Onchocerciasis (River Blindness) Deepika Sundararaj March 20, 2012

River blindness is caused by a nematode parasite: Onchocerca volvulus Onchocerciasis is a parasitical disease caused by the filarial worm Onchocerca volvulus. Only when explorers entered these regions was the disease recognized for the first time. The diseased people were observed to experience blindness of unknown cause as well as scaly, itchy, nodular skin, which was known as kru kru or craw craw in West Africa. First visual identification of the worm was in 1874 by Dr. John O’Neill in Ghana.

It is predominately found in Africa, the Arabian Peninsula, and in Latin America. Endemic in 36 countries across Africa, Latin America and Yemen, and these areas usually coincide with the path of rivers and streams. About 85.5 million people live in endemic areas and 50% of these reside in Nigeria. Currently affects over 18 million people, and 99% of all those live in Africa. The disease exists in isolated foci in Latin America (6 countries)

The parasites are transmitted by the black fly Simulium: black fly or buffalo gnat Found near rivers and streams because larval stages require fast-flowing and aerated water for development. Species of fly depends on the area. Flies tend to bite the upper body in the Americas and lower body in Africa (different nodule distribution). Deforestation has changed the habitats of the flies. Need hundreds of bites in order to develop onchocerciasis

Life cycle involves six main stages A Simulium female black fly takes a blood meal on an infected human host, and ingests microfilaria. The microfilaria enter the gut and thoracic flight muscles of the black fly, progressing into the first larval stage (J1.). The larvae mature into the second larval stage (J2.), and move to the proboscis and into the saliva in its third larval stage (J3.). Maturation takes about 7 days. The black fly takes another blood meal, passing the larvae into the next human host’s blood. The larvae migrate to the subcutaneous tissue and undergo two more molts. They form nodules as they mature into adult worms over six to twelve months. After maturing, adult male worms mate with female worms in the subcutaneous tissue to produce between 700 and 1,500 microfilaria per day. The microfilaria migrate to the skin during the day, and the black flies only feed in the day, so the parasite is in a prime position for the female fly to ingest it. Black flies take blood meals to ingest these microfilaria to restart the cycle.

Symptoms are caused by the inflammatory response to dying microfilaria The normal microfilariae lifespan is 1–2 years; however, their presence in the bloodstream causes little or no immune response until death or degradation of the microfilariae or adult worms.

Symptoms are caused by the inflammatory response to dying microfilaria The normal microfilariae lifespan is 1–2 years; however, their presence in the bloodstream causes little or no immune response until death or degradation of the microfilariae or adult worms.

Symptoms are caused by the inflammatory response to dying microfilaria The normal microfilariae lifespan is 1–2 years; however, their presence in the bloodstream causes little or no immune response until death or degradation of the microfilariae or adult worms.

Symptoms are caused by the inflammatory response to dying microfilaria The normal microfilariae lifespan is 1–2 years; however, their presence in the bloodstream causes little or no immune response until death or degradation of the microfilariae or adult worms.

Only 5% of the cases experience ocular symptoms

At present, there aren’t any early diagnoses that are 100% reliable Palpating Skin snips Mazzotti Test DEC Patch Test Slit Lamp Exam – ocular infection Nodulectomy ELISA Alternative: Rapid-Format Antibody card tests PCR – expensive, less invasive

Ivermectin has been the miracle drug since 1987 Provided free of charge by Merck & Co. since 1988 Ivermectin: selectively targets invertebrate nerve and muscle cells Found in 1987 by Merck Only kills microfilaria Drug resistance 1-5% experience severe adverse side effects

New studies show many of the symptoms are caused by endosymbiont, Wolbachia Mutualistic relationship with O. volvulus Transmitted vertically like mitochondria Linked to female fertility Stimulate inflammatory response to microflaria Release cytokines to recruit neutrophils New evidence also indicates that doxycycline treatment for 6 weeks can make the female worms sterile for up to two years and thus unable to produce L1 microfilariae (Smith et al. 2006). Tetracycline antibiotics for Wolbachia Limits bacteria-induced immunopathology Sterilization of female worms Reduced Ivermectin side effects Administrative difficulties

Public health initiatives were launched to stop the spread of Onchocerciasis OCP was launched in 1975 and discontinued in 2002.

OEPA and APOC provide resources for local self-sustaining programs

Works Cited Smith, D. S., D. Goverman, and J. Bass. 2006. Onchocerciasis. http://www.stanford.edu/class/humbio103/ParaSites2006/Onchocerciasis/ Andre, A. S., N. M. Blackwell, L. R. Hall, A. Hoerauf, N. W. Brattig, L. Volkmann, M. J. Taylor, L. Ford, A. G. Hise, J. H. Lass, E. Diaconu, amd E. Pearlman. 2002. The role of endosymbiotic Wolbachia bacteria in the pathogenesis of river blindness. Science 295(5561):1892-1895. Eezzuduemhoi, D., and D. Wilson. 2005. Onchocerciasis. Sinha,S., R. A. Schwartz, R. Kapila, and M. A. Forgione, Jr. 2006. Onchocerciasis. http://emedicine.medscape.com/article/224309-overview Strategic Direction for Research. Feb. 2002. WHO: Tropical Disease Research. < http://www.who.int/tdr/diseases/oncho/direction.htm> Onchocerciasis Disease Information. 1992. WHO: Tropical Disease Research. <http://www.who.int/tdr/diseases/oncho/diseaseinfo.htm>. "Distribution of Onchocerciasis " Map. 1995. Mectizon Donation Program . http://www.mectizan.org/maps.asp African Program for Onchocerciasis Control. 2006. World Health Organization. << http://www.who.int/blindness/partnerships/APOC/en/index.html>> Onchocerciasis Elimination Program for the Americas. 2006. World Health Organization. <<http://www.who.int/blindness/partnerships/onchocerciasis_oepa/en/index.html>> Impact of long-term treatment of onchocerciasis with ivermectin in Kaduna State, Nigeria: first evidence in the operational area of the African Programme for Onchocerciasis Control, February 2012. Authored by: Afework H Tekle, Elizabeth Elhassan, Sunday Isiyaku, Uche V. Amazigo, Simon Bush, Mounkaila Noma, Simon Cousens, Adenike Abiose and Jan H. Remme http://www.parasitesandvectors.com/content/5/1/28/abstract Onchocerciasis Treatment Figures. 2006. WHO: Prevention of Blindness and Visual Impairment. <http://www.who.int/blindness/partnerships/onchocerciasis_treatment/en/index.html>