Dirofilaria repens infection of the eye with concomitant microfilaremia in a traveller

Case Report

In February 2018, a 79-year-old male presented with progressive pain in the left eye accompanied by visual impairment. He has previously been to Sri Lanka in December 2017, where he had contact with multiple feral dogs. During his vacation he noticed a wandering redness with a suspected insect bite on the left forearm. Back in Germany, a worm was discovered in the conjunctiva of the left eye. The parasite was removed in local anaesthesia (Supplementary Video 1), but histological identification was inconclusive. However, peripheral blood smear showed microfilaremia accompanied by eosinophilia, and a nematode-specific cytochrome oxidase polymerase chain reaction from filtered peripheral blood was positive. Sequencing of the amplicon followed by BLAST analysis (www. https://blast.ncbi.nlm.nih.gov/Blast.cgi) revealed 100% nucleotide homology to Dirofilaria repens, with an Asian genotype. Magnetic resonance imaging of the brain showed no abnormalities. Ivermectin (200 μg/kg, single dose) was given, and the patient complained of dizziness and a symptomatic hypotonic phase during treatment. As this might have been due to the medication, the patient was treated with parenteral fluid substitution. In the ophthalmological examination impressed still redness dexamethasone-containing eye drops and tear substitutes were applied. Serial blood samples 42 days after therapy showed a persistent microfilaremia. With improving local symptoms we refrained from another therapy attempt, and the patient was discharged. In the subsequent outpatient check, the patient reported an itching sensation that persisted for months and then slowly ceased.

Dirofilariasis is a zoonotic mosquito-borne disease known worldwide. In Europe, the species D. repens and D. immitis are present, which normally cause dirofilariasis in animals, most commonly in canids. Many human cases are travel-related, but autochthonous cases have also been reported in several European countries.¹ Larvae left in the wound during blood sucking penetrate the host skin and usually develop in the circulatory system, subcutaneous tissue, eye or other tissue types.² In rare cases, it can lead to organ or life-threatening risks in humans, for example loss of sight or meningoencephalitis.¹  D. repens usually does not replicate in humans and the larvae persist after migration from the site of the mosquito bite to different tissues, leading to disease symptoms.¹ This is contrasted by several reports of D. repens microfilaremia, most recently reported in a case from Austria,³ as well as in a case from Belgium, presumably imported from Senegal,⁴ and from Poland.⁵

An anthelminthic therapy is usually not recommended for human dirofilariasis. In veterinary medicine, ivermectin, which is also approved in humans, is recommended as a therapeutic. Due to the presence of Wolbachia endosymbiont bacteria in D. repens, doxycycline could be used as an alternative.^2,5 However, there are divergent study results and lack of experience in humans, and thus we opted for an ivermectin treatment attempt.

In summary, this case highlights the need for specific parasitological diagnostics. In addition to the possibility of a solitary worm, persistent microfilaremia with prolonged symptoms must be considered, possibly requiring combined treatment with ivermectin and doxycycline.

Conflict of interest

None declared.

Author contributions

Frederik Stephan Frenzen is the main author, knows and treated the patient; Ines Loewe is co-author, treated the patient’s eye; Gernot Müller also knows and treated the patient; Jacqueline Schoenlebe performed histopathology; Dennis Tappe is co-author, involved in diagnostic process and is also reviewer for this study; Dieter Teichmann is also co-author, knows and treated the patient.

References