Scrotal filariasis: a case report and clinical considerations

Highlights

• •Scrotal filariasis can be diagnosed even outside endemic regions.
• •Every scrotal mass requires histopathological analysis even in filariasis cases.
• •Geographic spread of parasitic diseases shift due to climate change and migration.
• •Sustained action programs against filariasis remain essential to limit its impact.

Abstract

Objectives

Lymphatic filariasis is a tropical disease caused by filariae such as Wuchereria bancrofti, which is often associated with rare complications in endemic areas. We report a case of a 56-year-old patient from French Polynesia with an 18 cm scrotal swelling. Surgery revealed a filarial worm and diffuse necrosis. The diagnosis of scrotal filariasis was confirmed by positive filariasis serologies. This is a rare case in French Polynesia due to its size.

Design

We describe clinical manifestations, diagnosis and management, highlighting epidemiological considerations specific to filariasis.

Results

This case of scrotal filariasis served as a starting point for reflection on the links between chronic lymphatic obstruction and persistent inflammation. In the coming years, it will therefore become increasingly common to treat patients with parasitic diseases outside endemic areas, whether due to changes in the distribution of pathogens or to increasing travel and migration.

Conclusion

Clinicians should be aware of the pathogenic links between lymphatic obstruction and chronic inflammation.

Introduction

Lymphatic filariasis (LF) is a tropical disease caused by three filarial worms, including Wuchereria bancrofti, which accounts for 90% of infections [1]. Human filarial worms are nematodes that require a blood-feeding insect vector to complete their life cycle. Wuchereria bancrofti and others filarial worms (Brugia malaysi and Brugia timori) are primarily transmitted by mosquitoes [2]. Transmission occurs when an infected mosquito takes a blood meal and deposits infective third-stage (L3) larvae onto the skin, which then penetrate the bite site. After entering the host, the larvae migrate through the tissues to the lymphatic system, where they develop through successive stages until they mature into adult worms. Once fertilized, adult female filarial worms release microfilariae that circulate in the peripheral blood. During subsequent blood meals, other mosquitoes ingest these microfilariae, which then develop within the vector through the L2 (second-stage larvae) and L3 (third-stage larvae) stages, completing the cycle and enabling transmission to a new human host [3].

By 2018, 51 million patients worldwide were infected [1].

LF remains endemic in 72 tropical and subtropical countries. The global distribution is highly uneven, with sub-Saharan Africa being most affected (approximately 65% of all cases) and Southeast Asia being second (30% of all cases) [1].

Although most individuals infected with LF remain asymptomatic despite the presence of adult worms in the lymphatic system, a small proportion develop chronic conditions such as hydrocele or lymphedema. Elephantiasis of the limbs is the classic manifestation of LF; however, scrotal involvement, although less common, can cause significant morbidity. We describe a scrotal filariasis case and focus on the management of LF and its chronic complications.

Case report

A 56-year-old man from Tahiti traveled for the first time abroad to mainland France in January 2024. The patient provided signed informed consent, including sharing physical examination and radiological images.

He had no previous medical history. He consulted at the Nancy Regional Hospital University Center in July 2024 for a nonpainful scrotal discomfort. Family history was unremarkable, and no similar case was known in his family.

Clinical examination revealed an 18-cm left scrotal bursa swelling (Figure 1A), which was indurated, painless without skin erythema, and present for several years. The patient denied previous unexplained fever or lower limbs lymphedema.

Figure 1.

Illustration of scrotal filariasis case. (A) A clinical examination revealed an 18 cm swelling of the left scrotal bursa. (B) Scrotal filariasis: T2-weighted magnetic resonance image of the axial and frontal section. (C) Ultrasound image of scrotal filariasis.

Complete blood count showed eosinophilia of 1.18 × 10⁹/l. Filariasis serology showed positive anti-dipetalonema vitae antibodies. Blood collected once at 22 hours (nocturnal) showed no filariae on smear stained with Giemsa.

A computed tomography scan and magnetic resonance imaging (Figure 1B) revealed a voluminous, partly fluid formation (18 cm × 11 cm), with a markedly elevated protein content, without adenomegaly, hepatosplenomegaly, or signs of tuberculosis or hematopathy.

A scrotal ultrasound identified the pathognomonic “filarial dance sign” [4] (Figure 1C). The mass was characterized by a heterogeneous echogenic structure comprising anechogenic areas.

