onchocerca volvulus
DESCRIPTION
Biology Dept. / Parasitology SeminarTRANSCRIPT
By Peshawa Yasin
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.
Kingdom: Animalia
Phylum: Nematoda
Class: Secernentea
Order: Spirurida
Family: Onchocercidae
Genus: Onchocerca
Species: O. volvulus
Black Fly
Is a major vector of
Onchocerca volvulus
in Africa.
Are the only natural
definitive host for
O. volvulus.
Humans
SaudiArabia
Guatemala
Mexico
Venezuela
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.
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
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.
The adult worms and the microfilariae contribute to the pathogenesis of onchocerciasis.
Adults are the least pathogenic, mostly causing subcutaneous nodules called onchocercomas.
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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.
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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.
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Elephantiasis
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.
Eye Lesions
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.
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. 8th Edition. November 30th, 2008.
Website:http://www.dpd.cdc.gov/dpdx/HTML/Filariasis.htmhttp://www.uniteforsight.org/course/riverblindness.php