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Human dirofilariasis – Unforeseen lesion in subcutaneous nodules: Case series from a tertiary care hospital, Wayanad

 Department of Pathology, Dr. Moopen's Medical College (Formerly known as DMWIMS), Meppadi, Wayanad, Kerala, India

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Date of Submission27-Oct-2021
Date of Decision11-May-2022
Date of Acceptance16-May-2022
Date of Web Publication08-Dec-2022


Human dirofilariasis is a type of zoonotic infection caused by the Dirofilarial species. It is a type of roundworm which is commonly seen in dogs, cats and is transmitted to humans by mosquito bite. Microfilaria is rarely produced in humans. Although clinically they can have varied presentations, it usually presents as ocular or subcutaneous nodules. Definitive diagnosis requires histopathological findings of this worm. We hereby report three cases of Dirofilariasis from a tertiary care hospital in Wayanad.

Keywords: Dirofilaria, parasite, subcutaneous nodule

How to cite this URL:
Gitanjali M M, Konapur PG, Kolakkadan H, Azeez K N. Human dirofilariasis – Unforeseen lesion in subcutaneous nodules: Case series from a tertiary care hospital, Wayanad. Indian J Pathol Microbiol [Epub ahead of print] [cited 2023 Nov 30]. Available from:

   Introduction Top

Dirofilariasis is a filarial infection which mainly affects vertebrate animals like dogs, cats and racoons.[1] Human beings are infected accidentally by mosquito bites. Many different types of species are recognised like Dirofilaria repens, Dirofilaria ursi, Dirofilaria tenuis, and Dirofilaria striata which mainly cause subcutaneous nodules.[2] The infection is endemic in continents like Asia, Africa and Europe.[3] In Asia, this infection is relatively common in Sri Lanka and southern states of India like Kerala.[4]

Different sites of infection with dirofilariasis include eyes, subcutaneous tissue, breast, mesentery, and lungs, and most cases of Dirofilarial infection in India has been reported in the eyes.[3],[5] It has been noted that Human Dirofilariasis infection is increasing in Southern parts of India and thus regarded as an emerging filarial zoonotic infection.[4]

   Case Reports Top

Case 1

A 35-year-old female from Kerala presented to the ophthalmology OPD with a painful ocular lesion in the right upper eyelid. The lesion was tender on palpation. No punctum noted on the surface. A clinical diagnosis of eyelid abscess was made.

Case 2

A 40-year-old male residing in rural part of Kerala presented to the surgical OPD with complaints of a mildly painful swelling in the anterior abdominal wall for the past two months with gradual increase in size.

On examination, a nodule measuring 3 × 3 cm was palpated in the anterior abdominal wall over right iliac region. Mild tenderness and redness noted locally. A provisional clinical diagnosis of lipoma was made. Ultrasonography disclosed a spherical isohypoechoeic lesion in the subcutaneous plane of hypochondrium on the right side suggestive of lipoma. Material aspirated on cytology from the nodule showed an acute suppurative lesion.

Case 3

A 22-year-old female presented with a subcutaneous swelling in the right calf region for one month. The swelling was non-tender, measuring 2 × 2 cm. A provisional clinical diagnosis of lipoma was made.

None of the three patients gave a history of fever and their blood counts were within normal limits. In all the cases, the nodules were excised and sent for histopathological examination.

Gross examination showed firm gray brown areas of discoloration in all three specimens, surrounded by fat [Figure 1].
Figure 1: Gross: Grey white firm nodule with central grey brown discolouration. Microscopy: Cross sections of multiple parasites showing classical double uterus, gut and longitudinal muscle covered by multilayered cuticle with spikes (Case 2)

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Microscopy of the lesions

Microscopy revealed cross section of the parasite with the cuticle and external spikes. The classical double uterus, gut, and longitudinal muscle layers were discernible. The parasite was surrounded by dense mixed inflammatory infiltrate and granulation tissue [Figure 1]. Cases 1 and 3 showed degenerated parasites.

On the basis of these typical histopathological findings, a final impression of Dirofilarial infection was made in all the three cases.

The patients recovered completely following surgery and no further treatment is required, as microfilaremia was not seen in these cases.

   Discussion Top

Human dirofilariasis is a rare infection. Humans are accidental hosts of this infection and the presentation is quite assorted.[5],[6] Human infection is caused by at least 6 of the total of 40 species of Dirofilaria that have been discovered. Dirofilariasis in India is most commonly caused by the agent D. repens followed by D. Immitis. The primary definitive hosts are animals like dogs, cats, and racoons and is transmitted to humans by the bite of mosquitoes like Culex, Aedes, and Anopheles.[3],[7],[8]

Following infection in humans, the clinical presentation can differ from person to person mostly manifesting as ocular and subcutaneous nodules. It can also cause swellings in the muscle, internal organs, breast tissue, and pelvic cavity.[1],[4] In India, most cases of infection by D. repens have been reported in the ocular region, followed by subcutaneous swellings in the extremities.[8]

Ultrasonographically, a diagnosis of lipoma or sebaceous cyst is usually made in these lesions.[1] The anterior abdominal wall nodule (Case 2) and the calf mass (Case 3) were diagnosed as lipoma on radiology in our cases.

Increase in blood eosinophils and IgE levels are not seen in most cases.[6],[7],[8] In our cases, the blood counts were within normal limits.

Definitive diagnosis is made by histopathological examination on biopsy specimen based on the morphology. Infection by female worm is more commonly seen, and the sex of the worm can be determined by studying the morphology on histopathology. The female worms have two reproductive tubes compared to one in male worms.[5],[7],[8] In our cases, the cross-section of the worms revealed a double uterus determining the sex of the worm as female.

Microfilaremia is infrequent in humans as the worms rarely reach maturity, due to which anti-helminthic medications are usually not helpful.[5] Surgery is the suggested treatment in the majority of cases.[2],[4]

In some exceptional cases when there is microfilaremia, treatment with doxycycline may be considered as an alternative to anti-helminthic drugs.[9]

   Conclusion Top

Since the incidence of dirofilariasis is on the rise, it should be considered in the differential diagnosis in patients presenting with subcutaneous or ocular nodules, particularly in those coming from endemic areas of South India. Surgeons, ophthalmologists, and pathologists should be observant of this entity.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.

   References Top

Cheung BM-H, Huang Y-L, Lin Y-W, Chang Y-S, Liu S-M. An Unexpected cause of a subcutaneous nodule: A case report of dirofilaria infection. Case Rep Infect Dis 2012;e191245.  Back to cited text no. 1
Jayasinghe RD, Gunawardane SR, Sitheeque MA, Wickramasinghe S. A case report on oral subcutaneous dirofilariasis. Case Rep Infect Dis 2015;e648278.  Back to cited text no. 2
Hussain T, Wyawhare AS, Mulay M. Subcutaneous dirofilariasis: A case report. Int J Biol Med Res 2018;9:6446-6447  Back to cited text no. 3
Rai R, Karnaker VK, Naik J. An unanticipated cause of intramuscular mass – a case report. J Health Allied Sci NU 2014;04:118-9.  Back to cited text no. 4
Acharya D, Chatra PS, Padmaraj SR, Ahamed A. Subcutaneous dirofilariasis. Singapore Med J 2012;53:e184-5.  Back to cited text no. 5
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;28:394-6.  Back to cited text no. 6
[PUBMED]  [Full text]  
Chisthi MM, Reghukumar A. Dirofilarial worms inside cutaneous nodules: A report with review of literature. Int J Res Dermatol 2015;1:24-7.  Back to cited text no. 7
Damle AS, Iravane JA, Khaparkhuntikar MN, Maher GT, Patil RV. Microfilaria in human subcutaneous dirofilariasis: A case report. J Clin Diagn Res JCDR 2014;8:113-4.  Back to cited text no. 8
Lechner AM, Gastager H, Kern JM, Wagner B, Tappe D. Case report: Successful treatment of a patient with microfilaremic dirofilariasis using doxycycline. Am J Trop Med Hyg. 2020;102:844-6.  Back to cited text no. 9

Correspondence Address:
K Nabeel Azeez,
Dr. Moopen's Medical College (Formerly known as DMWIMS), Meppadi, Wayanad, Kerala
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijpm.ijpm_1051_21


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