Indian Journal of Pathology and Microbiology

: 2020  |  Volume : 63  |  Issue : 1  |  Page : 159--160

Tender migratory nodules on lower limb – A case report of human subcutaneous dirofilariasis

Anuradha Kakkanatt Babu 
 Department of Dermatology, Aster Medcity, Kochi, Kerala, India

Correspondence Address:
Anuradha Kakkanatt Babu
Department of Dermatology, Aster Medcity, Kochi, Kerala

How to cite this article:
Babu AK. Tender migratory nodules on lower limb – A case report of human subcutaneous dirofilariasis.Indian J Pathol Microbiol 2020;63:159-160

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Babu AK. Tender migratory nodules on lower limb – A case report of human subcutaneous dirofilariasis. Indian J Pathol Microbiol [serial online] 2020 [cited 2023 Jan 29 ];63:159-160
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Human subcutaneous dirofilariasis (HSD) is a rare zoonotic infection caused by filarial worms of the species Dirofilaria. The reported cases of human dirofilariasis are caused by two species namely Dirofilaria immitis and Dirofilaria repens. It is transmitted to humans by mosquitoes, which ingest blood containing microfilaria from affected dogs, cats, or racoons. It clinically presents as inflammatory nodules in the eyes, lungs, or subcutaneous tissues. Excision of the nodule is both diagnostic and therapeutic.

A 47-year-old man presented with recurrent reddish painful swellings on his right lower limb for the past 2 months. Each swelling disappeared in 2–3 days and a new swelling reappeared at a different site on the same limb almost in a migratory pattern. He hailed from a highly mosquito dense part of central Kerala. There were many stray dogs in his locality. On examination, he had a tender, firm, erythematous nodule on the right thigh of 3 × 2 cm size. Our differential diagnoses were panniculitis and soft tissue infection. The routine blood investigations were normal. A deep excision biopsy of the nodule was done. During gross examination, a thread-like worm extruded from the specimen while cutting it. Histopathological examination showed a tissue reaction to parasite as a tract lined by heavy inflammatory infiltrates with plenty of eosinophils in the subcutaneous fat [Figure 1]. Section from the worm showed thick cuticle with longitudinal ridges. A muscular layer was also noticed beneath the cuticle. Paired uteri were clearly seen in the body cavity [Figure 2]. Presence of ridges on cuticle ruled out Wuchereria bancrofti and Brugia malayi. Thus, the identification of the worm was narrowed down to Dirofilaria species. The diagnosis was, hence, confirmed as subcutaneous dirofilariasis. The patient was asymptomatic after the excision of the nodule.{Figure 1}{Figure 2}

Dirofilariasis is a zoonotic disease. HSD is caused by filarial worms of the genus Dirofilaria. The life cycle of the worm depends upon two hosts, a vertebrate species, like a domestic or wild animal such as dog, fox, wolf, or raccoon, which is a definitive host and a blood sucking zoo-anthropophilic arthropod such as Culex, Anopheles, or Aedes mosquito, which acts as an intermediate host for D. immitis and D. repens.[1]

The adult worm of D. repens lives in the subcutaneous tissues of the definitive host and produce microfilaria that circulates in the blood and are transmitted through blood-sucking insects such as mosquitoes. D. immitis inhabits the right ventricle and pulmonary arteries of the dogs. D. immitis has been found to be associated with human pulmonary dirofilariasis. Both species can infect human beings. The development in the mosquito takes about 2 weeks and the infective third stage larvae migrate actively through the mouth parts and enter the tissue of the vertebrate. Humans happen to be the accidental host. After inoculation of the infective third-stage larvae into the humans by the bite of an infected insect, they can invade a variety of tissues and undergo some development without any response from the host. The humans are the dead-end hosts of Dirofilaria because adult worms do not reach maturity in the skin. Most infected larvae injected into the humans are thought to perish. Hence, microfilaremia will not occur in humans.[2] The dead worms evoke a chronic inflammatory reaction with foreign body giant cells.

The most important risk factors regarding human infections are mosquito density, warm climate with extended mosquito breeding seasons, outdoor human activities, and the abundance of microfilaremic dogs.

The first documented report of human dirofilariasis dates back to the report of Addario in 1885 from Italy.[2] Since then more than 800 cases are reported worldwide. Most of the reported cases are from Southern and Eastern Europe, Sri Lanka, Italy, France, Greece, and Spain. Pampligone has reported the largest series of 60 cases from Italy in 2001.[3]

Almost all human infections by D. repens are localized to the upper half of the body, mostly in and around the eyes, although it can occur in the extremities and thoracic wall as well.[4] Most cases reported from India are ocular dirofilariasis where the worm is detected most commonly in the sub conjunctival or peri orbital tissue. A few reports of subcutaneous dirofilariasis are from India.[1]

The symptoms, which signal their presence in human beings, include transitory inflammatory swellings or nodules that may or may not be painful. When living worms enter the conjunctiva, they may cause acute symptoms such as redness of conjunctiva, foreign body sensation, excessive lacrimation, and the affected individual then seeks medical attention. Similarly, gradual development of the worm to a nodule or formation of abscess in the subcutaneous tissue has also been reported to be painful.[5]

The definite diagnosis of HSD can be made after surgical excision or biopsy. Histopathological examination remains the gold standard to confirm the diagnosis. Blood eosinophilia or elevated serum IgE levels are rarely observed.[4] To confirm the diagnosis of D. repens infection, DNA extraction followed by pan filarial polymerase chain reaction may be performed. Surgical resection or excision of lesion is both diagnostic as well as therapeutic. There is no need of chemotherapy. In our case, a surgical excision was done, and there was no recurrence of the disease.

Experience from this case suggests that dirofilariasis should be considered as a differential diagnosis in patients presenting with tender migratory subcutaneous nodules.


Department of Microbiology and Department of Pathology, Amrita Institute of Medical Sciences, Kochi, Kerala, India.

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Conflicts of interest

There are no conflicts of interest.


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