Abstract

5. Trachoma

This chapter stresses the importance of clean water. Not only is it essential in order to prevent infection by orally invading pathogens such as amoebae or intestinal helminths, but it is also imperative for bodily hygiene. Additionally, the epidemological characteristics of a contaminating microbial pathogen are demonstrated. The elimination of the pathogen without the induction of a defensive immunological reaction, is simply attributed to the ruin of the affected tissue by the pathogen itself (see below).

Trachoma is, after the cataract, the second most frequent cause of blindness. At present, the disease is secondarily reduced to arid regions with insufficient water supplies. The pathogen Chlamydia trachomatis is an obligatory cell-parasitic bacterium with DNA together with RNA. It propagates by binary fission and its tissue colonies are imbedded in a matrix of carbohydrate. Culture of the pathogen in vitro is possible in cells of the chicken yolk sack .

Life cycle of the pathogen: the acidophilic elementary bodies in the tear liquid enter the connective tissue cells. Once inside, they change into basophilic reticular bodies, which give rise to a paranuclear colony. After the bursting of the cell, the elementary bodies are delivered and attack neighbouring cells.

Course of the disease (fig. 5.1, page 236): after contamination of the eye, the pathogen attacks cells of the connective tissue. Insufficient closure of the eyelids damages the cornea stepwise. In all stages, the infection is self-limitating. Repeated reinfections give rise to increasing secondary pathological alterations.

Stage I: conjunctivitis. After an incubation of 5 – 7 days, inflammation of the conjunctiva is followed by excessive secretion of tear fluid and hypertrophy of the conjunctiva with oedema of the upper eyelid and, later on, of the lower eyelid: ptosis. The tear fluid is highly infective. Diagnosis made on smears is positive when paranuclear colonies are found.

Stage II: florid trachoma. The inner lining of the upper eylids shows numerous follicles. Theese are small vesicles filled with lymph, which is highly infective when evacuated in order to alleviate pains. The cornea becomes cloudy, beginning from above: pannus.

Stage III: scaring trachoma. The upper eyelid rolls to the inside because the contraction of the scarred connective tissue. This is later repeated at the lower eyelid: entropium. The eyelashes drag on the cornea, which is damaged thereby. The closure of the eyeslit is incomplete and secondary bacterial infections cause suppurative inflammations (fig. 5.2, page 237). The Chlamydiae and thereby the infectivity disappear.

Stage IV: ceasing or "expired" trachoma. The eyelid pouch disappears and the connective tissue degenerates to a leathery layer, followed by desiccation of the eye cavity: xerosis. The opening of the eye is narrowed to a slit. Chlamydiae are no longer present, however, because of the lack of suitable tissues.

Diagnosis is performed in the laboratory by molecular biological tests and in the field by microscopical investigation of smears, which are stained with iodo-iodo-potassium to demonstrate the carbohydrate matrix of the paranuclear bodies. An effective therapy of acute stages is possible by oral application of the antibiotic Azithromycine^®and of advanced stages by surgical correction of the entropium and of corneal damage by ceratoplasty.

Control: SAFE program of World Health Organisation (Surgery, Antibiotics, Facial cleanliness, Environmental improvement).

Epidemiology: transmission occurs by tear fluid mostly via the common use of contaminated water for washing. Other occasions include flies licking at the eyes of babies and children and accumulated infections in families attributable to the lack of sanitary conditions. The Crusaders brought the trachoma to Europe and this disease persisted thereafter in Irish monasteries. Napoleonic troops returning from Egypt caused a European pandemic that persisted endemically until the introduction of running water during the 20^th century.

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