Subcutaneous nodule: A case of Dirofilaria.

Human subcutaneous dirofilariasis is a rare helminthic infection. It is caused by filarial worms of the Genus Dirofilaria, which is the natural parasites of dogs, cats, foxes, and wild mammals. Zoonotic filariasis caused by Dirofilaria species is rarely seen in the region of Dakshina Kannada. Most of them are seen in patients who are along the border of the district which shares its boundary with the state of Kerala, where dirofilariasis is constantly reported to occur. Here, we report a case of subcutaneous dirofilariasis, presenting as a subcutaneous nodule on the left cheek of a 28-year-old male from Cochin (Ernakulam), Kerala, South India. Two live worms were recovered from the subcutaneous nodular swelling.

INTRODUCTION

Human subcutaneous dirofilariasis is a rare helminthic infection. It is caused by filarial worms of the genus Dirofilaria species, which is the natural parasites of dogs, cats, foxes, and wild mammals.[1] Dirofilaria species belongs to the filarial nematodes, causes zoonotic infections in man, occasionally. Subcutaneous dirofilariasis is caused mainly by Dirofilaria repens, which causes subcutaneous nodules in and around the eye. It is a common parasite of dog, seen mainly in the subcutaneous tissue. The mosquitoes Culex, Aedes, and even Anopheles species form the vector for this nematode.

CASE REPORT

A 28-year-old male hailing from Cochin, South India presented with a subcutaneous nodule on the left cheek of duration of 2 weeks, which was gradually increasing. On clinical examination, he had a firm oval swelling on the left cheek measuring 1.5 cm × 1 cm, which was non-tender and freely mobile. The systemic examination was unremarkable. A clinical diagnosis of a subcutaneous swelling/Sebaceous cyst was made, and the swelling was excised as an out-patient procedure under local anaesthesia. On excision two live thread like cylindrical worms, 0.5 mm thick measuring about 10-25 cm were found, coiled to each other. On macroscopic examination, of both the worms it was found that both the worms had a short and rounded tail [Figure 1]. No lips were seen in the mouth. Under the microscope, the outer surface of the nematode's cuticle was found to have fine transverse striations and prominent longitudinal ridges [Figure 2]. Shorter worm had unequal caudal spicules hence identified as male dirofilarial worm. The longer worm had oesophagus anterior to the vulva and was identified female dirofilarial worms. On the basis of macroscopic and, microscopic examination, worm was thus identified as D. repens.

Figure 1

Two live dirofilarial worms

Figure 2

Microscopic picture of the worm showing Cuticle and transverse striation

The hemogram showed hemoglobin 13 g%, total leucocyte count 10,200/mm3 and differential count showed eosinophilia, with absolute eosinophil count 2060/mm3. The peripheral smear showed relative eosinophilia without any parasite. No microfilaria were seen in peripheral blood. The patient did not review after the excision of the nodular swelling for follow-up.

DISCUSSION

Human subcutaneous dirofilariasis is a rare helminthic infection, caused by filarial worms Dirofilaria species. It is an occasional zoonosis disease. The worm is a natural parasites of dogs, cats, foxes, and wild mammals.[1] Dirofilaria parasites are transmitted to man by mosquitoes. Most of the dirofilariasis cases are asymptomatic. The symptomatic ones typically manifests as either subcutaneous nodules or lung parenchymal disease. Excision of the subcutaneous lesion is both diagnostic and therapeutic. The clinical implication of human dirofilariasis is that, these subcutaneous lesions may be initially misidentified as malignant tumors, requiring invasive investigation and surgery before the correct diagnosis is made. The pathology of the condition results from the aberrant localization of immature worms intended for nonhuman hosts. Among the documented cases of human dirofilariasis in India, most of them had ocular infections.[2-4] In India and the Asian subcontinent D. repens is the main causative agent of subcutaneous human dirofilariasis.[56] The Coastal Kerala is endemic for dirofilariasis due to the presence of the suitable vector and climatic condition.[1] Most of the cases of Dirofilariasis reported from the northern[3] and western parts[7] of India is caused by D. repens. Few cases of Dirofilaria immitis have been also reported from India.[67]

The cause of endemicity in Southern-India and Sri Lanka is mainly due to drastic changes in climatic conditions especially humidity and rainfall pattern, which favor the development of vector mosquitoes and the larval phase of the nematode in the mosquitoes. Recently two more cases have been reported from the Southern-India presenting as subcutaneous nodules.[8] Most cases are diagnosed retrospectively, when the histopathological sections of biopsy or excision material are viewed.[56] As microfilaremia is rarely seen in dirofilariasis chemotherapy is not called for.[56] Thus, this case emphasizes that Subcutaneous Dirofilariasis should be considered as the differential diagnosis in case of a single subcutaneous swelling, especially, when the patient is coming from an endemic area.