Dirofilaria in the anterior chamber: a rare occurrence.

Dirofilariasis is a parasitic infection of the carvivores that may present as a zoonotic infestation in humans. Systemic involvement in man is subcutaneous, pulmonary, or ocular. We report a rare occurrence of ocular dirofilariasis in a 25-year-old male patient who presented with pain and redness in the eye. A live, white, coiled, and highly motile worm was present in the anterior chamber. The worm, however, could not be detected in the anterior chamber, posterior segment, or the angle of the anterior chamber when the patient was taken to the operating room for surgical removal of the worm. The patient was made to lie prone till the worm reappeared in the anterior chamber and was removed by paracentesis. The worm was identified as Dirofilaria repens on the basis of microscopic and histopathological examination.

INTRODUCTION

Dirofilaria is a natural parasite of domestic and wild animals. The microfilariae are transmitted from the bloodstream of the definitive host by Culex, Aedes, and Anopheles mosquitoes which are also the intermediate hosts. The microfilariae are accidently transmitted to humans and they are the dead end host for the parasite. In human beings, systemic involvement is subcutaneous,1 pulmonary,2 and rarely ocular.3–5

We report a rare case of ocular dirofilariasis from Northern India wherein the live worm was freely floating in the anterior chamber.

CASE REPORT

A 25-year-old male patient presented with complaints of pain and redness in the right eye for 1 month. He had taken a short course of oral steroids 15 days ago. He was better while on oral steroids but the symptoms reappeared on discontinuing them. He also gave a history of visualizing a white floater in front of the right eye since a week.

On examination, his visual acuity was 6/6 in both the eyes. Ocular examination of the right eye revealed a live, long, white coiled, and highly motile worm in the anterior chamber [Figure 1]. The conjunctiva was slightly congested but rest of the ocular examination was unremarkable. Systemic examination did not reveal any abnormality.

Figure 1

Anterior segment photograph showing a white coiled worm in the anterior chamber

Patient gave no history of fever, subcutaneous nodules, or any localized swelling in or around the eye. There was no history of travel to endemic areas.

Complete blood picture and erythrocyte sedimentation rate were within normal limits with no evidence of eosinophilia. Peripheral blood smear was unremarkable, and no microfilariae were seen. Chest x-ray was also normal. Patient was immediately taken up for surgical removal of the worm from the anterior chamber as delay could have lead to posterior migration of the worm. However, in the operating room (OR) no worm could be visualized in the anterior chamber. Henceforth, we performed gonioscopy and a detailed fundus examination under mydriasis but the worm could still not be localized. The patient was then made to lie prone and after half an hour the worm reappeared in the anterior chamber. The pupil was constricted with pilocarpine to prevent the posterior migration of the worm and patient was again taken to the OR.

A side port incision was made in the nasal quadrant. The worm began to migrate toward the incision with the egress of the aqueous. The intact live worm was recovered from the side port incision itself and preserved in water and sent for identification.

On examination, the specimen was found to be an immature female nematode measuring 10 mm, with a maximum width of 290 μm. The worm was rounded at both the ends. The worm had a thick cuticle with longitudinal ridges and circular annulations giving the external cuticle a beaded appearance [Figure 2a]. Paired reproductive tubes were visualized at the lower cut end of the worm [Figure 2b]. Based on the morphological characteristics, the worm was identified as female adult Dirofialria repens.6 The images were sent to the Parasitology Division, CDC Atlanta, where the diagnosis was confirmed.

Figure 2

(a) Microscopic photograph showing the longitudinal ridges on the body which help in identification of the worm (b) Microscopic photograph showing adult female dirofilariae with the two ovarian tubes visible at the cut end

DISCUSSION

Dirofilariasis is a helminthic zoonosis endemic in Southern and Eastern Europe, central and minor Asia, and Sri Lanka.7 A review of literature shows that so far about 780 cases of human dirofilariasis have been reported worldwide.8 Our patient belonged to the state of Bihar, located in eastern India. This area is not endemic for dirofilariasis although it is endemic for filariasis (Wuchereria Bancrofti and Brugai Malayi). However, the patient had been residing in the state of Punjab in north India, which is not endemic for either filariasis or dirofilariasis. He had not traveled to his native state in the past 2 years preceding the onset of his symptoms. In India, dirofilariasis has been reported mainly from the southern coastal states of Kerala and Karnataka9 where it was found to be endemic in humans and dogs.10

Ocular involvement in dirofilariasis is usually periorbital,5 orbital,3 subconjunctival,4 or subtenon.11 This is because the worm has affinity for the subcutaneous tissues. In these cases, the worm is usually well localized. A few cases of intravitreal dirofilariasis have also been reported in the literature.12 One intraocular case of infection with Dilofilaria repens has been reported from Russia13 and another with Dilofialria immitis from Brazil.14 The microfilariae in these cases most likely migrate from the blood stream into the anterior chamber where it matures into an adult dirofilaria.

In our patient there was no subcutaneous nodule or inflammation around the eye or in the subcutaneous tissues of the eye.

The diagnosis of dirofilariasis is based on species identification. There are no blood tests to confirm dirofilaria and the presence of eosinophilia or microfialraemia is also inconsistent.

The morphologic features of most Dirofilaria make them relatively easy to identify to Genus level.15 They tend to be large, robust worms, and have distinctive longitudinal and circular cuticular ridging that gives the external cuticle a beaded or corn-row appearance. This can be seen easily in gross specimens that have been removed intact and is one of the more prominent features noted in histological section as well. Additionally, in sections, the worms have numerous strong muscle cells (polymyarian and coelomyarian) giving a strong body wall. Determining the species is more difficult, especially if a male worm is not present, and final diagnosis is often based on the presumed location of acquisition (i.e., Dilofilaria tenuis if in the United States, D. repens elsewhere).6 Recently, an integrated DNA barcoding of cox1 and 12S markers has been shown to be a powerful tool for the taxonomical identification of many filarioid species, including dirofilaria, even if small nematode fragments were available.16 The treatment in cases with ocular dirofilariasis is surgical removal of the worm. This was slightly challenging in our case as any manipulation or excess light from the microscope makes the worm more motile and increases the likelihood of its migration into the posterior segment. Preoperatively making the patient lie in the prone position facilitated the anterior migration of the worm into the anterior chamber. Subsequently the pupil was kept constricted wth pilocarpine and paracentesis was performed. Oral antihelminthic drugs are considered ineffective in the management of ocular dirofilariasis.

In conclusion, to the best of our knowledge, this is the first case of intraocular dirofilariasis from India. This case highlights the challenges in the management of live helminths in the anterior chamber and the preoperative use of pilocarpine to prevent their possible migration into the posterior segment.