Subconjunctival Dirofilaria repens Infestation: A Light and Scanning Electron Microscopy Study

BACKGROUND: To present a case of subconjunctival infestation with Dirofilaria repens which is very rare in Northern Europe. METHODS: A 61-year-old male presented with a swelling and redness of the left supraorbital region migrating to the eyelid and the left eyeball resulting in conjunctival injection, proptosis and diplopia. The patient underwent incisional extraction of a nine cm long worm, which was analysed histologically. RESULTS: The worm was structureless, greyish-white in colour and measuring nine cm in length and 0.5 mm in diameter. Histopathological examination of the worm showed an outer thick, multi-layered cuticle with longitudinal ridges. Beneath the cuticle, a thick muscle layer was observed and internally the intestine and a single reproductive tube containing spermatozoa were noted. Scanning electron microscopy of the worm showed tapered ends, transverse striations and longitudinal ridges at the anterior end. The tail was relatively short with spirally coiled ridges indicating a male Dirofilaria repens. CONCLUSIONS: Humans are an uncommon and accidental host of Dirofilaria repens which is rarely seen in Northern Europe but should be considered as a differential diagnosis to other nematode ocular infections. A travel history is helpful in diagnosing the potential involved organisms. No further treatment is necessary beyond surgical removal since this organism fails to mature and thereby does not cause microfilariaemia in humans.