ONCHOCERCA VOLVULUS Trisha Patel

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

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

ONCHOCERCIASIS Commonly known as river blindness 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

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

DISTRUBUTION MAP

LIFE CYCLE An infected female blackfly takes a blood meal from a host. The hosts skin is stretched by the fly’s apical teeth and cut by its mandible. Onchocerciasis is linked with fast flowing rivers where Simulium blackflies breed.

The smaller male worms may travel through nodules and mate. 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.

Thousands of microfilariae migrate in the subcutaneous tissue. 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.

Microfilariae also can travel to the eye, causing blindness. LIFE CYCLE Microfilariae also can travel to the eye, causing blindness. Some microfilariae die causing skin rashes, lesions, intense itching, or skin depigmentation.

LIFE CYCLE Inside the fly, the larvae travel to the fly’s 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.

OVERVIEW OF LIFE CYCLE

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).

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 doesn’t guarantee onchoceriasis.

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.

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

SOURCES Google Image Search. October 8, 2006. <http://www.google.com/imghp?hl=en&tab=wi&q=>. “Onchocerca volvulus.” September 29, 2006. <http://ucdnema.ucdavis.edu/imagemap/nemmap/Ent156html/nemas/onchocercavolvulus>. “Division of Parasitic Diseases.” Onchocerciasis/River Blindness Fact Sheet. Center Of Disease Control. September 27, 2004. October 8, 2006. <http://www.cdc.gov/ncidod/dpd/parasites/onchocerciasis/factsht_onchocerciasis.htm#think_have>. “Onchocerca volvulus.” Carlo Denegri Foundation. Pietro Caramello, MD. October 8, 2006. <http://www.cdfound.to.it/html/onc1.htm>. “Life-cycle of Onchocerca volvulus.” TDR. October 3, 2006. October 8, 2006. <http://www.who.int/tdr/diseases/oncho/oncho2.htm>. “Onchocerciasis.” Fred Opperdoes. November 28, 2002. October 8, 2006. <http://www.icp.ucl.ac.be/~opperd/parasites/onch1.html>.