Ophthalmomyiasis externa and interna in humans have been reported to be caused by many types of Dipterous flies, the most common being the sheep nasal botfly, Oestrus ovis. Cases of Ophthalmomyiasis externa by sheep botfly have been documented from different parts of the world. However, there are only few case reports from India, and none from the state of Madhya Pradesh. We describe a series of seven cases of external Ophthalmomyiasis caused by O. ovis, who reported to the Ophthalmology department of a tertiary health care centre of Madhya Pradesh during a 1 month period between March and April, 2012.
In the present series, six patients were young females between 14 and 25 years of age and one patient was a 65 year male. All patients presented in the spring season and belonged to middle socioeconomic strata with good personal hygiene except case no. 4 who was from low socioeconomic strata and had poor hygiene. In all cases, the involvement was unilateral [Fig. 1]. Visual acuity was 20/20 both eyes in all cases except case no. 4 in which vision was 20/40 both eyes and could be attributed to lenticular opacity. Conjunctivitis varying from mild to severe with/without discharge was seen [Fig. 2]. The anterior segment, fundus examination and ear nose and throat examination did not reveal any abnormality. Diagnosis of Ophthalmomyiasis external was made after direct visualization of the larvae on slit lamp examination [Fig. 3]. The clinical profile of the patients is shown in Table 1.
In all cases, anesthetic eye drops were instilled to immobilize the larvae. The lids were everted and larvae were then removed by fine smooth forceps under operating microscope and fixed in formalin. After removal, the affected eye was irrigated copiously with normal saline and topical antibiotic-steroid combination eye drops were prescribed 4 times a day, for a week. Next day DPX mount slide was made.
Follow-up examinations on subsequent days in case nos. 2 and 4 showed residual larvae which were removed. Ocular symptoms had largely resolved in all except case no. 4 where mild conjunctivitis persisted which resolved over next 5 days. All patients were followed up for 1 week and no complications were noted.
On examination under microscope, the organisms in all cases were identified as the first instar larva of O. ovis (Linn.), Family Oestride: Cyloerrhpha: Brachycera: Diptera, commonly known as sheep bot fly.
The larva is characterized by a pair of sharp, dark brown oral hooks, connected to a large internal cephalopharyngeal skeleton. The body is divided into 11 segments and each segment is covered by tufts of numerous brown hooks with spinose tips on the anterior margin. Terminal hooks are arranged in two scallops [Fig. 4].
Ophthalmomyiasis externa in our series of patients manifested as acute catarrhal conjunctivitis and presented with varied symptoms like redness, lacrimation, pain, itching and mucoid discharge along with foreign body sensation. Similar findings have been reported in various studies.
Sergent (1952), in summarizing oculonasal myiasis in man due to O. ovis appears to be the first to record the infection as far back as in 1907. O. ovis is a large, yellowish gray fly about 10-12 mm long. Its larvae can parasitize the host, soon after birth. In its normal life cycle, the adult female deposits larvae around the nostrils of sheep and goats, from where they migrate in to sinuses. The larvae mature by going through three progressive developmental larval stages (instars). After several months the 3rd instar (mature larval stage) passes out of the sheep and goat nostrils and pupate on the ground. Adult flies emerge from the pupa 3 to 6 weeks later and live for approximately 1 month. The usual hosts are sheep, cattle and horse. Man may serve as an accidental host when the bot fly deposits a stream of larvae near human eyes and/or nose while it is flying.
External Ophthalmomyiasis manifests as acute catarrhal conjunctivitis. Ophthalmomyiasis interna is commonly associated with cattle bot fly (Hypoderma bovis) but cases have also been reported due to larvae of O. ovis. Hence, Ophthalmomyiasis by O. ovis should not be regarded as a benign condition and must be treated promptly to prevent serious complications of intraocular invasion. Irrigation of conjunctival sac with normal saline is unsuccessful in washing out the larvae because they grab the conjunctival firmly by their hooks. So it is prudent to remove the larval form promptly under magnification after anaesthetizing the conjunctiva with the help of plain forceps. Follow-up examination is recommended to avoid possible complications of residual larvae and internal Ophthalmomyiasis.
The presentation of O. ovis myaisis is similar to viral or allergic conjunctivitis, and may present with foreign body sensation, pain, itching, redness, watering and discharge in the affected eyes. Awareness of larval conjunctivitis especially during spring and summer seasons would lead to a more prompt diagnosis and treatment. Ophthalmomyiasis externa is an under diagnosed condition and may result in serious complications. We, as ophthalmologists need to be aware of this entity and should examine all patients of conjunctivitis with or without history of insect striking the eye after lid eversion, to rule out Ophthalmomyiasis.
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Conflict of Interest: None declared.