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Video Report

Subconjunctival Dirofilariasis

¹Aravind Eye Hospital, Coimbatore, India; ²Eye Pavilion, Royal Infirmary of Edinburgh, Scotland

Correspondence: Dr K Myint
Princess Alexandra Eye Pavilion Chalmers Street, Edinburgh, EH3 9HA, UK
Email: kmyintuk@yahoo.co.uk

Date of acceptance: November 1, 2005

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Background

Zoonotic dirofilariasis has a worldwide distribution. These are natural parasites of domestic dogs, cats and wild mammals. The mosquito genus Aedes, Anopheles, Aegypti, and Armigeres have been incriminated as possible vectors for the transmission. The mosquito takes up the microfilaria whilst feeding on an infected host and transmission takes place when the vector bites, including the human during a subsequent blood meals.[1]

The species Dirofilaria immitis found in the right ventricle and pulmonary artery of the dogs is commonly known as dog heartworm. Another species Dirofilaria repens has reported in subcutaneous tissue of dogs.[1]

In human Dirofilariasis, a variety of organs are affected e.g. lungs, liver, male genitalia and female breast tissue have so far been reported.[1] This can lead to incorrect diagnoses as inflammatory nodules or malignant tumour. The two common species involving the eye as a subconjunctival or subcutaneous nodule of eyelid are D. tenuis and D. repens. D. tenuis has been reported in United States as a natural parasite of raccoons.[3] D. repens infection however, is a fast emerging zoonosis in SE Asia, Middle East, Africa and Europe.

Case Report

A 63-year-old woman presented at the Aravind Eye Hospital with pain over her right supraorbital region with redness on the nasal side of right eye for a week's duration. She had been treated with topical antibiotics and steroids by a local ophthalmologist. After a brief respite, the symptoms recurred with swelling and pain in the right eye.

Examination revealed an undulating vermiform mass in the sub-Tenon's space with localized congestion on the nasal side of right eye. The rest of ocular examination was within normal limits and her visual acuity was 20/20 in each eye. The haematology and stool test results were normal and no microfilaria was detected in the blood smears. Under local anaesthesia, the coiled worm was removed surgically intact from subconjunctival space. It was preserved in 10% formaldehyde and sent for identification.

Parasitologic findings

The worm was thin and cylindrical, measuring 9.5cm in length with a maximum diameter of 536µm. The anterior end was bluntly rounded with a greater diameter than the posterior end. The genital pore was located 1.3 mm from the anterior end. The cuticle of the worm was thick marked with longitudinal ridges and transverse striations. The uterus was didelphic, opisthodelphic and packed with immature eggs. The anus opened almost terminally. The tail was 100 µm long and had obtuse tip. Based on the size, cuticular and internal morphologic features, the worm was identified as an immature and infertilised female D. repens.

Comment

Human Dirofilariasis infection is uncommon. However, the incidence of subconjunctival dirofilariasis in Kerala is emerging due to public health awareness. The prevalence of infection in domestic dogs has been estimated to 24% and much more in the stray dogs.[1] Kerala also has a network of backwaters, serving as a breeding ground for mosquitoes. The worms obtained in Kerala are mostly immature females, measuring 9 to 13.5cm in length. It is not uncommon to find a female worm reaching a length up to 18cm in the natural host.[1]

As humans are sub-optimal hosts, the worm will not attain full size and achieve sexual maturation. The microfilaria is not always present in humans. The worm develops gradually to a painful nodule or abscess in the subcutaneous tissue or subconjunctival space.[4] Surgical extraction is the treatment of choice. Since the worm is unable to replicate itself in human, no additional systemic microfilaricide is necessary.[2]

References

1. Sabu L, Devada K, Subramanian H. Dirofilariasis in dogs & humans in Kerala. Indian J Med Res, May 2005; 121:691-693
2. Gicquel JJ, Berthonneau J, Curutchet L et al. Management of subconjuntival Dirofilaria repens. Arch Ophth 2004; 122(3) 416-417
3. Ruiz Moreno, Jose M, Fernando J et al. Subconjuntival infection with Dirofilaria repens: serological confirmation of cure following surgery. Arch Ophth .Oct 1998; 116(10) 1370-1372
4. George M, Kurian C. Conjuntival abscess to Dirofilaria conjunctivae. Indian J Med Assoc.1978; 71(5) : 123-124