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Onchocerciasis is an infection caused by a nematode worm called Onchorcerca volvulus, which results in different skin and ocular manifestations including blindness; hence the name river blindness.


Symptoms may not appear for several months after the initial infection until the larvae mature into adult worms. Once developed, they cluster in subcutaneous nodules and cause pruritus. Onchodermatitis may also be present, which is a papular itchy rash [7] [8]. In early stages, the rash may be transient; however, as the infection progresses into chronic infection it leads to loss of skin elasticity, atrophy, depigmentation, and lichenification [3]. Ocular infections manifest as itching and redness in the eyes, as well as photophobia. Blindness may occur as the disease and the scarring advances. General symptoms such as weight loss and generalized pain in the muscles may also be observed.

Physical examination of the skin will reveal firm nontender and mobile subcutaneous nodules over bony prominences, papular rash, lymphedema, enlarged inguinal or femoral nodes, depigmentation, and other atrophic changes. Vesicles or pustules may also be noticed.

Infection of the eyes causes punctuate keratitis, which is an acute inflammatory infiltrate resulting from the dying microfilariae. It usually resolves without permanent complications or damage. Furthermore, sclerosing keratitis (which may lead to subluxation of the lens and blindness), as well as anterior uveitis (which deforms the pupil) may be observed. Other symptoms in the eye include optic neuritis, optic atrophy, and chorioretinitis.

Blindness or visual impairment is the most severe prognosis or outcome of onchocerciasis [7].

Retinal Damage
  • Local invasion of microfilariae into retinal tissue has been postulated as a mechanism for retinal damage ( Burnham 1998 ).[doi.org]
  • Such patients represent a subset of travelers in whom dermatitis should prompt evaluation for onchocerciasis.[ncbi.nlm.nih.gov]
  • Onchocercal dermatitis is generalized in most patients, but a localized and sharply delineated form of eczematous dermatitis with hyperkeratosis, scaling, and pigment changes (Sowdah) is common in Yemen and Sudan.[merckmanuals.com]
  • Physicians should consider this tropical disease when caring for migrants and travellers/expatriates with pruritus, skin lesions and eosinophilia.[ncbi.nlm.nih.gov]
  • […] worms, pruritus, and ocular lesions Applies To Onchocerca volvulus infection Onchocercosis ICD-9-CM Volume 2 Index entries containing back-references to 125.3 :[icd9data.com]
  • Contenuti: Skin: basic structure and function -- Cutaneous signs and diagnosis -- Dermatoses resulting from physical factors -- Pruritus and neurocutaneous dermatoses -- Atopic dermatitis, eczema, and noninfectious immunodeficiency disorders -- Erythema[worldcat.org]
  • The differential diagnosis for the chronic skin lesions of the African variants includes tertiary yaws, eczema, malnutrition, and old age.[web.archive.org]
Hypopigmented Macule
  • We present this interesting patient with onchocerciasis to expand our differential of hypopigmented macules, especially in the African population.[ncbi.nlm.nih.gov]
  • Patients generally present with hypopigmented macules, 1-3 cm in diameter (see Media File 30 ) that resemble tuberculoid leprosy; however, anesthesia is absent.[web.archive.org]
Tonic-Clonic Seizure
  • Persons with onchocerciasis-associated epilepsy present with a wide spectrum of seizures, including atonic and myoclonic neck seizures; but also absences and most frequently generalized tonic-clonic seizures.[ncbi.nlm.nih.gov]
Neurologic Manifestation
  • In addition to these cases, patients w with high Loa microfilaremia also developed milder neurologic manifestations causing functional impairment lasting for at least one week after treatment.[ncbi.nlm.nih.gov]
  • An Hotterbeekx, Vivian Namale Ssonko, William Oyet, Thomson Lakwo and Richard Idro, Neurological Manifestations in Onchocerca volvulus infection; a Review, Brain Research Bulletin, 10.1016/j.brainresbull.2018.08.024, (2018). Michele E.[doi.org]


A biopsy sample is taken from the lesion and examined to demonstrate microfilariae. This technique has a very high specificity; however, it has low sensitivity especially in early stages of the infection. Surgical specimens obtained through excision of the lesions or nodules should be examined to confirm the diagnosis, which is also beneficial as a sort of treatment through the elimination of the adult worms in the excised nodule.

Polymerase chain reaction (PCR) should be performed using the biopsy sample, as it has higher sensitivity and specificity; however, it is usually used only in research [4] [9].

Screening with ultrasonography is not useful; however, adult worms may be revealed using ultrasound as a homogenous echogenic area, which contains echodense particles. Pruritus, dermal edema and other localized cutaneous reactions are elicited when diethylcarbamazine (DEC) cream is applied to the skin, which is in response to dying microfilariae (the sensitivity of this test is increased when higher concentrations of DEC are applied for longer times) [10] [11].

A positive serologic test does not have high value, neither does it distinguish between old and current infections.

