By the end of this presentation you should be able to: - Explain the natural history of trachoma, and - Describe its clinical features. Trachoma is the leading infectious cause of blindness. It has been around for a long time and was documented in ancient Egyptian and Chinese writings. The cause of the infection is a bacterium called Chlamydia trachomatis which grows and reproduces inside the cells of its hosts. Specifically it is the A, B, Ba and C variations - known as serovars - that are associated with trachoma eye disease. Other serovars, D to K, are associated with genital chlamydial infection. The Chlamydia bacterium has a unique life cycle. It starts as an inert, but infectious, particle called an elementary body (EB).
This EB can enter into a human cell enclosed in a vesicle. A vesicle is a membranous sac containing fluid. Within just 2 hours the EB changes into an active reticulate body (RB) and begins to multiply rapidly within the vesicle. The RB go on replicating and can occupy up to 90% of a cell. This is known as an inclusion body when seen through a microscope. About 48 hours after a cell is infected it ruptures, and releases a large number of elementary bodies and active reticulate bodies into the surrounding tissues. This spreads the infection to more cells.
We can detect chlamydial infection
in the laboratory using a range of methods: - Microscopy: Smears of human tissue are stained and examined for inclusion bodies through a microscope. - Cell culture: this is a series of complex steps to isolate and identify infected cells. Diagnosis is confirmed by microscopy. - A blood test - serology - and indirect immunofluorescent assay can be used to detect anti-chlamydial antibodies in serum or tears. These tests may be positive in people who were previously, but not currently, infected. -More recent tests such as nucleic acid amplification tests using the polymerase chain reaction (PCR) can be used to detect Chlamydia trachomatis DNA.
The highest levels of ocular chlamydia infection are found in young children living in communities affected by trachoma.
There is a challenge with using laboratory tests to identify chlamydia infection. The test results sometimes contradict the clinical features of trachoma we see in patients. Sometimes we get a positive result for someone with clinically “normal” eyes. On the other hand, some people will show signs of clinically active trachoma whilst receiving a negative test result. These variations occur because the development and resolution of clinical features lags behind the start and finish of a positive laboratory test. We also don’t yet have an accurate, quick and inexpensive way to test for infection in the field, at the community level.
Because of these two issues, the best way to monitor the level of trachoma disease in communities is to examine people for the presence of clinical features rather than to rely on laboratory tests.
The clinical features we see in people with trachoma are caused by the body’s response to conjunctival infection with Chlamydia trachomatis. There are two major phases to trachoma. First, the active or inflammatory phase and then the cicatricial scarring phase.
In communities affected by trachoma, we find that active inflammatory disease is mainly found in children. Children who have repeated or persistent episodes of chlamydial infection develop follicles and papillae on their conjunctiva. The conjunctiva is a thin tissue which lines the inside surfaces of the eyelids and covers the white part of the eye, the sclera.
Follicles are small yellow or white ‘lumps’ containing lymphoid cells.
Papillae are swollen, inflamed membranes around the small blood vessels on the conjunctiva. In severe cases the inflammation can cause the conjunctiva to obscure the deeper blood vessels that are normally visible running vertically beneath the conjunctiva. New blood vessels may occasionally grow onto the cornea - the transparent front part of the eye. This produces a corneal pannus - a growth of vascular connective tissue into the cornea. A child with trachoma often has no symptoms.
The common symptoms children with trachoma may complain of are: - Irritation of the eyes. - Mucus or even pussy (purulent) discharge from the eyes - Swelling of the upper eyelids. Multiple infection and episodes of inflammation over time result in the cicatricial or scarring phase of trachoma. This can begin in adolescence or adulthood. Trachomatous scarring starts with star-like scars in the position of old follicles. These small scars eventually coalesce into larger and deeper scarring. In the early stages the eyelids are not distorted and vision is normal. If the scarring progresses it can cause the eyelashes to turn inwards. This is called trichaisis. These in-turned eyelashes rub on the cornea causing pain.
A combination of trichiasis, lack of tear production and secondary bacterial infection can all lead to corneal scarring, loss of vision and eventually irreversible blindness. The World Health Organization recommends a simplified grading scheme for assessing trachoma at the community level based on clinical signs of disease. Trachoma is spread through direct contact between people or by flies. Flies - particularly Musca sorbens which is an eye seeking fly - spread chlamydia infection as they land and feed on ocular and nasal discharge on people’s faces, especially young children. People also transmit the infection through touch and by sharing cloths. Facial discharge and lack of a clean face is related to the presence of infection.
Mothers and women in close contact with small children with active disease are at risk of being infected.
Overcrowding, poor personal hygiene, lack of water to clean faces and inadequate community sanitation are further risk factors for the spread of trachoma within communities.
Musca sorbens flies lay their eggs in waste and faeces, preferring human faeces, but they also breed in faeces from other animals. We can reduce the risk of transmission of trachoma by improving environmental sanitation. In summary, - Trachoma is caused by infection by an intracellular bacterium called Chlamydia trachomatis. - Infection results in inflammation of the conjunctiva. - Active trachoma causes follicles and papillae in the conjunctiva. - Cicatricial trachoma results in scarring of the conjunctiva. Scarring can cause the eyelashes to turn inwards and scrape on the cornea. This is known as trichiasis. - With repeated and persistent chlamydial infection, trichiasis can lead to corneal scarring and blindness. - Children in communities affected by trachoma have the highest levels of chlamydia infection.
Trachoma is spread between people through contact with infected ocular and nasal discharge in overcrowded settings with poor hygiene. - Flies also spread trachoma in communities with poor environmental sanitation.