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Skin-nontumor / Clinical Dermatology

Infestations

Onchocerciasis

Reviewer: Nat Pernick, M.D., PathologyOutlines.com, Inc. (see Reviewers page)
Revised: 7 July 2011, last major update July 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.

Definition
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● Onchocerciasis is a parasitic disease caused by Onchocerca volvulus, a microfilaria

Terminology
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● Also called river blindness, Robles' disease

Clinical features
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● #2 infectious cause of blindness worldwide (#1 is Trachoma), due to its endosymbiont, Wolbachia pipientis, a bacteria that causes the severe inflammatory response that leaves many blind (Wikipedia)
● Worldwide affects 18 million people, and causes 270,000 cases of blindness
● Transmitted to humans through the bite of blackfly of genus Simulium
● Larva spread throughout the body, and when worms die, their Wolbachia symbionts are released, triggering a host immune system response that causes intense itching and can destroy nearby tissue, such as the eye
● Adult worms live in nodules where the female worms produce high numbers of first-stage larvae known as microfilariae; they migrate from the nodules to the sub-epidermal layer of the skin, where they can be ingested by blackflies (WHO)
● Most infections occur in sub-Saharan Africa, although global effort is reducing incidence (Disease and Mortality in Sub-Saharan Africa, 2nd edition); also occurs in Yemen and isolated areas of Central and South America (Wikipedia)

Treatment
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● Ivermectin throughout entire affected community; single dose may kill first-stage larvae (microfilariae) in infected people and prevents transmission for many months in the remaining population (eMedicine)
● Also doxycycline

Clinical images
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Adult black fly

Micro images
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Microfiliaria and adults

36 year old Ethiopian man with no previous history, and a clinical diagnosis of inclusion cyst / pilomatrixoma of left thigh. This was a subcutaneous mass.

End of Skin-nontumor / Clinical Dermatology > Infestations > Onchocerciasis

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