Cross-sections of adult worms with eosinophils and lymphocytes are revealed through microscopic examination of excised nodules.

Slit-lamp examination may reveal microfilariae in the cornea and the anterior chamber of the eye.

Liver Enzymes Abnormal
  • Adverse outcomes Adverse outcomes, such as photosensitivity, liver enzyme abnormalities, diarrhea, rash, fever, arthralgia, or nausea and vomiting, were recorded as defined in the respective trials.[doi.org]
Tissue Nematode
  • Although infection with tissue nematodes is a significant health problem in many parts of the world, such cases are unusual in the continental United States.[ncbi.nlm.nih.gov]
  • Tissue Nematode Infections. Goldman’s Cecil Medicine. 2011. 193-200. 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].[emedicine.com]


The drug of choice for treatment of onchocerciasis is ivermectin with repeated doses every 3 to 12 months, over a time period of 12 to 15 years (until the end of the lifetime of the female adult worm) [5] [12]. Another drug that can be used in the treatment, and which is currently being studied by the WHO, is moxidectin [13]. Surgical excision of the nodules may help in the management; however, it is not a practical option because all the nodules with all the worms should be removed to ensure cure from the infection.

Ivermectin does not kill the adult female worms; however, it decreases their fertility and reduces microfilariae in the skin and the eyes.

It is not advised to use diethylcarbamazine in the treatment of onchocerciasis because it may cause severe hypersensitivity reaction, which could lead to further damage in the skin and the eyes and may result in cardiovascular collapse. Ivermectin may have similar adverse effects; however, they are not common and less severe.

Onchocerca volvulus worms require Wolbachia bacteria for survival and embryogenesis. Doxycycline is used to kill these bacteria.


Treatment with ivermectin for approximately 12 to 15 years, wich is the lifetime of the adult worm, may resolve some symptoms like dermatitis and mild eye manifestations and shows good prognosis. However, skin atrophy, depigmentation, and blindness do not improve even after successful treatment.

Patients who undergo blindness may have decreased life expectancy because of the difficulty to cope with daily activities.


Onchocerciasis is the second most common cause of infectious blindness. It develops through the bite of Simulium blackflies infected with the nematode worm Onchocerca volvulus [1] [4] [6]. The resultant infection is called river blindness because the intermediate hosts (blackflies) responsible for the transmission of the worm develop and breed in flowing water and near rivers. Endemic areas are in particular concentrated on Africa and South America.


There are more than 20 million patients suffering from onchocerciasis worldwide, most of them come from tropical African countries [2]. Some cases are also reported in Central and South America. Onchocerciasis is the second most common cause of infectious blindness; the World Health Organization (WHO) estimates that more than 300,000 of the patients are blind and more than 800,000 of them are visually impaired.

In countries where the infection is endemic, the prevalence increases with age up to the fourth decade of life.

Sex distribution
Age distribution


The cycle begins when a blackfly bites a person who is infected with the worm, thus transferring the microfilariae from the human to the insect. Inside the fly, the immature forms of the worm develop into larvae. Through the bites of the infected blackfly, these larvae are passed to other humans, causing the infection. It takes up to 18 months for the worms to reach their adult form in the skin. Adult female worms may live for up to 15 years inside a human, producing around 1,000 eggs every day. Subsequently, the microfilariae migrate through the eyes and tissues causing the skin and ocular manifestations, including blindness.

People who visit endemic areas for a short period of time rarely get infected because many bites are required for the infection to develop. Permanent residents of endemic areas try to avoid living or working near rivers where the infected flies dwell. As a result, daily life and work habits are affected, because the fruitful area near the rivers is restricted for raising crops.


Endemic countries in Africa and South America decrease the incidence of infection by eliminating the intermediate host (Simulium blackflies). Regular ivermectin treatment is required for infected patients, which not only helps in the treatment of the infection but also reduces the risk of recurrence in people who are exposed to the worms repeatedly.

Different strategies may help in the prevention, such as avoiding endemic areas where the blackflies live, wearing protective clothes, and using insect repellents. Tourists and travelers to endemic areas should be educated about the infection and instructed to evade risky areas for their safety.


Onchocerciasis is a filarial infection caused by the nematode Onchocerca volvulus [1]. It is also called river blindness because the resultant infection is the second common cause of infectious blindness and the intermediate hosts (Simulium blackflies) develop near rivers.

The infection is endemic in some countries in Africa and in South America; however, 99% of the reported cases are in Africa [2]. According to the World Health Organization (WHO), there are more than 20 million reported cases worldwide, with more than 300,000 cases that are blind.

The cycle of the worm begins in infected humans. A blackfly bites an infected person and the microfilariae get transferred from the human to the insect, hence larvae develop inside the blackfly. In the following, the larvae are passed to other humans by bites of the infected fly. Usually, many bites are required to cause the infection.

Infected patients present with itching, redness, and nodules, in addition to ocular manifestations including visual impairment and blindness [3]. However, the symptoms may not appear for several months after infection. Physical examination of infected patients will reveal nontender mobile nodules, rash, lymphedema, depigmentation, skin atrophic changes, and enlarged inguinal or femoral lymph nodes.

