Onchocerciasis
Background
- Also known as River Blindness
- Second most common cause of infectious blindness worldwide (~300,000 people worldwide) (Another ~800,000 have visual disturbances)
- Second only to Trachoma
- 99% of infected individuals live in Africa
- Caused by Onchocerca Volvulus
- A round worm (Nematode)
- Spread by the black fly (genus Simulium)
- Bite during the day time
- Live in and near fast flowing streams and rivers
Clinical Features
- Mainly consist of cutaneous and ocular symptoms secondary to the inflammation reactions from migration of the larvae or death of the larvae
Cutaneous manifestations
- Pruritis
- Onchodermatitis
- pruritic cutaneous nodules (may be acute or chronic)
- Elephant skin
- Thickening of the skin
- Lizard skin
- Atrophy and wrinkling of the skin
- Leopard skin
- Areas of depigmentation
Ocular manifestations
- Thought to be caused by migration of the microfilariae to the corneal surface
- Causes localized punctate keratitis that can become sclerosing keratitis leading to opacification of the cornea
- Some evidence exists to suggest that the ocular manifestations are from the immune response to Wolbachia (an endosymbiant to Onchocera)
Diagnosis
- Skin snip
- Multiple small (1-2 gm) snips are placed in normal saline and presence of microfilariae detected
- Can PCR biopsy if negative for microfilariae
- Mazotti test
- Place diethylcarbazine (DEC) on patch of skin - localized pruritis and urticaria are positive reactions
Treatment
- Ivermectin
- 150mcg/kg one time dose
- Usually distributed in endemic areas as part of a mass drug administration (2 doses 6 months apart, every three years)