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Onchocercosis, or river blindness, is an infectious disease that occurs mainly in Africa, South America and the Arabian Peninsula. It is classified as filariasis, i.e. chronic parasitic diseases. Its culprit is the nematode Onchocerca volvulus. According to estimates by the World Health Organization, more than 18 million people worldwide suffer from river blindness, 270 of which suffer from river blindness. he completely lost his eyesight, and an additional 500 thousand. suffers from a significant reduction in visual acuity.
Onchocerciasis is carried by the daffodils that reproduce in fast-flowing streams. Hence the name of the disease – river blindness.
Nematode larvae penetrate the skin after a person is bitten by fluff. After 12-18 months, the larvae transform into adults. Female nematodes can live in subcutaneous tumors for up to 15 years, giving birth to more microfilariae that travel under the skin towards the eyes.
Onchcercosis is the second most common cause of blindness in the world. Trachoma comes first.
Symptoms of river blindness
In patients without any symptoms, subcutaneous or slightly deeper nodules with adult worms may be visible. They consist of inflammatory cells and fibrous tissue in varying amounts. Old nodules or lumps may become cheesy or calcified.
Symptoms of infection may also include other symptoms.
Onchocercosis dermatitis develops in the microfilariae phase of the parasite’s life cycle. Increased itching of the skin may be the only symptom in patients with minimal infestation, i.e. parasite infestation. Uncharacteristic skin lesions take the form of a macular-lumpy rash with occlusions, scaly ulcers and lifenification (thickening of the skin with visible furrows). Symptoms of the disease may also include premature skin aging, its atrophy and enlargement of the inguinal and femoral lymph nodes, lymphatic stasis, tuft skin discoloration, local swelling and erythema. This form of dermatitis is generalized.
Ocular pathology can be characterized by a slight visual impairment, but also by its complete loss. Anterior lesions include punctate keratitis, acute inflammatory infiltrate around dying microfilariae that resolves without permanent damage, hardening keratitis with ingrown fibrous vascular tissue that can cause lens subluxation and blindness, and anterior membrane inflammation vascular or ciliary body that can damage the pupil.
In addition, inflammation of the retina and the optic nerve, or even atrophy, can develop.
Diagnosis of onchocercosis
The diagnostic method of choice is still the visualization of microfilariae in skin sections. Worms can also be seen in the cornea or the anterior chamber of the eye when examined with a slit lamp. Some laboratories around the world carry out serological tests. However, their results are not distinctive enough to be useful in the evaluation of a recent infection. In skin lesions, ultrasound or magnetic resonance imaging is often performed. The tests allow to assess the nodules under the skin and those formed deeper. Often during the examination, nodules are removed and it is analyzed whether they contain adult nematodes.
What treatment?
Until recently, there was no drug that could effectively combat river blindness. Currently, patients are administered orally ivermectin. The dose is adjusted according to the patient’s body weight (usually 150 micrograms per kilogram body weight). Subsequent doses are then given every 6-12 months. The treatment lasts until the symptoms disappear.
It works by reducing the microfilariaemia in the skin and eyes. In addition, the drug inhibits larvae reproduction for several months. The researchers believe the drug does not kill adults, but it certainly inhibits the release of new microfilariae by females.
How can I prevent infection?
None of the available drugs or preparations protect against nematode infection. However, it is known that administering ivermectin once or every six months reduces the risk of infection. Currently, surgical procedures to remove tumors accumulating microfilariae are rarely performed.
To minimize the risk of fluff bites, appropriate protective clothing should be worn and repellants (repellants) should be used frequently.
Tekst: Anna Jarosz