Introduction

Dirofilaria is the genus of the family Onchocercidae of the superfamily Filarioidea [1]. It is an uncommon vector-borne disease caused by filarial nematodes associated with mainly carnivores as hosts such as dogs, cats, and wild mammals. Humans are accidental hosts. Only six species cause disease in humans. The most common species infecting are Dirofilaria repens and Dirofilaria tenuis (causes subcutaneous infection) and Dirofilaria immitis (causes pulmonary dirofilariasis)[2] [3]. Species differ depending on the geographical location and are endemic to Southern and Eastern Europe, and Asia, mainly Sri Lanka, Malaysia, and India [4]. Transmission is by the bite of a mosquito (Anopheles, Aedes and Culex species)[5].

Case Reports

In our first case, a 19-year-old boy, hailing from Kannur, came with swelling over his right ankle near the tendon Achilles region. The hemogram was normal with a mild increase in eosinophils (08%), an absolute eosinophil count of 510 cells/ml of blood indicating mild eosinophilia and an ESR = 21 mm at the end of one hour. A soft tissue scan revealed an oval hypoechoic lesion measuring 2 x 1.4 x 0.4cm just deep to the deep fascia in the posterior aspect of the lower 1/3^rd leg. Within the centre of the hypoechoic lesion, a tubular coiled structure with hyperechoic walls was noted having a diameter of 0.6mm. Mass was excised and sent for histopathological examination. A gross examination showed grey white and firm mass with normal overlying skin. The cut surface was solid grey-white. After haematoxylin and eosin staining, microscopy showed an area displaying dense inflammatory cells with a granulomatous response. Epithelioid and foreign body giant cells were noted [ Figure 1 ]. The Centre of the inflammatory process showed a parasite displaying longitudinal ridges with thick smooth cuticles, muscular layer and internal organs were seen [ Figure 2 ].

In our second case, a 61-year-old male, farmer hailing from Mangalore, Southern Karnataka came with swelling over the right anterolateral aspect of his thigh for 2 – 3 years. A provisional clinical diagnosis of lipoma was made. The hemogram

Figure 3: Cross-sectional morphology of the Dirofilaria worm with outer cuticle and longitudinal ridges with well-developed inner musculature. Intestinal tubule (IT) is seen. [H&E stain 40x], Department of Pathology, K.S. Hegde Medical Academy, Mangaluru

Figure 4: Cross-sectional morphology of the Dirofilaria worm with the outer cuticle, surrounded by intense granulomatous inflammatory response and fibrosis. [H&E stain 20x], Department of Pathology, K.S. Hegde Medical Academy, Mangaluru

Ophthalmologic examination of both cases was negative for parasite infestation.

Discussion

Human dirofilariasis is a zoonotic infection caused by a nematode [4]. Canines are the primary hosts for this filarial worm. Adult worms reside in the subcutaneous tissue of the infected hosts and produce microfilaria in their circulation. Transmission is by mosquitoes such as Aedes, Anopheles or Culex.

become aware of the infection and seek medical assistance. As opposed to this, pulmonary nodules are found deep within the body and are typically asymptomatic. Additionally, a small percentage of lung nodules are accidentally discovered during chest X-ray procedures, which are typically carried out for purposes unrelated to dirofilariasis [6].

Only after an excision biopsy can the diagnosis of dirofilariasis be determined with certainty, and the parasite's microscopic characteristics are used to identify its species. Therefore, pathologists must understand the parasite's histological characteristics as well. DNA analysis based on polymerase chain reaction can accurately identify species [3]. The only effective treatment for human subcutaneous dirofilariasis is surgical removal of the lesion. Benign or malignant tumours, lipomas, granulomas, and infected cysts or abscesses are among the differential diagnoses for subcutaneous dirofilariasis.

Treatment with diethylcarbamazine and ivermectin can be given as chemotherapy [4].

Conclusion

An infection by a parasite that is becoming more and more common in humans is subcutaneous dirofilariasis, particularly in tropical areas. It is vital to recognise and diagnose early because delaying diagnosis can result in unwarranted invasive tests and treatments. Insect bites can be avoided in endemic areas by taking appropriate precautions, such as using insecticide-treated bed nets or cosmetics that repel insects. Histopathological examination plays a crucial role in the diagnosis.

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The authors certify that they have obtained all appropriate patient consent forms. In the forms, the patients have given their images and other clinical information to be reported to 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.