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Oestrus ovis, the nasal botfly, is the most common cause of conjunctival ophthalmomyiasis in North America3 and the term ophthalmoestriasis has been proposed.4 This botfly is a common parasite in the nasal and paranasal cavities of goats and sheep, thus, the name, the sheep nasal botfly. It is common in sheep farming areas, especially in the Mediterranean countries, southern Africa, and Central America. The organism is rare in the United States, with few reported cases to date.3 Most cases have been reported from Santa Catalina Island, California, where there is a large indigenous wild goat population.5 A more dangerous form of conjunctival ophthalmomyiasis is due to the Russian botfly, Rhinoestrus purpureus, which is found in the nasal passages of equines in southern Europe, Asia Minor, and Africa.4 The cattle botfly, Hypoderma bovis, is frequently associated with ophthalmomyiasis interna.6
We report a case of ophthalmomyiasis externa in a young woman in Dallas County, Texas.
On examination she had a visual acuity of 20/20 with spectacle correction. There was significant conjunctival follicular reaction in both eyes. No other parasites were noted within the anterior segments. The specimen was examined at the Dallas County Hospital District Department of Microbiology. A 4.0 x 1.0 mm tan object consistent with fly larva was identified. A more definitive identification was not possible because the larva was dead and had not been properly preserved. It was suspected that the patient had eggs on her hands that were transmitted to the conjunctival sac.
No medications were prescribed and the patient was discharged with instructions to return for re-evaluation at a later date. The Infectious Disease service was consulted and concurred with the recommendations.
The patient did not return for follow-up examination. A telephone call to her home confirmed that she remained asymptomatic several weeks later.
Yoshimoto and Goff reported a case in a 63-year-old man in Hawaii who was infected while working on his car.9 They also indicated that there have been other cases in Hawaii. Other genera of fly larvae have also been reported to be associated with ophthalmomyiasis. Chodosh and others reported a case of nosocomial conjunctival myiasis in a debilitated nursing home resident in Texas.10 The larvae were identified as Cochliomyia macellaria. Chodosh and Clarridge later reviewed ophthalmomyiasis, and reported other causes included Cochliomyia hominivorax, Chrysomyia bezziana, Wohlfartia magnifica, Dermatobia hominis, Oedemagena tarandi, and Hypoderma spp.11 Many of these infections were in individuals with underlying illnesses, and were frequently the cause of opthalmomyiasis interna. Emborskey and Faden recently reported a case of periorbital swelling in a four year-old boy due to opthalmomyiasis caused by D. hominis.12 In this instance, the larva was removed surgically from the upper eyelid. Another recent case report from India, involving O. ovis, was somewhat similar to our case in that it was in a 12-year-old boy with conjunctival larvae.13 Although his father was a gardener, he had no history of animal contact.
First instar larvae, also known as sheep bot, are deposited by the adult female O. ovis into the external nares of goats and sheep and work their way up into the nasal and frontal sinuses where maturation takes place. The mature larvae drop to the ground and pupate. After three to six weeks, adult flies emerge from the pupae and their life-span may be up to a month.1,4 The adult fly is approximately 12 mm in length and mainly blackish-brown.14 Patients with ophthalmomyiasis externa due to O. ovis typically present with a history of close contact with sheep or goats in early summer to fall.4 The symptoms of conjunctival ophthalmomyiasis are similar to those of acute catarrhal conjunctivitis.6,15 There may be a history of a foreign object or an insect striking the eye, a few hours before the onset of eye pain and inflammation.1 The female flies are supposedly capable of ejecting a jet of larvae while in close proximity to the eye. The patient may present with burning, itching, mobile foreign body sensation, photophobia, watery discharge, and eyelid cellulites. A conjunctival pseudomembrane may be present in some cases.6 Follicular conjunctivitis and punctate keratopathy are considered characteristic.3 The larva may die in the host giving rise to a permanent nodule, which macroscopically resembles a sty.16
Visualization of the organism is aided by the slit-lamp examination, although the organism usually avoids the beam.15 The larvae are translucent and small (0.8-1.0 mm), making them difficult to detect.17 Larval identification is aided by the dark mouth claws and the active vermiform movements of its body against the congested and edematous conjunctiva.1 Double eyelid eversion may aid detection of the larvae in the conjuctival fornix. As many as 50 organisms have been removed from one eye. Heyde and others reported 50 organisms in the right eye and approximately 30 organisms in the left eye of a single patient.5 Treatment of the condition is by removal of the larvae. Paraffin oil can be used to stop the oxygen supply, thus aiding removal of the larvae. In addition, a topical anesthetic can be used to paralyze the larvae, thus making their removal by forceps easier.16 Generous amounts of Neosporin® (Warner Lambert, Morris Plains, NJ) (neomycin, bacitracin, and polymyxin B) ointment have been used to facilitate suffocation of the organism.5 Topical corticosteroids and antibiotics can be used to relieve the inflammation and prevent bacterial contamination.3 Follow-up examination by an ophthalmologist is recommended to avoid the possible complication of ophthalmomyiasis interna.18
In conclusion, although ophthalmomyiasis externa is an uncommon condition in North America, early diagnosis and management is important in preventing complications.
Received June 24, 2002. Accepted for publication September 25, 2002.
Acknowledgment: We thank Bobbie Wortham for assisting with the preparation of this manuscript.
Reprint requests: Paul M. Southern, Department of Pathology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9073, Telephone: 214-648-3587, Fax: 214-590-8037, E-mail: paul.southern{at}utsouthwestern.edu
Authors’ addresses: Ellen Sigauke, Rita M. Gander, Dominick Cavuoti, and Paul M. Southern, Department of Pathology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9073. Walter E. Beebe, Cornea Associates of Texas, 7150 Greenville Avenue, Dallas, TX 75231.
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  N Huynh, B Dolan, S Lee, J P Whitcher, and J Stanley Management of phaeniciatic ophthalmomyiasis externa Br. J. Ophthalmol., October 1, 2005; 89(10): 1377 - 1378. [Full Text] [PDF]
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