onchocerca volvulus

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Onchocerca volvulus River Blindness:

Onchocerca volvulus River Blindness


Overview Onchocerca volvulus : is a large worm that inhabits the lymphatic and subcutaneous tissues. Onchocerca volvulus causes a disease known as Onchocerciasis, but is more commonly known as River blindness. Causes disfigurement and blindness.


Classification Kingdom: Animalia Phylum: Nematoda Class: Secernentea Order : Spirurida Family : Onchocercidae Genus : Onchocerca Species : O.volvulus

Origin and Hosts:

Origin and Hosts Black Fly Humans Is a major vector of Onchocerca volvulus in Africa. Are the only natural definitive host for O. volvulus.

Geographical Location:

Geographical Location Africa Saudi Arabia Guatemala Mexico Venezuela Columbia

Geographical Location:

Geographical Location

Geographical Location:

Geographical Location

PowerPoint Presentation:

Microfilariae ( microscopic larvae ) are found in the subcutaneous tissue . Subcutaneous layer/tissue: This is the third of three layers. It contains fat, connective tissue, and houses larger blood vessels and nerves. It plays an important role in regulating the temperature of the skin and body.


Morphology 19-42cm long. 130-210µm wide. Posterior end is curled ventrally. Microfilariae are unsheathed. 33.5-50cm long. 270-400µm wide. Genital organ right behind the posterior end of the esophagus. These worms are usually found knotted together in pairs or groups in subcutaneous tissues. They are slender and blunt at both ends. They have two circles of four papillae each surround the mouth, and the lips and buccal capsule are absent. The esophagus is not conspicuously divided . Male Female

Adult O. volvulus worms (arrows) seen in a skin nodule.:

Adult O. volvulus worms (arrows) seen in a skin nodule. Microfilariae , a pre-larval form of O. volvulus in a skin nodule.

Life Cycle Overview:

Life Cycle Overview The black flies breed in fast flowing water and streams. When a Black fly bites an infected person, microfilariae are transferred from the person to the fly. Between 1-3 weeks the microfilariae develop in the fly and become infective larvae. These are passed to the human host and the larvae migrate to subcutaneous tissue, form nodules and slowly mature into adult worms Onchocerciasis is transmitted person to person through the bites of Simulium black fly vectors.


Pathogenesis The adult worms and the microfilariae contribute to the pathogenesis of onchocerciasis. Adults are the least pathogenic, mostly causing subcutaneous nodules called onchocercomas.


Adults Adults are the least pathogenic and usually cause no symptoms, but sometimes they cause the growth of subcutaneous nodules called onchocercomas . These nodules cause disfigurement and a person may have 1-over 100. Loss of skin elasticity causes the Hanging groin which is known as a true elephantiasis.

Microfilariae :

Microfilariae Live microfilariae have little inflammatory response but the degenerating juveniles in the skin cause a severe dermatitis. The first dermatitis symptom is intense itching, secondary bacterial infection, abnormal pigmentation of the skin. Next thickening, discoloration, and cracking of the skin called lichenification.

Eye Lesions:

Eye Lesions The worst complication of onchocerciasis involve the eyes. Eye lesions may take years to develop, but in Central America it develops early because of the worms concentrated in the head. Live microfilariae find the eye and do little, but when they die is the problem. The death causes the Wolbachia bacteria, and that causes a huge inflammatory and immune reaction. This causes the most important reason of blindness, which is sclerosing (scarring) keratitis, a hardening inflammation of the cornea.

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Eye Lesions

Diagnosis and Treatment:

Diagnosis and Treatment The best method for diagnosis is finding microfilariae in bloodless skin snips. A small piece of skin is raise with a needle and clipped with a razor or scissors.


Prevention Insecticides. Vector Control. Chemotherapy. Has prevented 125,000-200,000 people from going blind, and 30 million from ocular and skin lesions.


Book : Roberts, Larry S. and Jr. John Janovy . Foundations of Parasitology . 8 th Edition. November 30 th , 2008. Website: http://www.dpd.cdc.gov/dpdx/HTML/Filariasis.htm http://www.uniteforsight.org/course/riverblindness.php References:

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