Case Report: Ophthalmomyiasis Externa Caused by Cordylobia anthropophaga Masquerading as a Lid Abscess

ABSTRACT.

Myiasis is a neglected tropical disease caused by the larvae of dipterous flies. Cutaneous infestation is the predominant type documented in sub-Saharan Africa, and ocular involvement is uncommon. We report the rare occurrence of a case of eyelid ophthalmomyiasis caused by Cordylobia anthropophaga in a Nigerian female to raise awareness among practitioners in both tropical and nonendemic areas.

CASE REPORT

Myiasis is a neglected tropical disease characterized by parasitic infestation of human and other vertebrate animal tissue by the larval stage of two-winged flies (Diptera).^1,2 The disease, although cosmopolitan, is found predominantly in tropical and subtropical countries and is associated with poor hygiene, suboptimal housing conditions, dwelling close to domestic animals, alcoholism, and trauma, among other reported risk factors.³

Globally, fewer than 5% of cases involve the eye, and this proportion is even less in sub-Saharan Africa where most reported cases are cutaneous.^4,5 Eyecare practitioners may therefore be unfamiliar with ophthalmomyiasis, which encompasses infestations involving the eye, the ocular adnexa and the periorbital tissue.⁴ To illustrate one of the various presentations of this uncommon variant of myiasis, we report a rare case of ophthalmomyiasis mimicking a lid abscess.

In July 2023, a 24-year-old female presented to the emergency department of the University of Benin Teaching Hospital in Benin City, Nigeria, with complaints of a painful, progressive left upper eyelid swelling of 8 days’ duration. The onset of symptoms coincided with a fall sustained while cleaning the bathroom, after which she noticed mild soft tissue swelling but no break in the skin. This was accompanied by purulent discharge via a small opening 4 days later. There was no fever, malaise, or symptoms of upper respiratory tract infection. She did not recollect any insect bite. She resided within the Benin city metropolis in an apartment with shared bathroom facilities, often soiled with urine due to lack of pipe-borne water. Dwellings were not in close proximity to any animals, and there was no history of recent travel.

On examination, visual acuity was 6/5 in each eye. The left upper eyelid had a firm, erythematous, and tender swelling. There was no conjunctival injection or pain with eye movement. A diagnosis of lid abscess was suspected. However, on observing a central punctum and slight movement beneath the skin, cutaneous myiasis was considered. After sedation and administration of adequate analgesia, a larva was extracted with the aid of forceps via a horizontal skin incision made ∼4 mm from the eyelid margin (Figure 1). The wound was dressed with Eusol, and a drain was left in situ.

Figure 1.

Surgical extraction of Cordylobia anthropophaga larva from the eyelid.

After clinical microbiology consultation, the larva was placed in 70% ethanol and sent to the medical microbiology laboratory for entomological assessment. The larva, roughly cylindrical in shape, measured 13 mm in length, and possessed about 12 segments with densely arranged, backwardly directed, small spines sparing the posterior segments. On microscopic examination, the anterior end had two black, hook-shaped mandibles, and the posterior end demonstrated spiracles with three sinuous spiracular openings and weakly sclerotized peritreme. The physical characteristics were consistent with the third-stage larva of Cordylobia species as described by Zumpft.² On the basis of the history, geographic location, and morphology, a presumptive identification of Cordylobia anthropophaga was made.

The patient received topical instillation of ciprofloxacin and systemic antibiotics for 72 hours to prevent secondary bacterial infections. A drastic reduction in lid swelling was noticed the next day, followed by complete resolution of symptoms within 1 week. The patient was counseled on the need to observe high levels of sanitation and hygiene.

DISCUSSION

Ophthalmomyiasis has variable clinical presentations depending on the fly species, ocular structures involved, and level of penetration.⁴ It can be classified as ophthalmomyiasis externa (involving conjunctiva or eyelids), ophthalmomyiasis interna (involving the subretinal space or vitreous cavity), and orbital ophthalmomyiasis (invasion of the orbit).

