Case 26a

by Dr. Mahadhir Alhady & Professor Chua

A previously well 9-year-old boy from a border town with Kalimantan, Indonesia, some 100 Km from our hospital, complained of a two-week history of bloody discharge in his right ear. The local doctor noted ulceration of the right ear canal and the presence of live maggots. He was referred to our otolaryngologist who removed 45 maggots from the right middle ear cavity under general anaesthesia. While recovering at the hospital, the patient’s right eye was noted to be red. He was referred to our eye department. Apart from a right red eye, his vision was normal. Slit-lamp examination showed a breach in the the superonasal bulbar conjunctiva (Figure 1) and a live maggot could be seen lying deep in the wound. Attempt to remove the worm was unsuccessful as the patient was unable to cooperate. Under general anaesthesia, the conjunctival wound was extended to expose the maggot (Figure 2 and 3) which was removed whole with a pair of forceps. The worm measured 12mm (Figure 4). Based on the shape, mouth and tail part of the maggot, it was identified as the larva of  Chrysomya bezziana (screwworm fly).

Figure 1. The black arrow indicates site of the burrow.

Figure 2. The conjunctiva is incised to expose the worm.

Figure 3. More body of worm was exposed through deeper dissection.

Figure 4. The whole length of the worm measured about 12mm.

a. What is ophthalmomyiasis?

Myiasis is coined from the Greek word ‘myia’ denoting fly. It refers to the infestation of tissues by the larvae (maggots) of diptera (two-winged) flies. The condition is well recognised in animals but rare in humans. Cases of human myiasis have been reported in various parts of the world and could be attributed to one of the three dipteran families: Oestriade, Calliphroidae and Sarcophagidae.

In South-East Asia, animal myiasis is endemic and the main causative agent is Chrysomya bezziana, also known as screwworm fly of the Old World. This fly belongs to the Calliphoridae family and causes obligatory myiasis (it requires a living host for the development of the larval stages). It infests mainly domestic animals and may cause great losses in livestock industry if not treated rapidly.^1-3

b. How does Screwworm infestation occur?

Screwworm infestation is transmitted by the female fly that lays her eggs on a superficial wound, but occasionally on unbroken soft skin, especially if it has blood or mucous discharge on its surface. Eggs are deposited in batches of 150 to 500 and hatch in about 15 hours. The larval bodies, measuring 10 to 15mm are armed with broad, encircling bands of spines. The larvae feed on blood and serum and burrow deep into the tissue with their mouth-hooks causing considerable destruction.  Infested wounds often attract other female screwworms resulting in multiple infestations. After feeding for 5 to 7 days, the larvae leave the wound and fall to the ground where they burrow and pupate for one week or more to emerge as adult flies. The life cycle from egg to egg takes about 24 days. ^4-5

 

Figure 5. The screwworm fly.

 

Both otomyiasis and ophthalmomyiasis from screwworms are rare and there are only a handful of reported cases. Our case is unusual because of the simultaneous involvement of two sites. Otomyiasis may occur from neglected chronic lesions such as chronic suppurative otitis media with poor personal hygiene. The destruction of the auditory meatus can lead to deafness, meningitis and even death.⁶ Ophthalmomyiasis typically occurs in demented and debilitated patients with chronic eye diseases such as eyelid tumours.^7-8  In our patient, the concurrent ophthalmic infestation by a single screwworm is likely to be the result of migration of the screwworm from the aural cavity into the conjunctiva. Depending on the destruction caused, screwworm can cause external, internal or orbital ophthalmomyiasis. External ophthalmomyiasis involves the eyelid and conjunctiva, orbital ophthalmomyiasis the orbital content, and internal ophthalmomyiasis the intraocular spaces. The treatment of ophthalmomyiasis involves removal of the maggots and cleaning the lesion with saline and antibiotic solution. Prophylactic antibiotic therapy may prevent secondary infections.

Reference:

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3. Werner RM, Dohany AL, Vanniasingham JA, Huxsoll DL. Screwworm myiasis caused by Chrysomyia bezziana in

zoo and domestic animals in Malaysia: a report of 3 cases. Proc Annu Meet U S Anim Health Assoc. 1980;84:339-

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4. Goddard J. Physician’s guide to arthropods of medical importance. 4^th Edition. CRC Press 2002.

5. Mullen G, Durden L. Medical and Veterinary Entomology. Academic Press Inc.(London) Ltd. 2002. 

6. Talari S , Yeganeh-Moghadam A, Dehghani R. Chrysomyia bezziana infestation. Arch Irn Med 2002; 5 (1): 56-

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7. Radmanesh M, Khataminia G, Eliasi P, Korai MK, Ebrahimi A. Chrysomyia bezziana-infested basal cell

carcinoma destroying the eye. Int J Dermatol. 2000 Jun;39(6):455-7.

8. Sachdev MS, Mandal AK. External ophthalmomyiasis associated with herpes zoster ophthalmicus. Can J

Ophthalmol. 1990 Feb;25(1):42-3.