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.
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
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
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/
Notas del editor
Picture of Onchocerca volvulus.
blackfly
This diagram shows the full lifecycle of Onchocerca volvulus
I hope you found the presentation useful, and thank you all very much for attending and listening to me
