|Year : 2013 | Volume
| Issue : 4 | Page : 403-405
AB Khyriem1, KG Lynrah2, WV Lyngdoh1, A Banik1
1 Department of Microbiology, North Eastern Indira Gandhi Regional Institute of Health and Medical Sciences, Shillong, Meghalaya, India
2 Department of Internal Medicine, North Eastern Indira Gandhi Regional Institute of Health and Medical Sciences, Shillong, Meghalaya, India
|Date of Submission||11-Mar-2013|
|Date of Acceptance||10-Aug-2013|
|Date of Web Publication||25-Sep-2013|
A B Khyriem
Department of Microbiology, North Eastern Indira Gandhi Regional Institute of Health and Medical Sciences, Shillong, Meghalaya
Source of Support: None, Conflict of Interest: None
Subcutaneous Human Dirofilariasis is an uncommon zoonotic infection caused by Dirofilariarepens. The reports of this infection in humans in India are limited, although increasingly being reported worldwide. We report a case of Dirofilariasis with subcutaneous presentation from the state of Meghalaya and to emphasize the importance of considering this entity in the differential diagnosis of patients presenting with subcutaneous nodules.
Keywords: Dirofilariasis, D.repens, subcutaneous
|How to cite this article:|
Khyriem A B, Lynrah K G, Lyngdoh W V, Banik A. Subcutaneous dirofilariasis. Indian J Med Microbiol 2013;31:403-5
| ~ Introduction|| |
The genus Dirofilaria includes various species that are natural parasites of dogs, cats, foxes and wild animals.  The genus Dirofilaria has two subgenera: Dirofilaria and Nochtiella. While the nematodes in the subgenus Dirofilaria (e.g., D.immitis) have smooth cuticles and are typically found in the pulmonary arteries, those in the subgenus Nochtiella (e.g., D.repens) have longitudinal cuticular ridges and are usually found in the subcutaneous tissues.  The adult Dirofilarial worms exhibit tails which are short and rounded, the mouth is simple and without any lips. Caudal spicules are markedly unequal in males, and the vulva is posterior to the oesophagus in females.  Dirofilariasis has been reported worldwide and is caused by D.immitis, D.repens, D.tenuis and D.ursi. D.immitis is responsible for heartworm diseases in dogs and has been reported from many parts of the world, though infections in humans is rare. D.repens, a parasite of the subcutaneous tissue in dogs etc., can accidentally infect humans causing a condition referred to as subcutaneous Dirofilariasis.  Dirofilariasis is considered to be an emerging zoonosis and mosquitoes belonging to the genera of Culex, Aedes and Anopheles have been incriminated as suitable vectors for this parasite. Transmission takes place when a potential vector containing the infective 3 rd stage larva (L 3 ) bites susceptible hosts including humans during a subsequent blood meal. 
Human Dirofilariasis due to D.repens has not been widely recognised in India, though a focus of infection probably exists in Kerala.  The disease is relatively common in Sri Lanka, which is geographically closer to Southern India.  Most of the documented cases of Human Dirofilariasis recorded in India had ocular infections, , but very few subcutaneous Dirofilariasis have been reported. , There is dearth of reports of such cases from North-Eastern India. Here we report a case of subcutaneous Dirofilariasis by D.repens for the first time from the state of Meghalaya.
| ~ Case History|| |
A 27-year-old female presented with a subcutaneous nodule on the right cheek for 6 months. The patients had symptoms of discomfort in the neck and scalp with a crawling sensation under the skin for 1 year or so followed by appearance of the swelling on the cheek. The nodule gradually developed into an abscess which bursted spontaneously and revealed a white thread-like worm. The worm was mechanically extracted by the patient and brought to the hospital. The patient's blood did not show any microfilariae and other routine laboratory tests were within normal limits.
The worm was thin cylindrical, white, 0.5 mm thick and 12 cm in length [Figure 1]. The anterior end was rounded and of greater diameter than the posterior end. Under the microscope, the outer surface of the nematode's cuticle was found to have fine transverse striations and prominent longitudinal ridges, each separated from the next by a distance greater than the width of a ridge. The muscular layer below the cuticle was well developed as well [Figure 2]. The body cavity contained a female reproductive system laden with oocytes. Based on the size, cuticular morphologic features and internal features, the worm was identified as a female D.repens.
|Figure 2: A micrograph of part of the nematode showing fine tranverse striations and longitudinal ridges in the cuticle|
Click here to view
| ~ Discussion|| |
Human Dirofilariasis due to D.repens is a zoonosis naturally parasitising dogs, cats, foxes and transmitted by the bite of mosquitoes especially Anopheles, Aedes and Culex species.  The first documented report of Human Dirofilariasis dates back to the report of Addario from Italy in 1885.  Since then, infections have been reported from various regions of the world, mainly from Europe, Africa and Asia. Reports of this infection from India are, however, infrequent with most cases reported from Kerala, which is considered endemic for Dirofilariasis.
Most of the documented cases of Human Dirofilariasis recorded in India had ocular infections, with few case reports of subcutaneous Dirofilariasis. ,,,
D.repens is the main and probably the sole cause of subcutaneous Dirofilariasis in humans in Asia and India. D.repens is often identified by the presence of external longitudinal cuticular ridges and transverse striations, features which are similar to D.tenuis. The latter is endemic in USA, with a single report of D.tenuis from India. 
Exact identification of species may be possible only after studying the fully matured worm or Deoxyribonucleic acid (DNA) analysis. 
The infection may be asymptomatic or present as a migratory swelling which may or may not be tender and most humans involve only a single adult nematode. 
In our case, the patient harboured the worm for probably 6 months and presented to the hospital due to the swelling. As the worm was spontaneously expelled following rupture of the abscess, no intervention or treatment was necessitated in our case, as only a single worm was present and follow up of the patient after 3 months did not show recurrences.
Human cases of Dirofilariasis are mostly under reported and under diagnosed probably because of the varied clinical presentations and organs affected.
Human cases of Dirofilariasis in Meghalaya are probably still an uncommon zoonotic infection. Hence, though not a known endemic area of Dirofilariasis, this entity should be considered a differential diagnosis for single subcutaneous swellings.
| ~ Acknowledgement|| |
Dr. Elantamilan D for his technical support.
| ~ References|| |
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[Figure 1], [Figure 2]