Onchocerciasis: Infectious disease with symptoms of the skin and eyes

Onchocerciasis is a parasitic infectious disease caused by a worm. This disease mainly occurs in certain areas of America and Africa. Repeated exposure to bites from the black fly causes larvae to enter the body, which then grow into a worm. The death of the larvae causes symptoms in the eyes and skin in combination with severe itching. The tropical condition can be easily treated with a worm-killing medicine, but a long re-treatment is necessary. Onchocerciasis is also known, among other things, as “river blindness” because the black flies that transmit the worm breed in fast-flowing streams and rivers.

  • Synonyms onchocerciasis
  • Epidemiology tropical disease
  • Causes: Repeated bites of black flies
  • Symptoms of skin and eyes
  • Diagnosis and examinations
  • Treatment of worm larvae via anthelmintic
  • Infectious disease prevention

Synonyms onchocerciasis

Onchocerciasis is also known by these synonyms

  • onchocerciasis
  • river blindness
  • volvulosis
  • Robles disease

Epidemiology tropical disease

Onchocerciasis affects around 25 million people worldwide, of which 300,000 are blind and 800,000 visually impaired. After trachoma (severe conjunctivitis), this is the most common form of blindness due to an infection. Most patients are found in West and Central Africa and Central and South America and Yemen. About 120 million people are at risk of developing this tropical condition. Finally, the disease has no sexual, racial or age predilection.

Causes: Repeated bites of black flies

Onchocerciasis is the result of an infection with the parasitic worm Onchocerca volvulus . Transmission is by black flies of the genus Simulium that bite during the day. These black flies breed in fast-flowing rivers and streams, usually in remote villages near fertile land, where people depend on agriculture. The infestation of the parasitic eye infection occurs when the larvae enter humans through exposure to repeated bites from an infected black fly. The worms mature in two to four months and live for more than fifteen years. Adult worms reach a length of up to fifty centimeters but are less than 0.5 mm in diameter. The worms live in subcutaneous nodules, especially in bony prominences. These worms, which reside in the subcutaneous tissue, produce thousands of larvae that move into the skin and eye. The skin then contains enormous numbers of microfilariae (larvae) that may invade the eyes. Live larvae cause relatively little damage, but dead parasites lead to serious allergic reactions.

Symptoms of skin and eyes

Skin

Symptoms usually begin about one to three years after contracting the infection. Initially, the patient experiences severe, generalized itching (pruritus), which is accompanied by hives (skin disease with itchy bumps on the skin surface) and rapidly disappearing edema. Lumps appear under the skin. Skin discolouration occurs with a dark skin type. Over time, more chronic inflammatory changes occur, creating rough skin (leopard skin) that is no longer elastic. Loose folds of skin in the groin (drooping groin) and enlarged lymph nodes are other features of onchocerciasis.

Red eyes with conjunctivitis / Source: Marco Mayer, Wikimedia Commons (CC BY-SA-4.0)

Eyes
In the eye, dead larvae cause conjunctivitis, sclerosing keratitis, uveitis (type of eye inflammation in which the middle layer is inflamed) and secondary glaucoma (increased eye pressure that may damage the optic nerve, leading to vision loss). ). A number of patients also suffer from choroidoretinitis (inflammation of the choroid and retina in the eye). The eye problems associated with the eye disease occur with a chronic severe infection. With these eye problems, the patient suffers from itching and irritation of the conjunctiva. The eye problems develop slowly but spread, eventually causing the patient to become blind.

Diagnosis and examinations

Diagnostic research

In endemic areas, diagnosis is often made clinically. The larvae can be identified microscopically via a skin biopsy. The doctor also carries out a blood test and a condition of eosinophilia (increase in the number of eosinophil cells in the blood) is noticeable. Furthermore, a slit lamp examination of the eyes is useful because this eye examination reveals the presence of larvae.

Differential diagnosis

The doctor sometimes confuses the tropical condition with some other conditions, because its clinical picture mimics the symptom sequence of onchocerciasis.

  • leprosy
  • lichen planus (symptoms of the mouth, skin, genitals, nails and/or scalp)
  • Loa loa infection (infection with swelling around joints and eye worm)
  • lymphatic filariasis (flu-like symptoms and blocked lymphatic vessels)
  • pinta (bacterial infection with benign skin lesions)
  • scabies (contagious condition caused by a mite)
  • syphilis
  • treponematosis (endemic syphilis)
  • delayed hypersensitivity reactions
  • vitamin A deficiency
  • food allergy

Treatment of worm larvae via anthelmintic

Ivermectin is a so-called anthelmintic (worm-killing medicine) that the doctor uses in the treatment of onchocerciasis. This drug kills larvae and prevents them from returning within six to twelve months. The medicine has little effect on adult worms, so annual (or semi-annual) retreatment is necessary. The retreatment is necessary for ten to fifteen years because that is how long the worm will live. In patients infected with Loa loa (a parasitic worm that causes swelling around the joints and an eyeworm), Ivermectin occasionally causes serious allergic reactions, including toxic encephalopathy (dangerous brain disease).

Infectious disease prevention

The World Health Organization has established a black fly control program in West Africa since 1974. In 1989, mass treatment with ivermectin was initiated. This reduces the number of infections and causes fewer complications.

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