Onchocerciasis

Onchocerciasis (river blindness) is a filarial infection caused by Onchocerca volvulus, transmitted by blackflies (Simulium species) breeding in fast flowing rivers.

• About 21 million infected, with 99% in sub-Saharan Africa (Nigeria, DRC, Ethiopia, Uganda, Kenya foci), also Yemen and a few Latin American foci.
• Adult worms live in subcutaneous nodules; microfilariae migrate to skin and eye, causing inflammation on death.
• Leading infectious cause of blindness; over 1 million cases of visual impairment.
• Wolbachia endosymbionts contribute to pathogenesis.

• Intense pruritus, papular rash, lichenification, "leopard skin" depigmentation (shins), "hanging groin", and skin atrophy.
• Subcutaneous nodules (onchocercomas) over bony prominences (hips, ribs, knees, skull).
• Ocular: punctate keratitis, sclerosing keratitis, iridocyclitis, chorioretinitis, optic neuritis, and visual field loss progressing to blindness.
• Onchocerciasis associated epilepsy (nodding syndrome) in some hyperendemic areas.

• Skin snip biopsy (microfilariae in saline), slit lamp examination for microfilariae in the anterior chamber, and nodule excision with adult worms.
• Serology (Ov-16 IgG4 antibodies; rapid test), PCR.
• Mazzotti test (diethylcarbamazine patch) is no longer used.
• Test for Loa loa co-infection before treatment in co-endemic areas (blood film or LoaScope).
• Eosinophilia; exclude scabies, eczema, leprosy, and other filariases.

• Ivermectin 150 micrograms/kg single oral dose every 6 to 12 months for at least 10 to 15 years (microfilaricidal; community directed treatment in endemic areas).
• Moxidectin 8 mg single oral dose (adults and children aged 12 years and above): a more effective microfilaricide with longer suppression.
• Doxycycline 200 mg daily for 4 to 6 weeks kills Wolbachia, sterilises adult female worms, and is macrofilaricidal over time; given with ivermectin (avoid in pregnancy and young children).
• Loa loa co-infection: do not give ivermectin if Loa loa microfilaraemia exceeds 20,000/mL (risk of encephalopathy); use alternative strategies (doxycycline, test-and-treat).
• Treat adverse reactions to microfilaricides (Mazzotti like reactions) with antihistamines and NSAIDs.
• Nodulectomy, symptomatic itch control, and eye care; vector control (larvicides).