Ocular and orbital dirofilariasis is a rare but increasingly reported zoonotic infection caused by nematodes of the genus Dirofilaria, with D. repens being the most important species in Europe, followed by D. immitis and D. tenuis. It is transmitted by mosquito bites and the main hosts are dogs, foxes, wolves and raccoons. Occasionally, humans can be infected as accidental definitive hosts in which the parasites do not reach reproductive maturity and are not transmitted further. In humans, the disease can manifest as nodular lesions in subcutaneous tissue, various structures of the eye, lungs and/or visceral organs. Therefore, it can be divided into two clinical forms, ocular or subcutaneous dirofilariasis and pulmonary dirofilariasis. Pulmonary infections, most commonly caused by D. immitis, are usually recognised as coin lesions on radiographs and diagnosed by biopsy. Ocular or subcutaneous infections caused by D. repens and D. tenuis appear as mobile nodules under the skin or in the eye (Centers for Disease Control and Prevention, 2025). Involvement of the eye and orbit can present with a wide range of symptoms, from mild irritation and conjunctival hyperemia to subcutaneous migratory oedema, eyelid nodules and even orbital cellulitis-like symptoms. Due to the non-specific symptoms and the rarity of the disease, the diagnosis is often made late or not at all. Blood tests (eosinophilia) are unreliable for diagnosis in humans. Treatment consists of surgical removal of the parasite, although systemic therapy is generally not required if the parasite has been surgically removed. The prevalence of these infections is increasing, especially in Sisak-Moslavina County, where the majority of the population lives in rural areas and in the Lonjsko polje marshland, where there is high mosquito activity and close contact between humans and animals. A higher incidence has also been reported in endemic regions such as the Mediterranean, Central and Eastern Europe (Mus et al., 2025). Changes in climatic conditions, including increased temperature, relative humidity and rainfall, are known to contribute to the development of mosquitoes and larval stages of filarial parasites in their vectors (Momčilović et al., 2025). Here we present a series of four cases diagnosed and treated at the General Hospital of Sisak-Moslavina County in Croatia, highlighting clinical variability, diagnostic approach and treatment strategies.
The first patient was a 68-year-old man who presented to an ophthalmologist because of irritation of the right eye. He owned a pet cat and had occasional contact with stray dogs and cats. Slit lamp examination revealed a mobile worm-like structure under the conjunctiva with surrounding chemosis. The patient underwent surgical removal of the parasite through a conjunctival incision. Infectious disease work-up by a specialist revealed no systemic signs of parasitosis and systemic therapy was not initiated. The parasite was later confirmed as D. repens.
The second case was a 35-year-old woman who initially presented with suspected dacryocystitis. She had been prescribed oral azithromycin by her general practitioner and then clindamycin by an ophthalmologist without any clinical improvement. She then developed oedema of the upper eyelid with itching and a sensation of movement. On examination, a mobile subcutaneous mass was found in the upper eyelid. Surgical exploration confirmed the presence of a parasite. D. repens was detected. Following infectious disease counselling, no systemic treatment was required.
Later that year, a 65-year-old woman presented with pain in her right eye that had been present for 10 days and worsened at night. She had been treated by a general practitioner with tobramycin drops and ointment with no improvement. Clinical examination revealed oedema and hyperemia of the right upper eyelid (Fig. 1), and a subconjunctival parasite was visualised in the temporal quadrant of the conjunctiva of the right eye (Fig. 2). The parasite was surgically removed and identified as D. repens. Systemic therapy was also not required.
Right-sided upper eyelid oedema and hyperemia.
Visible parasite under the bulbar conjunctiva.
The last case concerned a 50-year-old woman who lived in a rural area and had contact with poultry and a pet dog. She initially noticed oedema of the temporal conjunctiva of the right eye, followed by a mobile, soft nodule on the medial lower eyelid (Fig. 3) and later on the lateral upper eyelid of the right eye. On examination, a soft, cyst-like mass was noted in the right upper lateral eyelid. Surgical exploration was performed but no parasite was found. The patient was treated with doxycycline 200 mg for 10 days and then 100 mg for a further 10 days. Regular follow-up examinations were recommended and the patient had no further symptoms. The patient continues to be examined regularly. All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional ethical committee and with the 1964 Helsinki declaration and its later amendments. Informed consent has been obtained and signed by from all individuals in this study.
