Introduction
Acanthameba is a free living protozoan found in diverse environments including soil, water, and air . The first note on Acanthamoeba was made in 1930, and the first human eye infection was reported in 1974. Acanthamoeba has been isolated from the throat & nasal passages of healthy humans. It can infect the cornea of the human eye in immunocompetent individuals & cause keratitis (AK). Acanthamoeba may lead to blindness in 15% of cases if diagnosis & prompt treatment are delayed. The risk factors associated with AK include contact lens wearing, soil work and swimming in pools. AK is typically unilateral and patients usually suffer from eye pain, hyperaemia, and photophobia. The objective of this study is to explore acanthamoebic etiology among patients suffering from chronic keratitis, where the infectious agent remains unknown.
Methods
This is a prospective analytic & descriptive study conducted at two referral eye hospitals in Khartoum. The study population included all patients who presented with chronic keratitis and who did not respond to standard therapy for bacterial, viral, or fungal infections during July 2003 to August 2005. Specimens were corneal swabs and corneal scrapes. We used light microscopy and culture techniques. A wet mount preparation from both the corneal swab & scrape was made. The specimen was suspended in 10 ml of 0.9% saline and centrifuged. Most of the supernatant was aspirated and the sediment suspended in the remaining fluid. A preparation was examined by microscopy for Acanthamoeba. Another similar specimen was cultured in a non- nutrient agar seeded with Escerichia coli bacteria and plates incubated at room temperature. Plates were examined daily for two weeks.
Results
Only six (4 males and 2 females) of the 138 patients were positive for Acanthamoeba. The age range was 30–65 yrs (mean 47.5 yrs).
Acanthamoeba trophozoite (arrow). Giemsa stain ( x 400)
This is the first study on Acanthamoeba eye disease from Sudan using culture and microscopy methods. Molecular methods are recognized laboratory methods for diagnosis of AK, but the high degree of heterogeneity limited their use in our study. Isoenzyme analysis for diagnosis and species differentiation of Acanthamoeba can be used, however they are not always reproducible. For example, while distinct differences in the acid phosphatase and esterase isoenzyme profiles in Acanthamoeba pustulosa and Acanthamoeba palestensis were reported by one investigator; identical isoenzyme patterns for these two species were found by another investigator. Contact lens wearing is a common risk factor for AK, mainly from western countries. However, minor eye trauma was the main risk factor in our case series and these findings are in agreement with reports from India.
Thickly scarred cornea indicating a blind eye
References
- 1.Imam A. Pathogenic free living amoebae. Postgraduate Doctor, Middle East. 1989;12(9):426–30. [Google Scholar]
- 2.Imam A, Mahgoub E. Blindness due to Acanthamoeba: first case report from Sudan. Int J Health Sci. 2008;2(2):247–9. [PMC free article] [PubMed] [Google Scholar]
- 3.Khan NA. Acanthamoeba: Bology and clinical significance. FEMS Microbiol Review. 2006;30:564–95. doi: 10.1111/j.1574-6976.2006.00023.x. [DOI] [PubMed] [Google Scholar]