Bye Bye Doctor Logo

    Bye Bye Doctor

    Back to all articles

    You May Also See

    Sunburn BlistersCanker Sore on TongueSkin UlcerSclerodermaGoiterAcromegalyShinglesAscitesVitiligoNoonan SyndromeHypovolemiaTooth AbscessLymphangitisLivedo ReticularisTeratoma
    Infections
    Medically Reviewed

    Onchocerciasis

    Overview

    Onchocerciasis, commonly known as river blindness, is a parasitic disease caused by the filarial worm Onchocerca volvulus. It is transmitted to humans through the repeated bites of infected blackflies, which breed near fast-flowing rivers and streams. Onchocerciasis is primarily found in sub-Saharan Africa, with smaller endemic areas in Latin America and Yemen. The disease mainly affects the skin and eyes, leading to severe itching, skin changes, and in advanced cases, irreversible blindness. River blindness is considered a major public health concern in affected regions, though mass drug administration programs have significantly reduced its impact in many areas.

    Causes

    The cause of onchocerciasis is infection with the parasitic worm Onchocerca volvulus. Transmission occurs through the following process:

    • Vector transmission: Blackflies of the genus Simulium acquire microfilariae (immature worms) by biting infected humans.
    • Parasite development: Inside the blackfly, microfilariae develop into infective larvae over 7-10 days.
    • Human infection: When the infected blackfly bites another person, larvae are deposited on the skin and enter the body through the bite wound.
    • Maturation in humans: Larvae mature into adult worms, forming nodules in the skin and producing microfilariae that migrate through skin and eye tissues.

    Symptoms

    Symptoms of onchocerciasis develop due to the immune response to dead and dying microfilariae in the skin and eyes. The main symptoms include:

    • Skin symptoms:
      • Intense itching (pruritus)
      • Rash with raised bumps or papules
      • Thickened, scaly, or depigmented skin, commonly known as “leopard skin”
      • Skin atrophy and loss of elasticity, sometimes leading to “hanging groin”
    • Eye symptoms:
      • Visual disturbances, such as blurred vision or visual field loss
      • Pain, redness, or light sensitivity in the eyes
      • Progressive vision loss, potentially leading to complete blindness in advanced cases
    • Nodules: Formation of painless subcutaneous nodules containing adult worms, often found over bony prominences.
    • Systemic effects: Generalized fatigue and social stigma due to disfiguring skin changes.

    Diagnosis

    Diagnosis of onchocerciasis involves clinical examination and parasitological testing:

    • Skin snip biopsy: A small skin sample is taken and examined under a microscope to detect microfilariae.
    • Nodule examination: Palpation for subcutaneous nodules, and sometimes surgical removal and analysis of adult worms.
    • Eye examination: Slit-lamp examination can reveal microfilariae in the eye tissues, corneal changes, or inflammation.
    • Serological tests: Blood tests to detect antibodies against Onchocerca antigens may be used in some settings.
    • Molecular tests: Polymerase chain reaction (PCR) testing can detect parasite DNA in skin samples.

    Treatment

    Treatment for onchocerciasis focuses on reducing microfilarial load, preventing blindness, and managing skin symptoms:

    • Ivermectin: The primary treatment, administered every 6 to 12 months, kills microfilariae but not adult worms. It helps reduce symptoms and transmission.
    • Doxycycline: An antibiotic that targets Wolbachia bacteria, which are symbiotic with the worms, leading to sterilization and gradual death of adult worms.
    • Nodulectomy: Surgical removal of nodules containing adult worms may be performed in some cases to reduce the worm load.
    • Skin care: Use of topical treatments and antihistamines to relieve itching and manage skin lesions.
    • Community-wide treatment: Mass drug administration (MDA) programs target entire communities to interrupt transmission.

    Prognosis

    The prognosis of onchocerciasis depends on early diagnosis and consistent treatment:

    • Favorable with treatment: Regular ivermectin significantly reduces microfilarial load, controls symptoms, and prevents blindness in many patients.
    • Vision outcomes: Once vision loss occurs, especially in advanced cases, it is often irreversible. Early treatment is crucial for vision preservation.
    • Skin recovery: Skin itching and rashes typically improve within weeks of treatment, though chronic skin changes may persist.
    • Public health impact: Ongoing mass treatment programs have led to major reductions in disease prevalence and risk of transmission in many endemic areas.
    • Lifelong management: Since adult worms live up to 10-15 years, long-term treatment and monitoring are necessary.

    With proper community-based strategies and individual treatment, the burden of onchocerciasis can be effectively reduced, improving the quality of life for affected individuals.