Onchocerca volvulus


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Biology Dept. / Parasitology Seminar

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Onchocerca volvulus

  1. 1. By Peshawa Yasin
  2. 2. 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.
  3. 3.  Kingdom: Animalia  Phylum: Nematoda  Class: Secernentea  Order: Spirurida  Family:Onchocercidae  Genus: Onchocerca  Species: O. volvulus
  4. 4. Black Fly Humans  Is a major vector of  Are the only natural Onchocerca volvulus definitive host for in Africa. O. volvulus.
  5. 5. MexicoSaudi Arabia Guatemala Venezuela
  6. 6. 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.
  7. 7. 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 19-42cm long.  33.5-50cm long. 130-210µm wide.  270-400µm wide. Posterior end is curled ventrally.  Genital organ right behind the posterior Microfilariae are unsheathed. end of the esophagus.
  8. 8. Onchocerciasis is transmitted person toperson through the bites of Simulium black fly vectors. 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
  9. 9. Path  The adult worms and the microfilariae contribute to the pathogenesis ofo onchocerciasis.ge  Adults are the least pathogenic, mostlyn causing subcutaneous nodules callede onchocercomas.sis
  10. 10.  Adults are the least pathogenic and usually cause no symptoms, but sometimes they A cause the growth of subcutaneous nodules called onchocercomas. d These nodules cause disfigurement and a u person may have 1-over 100. l Loss of skin elasticity causes the Hanging groin which is known as a true t elephantiasis. s
  11. 11. Mi  Live microfilariae have little inflammatoryc response but the degenerating juveniles in ther skin cause a severe dermatitis.of  The first dermatitis symptom is intensei itching, secondary bacterial infection,l abnormal pigmentation of the skin.ar  Next thickening, discoloration, and crackingi of the skin called lichenification.ae
  12. 12. Elephantiasis
  13. 13. 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.
  14. 14.  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.
  15. 15.  Insecticides. Vector Control. Chemotherapy.  Has prevented 125,000-200,000 people from going blind, and 30 million from ocular and skin lesions.
  16. 16. 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.htm http://www.uniteforsight.org/course/riverblindness.php