Onchocerciasis (River blindness)
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Introduction
- A common chronic filarial disease in tropical regions which frequently cause pruritus and blindness
- Causative organism is Onchocerca volvulus
- The microfilariae are transmitted by female Simulium, tiny black flies which breed along small, rapidly moving streams
- Female worms release motile microfilariae into the skin, subcutaneous issues, lymphatics, and eyes
- Interval from exposure to onset of symptoms can be as long as 1 - 3 years
Clinical features
- Skin lesions which may be localized or cover large areas
- Intense pruritus is a cardinal symptom; may occur in the absence of the skin lesions
- Dermatitis
- Skin eventually becomes lichenified from chronic scratching
- Post inflammatory confetti-like depigmentation on the skin ("leopard skins") may occur in late onchodermatitis
- Onchocercomata
- Subcutaneous nodules which develop on various sites of the body and contain myriad adult worms which can live for up to 14 years.
- Firm, non-tender lymphadenopathy is a common finding in patients with chronically infected onchocerciasis
- "Hanging groin" describes the pendulous loose, atrophic skin sac that contains these large nodes
- Microfilariae in the eye may lead to visual impairment and blindness
Differential diagnoses
- Scabies
- Pediculosis
- Papular urticaria
- Papulonecrotic tuberculids
- Pruritic papular eruption of HIV
- Other causes of generalized pruritus without a rash
- Other causes of subcutaneous nodules e.g.
- Sparganosis
- Paragonimiasis
- Gnathostomiasis
- Cysticercosis
- Echinococcosis
Complication
- Blindness
Investigations
- Skin snips or punch biopsy for microfilariae
- Excise nodule for adult worms
- Mazzotti test reaction
- Slit lamp eye examination
Treatment goals
- Kill the microfilariae
- Eliminate source of microfilarial release
- Prevent blindness
Drug treatment
Ivermectin
- As a single oral dose of 150 microgram/kg in adults and children over 5 years
- Repeat every 6 months for 2 years and yearly for 12 -15 years or longer
Eye involvement
- Prednisolone 1 mg/kg orally should be started several days before treatment with ivermectin
Surgical
- Excise individual nodules (nodulectomy)
Notable adverse drug reactions, contraindications, and caution
- No food or alcohol should be taken for at least 2 hours before or after dosage
- Pregnant women should not receive ivermectin until after delivery
- Breastfeeding mothers should not be treated until the infant is at least 1 week old
Prevention
- Use biodegradable insecticides to kill flies
- Netting and repellents remain crucial.
- Provide access to safe and portable water
- In hyperendemic areas, treat the whole population twice yearly with ivermectin