Onchocerciasis is diagnosed through the examination of a biopsy specimen taken from a nodule, which reveals the microfilariae. Surgically excised specimens may be examined to confirm the diagnosis. Polymerase chain reaction (PCR) test has higher sensitivity and specificity; however, it is only used in research [4]. The cornea and the anterior chamber of the eyes should be examined for the presence of microfilariae.

Ivermectin is used to treat onchocerciasis. It is given every 3 to 12 months until the symptoms have resolved, over a time period of at least 12 years since the lifetime of the adult female worm ranges from 12 to 15 years [5].

Dermatitis and mild eye manifestations will resolve after successful treatment of the infection. However, depigmentation, skin atrophy, and blindness will persist.

Decreasing the incidence of the infection is achieved through avoidance of endemic areas, wearing protective clothing and using insect repellents. Travelers to endemic areas should be informed about the infection and its complications.

Patient Information

Onchocerciasis is an infection caused by a worm called Onchocerca volvulus, which is usually found near rivers in endemic areas in Africa and South America. The worms pass from a blackfly to the affected person and penetrate the skin, causing the infection.

According to the World Health Organization (WHO), there are more than 20 million reported cases worldwide; however most of these cases are in Africa with only few cases in other countries, such as South America.

Symptoms may not appear for several months after infection; however, when they develop, they include itching, rash, nodules, and sometimes scarring of the skin. The eyes may be affected as well and symptoms will include visual impairment, pain when exposed to light, or blindness in severe cases.

The doctor will examine the skin looking for nodules, change of color, enlarged lymph nodes in the inguinal or femoral region or other changes of the skin. Examination of the eyes will be performed looking for evidence of eye involvement.

A biopsy sample will be taken from the nodule and examined, looking for microfilariae of the worms. Other diagnostic techniques may be used, such as ultrasound.

Onchocerciasis is treated with a drug called ivermectin, which is given every 3 to 12 months for 12 to 15 years (until the symptoms disappear and the adult female worms are dead).

Treatment with ivermectin will resolve some of the symptoms and shows a good outcome; however, some manifestations will persist even after successful treatment, such as change in skin color, destructive changes of the skin, visual impairment and blindness.

Prevention of the infection includes avoiding endemic areas where the flies live (especially near rivers), wearing protective clothing, and using insect repellents.

Education should be provided to tourists and travelers who visit endemic areas for their safety and in order to raise awareness about the infection and its complications.



  1. Burnham G. Onchocerciasis. Lancet. May 2, 1998; 351(9112): 1341-6.
  2. Basáñez MG, Pion SD, Churcher TS, et al. River blindness: a success story under threat? PLoS Med. September 2006; 3(9): e371.
  3. Murdoch ME, Hay RJ, Mackenzie CD, et al. A clinical classification and grading system of the cutaneous changes in onchocerciasis. Br J Dermatol. September 1993; 129(3): 260-9.
  4. Udall DN. Recent updates on onchocerciasis: diagnosis and treatment. Clin Infect Dis. January 1, 2007; 44(1): 53-60.
  5. Basáñez MG, Pion SD, Boakes E, et al. Effect of single-dose ivermectin on Onchocerca volvulus: a systematic review and meta-analysis. Lancet Infect Dis. May 2008; 8(5): 310-22.
  6. Hoerauf A, Büttner DW, Adjei O, et al. Onchocerciasis. BMJ. January 25, 2003; 326(7382): 207-10.
  7. Onchocerciasis and its control. Report of a WHO Expert Committee on Onchocerciasis Control. World Health Organ Tech Rep Ser. 1995; 852: 1-104.
  8. Vlassoff C, Weiss M, Ovuga EB, et al. Gender and the stigma of onchocercal skin disease in Africa. Soc Sci Med. May 2000; 50(10): 1353-68.
  9. Boatin BA, Toé L, Alley ES, et al. Diagnostics in onchocerciasis: future challenges. Ann Trop Med Parasitol. April 1998; 92 Suppl 1: S41-5.
  10. Toè L, Adjami AG, Boatin BA, et al. Topical application of diethylcarbamazine to detect onchocerciasis recrudescence in west Africa. Trans R Soc Trop Med Hyg. September-October 2000; 94(5): 519-25.
  11. Ozoh G, Boussinesq M, Bissek AC, et al. Evaluation of the diethylcarbamazine patch to evaluate onchocerciasis endemicity in Central Africa. Trop Med Int Health. January 2007; 12(1): 123-9.
  12. Reddy M, Gill SS, Kalkar SR, et al. Oral drug therapy for multiple neglected tropical diseases: a systematic review. JAMA. October 24, 2007; 298(16): 1911-24.
  13. Siva N. WHO researchers start trial on a new drug for river blindness. BMJ. 2009; 339: b2755.

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Last updated: 2019-07-11 21:59