Onchocerca volvulus; convoluted filaria (river blindness)

Epidemiology

• equatorial Africa
• Saudi Arabia
• Central & South America
• infection is transmitted by the bite of the blackfly (Simulium)
• the blackfly develops along freely flowing rivers & streams, particularly rapids

Pathology

• infects primary the skin, eyes & lymph nodes
• infective larvae from the blackfly develop into adults in subcutaneous nodules
• 7 months to 3 years after infection, the gravid female releases microfilariae that migrate out of the nodule & concentrate in the dermis
• infection is transmitted when a female blackfly ingests microfilaria from the host's skin
• males are 3-6 cm in lenth, females 40-60 cm in length
• adults live up to 18 years, average 9 years
• damage is induced by microfilariae, not adults
• inflammatory changes in the skin, with fibrosis & atrophy
• neovascularization & corneal scarring lead to corneal opacities
• inflammation in anterior chamber of the eye & posterior chamber of the eye results in anterior uveitis, chorioretinitis & optic atrophy

Clinical manifestations

• see onchocerciasis

Laboratory

• diagnosis is made by recovery of an adult worm in an excised nodule or of microfilaria on skin snips
  • material is incubated in tissue culture medium or saline on a glass slide for 2-4 hours or overnight
  • microfilariae emerge from the skin & may be seen under light microscopy
  • no sheaths

Management

• see onchocerciasis

More general terms

• Onchocerca

Additional terms

• onchocerciasis (river blindness)