Skin nontumor



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

Last author update: 1 May 2018
Last staff update: 19 July 2021

Copyright: 2003-2023,, Inc.

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

Priya Nagarajan, M.D., Ph.D.
Page views in 2022: 1,328
Page views in 2023 to date: 1,234
Cite this page: Wang J, Nagarajan P. Onchocerciasis. website. Accessed September 28th, 2023.
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

Images hosted on other servers:

Blackfly (Simulium damnosum)

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.
Missing Image Missing Image Missing Image Missing Image

36 year old Ethiopian man with no previous history and a clinical diagnosis of inclusion cyst / pilomatrixoma of left thigh

Images hosted on other servers:
Missing Image Missing Image

Figs C and D: Microfilariae of Onchocerca volvulus in tissue

Missing Image Missing Image

Figs B and D: Adults of 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 style answer #1
D. 90% of the disease occurs in sub-Saharan Africa.

Comment Here

Reference: Onchocerciasis
Back to top
Image 01 Image 02