as entropion. Scars around the bases of hair follicles can pull individual eyelashes into contact with the cornea, even entropion does not accompany. Corneal scarring, vascularization, ulceration, and even perforation resulting from these deformities can lead to visual acuity impairment and even blindness [20].

MacCallan developed a staging of the disease based on the conjunctival findings in 1908:

STAGE 1: Early lymphoid hyperplasia with immature follicle formation in the upper tarsal conjunctiva, diffuse punctate keratitis and early signs of pannus. STAGE 2A: Mature upper tarsal follicles.

STAGE 2B: Fluoride inflammation due to pretarsal and limbal follicle enlargement and papillary hypertrophy and complicated pannus.

### *Chlamydial Eye Infections DOI: http://dx.doi.org/10.5772/intechopen.111372*

STAGE 3: Papillary hypertrophy regression, persistence of tarsal follicles, and onset of conjunctival scarring. STAGE 4: No acute inflammation, scars replacing papillae and follicles, and regression of the pannus.

The WHO has developed a more practical grading system for trachoma, structured around diffuse inflammation, follicular conjunctivitis, trichiasis, tarsal scarring, and corneal opacification presence. The WHO simplified trachoma grading system is widely used for research and program monitoring purposes.

This system includes five signs:


The presence or absence of each sign should be independently determined for each person examined. In the WHO system, the presence of TF and/or TI in one eye is necessary and sufficient to confer the diagnosis of acute trachoma [17, 21].
