Biology Dept. / Parasitology Seminar

1. By Peshawa Yasin

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

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

5. Mexico
Saudi
Arabia
Guatemala
Venezuela

8. 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.

9. 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.

11. Onchocerciasis is transmitted person to
person 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

15. P
a
t
h  The adult worms and the microfilariae
contribute to the pathogenesis of
o
onchocerciasis.
g
e  Adults are the least pathogenic, mostly
n causing subcutaneous nodules called
e onchocercomas.
s
i
s

16.  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

18. M
i  Live microfilariae have little inflammatory
c response but the degenerating juveniles in the
r skin cause a severe dermatitis.
o
f  The first dermatitis symptom is intense
i itching, secondary bacterial infection,
l abnormal pigmentation of the skin.
a
r  Next thickening, discoloration, and cracking
i of the skin called lichenification.
a
e

19. Elephantiasis

20. 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.

22.  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.

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

24. 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