Considering the compelling evidence supporting scrotal filariasis, a treatment of doxycycline (200 mg/day) was initiated. After 4 weeks of treatment and in view of the discomfort caused by the scrotal mass, surgery was performed in October 2024. Given the mass’ size, adhesions, and contamination risk, a left scrotal orchidectomy was performed, followed by scrotal reconstruction via excision of excess tissue.

In accordance with the recommendation of the World Health Organization (WHO), the patient has continued treatment with doxycycline for 3 months, followed by a single 6-mg dose of diethylcarbamazine. Loa loa and Onchocerca volvulus are not endemic in Tahiti and were not ruled out in this case before diethylcarbamazine [5,6].

A pathological analysis revealed the presence of residual filaria and substantial inflammatory hydrocele fluid necrosis. There was no sign of testicle infiltration.

At 1 month post-operation, the patient exhibited complete skin healing, with no post-operative complications. During subsequent follow-up appointments over a 12-month period, no recurrences were observed, particularly, on the contralateral side. Follow-up visits over more than 5 years were planned to monitor the long-term impact of chronic inflammation and signs of malignancy.

Discussion

To combat LT, the WHO launched the Global Programme for the Elimination of Lymphatic Filariasis (GPELF) in 2000, targeting the disease through two key strategies [1]: mass drug administration to halt transmission and morbidity management, focusing on chronic conditions. These efforts have led to treatment for hundreds of millions worldwide, significantly reducing the disease burden.

Approximately 44.3 million LF cases could be prevented between 2000 and 2020 [7] and 46.4 million new irreversible cases between 2011 and 2030 [8].

The following antiparasitic mass drug administration regimens are recommended by the WHO based on the diversity of filarial diseases in a geographic area [9]:

• •Albendazole (400 mg) administered twice yearly in regions where loiasis is co-endemic,
• •Ivermectin (200 µg/kg) in conjunction with albendazole (400 mg) in countries affected by onchocerciasis,
• •Diethylcarbamazine citrate (6 mg/kg) administered in conjunction with albendazole (400 mg) in countries free of onchocerciasis, and
• •Ivermectin (200 µg/kg) administered in conjunction with diethylcarbamazine citrate (6 mg/kg) and albendazole (400 mg) in countries free of onchocerciasis and where other programmatic conditions are met.

The management of morbidity in LF centers on two principal chronic complications: hydrocele and lymphedema.

A literature review assessed the impact of LF [10] and current management strategies, highlighting the need for dedicated education and training programs on LF. No consensus exists regarding the management of urogenital manifestations, largely due to the absence of standardized case definitions. This lack of uniform criteria limits comparability across studies and underscores the need for a unified severity classification system.

Lymphedema, by contrast, requires a prolonged conservative approach grounded in complex decongestive therapy, incorporating meticulous skin care and hygiene, manual lymphatic drainage, compression bandaging, and adapted physical exercise. Central to disease management is also the prevention and early treatment of acute adenolymphangitis episodes, recognized as the primary drivers of lymphedema progression and typically addressed through prompt antibiotic therapy and local wound care. In alignment with the GPELF, the WHO advocates for the systematic integration of these interventions within the standardized Morbidity Management and Disability Prevention framework [1], with the overarching objectives of reducing disease burden, preventing progression to severe elephantiasis, and mitigating the substantial socioeconomic impact of this neglected tropical disease on affected individuals and communities.

Furthermore, any proposed solutions must also take account of the impact of climate change. The endemic filariasis distribution, comparable to that of all parasitic diseases, is changing and will change even more in the coming years because of climate change and alterations in the transmission vectors geographical distribution [11]. This phenomenon is already occurring in Europe, as evidenced by an increasing number of case reports of testicular heartworm disease in men, which is another form of filariasis [12].

The absence of the “filarial dance sign” is likely explained by the chronicity of the filarial disease and the death of the parasite [10]. It is important to recognize that a substantial proportion of symptomatic patients are no longer actively infected at the time of clinical presentation because adult worms may have already been cleared [13]. The shift in host immune responses from a T helper cell (Th)2-dominated, hypo-responsive state, which sustains chronic infection, toward Th1 pro-inflammatory mechanisms [14] is understood to contribute to parasite elimination yet simultaneously drives the pathological manifestations characteristic of chronic LF. Accordingly, negative Giemsa blood smear and absent filarial dance sign on ultrasonography do not exclude previous infection because these findings may reflect immunological clearance rather than non-filarial etiology.

The testicular pathological specimen of this case revealed extensive necrosis and evidence that most filarial organisms had died, accounting for the widespread tissue damage.

