Blinding infectious disease is more common in Malawi than anticipated

16 Feb 2010

Paul Chinnock

Source: PLoS ONE (see original article or PDF)

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Trachoma is the most common infectious cause of blindness. WHO has estimated that there are 1.3 million people living with blindness caused by this bacterial disease; some 1.8 million more have impaired vision and 8 million other trachoma-infected people have trichiasis – painful in-growing eyelashes. However, insufficient surveys have been conducted and it remains unclear how common the condition really is. Studies conducted in recent years have sometimes found much higher levels of prevalence than expected, for example in the Sudan [1]. A newly published survey from Malawi adds considerably to what is known about the disease in this country.

Unlike the Sudan, Malawi has not been devastated by prolonged civil war – and it is not an arid region so water for personal cleanliness is not in such short supply – but high rates of trachoma prevalence were recorded in the south of the country some 20 years ago. Since then, very little information has been recorded.

The researchers focused on two districts – one in the south and one in the centre of the country – each with a population approaching half a million. They used a cluster survey technique and visited over a thousand households in each district. In total nearly seven thousand people were examined for signs of trachoma.

The disease develops over several years and its various stages are set out in a WHO system of classification. The researchers recorded very few cases of blindness due to trachoma but found 1580 (0.6%) people in the southern district and 616 (0.3%) in the central district who had trichiasis at a stage where surgery was required. Without surgery, many patients at this stage will progress to blindness.

In order to determine which communities are at sufficiently high risk of trachoma to justify the launch of a preventive programme, WHO focuses on the stage of the disease known as “trachoma follicular” (TF). It is recommended that, when the presence of TF in a community exceeds 10%, then the so-called SAFE strategy for trachoma should be put in place. [SAFE = Surgery for those at immediate risk of blindness; Antibiotics to treat individual cases and to reduce infection in a community; Facial cleanliness and hygiene promotion to reduce transmission; Environmental improvements such as provision of water and household sanitation.]

The Malawi survey found 14% and 28% TF prevalence, in the central and the southern districts respectively. The researchers call for SAFE efforts to be launched in both districts. In particular, they would like to see the introduction of mass drug administration; they point out that, “It is important to note that certain activities of the SAFE strategy (antibiotic distribution) may be integrated with control of other diseases and some studies have reported success”.

The researchers stress that the survey findings in these two districts do not necessarily mean that similarly high levels are to be found throughout Malawi. Further surveys are needed in other parts of the country. However, it is noteworthy that, not only the district in the south where the disease has previously been of some concern, but also the district in the centre of Malawi both meet the criteria for the launch of SAFE efforts. There are likely to be other areas across Africa where trachoma is more common than has been recognized. Such studies as this one make it clear that there is a need for surveys to establish the true extent of the disease in specific locations.

For more information on trachoma and trachoma research, see a recent TropIKA.net review article.

Reference

1. Ngondi J, Ole-Sempele F, Onsarigo A, Matende I, Baba S, et al. (2006) Blinding Trachoma in Postconflict Southern Sudan. PLoS Med 3(12): e478.