Medscape is available in 5 Language Editions – Choose your Edition here.


Ophthalmologic Manifestations of Onchocerciasis

  • Author: Debora E Garcia-Zalisnak, MD; Chief Editor: Hampton Roy, Sr, MD  more...
Updated: Oct 16, 2014


Onchocerciasis, commonly known as river blindness, is a vector-borne disease that affects millions of people in Africa, the Middle East, and South and Central America. This disease is caused by the filarial parasitic nematode Onchocerca volvulus, which is transmitted by the blackfly vector Simulium, which carries third-stage larvae.

Infection can lead to chronic skin disease, severe itching, and eye lesions that can progress to complete blindness. There are approximately 123 million people at risk for infection in 38 countries and at least 25.7 million people infected. Of infected persons, 1 million are blind or have severe visual impairments.[1]

Advances in prevention and treatment have decreased the prevalence of this disease in localized areas of Africa and Latin America. Most cases are found in Africa, south of the Sahara, in a wide zone that lies along the fifteenth parallel from Senegal to Ethiopia.

Multiple organizations have created programs whose goal is to prevent and treat onchocerciasis. These include the Onchocerciasis Control Programme (OCP) in West Africa, a program created by the World Health Organization (WHO) that lasted for 28 years, ending in 2002; the program successfully eliminated onchocerciasis as a public health problem in 10 of the 11 African countries involved. The River Blindness Elimination Program, created by The Carter Center, works in Latin America and Africa to eliminate river blindness.

Although multiple programs are working extensively to eliminate this disease, onchocerciasis is still a very relevant world health problem.



A Simulium female black fly takes blood from an infected human and ingests microfilariae. The microfilariae then enter the fly’s gut and grow into the first larval stage. After approximately 7 days, the larvae mature and move to the fly’s saliva, where it is transmitted to another human during the fly’s next blood meal.

Development to the adult stage occurs in the human host. The adult worms pair and mate in the human host, and, unlike most nematodes that produce eggs, the female Onchocerca gives birth daily to thousands of microscopic larvae known as microfilariae. These larvae mature to adult worms in about 1 year. The life span of microfilariae is 6-30 months. Those adult worms that complete their life circle may survive a decade, during which time they release millions of microfilariae.

While alive, O volvulus causes little disease. The adults protect themselves in fibrous painless subcutaneous skin nodules called onchocercomas. These nodules are found predominantly on the head, face, and torso, although they can also be seen in the pelvic girdle, in the lower extremities, or near the joints. In most cases, 2-3 females and daughter microfilariae live inside the onchocercoma. Their death leads to an inflammatory cascade in the human host. Antigens released from the dead nematode cause a TH2 helper cell response, which then activates interleukins, neutrophils, eosinophils and antibodies released by plasma cells to create the inflammatory response, which, in turn, creates the manifestations of the disease.

O volvulus endosymbionts, such as the Wolbachia bacteria that are released upon its death, also cause an immunogenic response. Strains of O volvulus that carry Wolbachia DNA are associated with a higher incidence of ocular disease. It is also proposed that ocular inflammation, specifically in the posterior pole, is a consequence of antigen mimicry. There seems to be cross-reactivity between the Onchocerca antigen Ov39 and the retinal antigen hr44, which can explain the chorioretinitis seen in some humans despite proper treatment and evidence of decreased microfilariae in their blood.




United States

No cases of onchocerciasis due to O volvulus have been reported in the United States.