In the context of scrotal LF, pathological analysis of the vagina and testicle is of particular importance to avoid missing a genuine tumor that would be difficult to detect given the anatomical anomaly caused by filariasis. Here, histopathological evaluation confirmed the absence of testicular cancer. Nevertheless, we found reports of cancers associated with filariasis [15], some cases exhibiting pseudo-tumoral characteristics in the testicles.

Testicular tumors associated with filariasis are predominantly classified as leiomyosarcoma [16]. The presence of filarial worms in malignant tumors of other organs has been documented [[17], [18], [19], [20]]. The leading causal hypothesis linking filariasis to neoplasm development implicates chronic inflammation and lymphatic obstruction as the primary driving mechanisms.

Research indicates that lymphangiectasia and inflammatory reactions extend beyond the immediate vicinity of worm-infected lymphatic vessels [21], suggesting a process mediated by inflammatory factors acting on lymphatic endothelial cells [22]. Such chronic infection may generate a microenvironment that facilitates tumor progression.

Chronic inflammation is the likely carcinogenic process involved in filariasis and has already been documented in other tumors of the digestive system (Helicobacter pylori infection and gastric adenocarcinoma) or urinary system (urinary schistosomiasis and bladder tumors).

The association between lymphatic obstruction and an increased risk of developing lymphangiosarcoma is a well-documented phenomenon. The Stewart–Treves syndrome primarily occurs after lymph node dissection in breast cancer cases [23]. Although the mechanism differs from that of filariasis, lymphatic obstruction can lead to comparable pathological outcomes, exemplifying the synergistic role of lymphatic dysfunction and chronic inflammation in promoting cancer development.

Chronic lymphatic obstruction impairs the drainage of interstitial fluids and immune cells [24], fostering a hypoxic and pro-inflammatory microenvironment that facilitates tumorigeneses [25]. The resulting lymphatic stasis promotes the accumulation of pro-inflammatory cytokines, activated immune cells, which collectively induce deoxyribonucleic acid damage, enhance cellular proliferation, and suppress apoptosis [26]. This persistent inflammatory milieu further activates oncogenic signaling pathways, notably, NF-κB and STAT3, thereby driving malignant transformation [27].

Notwithstanding these considerations, LF is not classified by the International Agency for Research on Cancer as a carcinogenic infection, in contrast to certain other helminthic infections (e.g. Schistosoma haematobium) [28].

In summary, the primary burden of LF remains its chronic complications related to lymphedema and hydrocele, which result in associated physical disability and profound social stigma.

These sequelae have a significant impact on quality of life and result in a substantial increase in disability-adjusted life years, with the greatest impact concentrated among marginalized populations in low-income endemic areas [29].

Furthermore, the immunological vulnerability of non-endemic individuals (short-term travelers, immigrants, and recently arrived migrants) is of clinical importance. In the absence of the antigen-specific immune tolerance typically acquired through prolonged exposure during childhood, these individuals develop exaggerated Th1/pro-inflammatory responses during primary infection, which significantly increases their risk of developing acute clinical manifestations, even with a low parasite load [30].

Conclusions

This case of scrotal filariasis in a Tahitian patient in mainland France serves to illustrate the necessity of continued research into travel to endemic areas for all parasitic and infectious diseases. Sustaining the efforts of the WHO’s GPELF is essential to achieving eradication, including the often-debilitating urogenital forms of the disease.

In this case, surgical intervention was undertaken, with the primary objectives of alleviating local symptoms. It is crucial to underscore that in non-endemic regions, this condition should be considered a potential differential diagnosis when evaluating a scrotal mass, even if the disease is not prevalent in the area [15].

In the coming years, it will, therefore, become increasingly common to treat patients with parasitic diseases outside endemic areas.

CRediT authorship contribution statement

Clément Larose: Conceptualization, Investigation, Methodology, Project administration, Validation, Writing – original draft, Writing – review & editing. Laura Bollaro: Data curation, Conceptualization. Alix Martin-Bertaux: Data curation. Sandra Isabel: Writing – review & editing. Charles Mazeaud: Validation. Pascal Eschwege: Supervision, Writing – review & editing. Roxanne Tourigny: Methodology, Project administration, Validation, Writing – review & editing. Vincent Fradet: Funding acquisition, Methodology, Project administration, Resources, Supervision, Validation, Writing – review & editing.

Declaration of competing interest

The authors have no competing interests to declare.