Introduction:
Dirofilaiasis is an uncommon zoonotic disease, which is common to a many geographical locations. Nearly 40 species of Dirofiliaria have been identified but only lesser than six species have known to cause human infections. (1, 2)
The genus Dirofilaria includes various species that are habitual parasites of canines, cats, and wild mammals and rarely cause infections in human beings. (3) Its transmission to the humans is via the bite of anthropophilic (mosquito) vector—Anopheles, Aedes and Culex species. (1) Of the known species involved with the humans, Dirofilaria repens, Dirofilaria ursi, Dirofilaria tenuis and Dirofilaria striata are localized to the subcutaneous tissues, Dirofilaria immitis and Dirofilaria spectrum to the heart and blood vessels. (4) In India, Dirofilaria repens is the commonest species identified, belonging to the subgenus Nochtiella.
Clinically infection is apparent as a solitary subcutaneous nodule commonly in the head and neck region with or without pain. Here we report a case of dirofilariasis presenting as a subcutaneous nodule on the cheek.
Case Report
A 32 year old female patient presented to the department with a slowly enlarging non tender subcutaneous nodule over the right side of the face since 3 months and over the past week there had been a mild increase in the size of the swelling with tenderness. The nodule was 1.5 cm* 1.0 cm in size, regular, freely mobile and firm in consistency with no local rise of temperature. Ultrasonography showed an oval hypoechoic lesion of 1.3 cmX0.7 cm in size, with a tubular hyperechoic structure in the center suggestive of a parasitic infestation (Figure 1A- 1B).
Considering the zoonotic infections, she was asked about any contact with domestic animals or pets, the presence of mosquitoes in the area where she lived or of any intake of partially cooked meat. She gave a history of close contact with her pet, and lived in a mosquito infested area. Hematological examination revealed no abnormalities.
The nodule was surgically excised intra orally under local anesthesia (Figure 1C, 1D). Upper vestibular incision was given after administering 1:1,00,000 lignocaine with adrenaline. Blunt dissection was performed and nodule was excised in-toto. Suturing was done in layers with 3-0 vicryl suture. Post operative healing period was uneventful.
The specimen was sent for histopathological examination and on gross examination; the specimen was a pearly white coloured oval mass of size 1.6 x 0.5 x 0.8 cm. The cut surface showed an opaque white, gel like structure in the center (Figure 1E).
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Figure 1A: Subcutaneous swelling on the cheek. 1B: Linear hyper echoic area in the centre of an hypoechoic area. IC: Surgical Excision, 1D: Excised Intact Nodule, 1E: Cut section of nodule showing the worm |
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Figure 2A, 2B: Transverse sections of parasite. 2C: Eosinophilia in connective tissue, 2D: Parasite surrounded by granulation tissue, 2E, 2F: Prominent external cuticular ridges, and well-developed, tall musculatures, within the cavity, intestine and male genital tubule containing spermatocytes. |
Histopathological examination revealed multiple transverse sections of the adult filarial worm [Figure 2A] with outer layered cuticle and a well-developed inner tall muscular layer lining a pseudocoele cavity. Within the cavity, intestine and male genital tubule containing spermatocytes were observed [Figure 2B, 2F]. The cross sections of the worm showed prominent external cuticular ridges, and well-developed, tall musculatures [Figure 2D, 2E], characteristic of D. repens. The surrounding connective tissue showed granulomatous reaction with dense inflammatory infiltrate consisting of lymphocytes and eosinophils [Figure 2C]. The morphological features of the filarial worm were consistent with male dirofilaria and the lesion diagnosed as subcutaneous dirofilariasis.
A confirmatory diagnosis was obtained from Center for Disease Control, India. The clinical and histopathological images were uploaded to DPDM DPDx, a website developed and maintained by Division of Parasitic Diseases and Malaria under the Center. The diagnosis and the species were confirmed as Dirofilaria repens based on the geographical location. Review of the patient after 3 weeks showed complete resolution and the healing was uneventful.
