May 25, 2016
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Onchocerciasis (cont.)

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Is there an incubation period for onchocerciasis?

Although the infection with larvae begins immediately, the disease may not become apparent in an individual for months to years. In most individuals, it develops slowly in the skin although some patients may present initially with eye problems.

How is onchocerciasis diagnosed?

Clinical presumptive diagnosis is made if the patient lives or visits areas where the disease is endemic and has characteristic skin or eye changes described above. Definitive diagnosis is simply done by seeing adult worms in excised skin nodules, eye lesions, or by finding microfilariae in skin shavings or punch biopsies of the skin. In addition, an immunological test for antibodies developed against the parasites early in the infection is useful to determine if a person is infected before microfilariae are detectable. This test is available from the CDC. It is important to obtain a definitive diagnosis so that appropriate treatment can be started (see treatment section below). Onchocerciasis is a type of filariasis that does not respond well to some other drugs used to treat other similar filarial diseases. Diethylcarbamazine, a commonly used drug that is a derivative of piperazine, actually has been linked to severe and sometimes fatal patient reactions when used to treat onchocerciasis.

What is the treatment for onchocerciasis?

Treatment is done by giving the patient ivermectin, an antiparasitic drug once or twice per year for about 10-15 years (the life span of adult worms). This drug is effective in killing the microfilariae but does not kill the adult worms. The mature worms may remain alive for 10-15 years in the patient. Most clinicians recommend that subcutaneous nodules should be excised, if possible, thereby removing the adult worms that may reproduce more microfilariae over time. Some clinicians recommend that after ivermectin treatment, patients may benefit from a six-week dose of doxycycline antibiotic. Doxycycline damages and kills Wolbachia bacteria that are inside the microfilariae and adult worms, resulting in the death of microfilariae and ineffective microfilariae produced by the surviving adult worms. This may slow or halt further disease development.

The use of diethylcarbamazine (a treatment used before ivermectin became available) is contraindicated. It may cause severe or fatal patient reactions in individuals with onchocerciasis.

A new drug capable of killing the adult worms of onchocerciasis is under study for use in humans. It's named moxidectin but has not yet been approved for use in humans.

Medically Reviewed by a Doctor on 4/15/2015


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