Etiology and Epidemiology

Trachoma generally requires prolonged contact among individuals in filthy and overcrowded living conditions for transmission. In endemic areas, infection first occurs in childhood as a result of close family contact. Transmission may be from mother to baby, from eye to eye, by fingers, and by eye-seeking flies. In urban slums or poor villages where people live crowded together under unsanitary conditions, garbage and raw sewage attract flies that breed copiously. As the insects swarm on the faces of infants and children, they feed on the infected eye discharges of those with trachoma and carry it to the eyes of other victims. Most children in endemic areas have trachoma at an early age, but hosting the disease in childhood does not provide a lifelong immunity.

Trachoma transmission may also occur by direct touch, by the contamination of clothing or bedding, possibly by bathing in pools in which people swim and wash, and by sexual means. According to B. R. Jones:

[I]n the vast majority of cases infection (with the TRIC agent) is transmitted from person to person by intimate sexual contact involving at various times genital, rectal, oral or other mucosal surfaces. No doubt it can be directly transferred to the eye during such activities. However, in the vast majority of cases it appears to be transferred to a genital mucosal area, and then by means of transferring a genital discharge by hand, or other vectors, it reaches the eye. (Cited by Rodger 1981)

Factors that contribute to the severity of trachoma are ocular irritants and bacterial conjimctivitis. It is most prevalent where the climate is hot and dry, and low humidity leads to excessive drying of the conjunctiva. Winds and dust, along with smoke in un-ventilated huts, further irritate the eyes. Bacterial infections, particularly the seasonal outbreak of bacterial purulent conjunctivitis, often cause the worst cases. Frederick Rodger (1981) suspects that such infections are "related to the peak period of reproduction of the fly population."

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