ONCHOCERCA VOLVULUS

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ONCHOCERCA VOLVULUS

• Trisha Patel

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TAXONOMY

• Kingdom Animalia
• Phylum Nematoda
• Class Secernentea
• Order Spirurida
• Family Filariidae
• Genus Onchocerca
• Species O. volvulus

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ONCHOCERCA VOLVOLUS

• A helminthes worm
• The male is usually 2-3 cm long the female is
  usually 50 cm long
• Adults occur in the subcutaneous tissue and in
  nodules
• Microfilaria are usually 300 X 8 micrometers long
• An adult female worm can produce over 1000
  microfilariae in a day, resulting in millions
  over a lifetime
• Adult worms have a life span of 10-15 years
• Lips and a buccal capsule are absent

Adult O. volvolus
Microfilaria
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ONCHOCERCIASIS

• Commonly known as river blindness
• The worlds 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

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DISTRIBUTION

• 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)
• Predominantly located in rural agricultural
  villages located near rapidly flowing streams

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DISTRUBUTION MAP
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LIFE CYCLE
An infected female blackfly takes a blood meal
from a host. The hosts skin is stretched by the
flys apical teeth and cut by its mandible.
Onchocerciasis is linked with fast flowing rivers
where Simulium blackflies breed.
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LIFE CYCLE
The smaller male worms may travel through nodules
and mate.
The third stage larvae enter subcutaneous tissue,
migrate, form and lodge in nodules, and slowly
mature into adult worms. New worms form new
nodules or find existing nodules and cluster
together.
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LIFE CYCLE
Thousands of microfilariae migrate in the
subcutaneous tissue.
After mating, eggs form inside the female worm,
develop into microfilariae and leave the worm one
by one.
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LIFE CYCLE
Microfilariae also can travel to the eye, causing
blindness.
Some microfilariae die causing skin rashes,
lesions, intense itching, or skin depigmentation.
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LIFE CYCLE
Inside the fly, the larvae travel to the flys
thoracic muscles and develop into a third stage
larvae. The cycle begins again
The infected host is bitten by another female
fly. Microfilariae are transferred from the host
to the blackfly, where they develop into
infective larvae.
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OVERVIEW OF LIFE CYCLE
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ONCHOCERCIASIS

• The intensity of human infection (number of worms
  in an individual) is related to the number of
  infectious bites endured by an individual.
• Blindness is almost always in persons with
  intense infection.
• An individual may be asymptomatic. Those with
  symptoms usually experience nodules, skin rashes,
  eye lesions, bumps under the skin. The eye
  lesions can manifest into blindness.
• Incubation periods last from nine to 24 months
  after the initial bite.
• The hosts white blood cells usually release
  cytokines that effect the infected tissue and
  thus killing the microfilariae, which causes
  lizard skin (swelling and thickening of skin)
  and leopard skin (loss of pigment).

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DIAGNOSIS

• The most common is fresh examination of
  blood-free skin snips however, this does not
  always show the presence of the parasite.
• Serologic testing for antibodies is available
  however, a positive result doesnt guarantee
  onchoceriasis.

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TREATMENT

• Ivermectin (mectizan) is administered as an oral
  dose of 150 micrograms per kilogram (maximum 12
  mg) every 6-12 months.
• The drug paralyses the microfilariae and prevents
  them from causing itching.
• Ivermectin does not kill the adult worm it does
  prevent them from producing additional offspring.
  
• Surgical removal of the nodules is also
  available.
• There is no vaccine.

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FURTHER PREVENTION

• Avoiding the day when the Simulium blackflies
  tend to bite
• Using insecticides such as DEET
• Wearing long sleeves and pants

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SOURCES

• Google Image Search. October 8, 2006.
  lthttp//www.google.com/imghp?hlentabwiqgt.
• Onchocerca volvulus. September 29, 2006.
  lthttp//ucdnema.ucdavis.edu/imagemap/nemmap/Ent156
  html/nemas/onchocercavolvulusgt.
• Division of Parasitic Diseases.
  Onchocerciasis/River Blindness Fact Sheet.
  Center Of Disease Control. September 27, 2004.
  October 8, 2006. lthttp//www.cdc.gov/ncidod/dpd/p
  arasites/onchocerciasis/factsht_onchocerciasis.htm
  think_havegt.
• Onchocerca volvulus. Carlo Denegri Foundation.
  Pietro Caramello, MD. October 8, 2006.
  lthttp//www.cdfound.to.it/html/onc1.htmgt.
• Life-cycle of Onchocerca volvulus. TDR.
  October 3, 2006. October 8, 2006.
  lthttp//www.who.int/tdr/diseases/oncho/oncho2.htmgt
  .
• Onchocerciasis. Fred Opperdoes. November 28,
  2002. October 8, 2006. lthttp//www.icp.ucl.ac.be
  /opperd/parasites/onch1.htmlgt.