Case Report A case of bilateral microsporidial keratitis from Bangladesh – infection by an insect parasite from the genus Nosema Alan Curry, 1 Hardeep Singh Mudhar, 2 Sumedh Dewan, 3 Elizabeth U. Canning 4 and Bart E. Wagner 5 Correspondence Alan Curry Alan.curry@cmmc.nhs.uk or dracurry@btinternet.com 1 Electron Microscopy, Clinical Sciences Building, Manchester Royal Infirmary, Manchester M13 9WL, UK 2 National Specialist Ophthalmic Pathology Service, Department of Histopathology, E Floor, Royal Hallamshire Hospital, Sheffield S10 2JF, UK 3 Cornea Clinic, Chittagong Eye Infirmary, PO Box 729, Pahartali, Chittagong 4000, Bangladesh 4 Department of Biological Sciences, Imperial College London, Silwood Park Campus, Ascot SL4 7PY, UK 5 Electron Microscopy Unit, Department of Histopathology, Northern General Hospital, Herries Road, Sheffield S5 7AU, UK Received 19 March 2007 Accepted 16 May 2007 An HIV-negative patient from Bangladesh with bilateral keratitis was found to be infected with a microsporidian parasite belonging to the genus Nosema. Significantly, the patient had bathed in a rural pond 7 days prior to the development of ocular symptoms. Nosema parasites are common insect parasites and the source of this microsporidial infection was possibly from mosquito larvae developing in the pond in which the patient bathed. The reduced temperature of the human eye and its immune status may have allowed a poikilothermic insect parasite to establish infection in the cornea of a homeothermic human host. This case highlights the opportunistic potential of insect microsporidial parasites to infect immunocompetent humans as well as those who are immunodeficient. Introduction Microsporidia are all tiny unicellular obligately intracel- lular parasites. Over half of the known microsporidial species are parasites of insects. Few microsporidia infect humans and most infections are enteric and associated with HIV/AIDS. In the early 1990s, several cases of keratoconjunctivitis associated with HIV infection were reported from the USA (Orenstein et al., 1990). Sub- sequently, there have been several reports of ocular microsporidial infection in healthy, non-HIV-infected individuals (Chan et al., 2003). Sources of ocular infection with microsporidia remain speculative but it has been suggested that the infection could originate from animals and that it is initiated by direct inoculation into eye abrasions (Curry, 1999). Case report The patient was a physically fit and well male, living in Bangladesh. Seven days before the onset of keratitis in both eyes, he visited his rural home where he stayed for 3 or 4 days. Significantly, whilst at his rural home he bathed in a local pond. Seven days later, he presented to his local ophthalmologists with bilateral blurred vision and red eyes. The visual acuities were 6/12 (left and right). Slit lamp examination revealed multiple white spots at an epithelial level, around the corneal periphery of both eyes. No stromal infiltrates were identified. Superficial punctate keratoconjunctivitis was diagnosed, of probable infective aetiology. The referring ophthalmologist performed a corneal scrape from the left eye and fixed the slides in methanol. The methanol-fixed slides were sent to the UK (Sheffield Eye Pathology Laboratory-HSM). The patient was treated with topical steroids and antibiotics with little effect. After detection of the keratitis, the patient was tested for HIV infection, but the result was negative. One of the slides was stained with a modified Ziehl– Neelsen stain. The corneal scrape on a second slide was processed into TAAB Emix medium hard resin and sectioned for electron microscopy. After staining with uranyl acetate and lead citrate, the sections were examined with either a Philips CM10 or a Philips EM400 electron microscope and images were recorded. The modified Ziehl–Neelson-stained scrape showed 3–5 mm pink, non-budding, oval organisms on light microscopy, on Journal of Medical Microbiology (2007), 56, 1250–1252 DOI 10.1099/jmm.0.47297-0 1250 47297 G 2007 SGM Printed in Great Britain