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 - skin thickening
• Lizard skin - skin atrophy and wrinkling
• Leopard skin - areas of depigmentation

Ocular manifestations

• Localized punctate keratitis that can become sclerosing keratitis → opacification of the cornea
  • Thought to be caused by migration of the microfilariae to the corneal surface
  • Some evidence exists to suggest that the ocular manifestations are from the immune response to Wolbachia (an endosymbiant to Onchocera)

Differential Diagnosis

Travel Related Skin Conditions

Papules

• Insect bites
• Scabies
• Seabather's eruption
• Cercarial dermatitis (Swimmer's Itch)

Sub Q Swelling and Nodules

• Myiasis
• Tungiasis
• Loa loa
• African Trypanosomiasis
• Onchocerciasis

Ulcers

• Pyoderma
• Leishmaniasis
• Mycobacterium marinum

Linear and Migratory Lesions

• Cutaneous Larvae Migrans
• Photodermatitis

Evaluation

• 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 pruritus and urticaria are positive reactions

Management

• 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)

Disposition

• Discharge

See Also

• Parasites
• Travel medicine

External Links

• World Health Organization - Onchocerciasis

References

Authors

Ross Donaldson