The commonest cause of ophthalmomyiasis externa worldwide is Oestrus ovis (Linnaeus, 1758), the sheep nose botfly.⁴ It affects the conjunctiva and presents with a sudden onset of symptoms such as foreign body sensation, redness, tearing, itching, swelling, photophobia, burning, and ocular discharge.⁴ Ophthalmomyiasis externa confined to the palpebral structures resembles cutaneous myiasis outside the eye, presenting as a furuncular lesion on the eyelid as seen in our patient. This variant is caused mostly by the human botfly, Dermatobia hominis (Linnaeus Jr. in Pallas, 1781) in Central and South America and Cuterebra species, botflies of rodents and rabbits, in North America with documented cases often citing a history of insect bite.^6,7 In Africa, ophthalmomyiasis is seldom reported, constituting only 36 (4.2%) out of 849 cases of myiasis in a recent review spanning 2 decades.⁵ Of these few cases, just two involved the eyelid: in one case, the identity of the larva was unknown, and the other, diagnosed in a 59-year-old man with a history of travel to Kenya, was caused by C. anthropophaga.^5,8

Cordylobia anthropophaga (Blanchard, 1893), or tumbu fly, belongs to the family Calliphoridae.³ It is the major causative agent of myiasis in Africa.^2–4 The adult is attracted by the odor of urine and feces and typically lays its eggs on contaminated soil or on clothes left to dry on the ground outdoors.⁵ Eggs hatch into larvae within 2–4 days. Human infestation, mostly affecting children, follows exposure to the larvae either through direct contact or via contaminated clothes. Infestation is common during the rainy season, as noted in the index case.⁵ Larvae can penetrate intact skin unnoticed within 60 seconds. Over 8–12 days, the larvae pass through three developmental stages, mature, and emerge from the skin, dropping to the ground to pupate and subsequently become adult flies. Most human infestations involve nonexposed body parts, such as the trunk, buttocks, and thighs.³ The face, arms, and legs are less frequently affected. According to scientific literature, C. anthropophaga is common and well known in Nigeria for causing furuncular myiasis involving nonexposed body parts, but ocular cases have not been documented. In the index case, unhygienic conditions in the shared facility probably provided a suitable breeding ground for the deposition of eggs, and the patient’s fall facilitated transmission through the thin skin of the eyelid, resulting in infestation in an unusual anatomic location.⁹

Because lid swelling from larval infestation is uncommon, it is unlikely to be among the top differentials considered by ophthalmologists, even those practicing in the tropics. The lesion may be mistaken for more common conditions such as chalazion, preseptal cellulitis, or lid abscess and may precipitate inappropriate antibiotic prescriptions. Complaints of a wriggling sensation within the lesion and observation of the respiratory pore are useful clues that point to the diagnosis.¹⁰

Although finding larvae in tissue is diagnostic of myiasis, genus- or species-level identification requires careful examination of morphological structures, including the anterior and posterior spiracles, mouthparts and cephalo-pharyngeal skeleton, and cuticular spines as well as consideration of travel history.^2,3 Molecular identification has been used in several cases but is not routinely feasible in low-resource settings.¹¹ Treatment involves surgical extraction of larvae and control of any local inflammation. Alternatively, larvae may be coaxed to emerge spontaneously by occluding the pore with ointment or petroleum jelly causing suffocation.⁴ Treatment with ivermectin has also been documented.⁴ Preventive measures in endemic areas include appropriate laundry management (sun-drying off the ground and ironing of clothes and linen) to destroy the eggs of dipterous flies and improving living conditions by providing good housing, water, sanitation, and hygiene.

There are two, less common species of Cordylobia (Cordylobia rhodaini [Gedoelst, 1910] and Cordylobia ruande [Fain, 1953]) with larval stages that may be difficult to distinguish from C. anthropophaga. C. ruandae affects forest mice and has not been reported in humans, whereas the usual hosts of C. rhodaini are various mammals with human cases reported occasionally in travelers to Cameroon, Ghana, and Ethiopia. Slight differences are described by Zumpt,² such as fragmentation of the sinous slit in the poaterior spiracle of C. rhodiani, but such distinctions may only be discernible by experienced entomologists. Molecular assessment is confirmatory but not readily accessible in resource-limited settings. Other fly larvae may be considered in the differential diagnosis of ophthalmomyiasis externa, but this should be guided by ocular structures involved (i.e., conjunctiva or eyelid), geographic location, and history of travel.

In conclusion, although myiasis is common in sub-Saharan Africa, ocular manifestations are rarely reported, and involvement of the eyelid has been documented only in a few instances including the present one. This case emphasizes the need for careful history-taking and prompts ophthalmologists and other healthcare practitioners in both tropical and nonendemic areas to think outside the box when confronted with patients presenting with eyelid swellings, thereby preventing misdiagnosis and unwarranted antibiotic use.