Onchocerca volvulus is a filarial worm that causes onchocerciasis, also known as river blindness. It has a life cycle involving microfilariae that infect blackflies which transmit the larval forms to humans. The microfilariae develop into adult worms in human subcutaneous tissue, producing more microfilariae that can cause skin disease and blindness. Onchocerciasis is treated and prevented through ivermectin treatment programs and avoiding blackfly bites in endemic regions, mainly in rural Africa and some parts of Central and South America.

1. Onchocerca volvulus
GROUP 7
Musah Mohammed (PS/LBT/13/0027)
Macben Denchie (PS/LBT/13/0018)
Ebenezer Tetteh (PS/LBT/13/0008)

2. TABLE OF CONTENTS
 TAXONOMY
 MORPHOLOGY
 EPIDEMIOLOGY AND GEOGRAPHICAL
DISTRIBUTION
 LIFE CYCLE
 CLINICAL MANIFESTATION
 DIAGNOSIS
 TREATMENT
 PREVENTION
 SOURCES

3. TAXONOMY
Kingdom: Animalia
Phylum: Nematoda
Class: Secernentea
Order: Spirurida
Family: Filariidae
Genus: Onchocerca
Species: volvulus

4. MORPHOLOGY
 Onchocerca volvulus is a filarial worm that
causes onchocerciasis
 Has a five-stage life cycle; 4 larval stages
and an adult stage
 Microfilaria are usually 300 X 8
micrometers long
 Adult male is usually 2-3 cm long; the
female is usually 50 cm long
 Adults occur in the subcutaneous tissue and
in nodules
 An adult female worm can produce over
1000 microfilariae in a day
 Adult worms have a life span of 10-15 years
Adult O. volvolus
Microfilaria

5. EPIDEMIOLOGY AND
GEOGRAPHICAL DISTRIBUTION
 Commonly known as river blindness
 Transmitted by blackflies of the Similium species flies breed in fast-
flowing streams and rivers
 The world’s second leading infectious cause of blindness. The World
Health Organization's (WHO) estimates the global prevalence is 17.7
million, of whom about 270,000 are blind

6.  Predominantly located in rural agricultural villages located
near rapidly flowing streams
 Tropical Africa between the 15° north and the 13° south (high
endemicity in Burkina Faso and Ghana)
 Foci are present in Southern Arabia, Yemen and in America
(Mexico, Guatemala, Colombia, Ecuador, Brazil, Venezuela)
 In Ghana Onchocerciasis has an estimated at risk population
of 3,400,000 in 3204 communities in 66 endemic districts in
nine out of ten regions. Greater Accra Region the only region
that is not endemic for Onchocerciasis.
CONTINUATION

7. DISTRUBUTION MAP

8. LIFE CYCLE
 Similium fly ingest microfilariae during feeds
 Microfilariae undergoes development in the fly
 Development in the fly takes about 15 days
 Larval forms are transmitted to humans during feeds
 The larva migrates to the subcutaneous tissue of the new host

9.  They mature into adult worms over six to twelve months
 Mature adult worms mate in the subcutaneous tissue
producing microfilaria
 Microfilaria migrate to the skin where they are fed on by the
Similium flies
 The cycle then starts again
CONTINUATION

10. OVERVIEW OF LIFE CYCLE

11. CLINICAL MANIFESTATION
Intense itching
Depigmentation of the skin
Elephant skin
Blindness

12. DIAGNOSIS
 Skin snip
 Slit-lamp examination of the anterior part of the eye
 Surgical removal and examination of nodules
 Serological test

13. TREATMENT
 Ivermectin (mectizan) is administered as an oral dose of 150
micrograms per kilogram (maximum 12 mg) every 6-12
months.
 Surgical removal of the nodules is also available.

14. PREVENTION
 Avoiding the day when the Simulium blackflies tend
to bite
 Using insecticides such as DEET
 Wearing long sleeves and pants

15. SOURCES
Centers for Disease Control and Prevention. (2011). Onchocerciasis: Prevention and
Control. http://www.cdc.gov/parasites/onchocerciasis/prevention.html
Levine, R. (2007). Controlling Onchocerciasis (River Blindness) in Sub-Saharan Africa. In
Series Editor: Richard Riegelman. Case Studies in Global Health: Millions saved, 49-56.
Sudbury, Massachusetts: Jones and Bartlett.
Lucas, A., & Gills, H. (1990). A new short textbook of preventive medicine for the tropics.
(3rd ed.). Kent, UK: Edward Arnold
World Health Organization. (2011). Onchocerciasis disease information: Prevention of
Blindness and visual impairment.
fromhttp://www.who.int/blindness/partnerships/onchocerciasis_disease_information/en
/index.html
www.moh-ghana.org/