Sir,

Myiasis refers to infestation of living tissue of vertebrate animals by the eggs or larvae (maggots) of flies of the order of Diptera. Larval infestation occurs in the nose in 81% of cases, in the ear in 11%, and in the face in only 1%. Orbital myiasis cases are rare worldwide.1, 2, 3, 4, 5, 6, 7 Conventional treatment consists of the removal of the larvae from affected sites, a painful and cumbersome task, sometimes made impossible in smaller cavities.8, 9 There have also been reports of drugs used topically to facilitate the removal, sometimes with frustrating results. We describe a patient with destructive rhino-orbital myiasis caused by larvae of the New World screwworm Cochliomyia hominivorax successfully treated with oral ivermectin prior to surgery.

A 55-year-old male patient was admitted to the Department of Ophthalmology, State University of Campinas with a 4-day-history of intense pain in his left orbital region, a crawling sensation, and maggots coming out of the nose. One week earlier he had mild fever, anorexia, and frontal headache. The clinical examination showed no light perception in the left eye. Discrete diffuse oedema around the nose and left orbit was noted. The eyelid was thickened and there was a necrotic, loose tissue lesion invading the left orbit (Figure 1). A purulent rhinorroea with a marked foetor was also present. Examination of the right eye was unremarkable. He was known to suffer from advanced carcinoma of ethmoidal sinus previously treated by chemotherapy and radiotherapy without success. Rhinoscopy revealed necrotic material in the nose with crawling maggots which were identified as larvae of Cochlomyia hominivorax. Laboratory findings were within normal limits. Computed tomography (CT) of the orbit revealed diffusely increased soft-tissue density extending to the orbital apex and obscuring orbital details. Bony destruction of the medial wall of the orbit and opacification of the ethmoidal sinus were present (Figure 2). The patient was given a single oral dose of ivermectin (200 μg/kg) and intravenous clindamicin was initiated to control associated infection. The patient showed continuous improvement and a complete resolution of the myiasis was observed after a 48-h period. Orbital exenteration was performed. No larvae were observed during the surgery or in the pathological examination of the orbital contents. The patient was discharged home on the fourth postoperative day.

Figure 1
figure 1

Appearance of lesion in the left orbit of a 55-year-old man with rhino-orbital myiasis caused by Cochliomyia hominivorax.

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Figure 2
figure 2

Orbital CT scanning showing the extent of the lesion.

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Human myiasis is relatively common. It is more common in undeveloped and tropical countries, although there have been reports of myiasis all over the Planet. Most cases of myiasis probably occur when a female fly lands on the host and deposits eggs or larvae. The invasive parasitic larvae may result in destruction of orbital tissue, desfigurement, and even death. Once larvae are present on the eye or adnexa oculi, the symptoms depend on the location and invasiveness of the larvae. Facultative species tend to produce mild infestations, while obligatory species can be invasive.1, 2, 3

Nasal and orbital myiasis in the New World is usually caused by Cochliomyia hominivorax, the aetiology of this patient. The fly is attracted by the bad odour of exposed and diseased body cavities.1, 9, 10, 11 Early diagnosis and treatment are important to avoid gross destruction of the tissues and to control secondary infection. The proximity of the brain and the possibility for intracranial invasion from the orbital apex renders this a potential life-threatening condition.1, 10, 11

Compromise of periorbital tissues by malignant disease, surgery, ischaemia, or infection may predispose the patient to myiasis. Crowded conditions, debility, low socio-economic status, and poor personal hygiene are other predisposing factors.2 Advanced carcinoma of the ethmoidal was the predisposing factor in our case. The patient also was from a rural background and was in a low socioeconomic status. The foetor coming out of the nose and poor local hygiene probably encouraged deposition of eggs.

Cochliomyia hominivorax, of the Callipharidae family, is an obligatory parasite with the capacity to produce deep, festering, disfiguring wounds that occasionally result in death. It is found throughout Central and South America, although reports have identified this parasite in Asia and Africa. Adult females deposit eggs in open wounds or discharging orifices such as the nose. Larvae invade adjacent living tissue, including cartilage and bone.8

Management of nasal and orbital myiasis consists of mechanical removal of the larvae followed by treatment of any sequelae. Topical preparations reported to immobilize maggots for easy removal include chloroform, ether, ethanol, turpentine, oily drops, and hydrogen peroxide.1, 2, 11 In our patient, the larvae were eliminated prior to surgery after a single oral dose of ivermectin (200 μg/kg), making the manual removal of the larvae, which is an unpleasant treatment for the patient and the doctor, an unnecessary procedure. Ivermectin is usually used in veterinary medicine and is effective in humans for the treatment of filarial, scabies, and strongyloidosis.12 We suggest that oral ivermectin should be considered as an option for treatment of human cavitary myiasis.