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?
A skin and eye disease caused by onchocerca volvulus. (Blanks et al. 1999) Affects about 17.7 million people (WHO)
Figure 1: patient suffering from Onchocerciasis (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 – 15 years (adults worms) Figure 2: Image of Onchocerciasis 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. volvulus microfilariae
1875 – O’Neill associated the microfilariae of O. volvulus with an irritating dermatitis called “craw craw” in Ghana.
1916 – Development of medicinal drug Suramin by Oskar Dressel.
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 black fly. Black flies breed near fast flowing waters. Figure 4: An adult blackfly (Simulium damnosum) Animal reservoirs have not been found. taking a bloodmeal on human 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 worm produces thousands of larval worms death of microfilariae is toxic Years of exposure may cause blindness and skin disfiguration. Figure 7: Image of a patient with leopard skin
…continued
Ocular symptoms caused by wolbachia antigens
Can also cause inflammation of lymph glands.
Figure 8: ocular lesions in a patient with onchocerciasis blinded from sclerosing keratitis.
Diagnosis
Palpating Skin snips Slit lamp exam PCR ..diagnosis
Figure 9 : palpating Figure 10: skin snip
..diagnosis
Figure 11: slit lamp exam Figure 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 foci of 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