Could acanthamoeba keratitis be more common in non-contact lens-wearing Nigerians than reported? Evidence from Abakaliki

Abstract

Background: Although acanthamoeba keratitis (AK) is more common in contact lens wearers, there have been many reports in those who do not wear contact lenses, especially in developing countries and particularly among agricultural workers and manual labourers. Available literature suggests that acanthamoeba keratitis is not a common cause of corneal ulcer in Nigeria. This might be due to a low index of suspicion as a result of low use of contact lens by the general population in Nigeria. Perhaps a routine search for the amoebic organism in corneal scrapings may actually reveal more cases of AK than reported among non-contact lens wearers. Despite the lack of sophisticated laboratory facilities, in resource-constrained settings, for definitive diagnosis of this amoebic organism in corneal scrapings, several stains are available for the detection of amoebic cysts in samples. However, the modified Field’s stain, which is readily available, gives a very good colour contrast as compared with other stains, and has been found to be very useful for the early detection. This study is therefore aimed at presenting the utility of modified Fields stain for the rapid diagnosis of acanthamoeba keratitis with a view to highlighting the need to routinely search for amoebic organism in patients with corneal ulcers, particularly in agrarian communities with muddy farmlands; using a readily available simple stain such as the modified Field’s stain.

Objectives: To demonstrate the utility of modified Field-stain in the microscopic diagnosis of acanthamoeba keratitis in a resource –constrained setting.

Materials and Methods: This is a cross sectional descriptive study of all consenting corneal ulcer patients managed at the FETHA eye clinic over a 4-month period (May to August 2015). Acanthamoeba diagnosis was based on Giemsa and modified Field’s staining techniques. Potassium hydroxide (KOH) wet mount and Gram′s stain were used for diagnosis of fungi and bacteria respectively, before culture results were available.

Results: The microbial diagnoses were staphylococcus aureus (37.5%), Fungal keratitis (fusarium spp. and aspergilus, 25%) and acanthamoeba (25%). None of the patients ever used contact lenses.

Conclusion: The use of modified Field-stain in the microscopic examination of corneal ulcer scrapings yielded a high microscopic diagnosis of acanthamoeba among the corneal ulcer patients seen at Federal Teaching Hospital Abakaliki. It is recommended that a larger study be done to confirm the usefulness of the modified Field’s stain in the diagnosis of acanthamoeba keratitis.