Babu Aebeena¹, Peter Joji ², Mathew Deepu George ¹, Thomas Priya ¹

¹Department of Oral Pathology & Microbiology, Annoor Dental College & Hospital, Muvattupuzha.

²Department of Oral and Maxillofacial Surgery, Annoor Dental College & Hospital, Muvattupuzha

Running title – Dirofilariasis

Received: 27-09-2023

Revised: 2-10-2023

Accepted: 5-10-2023

Address for correspondence:  Dr. Priya Thomas, Department of Oral and Maxillofacial Pathology, Annoor Dental College & Hospital, Muvattupuzha Ernakulam dist, Kerala-686673, India.

E-mail: priyathomask@gmail.com

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 How to cite this article: Babu A, Peter J, Mathew D G, Thomas P. Human Dirofilariasis – A Case Report. J Oral Biomed Sci 2023; 2(3):124-128

ABSTRACT

Dirofilariasis is an emerging zoonotic parasitic infection caused by a habitual parasite of canines which rarely can cause accidental infections in human beings D. repens is commonly seen in the subcutaneous tissues of dogs. We present a case of a 46-year-old female patient who came with a swelling on the right buccal mucosa. The nodule was regular, freely mobile, and firm in consistency. The excision specimen showed a brownish-white-coloured oval mass with a white color gel-like structure. The lesion was diagnosed as a parasitic cyst. The pathogenesis and the differential diagnosis are discussed in this case presentation.

Keywords: Dirofilaria, Subcutaneous, Zoonosis

INTRODUCTION

Human dirofilariasis is a zoonotic infection most commonly caused by parasites of the genus Dirofilaria, of the family Onchocercidae⁽¹⁾. It is caused by D. repens, D. immitis, D. tenuis, D. ursi etc. D. repens is commonly seen in the subcutaneous tissues of dogs while D. immitis in the right ventricle and pulmonary artery of the dogs. Its occurrence in the oral cavity is infrequent^(1).

Culex, Aedes, Armigeres and Anopheles mosquitoes are vectors for this parasite, which take up the microfilaria (mf-L1) while feeding on an infected host. Microfilaria develops in the malpighian tubules to the infective third-stage larva (L3) and then migrates to the trunk through the body cavity. During a subsequent blood meal, transmission takes place when a potential vector bites dogs or other hosts including humans^(1).

The prevalence of Dirofilaria infections is often higher in areas where the vectors are abundant. It’s important to note that prevalence rates can change over time due to factors such as climate change, movement of infected animals, and vector control measures^(2).

Local health authorities, veterinary organizations, and public health agencies often monitor and report on the prevalence of parasitic infections, including those caused by Dirofilaria species, to help guide prevention and control efforts⁽²⁾. For the most up-to-date and specific information on the prevalence of Dirofilaria infections in a particular region or population, it is recommended to consult recent scientific literature, veterinary reports, and public health resources ⁽³⁾.

The importance of Dirofilaria repens has grown over time, partly due to an increased awareness of this parasitic infection. Enhanced diagnostic techniques and improved surveillance contribute to better detection and reporting of cases.

Dirofilariasis is common in Europe, Asia, and Africa, but rarely seen in India. In India, Kerala is considered an endemic for dirofilariasis⁽⁴⁾. Joseph et al. Initially reported the presence of Dirofilaria repens in India, describing a case of ocular Dirofilaria in a patient from the southern coastal state of Kerala. Subsequently, isolated case reports of Dirofilaria emerged throughout the nineties(4). The recent surge in cases over the past decade is likely attributed not only to an increased awareness of this condition but also to a genuine rise in its incidence. We report a case of human oral dirofilariasis   involving the right cheek.

CASE REPORT:

A 46-year-old female patient came to the department with a swelling on the right buccal mucosa since 1 month (Figure 1A). The nodule was regular, freely mobile, and firm in consistency with no rise in the temperature. Ultrasonography showed an approximately 1 X 0.9 cm hypoechoic lesion noted at the right cheek 3cm lateral to the angle of mouth without significant vascularity suggestive of an infected lymph node. The patient gave a history of close contact with domestic animals or pets and mosquitoes in the area where she lived. No abnormalities revealed on hematological examination.

The nodule was surgically excised intra-orally under local anesthesia (Figure 1B, 1C).The specimen was sent for histopathological examination. On gross examination; the specimen was a brownish-white-coloured oval mass of size 2 x 1.3 cm. The center part of the core showed a white color gel-like structure (Figure 1D).

Figure 1A: Subcutaneous swelling on the cheek. 1B, IC: Surgical Excision

Figure 1D: Excised Intact Nodule, 1E: Cut section of nodule showing gelatinous white areas in the center

Histopathological examination showed a fibrovascular connective tissue capsule exhibiting dense chronic inflammatory cell infiltrate (Figure 2A). The cystic lumen showed a necrotic tissue mixed with inflammatory cell infiltrate.The cystic lumen also showed a section of parasite exhibiting an external cuticular layer,hypodermic ,lateral chords, well-developed musculature, and intestinal tubule (Figure 2B,2C). The periphery of the cyst wall exhibited adipose tissue and the lesion is diagnosed as a parasitic cyst.

