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Indian Journal of Medical Microbiology, Vol. 28, No. 4, October-December, 2010, pp. 399-402 Case Report Oestrus ovis ophthalmomyiasis with keratitis RS Sreejith1, AK Reddy2, SS Ganeshpuri1, P Garg1 1 Cornea and Anterior Segment Services, Hyderabad Eye Research Foundation, L.V. Prasad Eye Institute, Hyderabad-500 034, India Date of Submission: 13-Mar-2010 Code Number: mb10118 PMID: 20966582 Abstract A 35-year-old male patient presented with complaints of redness, swelling around the eyelids, watering, and irritation in the right eye. At presentation his best-corrected visual acuity was 20/20 partial in the right eye. The tarsal conjunctiva of the upper eyelid showed injection with pseudomembrane. Underneath the pseudomembrane we noticed four motile larvae. The cornea showed an irregular cobweb-like mucous plaque adherent to the epithelium, with a clear stroma. The pseudomembrane was easily peeled-off under topical anaesthesia. The organisms were removed and identified as Oestrus ovis. Three days later the patient was comfortable and his visual acuity was 20/20 in the right eye.Keywords: Keratitis, Oestrus ovis, ophthalmomyiasis Introduction Ocular myiasis may be assumed as clinical conditions of varying severity ranging from simple irritation to complete destruction of the orbit. [1] External ophthalmomyiasis refers to superficial infestation of ocular tissue, involving the conjunctiva. Oestrus ovis is the most common cause of ophthalmomyiasis externa worldwide. [2] However, the clinical course of the disease is still unknown. Most cases reported in the literature are of catarrhal conjunctivitis. We report a rare case of keratitis caused by Oestrus ovis infestation. Case Report A 35-year-old male presented on 8 October 2008 with complaints of redness, swelling around the eyelids, watering and irritation in the right eye of a day's duration. The symptoms started following due to the entry of dust particles into the eye the previous day. There were no complaints in left eye. No medication had been taken for the complaint. There was no history of any systemic illness. At presentation his best-corrected visual acuity was 20/20 partial in the right eye and 20/20 in the left eye. Examination of the right eye revealed periorbital puffiness with non-tender eyelid oedema. There was a ropy mucous discharge in the conjunctival fornix and the conjunctiva was chemosed. The tarsal conjunctiva of the upper eyelid showed injection with pseudomembrane and a few petechial haemorrhages. Underneath the pseudomembrane we noticed four motile larvae. The larvae were photosensitive and tended to move towards the fornix under slit lamp illumination. The cornea showed an irregular cobweb-like mucous plaque of approximately 6×7 mm adherent to the epithelium with a clear stroma. Multiple isolated epithelial defects were seen at the margin of the mucous plaque. The anterior chamber was quiet. The fundus was within normal limits with a cup to disc ratio of 0 : 4. Anterior and posterior segment examination of the left eye was within normal limits. Based on these findings, we diagnosed unilateral allergic conjunctivitis with keratitis secondary to parasitic infestation. The pseudomembrane was easily peeled-off under topical anaesthesia and the organisms were removed along with the membrane. The patient was prescribed carboxymethyl cellulose 1% eye drops 2 hourly and moxifloxacin eye drops 0.5% for six times a day. The patient was advised to come for a review the next day. When he presented three days later, he was comfortable. On examination, the right eye was quiet and visual acuity was 20/20 in both eyes. He was advised to stop all medications. The larvae were transparent, segmented and were seen to have black mouthparts in the anterior region. The larvae were mounted on a glass slide and examined under the microscope. They were identified as Oestrus ovis based on their spindle shape and the presence of a pair of sharply curved mouth hooks. The microscopy photographs [Figure - 1] of the larvae were sent to the parasitology division of the Centres for Disease Control, Atlanta, USA for confirmation and the parasite was identified as Oestrus ovis on 18 March 2009 (CDC 2009005461). Discussion Three dipteran families are considered to be the main cause of myiasis in livestock and also occasionally in humans. These families include Oestridae, Calliphoridae (blowflies), and Sarcophagidae (flesh flies). [1] An Oestrus ovis (sheep nasal botfly) from the class: Insecta, order: Diptera and family: Oestridae, is one of the common causes of human myiasis in the reported cases. Other species that cause human myiasis are Dermatobia hominis (human botfly) and Cordylobia anthropophaga (tumbu fly). [3],[4] Sheep bot (Oestrus ovis) is a cosmopolitan parasite of sheep and goats. The sheep nose bot is a hairy, yellowish, bee-like fly about the size of a common horsefly. Adults are 12−14 mm in length but are rarely seen. [5] The adult female fly is active during summer and early fall. Eggs are retained in the body until they hatch. The gravid adult female fly swarms around the head of the animals and ejects the first-instar larvae, which have previously hatched from the eggs in the fly vagina, in a stream of milky fluid on to the nostrils of the host. [1] Flies may deposit as many as 500 larvae in the nostrils of sheep. Direct contact between the fly and its host is not necessary for the infestation. [2] The larvae of Oestrus ovis mature in the mucous membrane of the nasal cavities, where they remain for up to ten months and then are sneezed out of the nostrils. [5] The larvae pupate in the soil with the pupal period lasting three or more weeks, depending on temperature. Adults then emerge from the pupae and may live as long as 28 days. [5] Occasionally, due to an aberration in the life cycle, man becomes the intermediate host, with the eye being the site of infestation. [2] Oestrus ovis larvae are unable to secrete proteolytic enzymes, so they are mostly confined to the outer membranes of the eye. [2] However, small conjunctival haemorrhages may be apparent at sites where the larva clings with its mouth claws. [2] In man, the larvae cannot survive beyond the first larval stage and are believed to die within ten days if not removed. [1] The literature available on Oestrus ovis infestation is summarized in [Table - 1]. The six reports describe 14 cases of Oestrus ovis ophthalmomyiasis externa. All the cases had conjunctival injection along with foreign body sensation, nine cases mentioned periorbital lid oedema, and in two cases there was follicular conjunctival reaction. Pseudomembrane formation was seen in one case. A single case mentions stromal keratitis along with subepithelial linear opacities and uveitis. [10] External ophthalmomyiasis in humans can also be caused by Dermatobia hominis, which unlike Oestrus ovis is capable of invading the ocular coats and causing significant morbidity. [3] Patients with D. hominis ophthalmomyiasis externa usually complain of discomfort related to the perception of movement within the lesion, pruritus, and sometimes pain. When the eyelids are involved, swelling is always present. The lesion may be misdiagnosed as a chalazion if the swelling is mild or as preseptal cellulitis if the swelling is significant. [3] A wriggling sensation within the lesion and identification of the respiratory pore are both helpful in making the diagnosis. [3] Ocular pruritus may be related to the accumulation of larval excretion in the inferior fornix, especially if the respiratory pore is on the free palpebral margin or in a conjunctival fornix. On slit-lamp examination, the moving larva may be identified within the lesion, intermittently protruding through the respiratory pore. Dermatobia hominis is also capable of causing internal ophthalmomyiasis. [3] It is hence of importance to identify the two larvae morphologically. Acknowledgement The authors thank the members of the Parasitology Division, Centres for Disease Control Atlanta, USA for confirming the identification of the larvae. References
Copyright 2010 - Indian Journal of Medical Microbiology The following images related to this document are available:Photo images[mb10118f1.jpg] [mb10118t1.jpg] |
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