Onchocerciasis

Synonyms

Elephantiasis.

Epidemiology

In tropical and subtropical humid endemic areas, mostly commonly in sub-Saharan Africa. “Improted” cases have been reported from other areas.

Onchocerciasis is one of the most frequent causes of (“river”) blindness.

Definition

Parasitic infectious disease caused by the filarial nematode Onchocerca volvulus, causing dermatologic, ocular, and systemic manifestations.

Aetiology & Pathogenesis

In endemic areas of Africa and Central America, the black fly (buffalo gnat; which breed near fast-flowing rivers) is the vector for Onchocerca volvulus. Subsequent to the bite of a fly, thousands of microfilariae (immature worms) migrate via blood into the subcutaneous tissue and eyes where they cause mature into adult worms and cause symptoms.

Signs & Symptoms

Painless, freely mobile, subcutaneous onchcercal nodule (1-3 cm; onchocercoma), replete with organisms are most commonly found at bony prominences. There also is severe pruritus, eczematous dermatitis, lichenification, subcutaneous and dermal atrophy and spotted depigmentation (“leopard skin”); accompanying blindness (“river blindness”).

Localisation

Extremities, trunk, buttocks, waist, and upper aspect of the thighs.

Classification

Acute papular onchodermatitis.
Chronic papular onchodermatitis.
Lichenified onchodermatitis.
Atrophy.
Depigmentation.

Clinical classification and grading system (Murdoch).

Laboratory & other workups

Eosinophilia (up to 40%). Microscopic examination of microfilaria, emerging from skin snips and in subcutaneous nodules respectively.

Dermatopathology

Multitude of entangled worms of both sexes (paired worms) within encapsulated nodules (onchocercoma).
Microfilaria in the papillary dermis.
Subepidermal edema and strong inflammatory response with formation of microabscesses around necrotic larvae.
Mixed cellular infiltrate, with histiocytes, lymphocytes, neutrophils, eosinophils, and plasma cells.

Course

Chronic; see classification.

Complications

In endemic areas, onchocerciasis is one of the most frequent causes of (“river”) blindness.

Diagnosis

Clinical, eosinophilia, microscopic identification of microfilaria.

Differential diagnosis

Podoconiosis; other tropicalparasitic infestations.

Prevention & Therapy

Ivermectin: 0.15-0.2 mg/kg PO 3 1 dose; may repeat in 3-12 months for the life of an adult worm.
Doxycycline: 100 mg QD PO 3 6 wks.

Special

None.

10.4.2 Onchocerciasis