Filariasis

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Filariasis is a disease group affecting humans and animals, caused by filariae; ie, nematode parasites of the order Filariidae.[1] Of the hundreds of described filarial parasites, only 8 species cause natural infections in humans. The World Health Organization (WHO) has identified lymphatic filariasis as the second leading cause of permanent and long-term disability in the world, after leprosy.

In lymphatic filariasis, repeated episodes of inflammation and lymphedema lead to lymphatic damage, chronic swelling, and elephantiasis of the legs (see the image below), arms, scrotum, vulva, and breasts .

Signs and symptoms

Lymphatic filariasis

  • Fever
  • Inguinal or axillary lymphadenopathy
  • Testicular and/or inguinal pain
  • Skin exfoliation
  • Limb or genital swelling – Repeated episodes of inflammation and lymphedema lead to lymphatic damage, chronic swelling, and elephantiasis of the legs, arms, scrotum, vulva, and breasts.

The following acute syndromes have been described in filariasis:

  • Acute adenolymphangitis (ADL)
  • Filarial fever – Characterized by fever without associated adenitis
  • Tropical pulmonary eosinophilia (TPE)

Onchocerciasis

The clinical triad of infection in onchocerciasis is as follows:

  • Dermatitis – Skin lesions include edema, pruritus, erythema, papules, scablike eruptions, altered pigmentation, and lichenification
  • Skin nodules (ie, onchocercomas) – Skin nodules tend to be common over bony prominences
  • Ocular lesions – Eye lesions are usually related to the duration and severity of infection and are caused by an abnormal host immune response to microfilariae; loss of visual acuity may occur

Loiasis

The diagnostic feature of loiasis is a Calabar swelling, ie, a large, transient area of localized, nonerythematous subcutaneous edema. This is most common around the joints.

Mansonella infections

These are usually asympt omatic. If symptoms are present, they may include fever, pruritus, skin lumps, lymphadenitis, and abdominal pain.

See Clinical Presentation for more detail.

Diagnosis

Microfilariae can be detected through examination of the following:

  • Blood – The microfilariae of all species that cause lymphatic filariasis and the microfilariae of Loa loa, Mansonella ozzardi, and M perstans are detected in blood[8]
  • Urine – If lymphatic filariasis is suspected, urine should be examined macroscopically for chyluria and then concentrated to examine for microfilariae
  • Skin –Onchocerca volvulus and M streptocerca infections are diagnosed when microfilariae are detected in multiple skin-snip specimens from different sites located on both sides of the body; the Mazzotti test allows a presumptive diagnosis of cutaneous filariasis to be made when skin snips are negative for microfilariae
  • Eye – Microfilariae of O volvulus may be detected in the cornea or anterior chamber of the eye using slit-lamp examination

The following imaging studies can be used in the evaluation of filariasis:

  • Chest radiography – Diffuse pulmonary infiltrates are visible in patients with TPE
  • Ultrasonography – Can be used to demonstrate and monitor lymphatic obstruction of the inguinal and scrotal lymphatics; has also been used to demonstrate the presence of viable worms
  • Lymphoscintigraphy[9]

Histologic findings include the following:

  • Lymphatic filariasis – Affected lymph nodes demonstrate fibrosis and lymphatic obstruction with the creation of collateral channels
  • Elephantiasis – The skin is characterized by hyperkeratosis, acanthosis, lymph and fatty tissue, loss of elastin fibers, and fibrosis
  • Onchocerciasis – Onchocercomas have a central stromal and granulomatous, inflammatory region where the adult worms are found and a peripheral, fibrous section; microfilariae in the skin incite a low-grade inflammatory reaction with loss of elasticity and fibrotic scarring

See Workup for more detail.

Management

Anthelmintics used in the treatment of filariasis include the following:

  • Diethylcarbamazine (DEC)
  • Ivermectin – Drug of choice for Wuchereria bancrofti
  • Suramin – Only drug in clinical use for onchocerciasis that is effective against adult worms
  • Mebendazole
  • Flubendazole
  • Albendazole

Surgery

In lymphatic filariasis, large hydroceles and scrotal elephantiasis can be managed with surgical excision. Correcting gross limb elephantiasis with surgery is less successful and may necessitate multiple procedures and skin grafting.

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