Uveitis is intraocular inflammation originating from the uveal tract and adjacent structures. Its prevalence varies globally. In the United States of America (USA), a prevalence of 115.3 cases per 100,000 of population has been reported.(1) In India, this was estimated at 714 per 100, 000.(2) Aetiology of uveitis also varies around the world. In the United Kingdom (UK), Fuchs heterochromic uveitis (11.5%), sarcoid (9.7%), idiopathic uveitis (14.9%) and toxoplasmosis (6.9%) were the most common known diagnoses.(3) In the USA these were idiopathic uveitis (34.9%), seronegative spondyloarthropathies (10.4%) and sarcoidosis (9.6%).(4) In China, idiopathic anterior uveitis accounted for 27% of anterior uveitis, and Behcet disease (6.5%) and Vogt-Koyanagi-Harada syndrome (15%) represented the most panuveitis cases.(5) In India, uveitis was caused by tuberculosis in 14.5%, toxoplasmosis in 11.7% and serpiginous choroidopathy in 14.6%.(6)
West Africa has unique epidemiological characteristics with many endemic infectious diseases. It is therefore challenging to extrapolate study results from other parts of the world to make inferences for Sierra Leone's uveitis population. Studies of uveitis aetiology in West Africa are limited. In Nigeria, anatomical subtypes of uveitis patients have been reported and Ayanru reported that the majority of posterior uveitis was of toxoplasmic origin.(7) The role of non-infectious autoimmune-disease related uveitis in Nigeria has also been highlighted.(8) In Benin, 85.7% of 489 patients with uveitis were reported to be idiopathic.(9) The challenges for studies in West Africa to obtain accurate epidemiological data include a lack of retinal imaging equipment and laboratory investigations.
What is known for certain is that uveitis is a significant cause of ocular morbidity in Sierra Leone. In 1992, Ronday published a hospital-based retrospective study. Uveitis was the second leading cause of blindness.(10) In another study by Ronday in 1996, infection accounted for over 50% of cases of uveitis with Toxoplasma Gondii and Treponema Pallidum, causing 43% and 20% of infective cases, respectively.(11) Sierra Leone has a population of 8.3 million and based on the afore mentioned prevalence studies from the USA and India, could have between 9000 and 55,000 cases of uveitis.(1, 12, 13) In reality, this figure may be even higher considering the significant amount of endemic infectious diseases in-country. This represents a significant burden from a condition which affects people throughout their life course. Sight threatening complications such as band keratopathy, cataract, macula oedema and glaucoma, have a major impact on quality of life and blindness also has socioeconomic costs.(14)
Between 2013 and 2016, the Ebola Virus Disease (EVD) epidemic of West Africa affected 28,600 individuals.(15) The PREVAIL study in Liberia reported that 26% of Ebola Virus Disease (EVD) survivors and 12% of control patients show evidence of uveitis, a staggering proportion of individuals with no direct exposure to Ebola infection.(16) Uveitis occurs in approximately 20% of EVD survivors, raising questions regarding its impact on the aetiologic landscape of uveitis.(17)
Although uveitis prevalence data is not available in Sierra Leone, data on other endemic infectious diseases, which may be associated with uveitis and have been reported by the Institute for Health Metrics and Evaluation as part of The Global Burden of Disease Study, may shed light on the scale of the problem.(18) In 2017, the prevalence of tuberculosis was 29%, syphilis was 1% and onchocerciasis (‘River Blindness’) was 5%. There was no estimation for toxoplasmosis or other viruses capable of causing uveitis. HIV, associated with increased risk of toxoplasma or cytomegaloviral uveitis, was confirmed in 17.8%.(19) Sarcoidosis was reported in 0.03%. This contrasts with the USA and the UK which, in 2017, had prevalence rates of 7% and 10% for TB, 0.2% and 0.1% for syphilis, 0.2% for sarcoidosis, 14% and 23% for HIV and 0% rates of Onchocerciasis respectively.(18, 19) The value of diagnostic tests vary according the prevalence of a disease in a specific population.(20)
The aim of this case series is to reveal the pattern of clinical phenotypes, sequelae, and disease associations of uveitis amongst patients presenting to the Eye Departments in Freetown, Sierra Leone. This study presents an opportunity to better understand uveitis in an understudied West African population who have been exposed to recent emergent public health threats including Ebola and Lassa fever. The impact on the population of these viral haemorrhagic fevers associated with uveitis is explored. Given the large number of uveitis sufferers in the country and the low number of ophthalmic trained staff available to manage them with limited resources, this condition represents a significant public health concern.