Right-sided nodule on the lower eyelid - medially.
Although ocular dirofilariasis in humans is rare, it presents with diverse and often misleading symptoms. Misdiagnosis is common and initial treatments, frequently empirical antibiotic therapy, may be ineffective. The four patients presented in this case series illustrate the broad clinical spectrum of ocular and orbital dirofilariasis, ranging from mild conjunctival hyperemia to eyelid oedema initially misdiagnosed as bacterial infection. This series emphasises the importance of obtaining a detailed patient history, including exposure to animals and residence in rural or endemic areas. In one of the cases, the diagnosis was made only intraoperatively, after visualization and extraction of the parasite. Preoperative symptoms such as itching, eyelid oedema and palpable subcutaneous movements were non-specific and often misleading, contributing to diagnostic delays. Several case reports describe conjunctival hyperemia with visibly motile parasites under the bulbar conjunctiva, where surgical extraction confirmed the same parasite genus, D. repens, as identified in our cases (Mus et al., 2025; Momčilović et al., 2025; Jha et al., 2023; Redón-Soriano et al., 2022; Engelsberg et al., 2022; Dababo et al., 2022). Other geographic regions have reported subconjunctival infections with D. immitis (Aghajani et al., 2024) and D. tenuis (Camacho et al, 2024), reflecting a wider global distribution and species variation. Other varied presentations of dirofilariasis have been documented in the literature, including perilacrimal infection (Jange et al., 2024), nodular scleritis (Sinha et al., 2024), blepharoconjunctivitis (Morosanu et al., 2024), preseptal abscess (Shaikh et al., 2023), orbital cellulitis (Shambhu et al., 2022) and even a case of mimicking rhabdomyosarcoma in a 12-year-old child (Pakdel et al., 2022). In clinical practice, nodules associated with dirofilariasis are therefore often misdiagnosed as neoplastic lesions. Surgical removal is often pursued for diagnosis and treatment, sometimes from very sensitive or difficult to access anatomical sites, which may be associated with complications or serious consequences (Momčilović et al., 2025; Raja et al., 2024). In another study it was found that the initial suspicion in subcutaneous and pulmonary dirofilariasis is predominantly a tumour, whereas in ocular dirofilariasis a parasite (but not directly Dirofilaria) is usually suspected (Simón et al., 2022). These findings underline the necessity of clinical awareness, especially in patients from high-risk areas, to avoid unnecessary interventions and ensure accurate, timely diagnosis. The most common species in subcutaneous and ocular infections is D. repens, in contrast to D. immitis, which typically causes pulmonary lesions. In our series, all extracted parasites were morphologically consistent with D. repens, except for the last case in which the parasite was not confirmed, and none of the patients showed systemic symptoms or required systemic antiparasitic therapy. This supports previous reports suggesting that surgical excision is both diagnostic and curative for localised ocular infections. The occurrence of four confirmed cases over a two-year period in a single Croatian county (estimated incidence: 1.79 per 100,000 per year) may seem low, but it is not negligible. These figures probably underestimate the true burden due to underdiagnosis and misclassification as common eye infections. This emphasises the need for greater awareness among ophthalmologists, especially in endemic or rural areas.
Although ocular dirofilariasis is rare, it should be an important differential diagnosis in patients with unexplained eye irritation, eyelid oedema or subconjunctival or subcutaneous nodules, especially in people who live in rural, mosquito-infested areas or have close contact with pets or stray animals. Whilst laboratory diagnosis is often inconclusive (eosinophilia), surgical exploration and extraction of the parasites are both diagnostic and curative. Early detection and timely intervention are essential to avoid unnecessary antibiotic use, prolonged patient discomfort or possible complications. Greater sensitisation of ophthalmologists, general practitioners and infectious disease specialists is necessary to improve detection rates and ensure optimal treatment of this emerging zoonotic infection.