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Video Report

A Case of Ophthalmyiasis Externa from Jordan in the Middle East

Stockport Eye Centre, Stockport, Cheshire

Thabit A Mustafa Odat, Flat 5, 25 Higher Hill Gate, Stockport, Cheshire SK1 3ED, United Kingdom.
Email: thabitodat{at}doctors.org.uk ADDRESS Tel: +44 (0)161 4777 518, +44 (0)7869 106580, +44 (0)7748 026044; Fax: +44 (0)161 419 4263

Date of acceptance: 12th Decemeber 2006

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Introduction

Ophthalmomyiasis Externa signifies an inflammatory response of the anterior segment and adnexae to a variety of larval infestations.[1] This infestation is caused by Oestrus Ovis larva which is mainly found in hot climates and is peculiar to places such as the Middle East,[2] America and Africa.[3]

Case Report

A 14-year old male patient was referred to the emergency clinic of the King Hussein Medical Centre in Amman (Jordan) with a sudden onset of irritation, foreign body sensation, and tearing of the left eye for 2 days. His symptoms developed while he was working on a farm in northern Jordan which was mainly concerned with raising livestock

His visual acuity was 6/6 in each eye. The lids of the left eye were swollen and mildly reddened. The conjunctiva was congested and chemotic, with evidence of a follicular reaction from the inferior tarsal surface. Additionally, there was pseudomembrane formation in the upper and lower tarsal conjunctivae. The cornea had diffuse punctate epitheliopathy, which in parts consisted of a linear track of punctate spots. At the superotemporal limbus of the left cornea (Figure 1) there was a refractile cylindrical larva measuring about 1 millimetre in length in addition to other similar transparent larvae on the conjunctival surface. Clinically, at one pole of these larvae there was a dark spot. A characteristic feature on examination was how these particles fled from the beam of the slit-lamp (Video). The remainder of the anterior segment, the posterior segment, and the ocular motility were all unremarkable.

Figure 1. A refractile cylindrical mass at the superotemporal limbus of the left cornea.

Clinical digital photography and video of the lesions was undertaken and submitted to the Microbiology Department. The microbiology team stated that this photographic evidence was in favour of a diagnosis of Sheep Nose Botfly (Oestrus Ovis) larvae on the ocular surface. This impression was confirmed by histological observation under the light microscope. Staining of the tissue was found to be suboptimal because of the immediate drying of the larva at the time of collection. Notably, complete blood count did not show an eosinophilia.

Discussion

Although Ophthalmomyiasis Externa is met commonly by ophthalmic practitioners in north of Jordan, the cases have been very poorly reported in the world literature.[2] This is chiefly a seasonal disorder, being found particularly in two peaks in the calendar. The first peak of incidence is from May to June when most of the cases are seen, with a later peak being seen from September to October. It is therefore an important differential diagnosis to bear in mind during these periods.

For the vast majority of patients the infestation is superficial, with the ocular surface being irritated by the presence of mobile foreign bodies. This expression of the infestation is relatively benign and does not result in serious morbidity. However, ingress of certain species of fly larvae (eg, Hypoderma, Cuterebra) into the globe can result in blindness. This aggressive variant of the disease is known as Ophthalmomyiasis Interna. Where orbital tissues are invaded by fly larvae a fulminant reaction can be expected with certain fly larvae such as Dermatobia hominis. An interesting characteristic of the Sheep Nose Botfly is that it sprays its larvae (previously hatched in the vagina of the fly) in a milky secretion onto the recipient animal during flight. Where the larvae land on livestock such as sheep or goats the whole life-cycle is realised by the expression of three progressive stages. With human infestation the life-cycle is terminated at the first larval stage after a survival on the recipient mucous membrane for about 10 days.

The typical clinical signs of Ophthalmomyiasis Externa are those expected of an acute allergic or viral conjunctivitis. The full-blown acute picture involving a follicular reaction can be induced by the milky substrate within which the larvae are injected, or independently by the larvae themselves. Exposure of the nasal mucous membrane to these agents can similarly result in an allergic rhinitis.

The most common management of ocular surface infestation by fly larvae is simple extraction with forceps. Owing to the hypermotile state of the larvae under the slit-lamp this technique can prove challenging or ineffective in resolving symptoms. The technique is considerably enhanced by the instillation of topical anaesthetic to decrease larval motility. Topical eye ointment is also a useful adjunct in the extraction process. The viscosity of the ointment reduces motility and creates a hypoxic environment. Another method that is sometimes favoured is the use of topical hypertonic saline which exerts an osmotic stress on the larva, thereby producing a state of debilitation. A less frequently seen method is the application of topical anticholinesterase solution.

In this patient's case topical benoxinate was instilled into the conjunctival sac and after a period of five minutes the larvae were found to be sluggish and therefore easily removed. A total of 36 larvae were extirpated. A crucial point in management is that the upper eyelid must be double-everted since the larvae have a predilection for the conjunctival fornix.

In conclusion, Ophthalmomyiasis Externa is largely a self-limiting disorder that should be borne in mind in the differential diagnosis of an acute conjunctivitis in certain parts of the world. Diagnosis is clinical and management is usually simple removal that can be aided by a variety of agents.

References

• Reingold WI, Robin JB, Leipa E, et al: Oestrus ovis ophthalmomyiasis externa. Am J Ophthalmol 1984 Jan; 97:7-10.
• Amr ZS, Amr BA, Abo-Shehada MN. Ophthalmomyiasis externa caused by Oestrus ovis L. in the Ajloun area of northern Jordan. Ann Trop Med Parasitol. 1993; 87(3): 259-262.
• Dar MS, Amer BM, Dar FK, Papazatos V. Ophthalmomyiasis caused by the sheep nasal bot, Oestrus ovis (Oestridae), larvae in the Benghazi area of Eastern Libya. Trans R Soc Trop Med Hyg. 1980 ; 74(3): 303-306.