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For further information, see CMDT Part 35-33: Onchocerciasis
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Essentials of Diagnosis
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Conjunctivitis progressing to blindness
Severe pruritus; skin excoriations, thickening, and depigmentation; and subcutaneous nodules
Microfilariae in skin snips and on slit-lamp examination; adult worms in subcutaneous nodules
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General Considerations
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Caused by Onchocerca volvulus
Infection transmitted by simulium flies (blackflies), which breed in fast-flowing streams and bite during the day
After the bite of an infected blackfly, larvae are deposited in skin, where adult worms develop over 6–12 months
Adult worms live in subcutaneous connective tissue or muscle nodules for a decade or more
Microfilariae are released from nodules and migrate through subcutaneous and ocular tissues
Disease is due to responses to worms and to intracellular Wolbachia bacteria
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An estimated 37 million persons are infected, of whom
Over 99% of infections are in sub-Saharan Africa, especially the West African savanna
Half of the cases are in Nigeria and Congo
In hyperendemic African villages,
Disease also prevalent in
Southwestern Arabian peninsula
Latin America (eg, Mexico, Guatemala, Venezuela, Colombia, Ecuador, Northwestern Brazil)
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Incubation period of up to 1–3 years
Inguinal and femoral lymphadenopathy
Systemic symptoms include weight loss and musculoskeletal pain
Skin
Erythematous, papular, pruritic rash, which may progress to chronic skin thickening and depigmentation
Itching may be severe and unresponsive to medications
Numerous firm, nontender, movable subcutaneous nodules of about 0.5–3 cm contain adult worms
Eye
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Differential Diagnosis
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Diagnostic Procedures
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Diagnosis is made by identifying microfilariae in
Skin snips stand in saline for 2–4 h or longer before examination
Identifying adult worms in biopsy or aspirate of a nodule also confirms diagnosis
Deep punch biopsies not needed
The Mazzotti test uses 50 mg of diethylcarbamazine