Onchocerciasis (River Blindness) Clinical Presentation

Updated: Jun 22, 2018
  • Author: Darvin Scott Smith, MD, MSc, DTM&H; Chief Editor: Mark R Wallace, MD, FACP, FIDSA  more...
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Presentation

History

Symptoms of onchocerciasis reflect the developmental stage of the parasite and the degree of immune response by the host. Clinical manifestations are highly variable.

Symptoms of onchocerciasis do not appear until after the L3 larvae mature into adult worms. On average, symptoms appear between 9 months and 2 years after the initial infecting bite. The interval between acquisition of the parasite and onset of symptoms is sometimes referred to as the prepatent phase.

Once developed, adult worms cluster in subcutaneous nodules (onchocercomata).

Generalized pruritus may occur early in the infection and may be severe. A papular rash known as onchodermatitis may be present. Initially, the rash may be transient, but chronic infection over several years may lead to lichenification, loss of skin elasticity, atrophy, and/or depigmentation.

Itchy eyes, redness, or photophobia may be early symptoms of ocular onchocerciasis. Over years, the scarring progresses to cause visual loss and ultimately blindness. Acute optic neuritis is less common but may also cause blindness.

Weight loss and generalized myalgias may occur.

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Physical

Skin examination in patients with onchocerciasis may reveal subcutaneous nodules, diffuse onchodermatitis, lymphedema, and/or atrophic changes.

Onchodermatitis consists of raised papules that are intensely pruritic. Vesicles and pustules may also be present. Scratching may cause secondary infection.

In its extreme form, skin atrophy may cause drooping of the inguinal skin, termed hanging groin.

In some cases, the skin is dry and resembles ichthyosis.

Bleeding on skin due to scratching of itchy skin ( Bleeding on skin due to scratching of itchy skin (onchodermatitis).

Sowda refers to severe pruritus and darkened skin, usually confined to one limb. It is most commonly described in Yemen but also occurs in Africa.

Patient from Cameroon with sowdalike lesions. Patient from Cameroon with sowdalike lesions.

Leopard skin refers to bilateral, symmetric, patchy depigmentation of the shins.

Skin of a West African person with leopard spot de Skin of a West African person with leopard spot depigmentation.

Lymphadenopathy may occur.

Subcutaneous nodules are firm, nontender, and mobile and are several millimeters to centimeters in size. They develop most commonly over bony prominences on the trunk and hip (Africa) or head and shoulders (Americas).

In the eye, the inflammatory response to dying microfilariae and Wolbachia antigens causes punctuate keratitis (snowflake opacities). Advanced cases may result in corneal fibrosis or opacification. Slit-lamp examination may reveal microfilariae in the cornea and anterior chamber. Other ocular manifestations include iridocyclitis, glaucoma, chorioiditis, and optic atrophy. [28]

Man blinded by microfilariae of Onchocerca volvulu Man blinded by microfilariae of Onchocerca volvulus.

 

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Causes

O volvulus is transmitted by the bite of infected Simulium flies. The fly bites during daylight hours. Simulium flies breed near fast-flowing rivers and streams.

Ocular symptoms are caused by the inflammatory response invoked by the release of Wolbachia antigens when microfilariae die.

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Physical Examination

Physical examination in a patient with onchocerciasis should focus on the skin, with attention to the changes described above, and the eyes. Slit-lamp examination to examine the anterior chamber of the eye is needed to appreciate specific physical changes and keratitis of onchocerciasis.

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Complications

High prevalences of nodding syndrome and epileptic seizures have been reported for decades in areas endemic for onchocerciasis in Africa. These neurologic disorders are termed ”river epilepsy” for their occurrence proximate to the fast-flowing rivers that are risk factors for onchocerciasis transmission. Microfilarial loads are significantly higher in individuals experiencing these seizures. A condition with similar features, but also associated with stunted growth, termed Nakalanga syndrome, was observed in Uganda in the 1950s but disappeared after the elimination of blackflies from the area. Nakalanga-like syndromes have been reported from a range of infection foci since and as distant from Uganda as Liberia and Mali. However, the pathophysiological mechanism that causes these neurological disorders is unknown. [29]

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