Question

Parasitic Infections

What are the symptoms of onchocerca volvulus?

A Answers (1)

  • General: The incubation period of onchocerciasis ranges from nine to 24 months following the bite of a black fly carrying the infective microfilariae. The incubation period is the time between exposure to a disease-causing organism and the first appearance of signs and symptoms. The adult worms are harmless compared with the microfilariae. The microfilariae cause intense inflammatory reactions in the skin, which lead to skin rashes, lesions, pruritus (intense itching), and changes in skin color. The microfilariae have the potential to invade other organs, but most commonly invade the eye directly, because it is a relatively easy target. Eye disease is caused by inflammatory responses to the microfilariae as they migrate through the eye. Skin lesions: The inflammatory lesions (called onchodermatitis) on the skin initially appear as small, round, red bumps on the skin, usually 0.5 centimeters or less in diameter, and they are accompanied by intense itching. Later, the elastic fibers and structural elements of the skin break down, causing the skin to appear thin and wrinkled like a "lizard's skin." Loss of skin color, or pigmentation, in the affected areas is also common in the later stages of infection and is known as "leopard skin." The skin may also thicken and appear as "elephant skin." Skin changes caused by the parasite vary from region to region. Eye: O. volvulus commonly affects the eye in infected individuals, leading to blindness. The blindness rates have reached up to 40% in the adult population of endemic areas. However, control of black fly breeding and treatment with an antiparasitic drug, ivermectin (e.g., Stromectol), has considerably reduced the incidence of new infections. Studies are currently being conducted to evaluate the effect of ivermectin in preventing disease.

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