Human dirofilariasis due to Dirofilaria repens in southern India

Abstract

Dirofilariasis is primarily confined to animals such as dogs, cats, foxes and raccoons. Human dirofilariasis is an accidental zoonotic infection acquired through mosquitoes. Human dirofilariasis due to Dirofilaria repens though endemic in Kerala, reports from Karnataka state are rare. We report a case of solitary subcutaneous dirofilariasis of the eyelid due to D. repens in a 47-year-old woman. She presented with periorbital edema. The swelling was soft, cystic with associated tenderness. A thin, white worm was noticed in the lesion and was removed by traction which was subsequently identified to be D. repens.

INTRODUCTION

Dirofilaria are natural filarial parasites of dogs, cats, foxes and raccoons.[1] There are 40 recognized species of Dirofilaria.[2] Human dirofilariasis is an accidental infection caused by species of Dirofilaria such as Dirofilaria immitis, Dirofilaria tenuis and Dirofilaria repens.[3] It is a zoonotic infection seen worldwide.[4] Mosquitoes belonging to the genera Culex, Aedes, Armigeres and Anopheles are vectors for the parasite. They take up microfilaria larva (mf-L1) while feeding on an infected host. In the malphigian tubules of the vector, the mf-L1 develop into infective 3^rd stage microfilaria (mf-L 3) which subsequently migrate through the body cavity to the proboscis of the vector. Transmission of the infective stage takes place when the potential vector bites dogs or other hosts including humans.[1] But for a solitary case of dirofilariasis due to D. tenuis[4] and a case due to D. repens,[5] dirofilariasis in humans are rarely reported from Karnataka state, South India. We report here a case of subcutaneous human dirofilariasis of the eyelid in a 47 years old woman caused by D. repens.

CASE REPORT

A 47-year-old female from rural South Kanara district of Karnataka state, came to KVG Medical College Hospital, Sullia with complaints of pain and swelling of one week duration in the left eyelid. The patient was of moderate build and well nourished, nondiabetic, nonhypertensive and afebrile. Hematological and other laboratory findings were within normal limits. The patient had no human immunodeficiency virus (HIV) infection. She presented with periorbital oedema. The swelling was soft, cystic with associated tenderness. A provisional clinical diagnosis of abscess was made and was aspirated. During the procedure a worm was noticed in the lesion which was subsequently removed by gentle traction.

The worm was thin, white and 10 cm long and 0.6 mm wide. Microscopic examination under 40× magnifications of the outer surface of the nematode's cuticle revealed longitudinal beaded ridges and transverse striations [Figure 1]. Based on size and cuticular features, the worm was identified as D. repens.[6] Blood examination of the patient did not reveal microfilaraemia and the fluid aspirate did not contain any microfilaria. The patient did not come for a subsequent follow up and could not be contacted.

Figure 1.

Microphotograph showing longitudinal beaded ridges and transverse striations onthe cuticle of the worm (×40)

DISCUSSION

Human dirofilariasis caused by D. repens have been reported from Asia, Africa and Europe.[7] A few cases of D. repens human infection have been reported from India too.[1,5,7,8] While adjacent Kerala state is considered to be endemic for human dirofilariasis, reports from Karnataka state is limited.[4,5] Though D. repens human infection is common in India, cases due to D. immitis[9] and D. tenuis[4] also have been reported. Occurrence of D. tenuis infection in India is in contrast to the general belief of most parasitologists that D. tenuis is restricted to USA.[8]

In most cases identification of the worm to species level is based on the phenotype of the worm. Analysis of the highly conserved mitochondrial 12 s RNA gene may be important to find strain variations of D. repens isolates.[10]

Subcutaneous dirofilariasis is mostly caused by D. repens in Asia. It is suggested that patients usually present with a single migratory nodule which may or may not be tender.[8] Ophthalmic involvement may be periorbital, subconjunctival, or intraocular. Such lesions are usually associated with moderate to severe inflammation. In the present case the worm was located in the eyelid and there was pain, periorbital swelling and tenderness.

Diagnosis of dirofilariasis in humans remains difficult as the symptoms exhibited by the patient are varying and nonspecific depending upon the location of worm.[1] Serologic results are of little value because of the lack of sensitivity and specificity. Identification of the worm in biopsy specimens or extraction of the worm from the lesion confirms diagnosis.[6] No chemotherapeutic agents are used since they appear to be ineffective. Surgical removal of the worm is the treatment of choice and its identification is essential for documentation to avoid treatment with antihelminthics. Cases of human dirofilariasis are under reported because either most remain undiagnosed, or unpublished or unidentified because of lack of awareness among the treating clinicians. Documentation by publishing the matter is important to understand the actual prevalence of human dirofilariasis in different regions of the world.