Figure 2A: Transverse sections of parasite. Eosinophilia in connective tissue, 2B: Parasite surrounded by granulation tissue, 2C: Prominent external cuticular ridges, and well-developed, tall musculatures, within the cavity

DISCUSSION:

Dirofilaria, a type of parasitic nematode that affects both domestic and wild animals, has the potential to accidentally infect humans through vectors. Its occurrence in the oral cavity is uncommon, typically manifesting as a solitary submucosal nodule devoid of inflammatory signs⁽⁵⁾. The condition can be attributed to various species, including D. repens, D. immitis, D. tenuis, D. ursi, and others ⁽²⁾. D. repens is frequently found in the subcutaneous tissues of dogs, whereas D. immitis tends to inhabit the right ventricle and pulmonary artery of infected dogs.

Dirofilariasis is common in Europe, Asia, and Africa, but rarely seen in India. In India, Kerala is considered an endemic for dirofilariasis(⁴⁾. Dirofilaria repens was first reported in Kerala, India in 1976 and Kerala has been one of the major geographical reservoirs for the infection⁽⁴⁾

Culex, Aedes, Armigeres, and Anopheles mosquitoes act as vectors for this parasite, taking up the microfilaria (mf-L1) during their feeding on an infected host. The microfilaria undergoes development in the malpighian tubules within the mosquito, transforming into the infective third-stage larva (L3), which then migrates to the trunk through the body cavity. Transmission occurs when an infected mosquito bites various hosts, including dogs and humans, during a subsequent blood meal(³⁾. However, certain observations have been made regarding its clinical features and prevalence:

Age:

Dirofilaria repens infections can occur across various age groups, including children and adults. The age distribution may vary based on exposure to mosquito vectors and other environmental factors. In some cases, infections have been reported in both pediatric and adult populations.

Gender:

Dirofilaria repens infections do not exhibit a specific gender predilection. Both males and females can be affected.

Clinical Manifestations:

In dogs, Dirofilaria repens infections may be asymptomatic or cause mild clinical signs such as subcutaneous nodules, dermatitis, and pruritus.

In humans, the infection can lead to subcutaneous nodules, itching, and skin inflammation. In some cases, the parasite may migrate to the eye, lung, or other organs, causing more severe symptoms. The risk of infection is primarily associated with exposure to infected mosquitoes rather than gender-specific factors(⁶⁾.

1. repens clinically presents as a subcutaneous nodule on the upper half of the body, eyes, eyelids, conjunctiva and all exposed areas. Intra-oral involvement is very rare and predilection for buccal mucosa and lips. Symptoms that prevail include transitory inflammation of nodules which may or may not be tender⁽⁷⁾.

During a blood meal, an infected mosquito introduces third-stage filarial larvae of Dirofilaria repens or D. tenuis onto the skin of the definitive host (canids and sometimes felids for D. repens, raccoons for D. tenuis), where they penetrate into the bite wound. Females produce microfilariae that are released into the peripheral blood. A mosquito ingests the microfilariae during a blood meal. After ingestion, the microfilariae migrate from the mosquito’s midgut through the hemocoel to the Malpighian tubules in the abdomen. There, the microfilariae develop into first-stage larvae and subsequently into third-stage infective larvae. The third-stage infective larvae migrate to the mosquito’s proboscis and can infect another definitive host when the mosquito takes a blood meal. In humans, D. repens usually manifests as worm in the subcutaneous tissue or a granulomatous nodule. D. tenuis follows a similar presentation and may also be found around the eye or on the conjunctiva. Because of this, the infection in humans was first known as Dirofilaria conjunctivae(⁶⁾.

For the confirmatory diagnosis of dirofilariasis histopathological examination of the dirofilaria worm in the tissue sections can be done. Treatment of choice is the surgical excision of the lesion or extraction of the parasite followed by the intake of antibiotics.

CONCLUSION:

The results of this study suggest that humans may act as a final host for D. repens, however its role as a source of D. repens infection is less clear. Therefore it is important for the clinician to be familiar with the diagnostic characteristics of the nematode to avoid misdiagnosis.

Prevention strategies play a crucial role in managing D. repens infections, including mosquito control measures and the use of preventive medications for dogs. Timely and accurate diagnosis, often based on clinical signs and laboratory tests, is essential for appropriate treatment. Antiparasitic medications, such as ivermectin or doxycycline, are commonly used to eliminate the adult worms.

Overall, understanding the pathogenesis of D. repens and implementing effective prevention and treatment measures are essential for the well-being of both animal and human populations in regions where this parasitic infection is prevalent. Regular veterinary care, including preventive measures and prompt treatment, contributes to the successful management of D. repens infections in dogs, while human cases require medical attention and appropriate antiparasitic therapy.

Conflict of interest: None

Source of support: Nil

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