More than 99% of African onchocerciasis cases occur in 27 sub-Saharan countries; 120 million people are at risk for infection on this continent. In West African savanna, the rate of infection has been as high as 80%-100% by age 20 years, with blindness peaking at age 40-50 years. In African forest areas, itching has affected 42% of the population older than 20 years, and skin lesions have appeared in 28% of persons aged 5 years.[2, 3]

Central and South America

Based on a report from the Centers for Disease Control and Prevention (CDC) in 2013, 231,467 people are at risk for onchocerciasis in Guatemala, making it the highest-risk country for river blindness in the Americas. Mexico is second, with 169,869 people at risk for infection. Venezuela has 119,358 people at risk. The Yanomami population in Brazil has 12,988 persons in 22 endemic areas at risk. Ecuador has 25,863 at risk. Although this is a relatively small number, they have the highest prevalence of microfilariae in the skin at baseline. Lastly, Colombia once had a single focus of infection, but, according to the WHO, the infection has been eradicated in Colombia as of 2012.[1]


Microfilariae elicit the onchocerciasis syndrome that includes blindness, lymphadenitis, and dermatitis. O volvulus infection reduces immunity and resistance to other diseases. According to data published in the OCP, from 1971-2001, 1,283 (5.2%) deaths were due to onchocerciasis.[4] Mortality was significantly associated with increased microfilarial burden but not blindness. Mortality rates peaked in the 1980s and decreased afterward.


No well-described racial differences in the incidence of onchocerciasis or susceptibility to the disease exist, although specific reports have documented higher, but not clinically significant, rates of infection in blacks.[5]

Socioeconomic differences have been clearly identified as a contributing factor.


Per OCP data, females had a risk of death approximately 7.5% less than males. Men may be affected more often than women because of farm and field occupations.[4]


As many as 50% of people older than 40 years may be blind in endemic areas, particularly in Africa.

Contributor Information and Disclosures

Debora E Garcia-Zalisnak, MD Resident Physician, Department of Ophthalmology, Eastern Virginia Medical School

Debora E Garcia-Zalisnak, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Ophthalmology, American College of Physicians

Disclosure: Nothing to disclose.


John D Sheppard, Jr, MD, MMSc Professor of Ophthalmology, Microbiology and Molecular Biology, Clinical Director, Thomas R Lee Center for Ocular Pharmacology, Ophthalmology Residency Research Program Director, Eastern Virginia Medical School; President, Virginia Eye Consultants

John D Sheppard, Jr, MD, MMSc is a member of the following medical societies: American Academy of Ophthalmology, American Society for Microbiology, American Society of Cataract and Refractive Surgery, Association for Research in Vision and Ophthalmology, American Uveitis Society

Disclosure: Nothing to disclose.

Specialty Editor Board

Simon K Law, MD, PharmD Clinical Professor of Health Sciences, Department of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles, David Geffen School of Medicine

Simon K Law, MD, PharmD is a member of the following medical societies: American Academy of Ophthalmology, Association for Research in Vision and Ophthalmology, American Glaucoma Society

Disclosure: Nothing to disclose.

R Christopher Walton, MD Professor, Director of Uveitis and Ocular Inflammatory Disease Service, Department of Ophthalmology, University of Tennessee College of Medicine

R Christopher Walton, MD is a member of the following medical societies: American Academy of Ophthalmology, Association for Research in Vision and Ophthalmology, Retina Society, American College of Healthcare Executives, American Uveitis Society

Disclosure: Nothing to disclose.

Chief Editor

Hampton Roy, Sr, MD Associate Clinical Professor, Department of Ophthalmology, University of Arkansas for Medical Sciences

Hampton Roy, Sr, MD is a member of the following medical societies: American Academy of Ophthalmology, American College of Surgeons, Pan-American Association of Ophthalmology

Disclosure: Nothing to disclose.


Deborah R Eezzuduemhoi, MD Assistant Professor, Department of Ophthalmology and Visual Sciences, Texas Tech University, Health Sciences Center School of Medicine

Deborah R Eezzuduemhoi, MD is a member of the following medical societies: American Academy of Ophthalmology, American Academy of Pediatrics, and Women in Ophthalmology, Inc

Disclosure: Nothing to disclose.

