Onchocerciasis
Epidemiology and Etiology:
- Onchocerca volvulus
- transmitted by
blackflies
- Endemic areas:
- Africa
- South America
- Yemen
- Second most common
preventable cause of blindness in sub-Saharan Africa
- Lifecycle:
- Adult parasites
mate in the dermis
- Large numbers of
microfilariae released by females
- Accumulate in the
skin and eye chambers
- Wolbachia are a symbiotic bacteria required
for worm fertility
Common sites:
Gross features:
- dermal nodule
(onchocercoma)
- chronic, itchy
dermatitis with focal darkening or loss of pigment and scaling
- leopard, lizard,
or elephant skin
- areas of epidermal
atrophy and elastic fiber breakdown
- punctate keratitis
- small, fluffy
opacities of the cornea
- leads to a
sclerosing keratitis that opacifies the cornea beginning at the scleral
limbus
Histologic features:
- areas of epidermal
atrophy
- pigment
incontinence
- fibrosis
- onchocercoma:
- fibrous capsule
surrounding adult worms
- mixed chronic
inflammatory infiltrate:
- fibrin,
neutrophils, eosinophils, lymphocytes, giant cells
- punctate keratitis
- eosinophilic
infiltrate surrounding degenerating microfilariae
Immunophenotype:
Marker:
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Sensitivity:
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Specificity:
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Molecular features:
Other features:
- clinical
features:
- blindness
- chronic pruritic
dermatitis
References: