Skin nontumor

Deputy Editor-in-Chief: Debra Zynger, M.D.
Priya Nagarajan, M.D., Ph.D.

Topic Completed: 1 May 2018

Minor changes: 28 August 2020

Copyright: 2003-2020,, Inc.

PubMed Search: Onchocerciasis [title] Infestations AND (Humans[Mesh])

Priya Nagarajan, M.D., Ph.D.
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Cite this page: Wang J, Nagarajan P. Onchocerciasis. website. Accessed October 28th, 2020.
Definition / general
  • Chronic dermatitis accompanied by progressive keratitis, uveitis and loss of sight caused by the filarial nematode, Onchocerca volvulus which is transmitted to humans through the bite of a blackfly (simulium species) (WHO: Onchocerciasis (river blindness) - disease information [Accessed 9 April 2018])
  • Larval worms (microfilariae) migrate in the skin and the eye and lead to irreversible blindness and skin diseases
Essential features
  • Caused by the filarial nematode Onchocerca volvulus, through the bite of a blackfly
  • Dying larvae evoke focal inflammation resulting initially in dermal microabscesses followed by granuloma formation
  • Pigmentation and atrophy of skin at advanced stage
  • Treatment is a single dose of ivermectin (150 mcg / kg) every month for 3 - 6 months until patient becomes asymptomatic
  • Also called river blindness
  • 90% in sub-Saharan Africa
  • Also found in Yemen as well as Central and Southern America
  • 37 million people infected worldwide in 2006 (PLoS Med 2006;3:e260)
  • Eye and skin
Clinical features
  • Onchocercal nodules are located close to bony prominences outside the inguinal and cervical regions (Postgrad Med J 2010;86:578 )
  • Acute and chronic onchodermatitis: scattered pruritic papules, vesicles or pustules distributed over the shoulders, waist or buttocks (Int J Dermatol 2004;43:170)
  • In advanced disease, the lesions can be spottily depigmented "leopard skin", scaly and atrophic "lizard skin" or thickened and hyperkeratotic "elephant skin"
  • May also have lymphedema of the groin or "hanging groin" and skin atrophy (Br J Dermatol 1993;129:260)
Case reports
  • 5 year old girl with a subcutaneous nodule on forehead and histopathologic analysis of the nodule revealed the presence of Onchocerca volvulus worm (Pediatr Dev Pathol 2015;18:164)
  • 7 year old girl with a conjunctival nodule (Neth J Med 2015;73:437)
  • 9 year old girl with papular, indurated and itching skin lesions located on the limbs and positive anti-filarial antibodies in serum (Klin Padiatr 2006;218:41)
  • 53 year old man presented with a 4 month history of intense, migratory urticaria (Int J Dermatol 2005;44:125)
  • 60 year old woman developed leopard skin-like changes, rashes and pruritus on the left leg and onchocercal microfilariae were identified by a skin snip (Pan Afr Med J 2015;22:298)
  • Ivermectin (150 mcg / kg) administered orally as a single dose and repeated every 3 to 6 months until the patient is asymptomatic (Lancet 2002;360:203)
Clinical images

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A blackfly (Simulium damnosum)

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Onchocerca volvulus

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Onchocercal nodule

Microscopic (histologic) description
  • At early stage, microfilariae concentrate in the papillary dermis with clusters of inflammatory cells surrounding vessels and adnexa
  • Focal microabscesses and granuloma is evoked by dying larvae
  • At advanced stages, secondary acanthosis, parakeratosis, pigment incontinence and melanophagocytosis appear
  • Worms may be calcified or degenerated with dermal scaring and atrophy
  • Onchocercoma (onchocercal nodule) is a subcutaneous ball of worms embedded in inflammatory granulation tissue
  • In cross - section, onchocerca typically has a cuticle, subjacent thin layer of muscle
  • Within the lumen are paired uteri containing microfilaria (J Am Acad Dermatol 2015;73:947)
Microscopic (histologic) images

Contributed by Eddie Fridman, M.D.
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36 year old Ethiopian man with no previous history and a clinical diagnosis of inclusion cyst / pilomatrixoma of left thigh

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Figs C and D: Microfilariae of Onchocerca volvulus in tissue

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Figs B and D: Adults of Onchocerca volvulus

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Onchocerca volvulus

Differential diagnosis
  • Other helminthic diseases such as:
Board review style question #1
    Which description of Onchocerciasis is not correct?

  1. A chronic dermatitis caused by the filarial nematode, Onchocerca volvulus which is transmitted to humans through the bite of a blackfly (simulium species).
  2. Dying larvae can evoke focal microabscesses followed by granuloma formation.
  3. Skin snips are the gold standard to diagnose Onchocerciasis.
  4. The disease occurs most commonly in South America.
  5. Treatment is a single dose of Ivermectin (150 mcg/kg) every 3 months.
Board review answer #1
D. 90% of the disease occurs in sub-Saharan Africa.

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Reference: Onchocerciasis
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