A 39-year-old white woman was in her usual good health working as a house painter in wetlands area of north Florida, when she developed sudden onset of left eye pain and subconjunctival swelling. She had no associated visual loss, fever, chills, nausea, or vomiting. There was no history of ocular trauma or splash exposures. She had no history of travel outside north Florida.
She was seen emergently by an ophthalmologist and, on examination, was noted to have superomedial swelling and erythema of the conjunctiva of the left eye which, on slit lamp microscopic examination, contained a filarid worm.
What is your diagnosis?
Diagnosis: The patient was found to have subconjunctival dirofilariasis (Fig. 1).
The conjunctiva was incised, and the worm was removed without complications. The worm was submitted to the Centers for Disease Control and Prevention for identification. The eye pain resolved over the ensuing 24 to 48 hours, and no further problems occurred.
On follow-up examination 1 week later, she had a small subconjunctival hemorrhage at the site of the worm removal and numerous excoriated insect bites over her upper and lower extremities. She had no lymphadenopathy, hepatosplenomegaly, or subcutaneous nodules. A chest x-ray was normal without evidence of pulmonary nodules. She refused having blood tests taken. She was advised that the worm was likely an ectopic dirofilarid, that no further therapy or diagnostic procedures were indicated, and that given her wetland habitat, it was important for her to regularly use insect bite precautions, that is, topical deet. She volunteered that 9 of the neighborhood dogs had died of heartworm in the past 12 months.
The Centers for Disease Control and Prevention subsequently confirmed that the subconjunctival filarid was Dirofilaria tenuis.
Dirofilariae are worldwide zoonotic filariae of a variety of animals, including cats, dogs, and raccoons. The adult filarids live in the host's subcutaneous tissue, with the exception of the heartworms; microfilariae are released and circulate in the animal's blood. Transmission occurs when the patently infected animal is fed upon by a mosquito, which then incubates the developing infective larvae over several weeks to be transmitted by bite to the next host. Man becomes an incidental dead-end host when fed upon by an infected mosquito. The filarid may develop to an adult in man; in which case, it may clinically present as a nodular lesion in virtually any part of the body. Dirofilaria immitis, the cause of heartworm in dogs and other canines, may cause asymptomatic solitary pulmonary nodules in man, usually found incidentally on radiological examination. In North America, D. tenuis, a parasite of raccoons, is reported as the most common cause of human dirofilarial infection, often presenting as soft tissue or visceral nodules. Dirofilaria repens, a subcutaneous parasite of dogs, cats, and other wild carnivores, is the most commonly reported cause of human dirofilariasis in Europe, particularly in Italy, Asia, and Africa.1,2
Periorbital and subconjunctival infections have rarely been reported from North America. There is only one other reported case of subconjunctival dirofilariasis from the United States in the last 15 years.3
Dirofilariae infections in man are diagnosed through histological examination of resected subcutaneous or deep tissue nodules or direct removal and identification of the filarid worm from an incised nodule. Infections in man are not patent, and removal of the worm is curative without any further surgical or antiparasitic therapy.4
1. Orihel C, Eberhard M. Zoonotic filariasis. Clin Microbiol Rev
2. Pampiglione S, Rivasi F. Human dirofilariasis due to Dirofilaria (Nochtiella) repens
: an update of the world literature from 1995 to 2000. Parassitologia
3. D'Heurle D, Kwa BH, Vickery AC. Ophthalmic dirofilariasis. Ann Ophthalmol
4. Gicquel J, Berthonneau J, Curutchet L, et al. Management of subconjunctival Dirofilaria repens
. Arch Ophthalmol