Human subcutaneous dirofilariasis is a rare helminthic infection caused by filarial worms of the genus Dirofilaria species. The natural hosts that cause infection in humans are dogs and wild canines such as foxes, wolves, and raccoons.1
Infected mosquitoes occasionally infect humans with the third stage larvae during a blood meal. In humans, Dirofilaria repens usually wanders in the subcutaneous tissue or produces a granulomatous nodule. Although considered rare, cases of human dirofilariasis are being increasingly reported in the past few decades from all over the world, and can be considered an emerging zoonosis.2 Dirofilariasis can be found in different sites such as the orbits, upper limb, lung, mesentery, breast, and male genitalia.2–5 In India, almost all reported cases of dirofilariasis in humans had involvement of the face in the form of ocular dirofilariasis with a few reports on subcutaneous dirofilariasis.4–12 Most of the reported cases are adults and presentation in an infant is extremely rare.13 We report a rare case of subcutaneous dirofilariasis of the eyelid in a 7-month-old infant.
A 7-month-old infant, a resident of Udupi, Karnataka, South India, presented to our clinic with a subcutaneous nodule over the right lower eyelid of 15 days’ duration. The mother gave a history of a gradually increasing subcutaneous nodule over the right lower eyelid just below the lateral canthus, not associated with any pain, redness, or discharge.
On examination there was a non-tender, subcutaneous swelling of 1 × 1 cm dimension with well-defined margins, firm to hard in consistency over the right lower eyelid just below the lateral canthus (Figure 1). The rest of the eye examination was normal. Systemic examination was unremarkable. A provisional diagnosis of dermoid cyst was made.
Firm, non-tender, pea-shaped, subcutaneous nodule over the right lower eyelid.
Laboratory investigations showed: hemoglobin 10.8 g/dL; total white blood cell count of 17,100 cells/mm3; differential count being neutrophils 7%, lymphocytes 84%, monocytes 4%, and eosinophil 5%; and erythrocyte sedimentation rate 14 mm/hr. Chest x-ray was normal.
Computed tomography scan of the orbit showed a thick-walled peripherally enhancing cystic lesion along the outer canthus of the right eye with minimal extension into the lateral extraconal space of the right orbit. A differential diagnosis of infected dermoid cyst or sebaceous cyst was considered (Figure 2).
Computed tomography scan showing thick-walled peripherally enhancing cystic lesion measuring 9 × 7 mm along the right lateral canthus with minimal extension into the lateral extraconal space.
The lesion was surgically excised under general anesthesia. Grossly, the specimen was gray-white in color, measuring 1 × 1 × 0.5 cm. The cut section showed gray-white areas with yellow cheesy areas.
Microscopically, a parasite with a thick chitinous wall, surrounded by epitheloid granulomas, foreign body giant cells, and granulation tissue composed of numerous proliferating capillaries, and dense mixed acute and chronic inflammatory infiltrate, with foam cells and eosinophils, and areas of fibrosis, was seen, suggestive of subcutaneous dirofilariasis (Figure 3).
Photomicrograph shows a cross-section of filarial worm with thick multilayered cuticle surrounded by dense inflammatory reaction (hematoxylin–eosin, original magnification ×100).
The patient was tested for microfilaremia and was found to be negative.
Because surgical resection of the lesion is both diagnostic and therapeutic for human subcutaneous dirofilariasis, no further treatment was given.
Dirofilariasis is primarily confined to animals such as dogs, cats, foxes, raccoons, and some wild animals that act as definitive hosts. Various mosquitoes serve as intermediate hosts that take up the microfilariae while feeding on an infected host. Microfilariae develop further in mosquitoes. The transmission to dogs or other hosts, including humans, occurs through mosquito bites during subsequent blood meals. In human infections, usually just one larva develops, which does not reach sexual maturity and is hence unable to express larvae in the blood stream.14 This probably explains the rarity of microfilaraemia in humans. Immature Dirofilaria worms can reach a branch of the human pulmonary artery or subcutaneous tissue, triggering an inflammatory response that destroys the worms. This occasionally results in pulmonary and subcutaneous nodules.
