Onchocerciasis
George R. Collins, DO
Joseph Susa, DO
Clay J. Cockerell, MD
Key Facts
Etiology/Pathogenesis
-
Caused by filarial nematode Onchocerca volvulus
-
Transmitted to humans via bite of black fly of genus Simulium found near free-flowing waterways
Clinical Issues
-
Early pruritus and urticaria of face and trunk
-
Papulovesicles, plaques, nodules, maculopapular rash
-
Small, closely packed or large, widely separated lesions occur anywhere and any time after infection
Microscopic Pathology
-
Lymphohistiocytic inflammation with eosinophils and histiocytes surrounding microfilariae in dermis
-
Microfilariae can occur in absence of inflammation and may be seen in lymphatic spaces
-
Microfilariae vary in length from 220-360 µm and have finely tapered tail
-
Onchocercoma: Bundle of adult worms encased by lymphohistiocytic inflammation and fibrosis
Numerous hyperpigmented papules  , lichenified plaques  , and nodules  are seen here diffusely involving the lower leg of a patient who recently returned from Africa. |
A large unilateral right inguinal mass, composed of enlarged lymph nodes, hernia, and worm(s), involves folds of inelastic, atrophic skin in the area and results in the “hanging groin” sign. |
TERMINOLOGY
Synonyms
-
“River blindness”
Definitions
-
Chronic systemic filarial infection most commonly involving skin and eyes
ETIOLOGY/PATHOGENESIS
Infectious Agents
-
Caused by filarial nematode Onchocerca volvulus
-
Lifecycle
-
Transmitted to humans via bite of Simulium black fly, found near free-flowing waterways
-
Bite results in microfilariae entering skin and developing into adult worms in subdermal connective tissues
-
CLINICAL ISSUES
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
