Keratitis due to an Unusual Pathogenic Social Amoeba, Dictyostelium polycephalum

To the Editor—Infections with pathogenic free-living amoeba including Acanthamoeba spp., Naegleria fowleri, Balamuthia mandrillaris, and Sappinia pedata have been documented in many countries [1]. However, social amoeba have not been reported earlier as etiological agents in human infections. In April 2010, we reported a case of keratitis in an immunocompetent person by social amoeba, Dictyostelium polycephalum [2]. In the present study, we report a second case of keratitis by D. polycephalum. A 15-year-old, non–contact lens wearer presented with a 20-day history of pricking sensation, redness, swelling, pain, and watering in the right eye after injury with a fingernail. The right eye showed lid edema, the conjunctiva was congested, and the cornea showed a large epithelial defect with a whitish yellow infiltrate measuring 10 × 10 mm involving almost all the cornea (Figure 1A). Visual acuity was expressed as the ability to see hand movements near the face. Ultrasonography of the right eye showed an attached retina with an echo-free vitreous cavity. At the time of the visit, the patient was using 0.5% moxifloxacin eye drops installed 5×/d. Corneal scrapings were collected using a sterile surgical blade (#15 on a bard parker handle) under topical anesthesia. Corneal scrapings were subjected to direct microscopic examination and inoculated onto blood agar, brain-heart infusion broth, Sabourauds dextrose agar, and non-nutrient agar (NNA). The direct microscopic examination of corneal scraping revealed double-walled C O R R E S P O N D E N C E