Onchocerciasis (River blindness) By: Mansi Shah Outline Taxonomy Etiology History Transmission Treatment & Prevention Current efforts Taxonomy * Phylum: Nematoda Class: Secernentea Order: Spirurida Superfamily: Filarioidea Family: Onchocercidae Genus: Onchocerca Species: O. volvulus
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Onchocerciasis(River blindness)By: Mansi Shah
Outline
Taxonomy Etiology History Transmission Treatment & Prevention Current efforts
Taxonomy* Phylum: Nematoda Class: Secernentea Order: Spirurida Superfamily: Filarioidea Family: Onchocercidae Genus: Onchocerca Species: O. volvulus
What is Onchocerciasis?
Figure 1: patient suffering fromOnchocerciasis (WHO)
A skin and eye diseasecaused by onchocercavolvulus. (Blanks et al.1999)
Affects about 17.7 millionpeople (WHO)
About O. volvulus
Helminthic worm Male: 2-3 cm long Female: 60 cm long Adults found in
subcutaneous tissues &nodules of host
Longevity of 10 – 15years (adults worms)
Figure 2: Image ofOnchocerciasis volvulus(adult worms)
Distribution
Figure 3: Distribution of Onchocerciasis
History
One of the leading causes of blindness due to infection.
1874 – John O’Neill, discovered presence of O. volvulusmicrofilariae
1875 – O’Neill associated the microfilariae of O. volvuluswith an irritating dermatitis called “craw craw” in Ghana.
1916 – Development of medicinal drug Suramin by OskarDressel.
1987 – Merck Mectizan Donation Program established.
Vector & transmission Vector is from genus
Simulium (black fly). Main vector is Simulium
damnosum in most of Africa O. volvulus is transmitted by
the bite of an infected blackfly.
Black flies breed near fastflowing waters.
Animal reservoirs have notbeen found.
Figure 4: An adult blackfly(Simulium damnosum)taking a bloodmeal onhuman skin.
About the black fly..
Female adults are known as buffalo gnats
The immature eggs are aquatic
The life cycle includes 4 stages.
Life cycle of the black fly
Figure 5: Stages of the black fly
Life cycle of O. volvulus
Figure 6: Transmission of O. volvulus larvae
Symptoms & affects
Appear after L3 stage Usually appear 9 months – 2 years after initial
infecting bite. Serious visual impairment Nodule formation Skin rashes, leisions, intense itching Chronic infection may lead to lichenification.
…continued
Adult female wormproduces thousands oflarval worms
death of microfilariae istoxic
Years of exposure maycause blindness andskin disfiguration.
Figure 7: Image of a patientwith leopard skin
…continued
Figure 8: ocular lesions in a patient withonchocerciasis blinded from sclerosingkeratitis.
Ocular symptomscaused by wolbachiaantigens
Can also causeinflammation of lymphglands.
Diagnosis
Palpating Skin snips Slit lamp exam PCR
..diagnosis
Figure 9 : palpating Figure 10: skin snip
..diagnosis
Figure 11: slit lamp examFigure 12: nodules
Treatment
Goal is to eliminate microfilarial stage of disease Suramin – only drug in clinical use that is effective
against worms of onchocerciasis. Ivermectin – considered to be drug of choice,
introduced in 1982 doxycycline
No vaccine available.
Control efforts
OCP – Onchocerciasis Control Program APOC – African Program for Onchocerciasis
Control OCPA - Onchocerciasis Control Program of
the Americas Merck Mectizan Donation Program Practical strategies (insect repellent etc.)
Conclusion
Taxonomy Etiology history Transmission Treatment Prevention and current efforts
Works cited World Health Organization. Onchocerciasis (river blindness). Wkly Epidemiol
Rec. Jul 6 2001;76(27):205-10. Dimomfu BL, Lubeji DK, Noma M, Sékétéli A, Boussinesq M. African
Programme for Onchocerciasis Control (APOC): sociological study in three fociof central Africa before the implementation of treatments with ivermectin(Mectizan). Trans R Soc Trop Med Hyg. Jul 2007;101(7):674-9.
"Image #9703894" TDR Image Library. 1997. WHO: Tropical Disease Research.22 May 2006.http://www9.who.int/tropical_diseases/databases/imagelib.pl?imageid=9703894
http://www.merck.com/mmhe/sec17/ch196/ch196m.html Burnham G. Onchocerciasis. Lancet. May 2 1998;351(9112):1341-6. Udall DN. Recent updates on onchocerciasis: diagnosis and treatment. Clin
Infect Dis. Jan 1 2007;44(1):53-60. http://www.sabin.org/digital-library/fact-sheets/onchocerciasis Okulicz, Jason F. "Onchocerciasis (River Blindness)." eMedicine. 14 July 2005.
18 May 2006 <.http://www.emedicine.com/derm/topic637.htm#section~clinical>. http://emedicine.medscape.com/article/1204593-overview http://www.dpd.cdc.gov/dpdx/images/ParasiteImages/A-
F/Filariasis/O_volvulus_LifeCycle.gif
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