Discussion
Human dirofilariasis is a rare helminthic zoonotic infection, usually presenting with a single worm infection of humans.
Dirofilaria repens is the most prevalent agent of zoonotic dirofilariasis in many parts of the world including Africa, Canada, Japan Kuwait France, Italy, Turkey, Africa, Thailand, USA and Southeast Asia. (5)
Dirofilaria repens was first reported in Kerala, India in 1976 and Kerala has been one of the major geographical reservoirs for the infection. (6) Many cases have been reported since then (Table 1). This suggests an increased incidence of the worm infection over the decade. Other areas reported with infection have been Karnataka, Northern (Maharashtra) and Eastern parts (Assam, Bihar Orissa and Haryana) of India. The country is endemic for malaria and lymphatic filariasis.
| Table 1: Epidemiology of Dirofilariasis in Kerala |
|
Author |
Age/gender |
Site |
1 |
Joseph et al, 1976 |
60/F |
Conjunctiva |
2 |
George M. 1978 |
- |
“ |
3 |
Senthivel and Pillai, 1999 |
- |
Subcutaneous |
4 |
Sekhar et al, 2000 |
26/F |
Eyelid |
5 |
Ittyerah and Mallik, 2004 |
14/F |
Eyelid |
6 |
Sabu et al. 2005 reported 12 cases and 11 from Kerala |
11 cases Females |
9 - Eye
3 - Subcutaneous |
7 |
G Mahesh et al, 2005 |
78/F |
Left eye |
8 |
Sathyan et al, 2006 |
63/F |
Subtenon |
9 |
Smitha et al, 2008 |
40/F |
Eyelid |
10 |
Jayashree et al, 2008 |
30/M |
Right heel |
11 |
Raju et al, 2008 |
33/F |
Eyelid |
12 |
46/F |
Eyelid |
13 |
Dhar and Nambiar, 2008 |
24/F |
Limbus |
14 |
Chakrabarti et al. 2009 |
60/F |
Sub Conjunctiva |
15 |
Joseph et al, 2011a,b - 21cases encountered during 8 yrs |
53/F |
Face – infratemporal region |
16 |
60/F |
Chest |
17 |
45/F |
Right Cheek |
18 |
19/F |
Arm |
19 |
1/M |
Left hypochondrium |
20 |
27/M |
Medial Canthus |
21 |
65/M |
Left Flank |
22 |
28/F |
Right Thigh |
23 |
48/M |
Neck |
24 |
34/F |
Abdominal wall |
25 |
35/F |
Arm |
26 |
38/F |
Right Inguinal region |
27 |
22/F |
Left Arm |
28 |
14/M |
Left Axilla |
29 |
25/M |
Left chest wall |
30 |
56/F |
Neck |
31 |
50/M |
Chest wall |
32 |
10/F |
Left Nasolabial fold |
33 |
39/F |
Parotid region |
34 |
1/M |
Epididymis |
35 |
24/F |
Infraorbit |
36 |
Teerthanath and Hariprasad, 2011 |
27/M |
Muscle |
37 |
Permi et al, 2011 |
40/M |
Cheek |
38 |
45/M |
Neck |
39 |
Sanjeev H et al, 2011 |
18/F |
Neck |
40 |
TN Gopinath et al, 2013 |
2/F |
Upper eyelid |
41 |
D’Souza R et al, 2013 |
28/M |
Subcutaneous nodule, left cheek |
42 |
Vinaykumar AR et al, 2014 |
56/M |
Left upper eyelid |
43 |
Manuel S et al, 2014 |
- |
Oral cavity, vestibule |
44 |
Bhageerathi S et al, 2014 |
2/F
50/F
13/M
11/F |
Finger
Upper abdominal wall
Right leg Calf
Left knee |
45 |
Janardhanan, et al. 2014 |
54/F |
Left cheek |
46 |
Premakumar P et al, 2014 |
32/M |
Right cheek |
47 |
Yaranal PJ et al, 2015 |
25/M |
Left forearm |
48 |
Guptha SS et al, 2015 |
65/F
32/M
63/F
32/M |
Right Eye
Left Eye
Right Eye
Right Eye |
49 |
Sukumarakurup S et al, 2015 |
40/M |
Right abdomen |
50 |
Krishna AS et al, 2015 |
64/F |
Left infraorbital region |
51 |
Anice Joy et al, 2017 |
12/F |
Lower anterior chest wall |
52 |
Seema KM, 2017 |
4/M |
Right eye |
53 |
Mohankumar et al, 2017 |
66/M |
Left arm |
54 |
Nambiar A et al, 2018 |
66/F |
Right atria( central chest) |
55 |
Babu AK, 2020 |
47/M |
Lower right limb |