Deborah Wilson, MD Director of Glaucoma Service, Assistant Professor, Department of Ophthalmology, Georgetown University Medical Center

Deborah Wilson, MD is a member of the following medical societies: American Academy of Ophthalmology and American College of Physicians

Disclosure: Nothing to disclose.

  1. CDC. Parasites - Onchocerciasis (also known as River Blindness). CDC. Available at Accessed: 25th July 2014.

  2. Yaya G, Kobangué L, Kémata B, Gallé D, Grésenguet G. [Elimination or control of the onchocerciasis in Africa? Case of Gami village in Central African Republic]. Bull Soc Pathol Exot. 2014 Aug. 107(3):188-93. [Medline].

  3. World Health Organization. Prevention of Blindness and Visual Impairment. Onchocerciasis Control Programme (OCP). World Health Organization. Available at Accessed: 25th July 2014.

  4. Little MP, Breitling LP, Basáñez MG, Alley ES, Boatin BA. Association between microfilarial load and excess mortality in onchocerciasis: an epidemiological study. Lancet. 2004 May 8. 363(9420):1514-21. [Medline].

  5. Cooper PJ, Proaño R, Beltran C, Anselmi M, Guderian RH. Onchocerciasis in Ecuador: ocular findings in Onchocerca volvulus infected individuals. Br J Ophthalmol. 1995 Feb. 79(2):157-62. [Medline].

  6. Kayembe DL, Kasonga DL, Kayembe PK, Mwanza JC, Boussinesq M. Profile of eye lesions and vision loss: a cross-sectional study in Lusambo, a forest-savanna area hyperendemic for onchocerciasis in the Democratic Republic of Congo. Trop Med Int Health. 2003 Jan. 8(1):83-9. [Medline].

  7. Vingtain P, Thillaye I. Longitudinal study of microfilarial infestation and humoral immune response to filarial and retinal antigens in onchocerciasis patients treated with ivermectin. Ophthalmic Res. 1988.

  8. Turner HC, Walker M, Churcher TS, Basáñez MG. Modelling the impact of ivermectin on River Blindness and its burden of morbidity and mortality in African Savannah: EpiOncho projections. Parasit Vectors. 2014 May 26. 7:241. [Medline]. [Full Text].

  9. Banla M, Tchalim S, Karabou PK, Gantin RG, Agba AI, Kére-Banla A, et al. Sustainable control of onchocerciasis: ocular pathology in onchocerciasis patients treated annually with ivermectin for 23 years: a cohort study. PLoS One. 2014. 9(6):e98411. [Medline]. [Full Text].

  10. Osei-Atweneboana MY, Awadzi K, Attah SK, Boakye DA, Gyapong JO, Prichard RK. Phenotypic evidence of emerging ivermectin resistance in Onchocerca volvulus. PLoS Negl Trop Dis. 2011 Mar 29. 5(3):e998. [Medline]. [Full Text].

  11. Hoerauf A, Mand S, Adjei O, Fleischer B, Büttner DW. Depletion of wolbachia endobacteria in Onchocerca volvulus by doxycycline and microfilaridermia after ivermectin treatment. Lancet. 2001 May 5. 357(9266):1415-6. [Medline].

  12. The Carter Center. River Blindness Elimination Program. The Carter Center. Available at Accessed: 25th July 2014.

  13. World Health Organization. African Programme for Onchocerciacis Control (APOC). Available at Accessed: 25th July 2014.

  14. Greene BM, Gbakima AA, Albiez EJ, Taylor HR. Humoral and cellular immune responses to Onchocerca volvulus infection in humans. Rev Infect Dis. 1985 Nov-Dec. 7(6):789-95. [Medline].

  15. Ament CS, Young LH. Ocular manifestations of helminthic infections: onchocersiasis, cysticercosis, toxocariasis, and diffuse unilateral subacute neuroretinitis. Int Ophthalmol Clin. 2006 Spring. 46(2):1-10. [Medline].

