Onchocerca volvulus – “River blindness” – Onchocercasis

o   Geog. Distribution -Endemic in tropical rainforest of Africa, south & Central America

o   Affecting

·        40 million people d world-wide

·        2 million people are blind due to the disease

o   Infection is commonly found near rivers and streams where the black flies (the vector for the disease) prefer fast running streams for breading.

Ø  Because of its association with river and because of the blindness it causes it’s known       as “River blindness”

v Habitat

·        Adults- Subcutaneous nodules and in skin

·        Mf- skin, eye, and other organs of the body.

·        Infective larval – in the gut, mouth parts and muscles of the genus Simulium (black fly)

v Morphology

·        Adults – curved and bulbous tail

·        Mf – has – no sheath and head end is slightly enlarged.

·        Anterior Nuclei – are positioned side by side.

·        No nuclei at the end of tail which is long and pointed.

v Pathology and clinical features

·        The Pathologic changes are due to microfilaria.

·        The subcutaneous nodules containing the adult worm cause little pathology.

o   Two forms of disease.

    1.     Ocular lesion

·        Nodular and erythematosus lesions in the skin, subcutaneous tissue, and eye

·        Ocular involvement consists of trapped microfilaria in;

·        The cornea, choroids, iris, and

·        Anterior chambers of eye – photophobia- lacrimation and blindness.  

     2. Dermatitis /skin disease

Ø  Elephant skin

Ø  Hanging groin- When the skin around groin become affected

v Laboratory diagnosis

·        Microscopy - Skin examination (‘Onchocerca nodule’)  wet smear with normal saline,Skin biopsy

·        Eye examination

·        Immunodiagnostic

v  Prevention and control

·        Destruction of Simulium – insecticide,

·        Avoid Simulium bite

Treatment of community