Among the gender noted, females are commonly affected (Table 1) with the age range from 1 to 75 year. (1) They are the natural parasites of dogs and survive in their subcutaneous tissues. They produce microfilariae that circulate in the blood and are transmitted by mosquito vectors to humans. Development in the mosquito requires about 2 weeks and several months to attain sexual maturity in their natural definitive hosts. (6) In the human body, if the parasite is not rapidly destroyed by defensive reactions of the host, it grows gradually and can reach adulthood within a span of about 6 months. (7) Humans are a dead-end host and further development of the parasite cannot take place in human tissue and the parasite dies subsequently. (8)
In humans, infection by D. repens clinically presents as a subcutaneous nodule on upper half of the body, localized around eyes, eyelids and conjunctiva, mainly all exposed areas. Intra-oral involvement is very rare and cases documented have shown a predilection for buccal mucosa (9) and lips. (10) Symptoms that prevail include transitory inflammation of nodules which may or may not be tender.
The definitive diagnosis of dirofilariasis can be done by histopathological identification of the dirofilarial worm in the tissue sections which remains as the gold standard. Its geographical distribution can add specificity to the species identification.
Surgical excision of the lesion or extraction of the parasite is the treatment of choice. Cryoprobes can be used for immobilizing the worm, if difficulty is encountered in surgical removal due to its excessive movement. (10) Antibiotic administration had shown to inhibit larval development and adult worm viability. (6)
Conclusion:
Over the last few years, an increase in the incidence of human dirofilariasis in the form of ocular, pulmonary and subcutaneous disease has led to the identification of this parasitic infection as an emerging zoonosis. The important risk factors in human infections include tropical (Monsoon) climate with prolonged mosquito breeding season, mosquito density and the abundance of microfilaremic dogs. This raises the need for intensive vector control and suitable diagnostic tool. The clinical presentation may mimic benign and malignant lesions. Therefore it is important for the clinician to be familiar with the diagnostic characteristics of the nematode to avoid misdiagnosis.
References:
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- Janardhanan M, Rakesh S, Savithri V. Oral dirofilariasis. Indian J Dent Res 2014;25:236-9.
- Bruijning CF. Human dirofilariasis. A report of the first case of ocular dirofilariasis in the Netherlands and a review of the literature. Trop Geogr Med 1981;33:295-305.
- Athari A. Zoonotic subcutaneous dirofilariases in Iran. Arch Iran Med 2003;6:63–65.
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- Pampiglione S, Rivasi F. Human dirofilariasis due to Dirofilaria (Nochtiella) repens: An update of world literature from 1995 to 2000. Parasitologia 2000;42:231-54.
- Tilakaratne WM, Pitakotuwage TN. Intra-oral Dirofilaria repens infection: report of seven cases. J Oral Pathol Med 2003;32:502-5.
- Geldelman D, Blumberg R, Sadun A. Ocular Loa Loa with cryoprobe extraction of subconjunctival worm. Ophthalmology 1984;91:300-3.
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