Onchocerciasis (cont.)

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What causes onchocerciasis?

The cause of onchocerciasis is the transfer of larvae of the parasite Onchocerca volvulus by the female blackfly when the fly gets a blood meal (bites) a human. The larvae enter the subcutaneous tissues and develop into adult male and female worms (filarial nematodes). These reproduce in the human tissue and form microfilariae that migrate to other areas of connective tissue and occasionally to the blood, urine, and sputum. In addition, both the adult worms and the microfilaria are colonized with bacteria termed Wolbachia that help these parasites survive. When the worms die, a host immune response ensues that can destroy optical tissue in the eye. The life cycle of the parasites is continued when a blackfly bites a human and, during its blood meal, ingests microfilariae. The complex life cycle is shown below.

Picture of the life cycle of O. volvulus
Picture of the life cycle of O. volvulus; SOURCE: CDC

What are onchocerciasis symptoms and signs?

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The symptoms and signs of onchocerciasis are as follows:

  • Skin inflammation that is very itchy and forms papules on the skin
  • Nodules in the skin (subcutaneous nodules)
  • Scarred, saggy, or drooping areas of skin
  • Patchy skin depigmentation (leopard skin)
  • Lymph node inflammation (lymphadenitis)
  • Eye (ocular) lesions
  • Visual problems (partial or complete blindness)
  • Eosinophilia (unusually high levels of eosinophils in the blood)
  • "Sowda" is a term used to describe the severe itching and skin discoloration (darkening), that is often confined to one limb, that can be found with onchocerciasis.
Medically Reviewed by a Doctor on 3/27/2013

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