The genus Dirofilaria consists of many species that infect a wide range of hosts including dogs, cats, foxes, and wild mammals.1 Humans are accidental hosts. Vectors for this parasite, such as Dirofilaria repens (dogs), Dirofilaria immitis (dog heartworm), Dirofilaria tenuis (raccoons), and Culex, Aedes, and Anopheles (mosquitoes) carry the microfilaria from an infected natural host after sucking blood from the host. The disease usually presents as a single painful subcutaneous nodule on the face, chest, arms, thigh, or abdomen. Ophthalmic involvement, including periorbital,2 subconjunctival,3 sub-Tenon,4 or intraocular,5 has also been described.
A 78-year-old woman had uneventful clear corneal temporal phacoemulsification with intraocular lens implantation in the right eye at our clinic. She was wheelchair-bound and came from a remote area. The postoperative 1-week follow-up was unremarkable, with the corrected distance visual acuity (CDVA) improving to 20/20. The patient was advised to come to the clinic for a follow-up after 3 weeks for refraction and final glasses prescription.
A few days later, the patient reported mild redness and swelling in the operated eye. Seeing the patient was logistically difficult; hence, we presumed the symptoms were caused by inflammation, infection, or an allergy to medication. She was advised to increase the frequency of the postoperative eyedrops and to see a nearby ophthalmologist, and she was prescribed oral medication. The symptoms improved with medication.
One week later, the patient reported to us that the symptoms had recurred and were accompanied by pain and watering from the eye. On biomicroscopic examination, a congested nodule was observed in the temporal conjunctiva of the right eye, which showed some movement. Careful examination showed a live, motile worm beneath the conjunctiva (Figure 1). The CDVA was 20/20 in the right eye and 20/200 in the left eye secondary to a macular scar caused by a previous branch retinal vein occlusion. The anterior chamber and fundus examination of the patient's right eye was normal. She was a known diabetic, was hypertensive, had arthritis in her knee, and was under the care of a neurologist for Alzheimer disease. There was no history of injury, allergy, or other systemic nodules. She said she had not traveled outside the country in the past few years. Her caregiver remarked that there was a pet dog in the patient's house.
The patient was taken for surgical removal of the worm (Figure 2) under local anesthesia. A blunt forceps was used to prevent damage to the worm while removing it. The worm was preserved in 10% formaldehyde and sent to the microbiology department for identification.
Hematologic examination did not show eosinophilia. Peripheral blood smears taken at different times were negative for microfilaremia. A stool examination for ova and cysts was negative. No systemic antihelminthic treatment was indicated, and the patient did well on antibiotic and steroid eyedrops.
The extracted worm was 10 cm long, thin, white, and thread-like, with a maximum diameter of 524 mm. It was identified as a female D repens based on morphologic features such as a thick cuticle, beaded longitudinal ridges with transverse striations, and a flared anterior end.
Cataract surgery is the most commonly performed surgery in the world and has a very high success rate. The need for postoperative care has decreased as a result of better techniques and excellent results. We routinely perform clear corneal cataract surgery under topical anesthesia and sometimes do not examine the patient even the next day if he or she must travel a long distance. A telephone interview is performed, during which the patient is asked about the condition of the operative eye.
This case was interesting because the patient did well for 2 weeks postoperatively and then suddenly developed symptoms. There were no preoperative findings to suggest an infection elsewhere in body. The increase in redness and watering was presumed to be caused by inflammation or an infection, and the frequency of medication was increased. Because the symptoms started to resolve, the patient did not go to a doctor because it was very difficult for the caregiver to arrange for transportation. However, when the symptoms worsened, the patient and caregiver came to our clinic. At that time, we saw a moving worm and diagnosed the condition. This infection is not commonly seen in our part of India.
Zoonotic filariasis is more commonly seen in rural areas and in animal handlers. Subcutaneous dirofilariasis, which is the most common presentation, presents as a nodule in and around the eyes and the periorbital region. It is rarely seen in the subconjunctival space or present in the anterior chamber. The skin nodules can be mistaken for a malignancy, which would warrant many diagnostic tests. Therefore, awareness about zoonotic filariasis is important.
The diagnosis can be confirmed based on morphologic features. The Dirofilaria genus is confirmed by the presence of a thick cuticle, a broad lateral end, and thick musculature. Dirofilaria repens has beaded longitudinal ridges and transverse striations.6Dirofilaria immitis can be identified by the absence of prominent longitudinal ridges. Males are shorter (4.0 to 4.8 cm) than females (8.0 to 13.0 cm).2
Eosinophilia occurs in less than 15% of cases with D immitis and rarely with D repens.7 Most infective larvae introduced into humans do not reach maturity and are thought to die.3 Humans are dead-end hosts, and there is no microfilaria in blood. Hence, the role of antihelminthic drugs is not established. There is no serious ocular morbidity unless the worm is intraocular (anterior chamber8 or retina), and patients do well with surgical excision.
The mode of infection in this patient was not clear. It could have been from the bite of a vector. The initial symptoms could have been caused as the worm migrated in the subconjunctival space. The symptoms intensified later, maybe as a result of an allergic reaction to the worm, causing marked chemosis and congestion of the conjunctiva. No difficulty was encountered when the worm was surgically removed, and the symptoms promptly resolved thereafter. At the last examination, the patient had normal vision and a quiet eye.
In conclusion, the D repens infection after cataract surgery in our case presented in an unusual manner. The live worm under slitlamp examination confirmed the diagnosis; this can be difficult when it presents as a nodule. Because the worm was subconjunctival, it could be easily removed with no impediment to the postoperative recovery.
Neither author has a financial or proprietary interest in any material or method mentioned.
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