Although approximately 40 different species of Dirofilaria are recognized, fewer than 6 are known to cause human infections, which can be found worldwide. In India and the Asian subcontinent, D. repens is the main causative agent of subcutaneous human dirofilariasis.5,15 In Asia, Southern India and Sri Lanka are endemic for Dirofilaria mainly due to drastic changes in climatic conditions, especially humidity and rainfall patterns, which favor the development of vector mosquitoes and the larval phase of the nematode in the mosquitoes. In India, Kerala and Tamilnadu are endemic areas of dirofilariasis.7,13
The prospective diagnosis of dirofilariasis in humans remains difficult because most are asymptomatic or exhibit varying and nonspecific symptoms depending on its location in the body1 (typically subcutaneous nodules or lung parenchymal diseases). Serologic results are of little value because of the lack of microfilariae in the blood stream. The diagnosis of dirofilariasis can be kept as a differential diagnosis in patients with solitary lesions and belonging to an endemic area. The cases are diagnosed retrospectively, when the histopathological sections of biopsy or excision material are viewed.5,15 Excision of the subcutaneous lesion is both diagnostic and therapeutic. Because there are no microfilariae in the blood stream, antibiotics are ineffective.13
In previous published reports, the age of the patients varied from 4 months to 100 years; the majority were in their 40s.2 Most of the documented cases of human dirofilariasis recorded in India had ocular infections, with a few case reports of subcutaneous dirofilariasis. One should include dirofilariasis in the differential diagnosis of patients presenting with a single subcutaneous nodule at any site of the body in endemic areas. Presentation in infants is extremely rare.13 A PubMed search did not show any report of periocular subcutaneous dirofilariasis in infants. We report the first case of periocular subcutaneous dirofilariasis in a 7-month-old infant.
- Sabu L, Devada K, Subramanian H. Dirofilariasis in dogs and humans in Kerala. Indian J Med Res. 2005;121:691–693.
- Pampiglione S, Rivasi F. Human dirofilariasis due to Dirofilaria (Nochtiella) repens: an update of world literature from 1995 to 2000. Parassitologia. 2000;42:231–254.
- Maltezos ES, Sivridis EL, Giatromanolaki AN, Simopoulos CE. Human subcutaneous dirofilariasis: a report of three cases manifesting as breast or axillary nodules. Scott Med J. 2002;47:86–88.
- Joseph K, Vinayakumar AR, Criton S, Vishnu MS, Pariyaram SE. Periorbital mass with cellulitis caused by dirofilaria. Indian J Med Microbiol. 2011;29:431–433. doi:10.4103/0255-0857.90190 [CrossRef]
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- Permi HS, Veena S, Prasad HK, Kumar YS, Mohan R, Shetty KJ. Subcutaneous human dirofilariasis due to dirofilaria repens: report of two cases. J Glob Infect Dis. 2011;3:199–201. doi:10.4103/0974-777X.81702 [CrossRef]
- Khurana S, Singh G, Bhatti HS, Malla N. Human subcutaneous dirofilariasis in India: a report of three cases with brief review of literature. Indian J Med Microbiol. 2010;28:394–396. doi:10.4103/0255-0857.71836 [CrossRef]
- Nath R, Bhuyan S, Dutta H, Saikia L. Human subcutaneous dirofilariasis in Assam. Trop Parasitol. 2013;3:75–78. doi:10.4103/2229-5070.113920 [CrossRef]
- Damle AS, Iravane Bajaj JA, Khaparkhuntikar MN, Maher GT, Patil RJ. Microfilaria in human subcutaneous dirofilariasis: a case report. J Clin Diagn Res. 2014,8:113–114.
- Acharya D, Chatra PS, Padmaraj SR, Ahamed A. Subcutaneous dirofilariasis. Singapore Med J. 2012;53:e184–e185.
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- D’Souza R, Jakribettu RP, Sudharsana SH, Aithala SP. Subcutaneous nodule: a case of dirofilaria. Int J Appl Basic Med Res. 2013;3:64–65. doi:10.4103/2229-516X.112243 [CrossRef]