Onchocerciasis

🌍 Overview

• Onchocerciasis (💡 “river blindness”) is a parasitic disease caused by infection with Onchocerca volvulus microfilariae.
• It is a leading cause of infectious blindness worldwide, mainly in sub-Saharan Africa 🌍.
• ✅ Treatable with ivermectin, an antiparasitic medication.

🧬 Pathophysiology

• 🦟 Transmitted via repeated bites of blackflies (Simulium spp.).
• Larvae mature into adult worms forming subcutaneous nodules → release microfilariae.
• Microfilariae migrate through skin & eyes, causing intense inflammation when they die.
• 👁️ In the eye: dead larvae trigger chronic inflammation → corneal opacities, chronic iritis, cataracts → progressive blindness.

🩺 Clinical Presentation

• Skin: Intense itching, nodules, and “leopard skin” 🐆 (hypopigmented patches).
• Eye: Microfilariae visible in anterior chamber; corneal scarring & blindness (“river blindness” 👁️).
• Lymph nodes: Chronic lymphadenopathy, esp. inguinal & femoral regions.

🔎 Investigations

• 🧪 Skin Snip Test: Gold standard – detects microfilariae under microscopy.
• 🧬 Serology: Antibody tests support diagnosis in non-endemic settings.
• 👁️ Ophthalmology: Slit-lamp exam to visualise microfilariae & check for corneal/retinal damage.

💊 Management

• 💊 Ivermectin: Single oral dose every 6 months → reduces microfilarial load, prevents blindness.
• 💊 Doxycycline: Kills Wolbachia bacteria (essential for worm survival) → long-term reduction in worm burden.
• 👥 Community MDA: Mass drug administration campaigns in endemic areas have drastically reduced prevalence.
• 👁️ Eye care: Manage chronic inflammation in advanced disease; prevention via early ivermectin is key.

🛡️ Prevention

• 🦟 Vector control → reduce blackfly populations near rivers (larvicides, environmental measures).
• 👥 Mass drug administration programs → cornerstone of control & elimination efforts.

📚 References

• WHO – Onchocerciasis (River Blindness)
• CDC – Onchocerciasis

Cases — Onchocerciasis (River Blindness)

• Case 1 — Pruritic dermatitis 🌍: A 28-year-old man from West Africa presents with intense itching, papular rash, and depigmented patches of skin on his legs ("leopard skin"). Multiple subcutaneous nodules are palpable over his iliac crest. Diagnosis: onchocerciasis with cutaneous involvement. Managed with oral ivermectin (microfilaricidal) given every 6–12 months.
• Case 2 — Ocular disease 👁️: A 36-year-old woman from an endemic region in Uganda reports progressive blurred vision and photophobia. Exam: punctate keratitis, sclerosing keratitis, and anterior chamber inflammation. Microfilariae visible in slit-lamp exam. Diagnosis: onchocerciasis with ocular involvement (river blindness). Managed with repeated ivermectin; doxycycline considered to target Wolbachia endosymbionts.
• Case 3 — Community outbreak 🚑: A 12-year-old boy living near a fast-flowing river in Cameroon presents with severe itching and multiple nodules over his chest and arms. Several children in the same village are affected. Skin snip: Onchocerca volvulus microfilariae. Diagnosis: paediatric onchocerciasis in endemic setting. Managed with community-directed ivermectin distribution (Mectizan programme, WHO).

Teaching Point 🩺: Onchocerciasis is a filarial infection caused by Onchocerca volvulus, transmitted by blackflies (*Simulium* species) near fast-flowing rivers. Main features: - Skin: severe pruritus, papular rash, "leopard skin" depigmentation, subcutaneous nodules. - Eye: keratitis, uveitis, optic atrophy → river blindness. Diagnosis: skin snip microscopy, serology, slit-lamp exam. Management: mass drug administration with ivermectin every 6–12 months; doxycycline targets symbiotic Wolbachia for sterilisation of adult worms.