  16. Awadzi K, Edwards G, Opoku NO, Ardrey AE, Favager S, Addy ET, et al. The safety, tolerability and pharmacokinetics of levamisole alone, levamisole plus ivermectin, and levamisole plus albendazole, and their efficacy against Onchocerca volvulus. Ann Trop Med Parasitol. 2004 Sep. 98(6):595-614. [Medline].

  17. Ayong LS, Tume CB, Wembe FE, Simo G, Asonganyi T, Lando G, et al. Development and evaluation of an antigen detection dipstick assay for the diagnosis of human onchocerciasis. Trop Med Int Health. 2005 Mar. 10(3):228-33. [Medline].

  18. Babalola OE. The peculiar challenges of blindness prevention in Nigeria: a review article. Afr J Med Med Sci. 2011 Dec. 40(4):309-19. [Medline].

  19. Basáñez MG, Pion SD, Churcher TS. River blindness: a success story under threat?World Health Organization. Prevention of blindness and visual impairment: priority eye diseases. PLoS Med. 2006. 3:e371.

  20. Berger RB, Blackwell NM, Lass JH, Diaconu E, Pearlman E. IL-4 and IL-13 regulation of ICAM-1 expression and eosinophil recruitment in Onchocerca volvulus keratitis. Invest Ophthalmol Vis Sci. 2002 Sep. 43(9):2992-7. [Medline].

  21. Brattig NW. Pathogenesis and host responses in human onchocerciasis: impact of Onchocerca filariae and Wolbachia endobacteria. Microbes Infect. 2004 Jan. 6(1):113-28. [Medline].

  22. CDC. Progress toward elimination of onchocerciasis in the Americas - 1993-2012. MMWR Morb Mortal Wkly Rep. 2013 May 24. 62(20):405-8. [Medline].

  23. Cooper PJ, Guderian RH, Proaño R, Taylor DW. Absence of cellular responses to a putative autoantigen in onchocercal chorioretinopathy. Cellular autoimmunity in onchocercal chorioretinopathy. Invest Ophthalmol Vis Sci. 1996 Feb. 37(2):405-12. [Medline].

  24. Cupp EW, Sauerbrey M, Richards F. Elimination of human onchocerciasis: history of progress and current feasibility using ivermectin (Mectizan(®)) monotherapy. Acta Trop. 2011 Sep. 120 Suppl 1:S100-8. [Medline].

  25. Dadzie Y, Neira M, Hopkins D. Final report of the Conference on the eradicability of Onchocerciasis. Filaria J. 2003 Feb 7. 2(1):2. [Medline]. [Full Text].

  26. Diemert DJ. Tissue Nematode Infections. Goldman’s Cecil Medicine. 2011. 193-200.

  27. Ejere HO, Schwartz E, Wormald R, Evans JR. Ivermectin for onchocercal eye disease (river blindness). Cochrane Database Syst Rev. 2012 Aug 15. 8:CD002219. [Medline].

  28. Etya’ale D, Taylor HR. Onchocerciasis. Duane's Ophthalmology. Lippincott Williams & Wilkins; 2006. 5: Chapter 62. [Full Text].

  29. Globisch D, Moreno AY, Hixon MS, Nunes AA, Denery JR, Specht S. Onchocerca volvulus-neurotransmitter tyramine is a biomarker for river blindness. Proc Natl Acad Sci U S A. 2013 Mar 12. 110(11):4218-23. [Medline].

  30. Higazi TB, Filiano A, Katholi CR, Dadzie Y, Remme JH, Unnasch TR. Wolbachia endosymbiont levels in severe and mild strains of Onchocerca volvulus. Mol Biochem Parasitol. 2005 May. 141(1):109-12. [Medline].

  31. Mbanefo EC, Eneanya CI, Nwaorgu OC, Otiji MO, Oguoma VM, Ogolo BA. Onchocerciasis in Anambra State, Southeast Nigeria: endemicity and clinical manifestations. Postgrad Med J. 2010 Oct. 86(1020):578-83. [Medline].

