Onchocerciasis

Onchocerciasis, also known as river blindness, is a parasitic disease caused by the filarial worm Onchocerca volvulus. It primarily affects the skin, eyes, and lymph nodes, leading to severe itching, skin lesions, and visual impairment, including blindness.

In an endemic area, any person with fibrous nodules in subcutaneous tissues may be affected.


Signs and Symptoms

1. Skin manifestations:

  •  Intense itching (pruritus).

  •   Skin rash, thickening, and depigmentation (leopard skin).

  •   Nodules under the skin (onchocercomas).

2. Eye lesions:

  • Inflammation of the cornea (keratitis).

  •  Sclerosing keratitis (leading to blindness).

  •  Uveitis, glaucoma, and optic nerve atrophy.

3. Lymphatic system:

  • Swelling of lymph nodes (lymphadenopathy).

  • Hanging groin (due to loss of skin elasticity).


Complications

  • Permanent blindness.

  • Severe skin disfigurement and scarring.

  • Secondary bacterial infections due to scratching.

  • Social stigma and psychological impact.


Transmission

  • Transmitted through the bites of infected blackflies (genus Simulium), which breed in fast-flowing rivers and streams.

  • The blackfly deposits larvae of *Onchocerca volvulus* into the human host during a blood meal.


Causative Agent

  • The disease is caused by the parasitic nematode Onchocerca volvulus.


Incubation Period

  • The incubation period ranges from 9 months to 2 years after the initial infection.

  • Symptoms may take years to develop as the larvae mature into adult worms.


Reservoir

  • Humans are the primary reservoir for Onchocerca volvulus

  • There is no animal reservoir.


Prevention and Control

  1. Mass Drug Administration (MDA):

  •    Distribution of ivermectin (Mectizan) to at-risk populations annually or biannually.

2. Vector Control:

  •    Use of larvicides to control blackfly breeding sites.

  •   Environmental management to reduce blackfly habitats.

3. Personal Protection:

  •    Use of insect repellent and protective clothing.

  •    Avoiding areas with high blackfly activity.

4. Health Education:

  •    Community awareness programs to promote prevention and treatment.


Treatment

1. Ivermectin:

  • The drug of choice for treating onchocerciasis.

  • Kills the microfilariae (larvae) and prevents the release of new larvae by adult worms.

  • Does not kill adult worms but reduces transmission and symptoms.

2. Doxycycline:

  • Used to target Wolbachia bacteria, which live symbiotically with Onchocerca volvulus.

  • Weakens adult worms and reduces their lifespan.

3. Surgical Removal:

  •  Nodules containing adult worms (onchocercomas) can be surgically removed.

4. Symptomatic Treatment:

  • Antihistamines and corticosteroids to manage itching and inflammation.


Global Efforts

  • The Onchocerciasis Control Programme (OCP) and the African Programme for Onchocerciasis Control (APOC) have significantly reduced the burden of the disease in endemic regions.

  • The goal is to eliminate onchocerciasis as a public health problem through sustained MDA and surveillance.

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