Ocular Dirofilaria repens infection in Lithuania, a case report

Abstract

Introduction: Dirofilaria is a roundworm that parasitizes carnivores and other animals. The infection is transmitted by the bite of an infected mosquito. In a life cycle, humans are an aberrant host and in most cases, larvae do not develop into adult worms. Three species of worms are infective to humans: Dirofilaria immitis, Dirofilaria repens, and Dirofilaria tenuis. Infection with D. repens and D. tenuis usually results in subcutaneous nodules and likewise in the subconjunctiva of the eye. This presentation covers the fourth case of human infection reported in Lithuania since 2011. Case description: In April 2022, a 44-year-old male with traveling history to Italy (two months ago) and Indonesia, Thailand (two years ago) complained of ocular swelling and a foreign body sensation in the left eye for a few days. Upon examination, the uncorrected visual acuity of the patient was 1.0 Snellen chart in both eyes. On slit-lamp examination, a motile subconjunctival roundworm was found in his left eye. The parasite was removed in local anesthesia (proxymetacaine hydrochloride solution 0.5%). Based on morphology the pale, thin, and cylindrical worm was recognized as immature D. repens. The conjunctival injection was observed without any remarkable eye disorders. Discussion: Some studies suggest, that, a combination of 10% phenylephrine and 0.5% tropicamide drops (to reduce the worm motility) or subconjunctival injection of 2% lidocaine with epinephrine 1:100,000 can be considered as an alternative to proxymetacaine solution. After removal, anthelminthic therapy is usually not recommended for human dirofilariasis while surgical removal is the mainstay treatment. In case of patient complains on prolonged symptoms, severe itching, or vision impairment, microfilaremia should be considered and the blood smear examined microscopically. Currently, histological testing has been used as the gold standard for the diagnosis of human dirofilariasis. Other diagnostic methods including immunochromatographic antigen detection, ELISA, or Polymerase chain reaction are rarely used. Conclusions: This case report highlights the relevance of surgical removal and specific parasitological diagnostics. Systemic treatment is not required once the causative agent has been removed surgically. Nevertheless, such clinical cases are very rare, and multidisciplinary collaboration and patient follow-up are very important. The earlier reported prevalence of D. repens in shelter dogs (19%) and pet dogs (1.9%), as well as infections in non-traveling patients, suggests the possible autochthonous origin of the present human case in Lithuania.