  32. McKechnie NM, Gürr W, Yamada H, Copland D, Braun G. Antigenic mimicry: Onchocerca volvulus antigen-specific T cells and ocular inflammation. Invest Ophthalmol Vis Sci. 2002 Feb. 43(2):411-8. [Medline].

  33. Mcleod SD. Parasitic Keratitis. Yanoff & Duke. Yanoff & Duker: Ophthalmology. 2008. 274-8.

  34. Murdoch ME. Onchocerciasis. UpToDate. Available at Accessed: 25th July 2014.

  35. Murdoch ME, Asuzu MC, Hagan M, Makunde WH, Ngoumou P, Ogbuagu KF, et al. Onchocerciasis: the clinical and epidemiological burden of skin disease in Africa. Ann Trop Med Parasitol. 2002 Apr. 96(3):283-96. [Medline].

  36. Ndyomugyenyi R, Tukesiga E, Büttner DW, Garms R. The impact of ivermectin treatment alone and when in parallel with Simulium neavei elimination on onchocerciasis in Uganda. Trop Med Int Health. 2004 Aug. 9(8):882-6. [Medline].

  37. Nguyen JC, Murphy ME, Nutman TB, Neafie RC, Maturo S, Burke DS, et al. Cutaneous onchocerciasis in an American traveler. Int J Dermatol. 2005 Feb. 44(2):125-8. [Medline].

  38. Norman FF, Pérez de Ayala A, Pérez-Molina JA, Monge-Maillo B, Zamarrón P, López-Vélez R. Neglected tropical diseases outside the tropics. PLoS Negl Trop Dis. 2010 Jul 27. 4(7):e762. [Medline]. [Full Text].

  39. Otranto D, Sakru N, Testini G, Gürlü VP, Yakar K, Lia RP, et al. Case report: First evidence of human zoonotic infection by Onchocerca lupi (Spirurida, Onchocercidae). Am J Trop Med Hyg. 2011 Jan. 84(1):55-8. [Medline]. [Full Text].

  40. Pearlman E, Hall LR, Higgins AW, Bardenstein DS, Diaconu E, Hazlett FE, et al. The role of eosinophils and neutrophils in helminth-induced keratitis. Invest Ophthalmol Vis Sci. 1998 Jun. 39(7):1176-82. [Medline].

  41. Remme J, Dadzie KY, Rolland A, Thylefors B. Ocular onchocerciasis and intensity of infection in the community. I. West African savanna. Trop Med Parasitol. 1989 Sep. 40(3):340-7. [Medline].

  42. Remme JHF, World Health Organization, Geneva. The global burden of onchocerciasis in 1990. 2004.

  43. Rowe SG, Durand M. Blackflies and whitewater: onchocerciasis and the eye. Int Ophthalmol Clin. 1998 Winter. 38(1):231-40. [Medline].

  44. Saint André Av, Blackwell NM, Hall LR, Hoerauf A, Brattig NW, Volkmann L, et al. The role of endosymbiotic Wolbachia bacteria in the pathogenesis of river blindness. Science. 2002 Mar 8. 295(5561):1892-5. [Medline].

  45. World Health Organization. A new drug for river blindness? Research and Training in Tropical Diseases (TDR) News. World Health Organization TDR News. Available at Accessed: 25th July 2014.

  46. World Health Organization. Prevention of Blindness and Visual Impairment. Priority eye diseases. WHO. Available at Accessed: 25th July 2014.

  47. Zimmerman PA, Dadzie KY, De Sole G, Remme J, Alley ES, Unnasch TR. Onchocerca volvulus DNA probe classification correlates with epidemiologic patterns of blindness. J Infect Dis. 1992 May. 165(5):964-8. [Medline].

All material on this website is protected by copyright, Copyright © 1994-2016 by WebMD LLC. This website also contains material copyrighted by 3rd parties.