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Loiasis FAQs

What is loiasis?

Loiasis is an infection caused by the parasitic worm, Loa loa, which is transmitted through the bite of the African deer fly (genus Chrysops). The disease can cause itchy swellings (Calabar swellings) of the body, eye worm, and elevated eosinophils on blood tests. There may be up to 13 million people with loiasis in affected areas of Central and West Africa.

How does one become infected?

One becomes infected by being bitten by an infected deerfly. Deerflies become infected by taking a blood meal from an infected person. Although the infection is more likely to be found in persons who travel to affected areas for long periods of time, short-term travelers (<30 days) have rarely been infected.

Where is it found?

The people most at risk for loiasis are those who live in the high-canopied rain forests of West and Central Africa. The deerflies that transmit the parasite typically bite during the day and are more common during the rainy season. They are attracted by the movement of people and by smoke from wood fires. Rubber plantations create a favorable environment for the flies, as the trees form a dense canopy.

How is it diagnosed?

In persons who have the signs or symptoms of infection and who have traveled to affected areas in West and Central Africa, the disease can be diagnosed by examining a blood smear for the presence of the larvae of the parasite, by a health professional providing documentation of visualization of an adult worm on the surface of the eye, or by specialized blood tests. Additionally, microscopic examination of a worm can confirm the diagnosis. Occasionally infection is indentified in a blood smear performed for other reasons in a person without symptoms.

Can this be transmitted human to human?

No. Loaisis is not spread person to person. The parasite completes an important part of its lifecycle inside the deerfly before it can be passed to another human.

What are the signs and symptoms?

Signs and symptoms include itchy swellings (Calabar swellings) anywhere on the body, that are usually non-tender and are often found near joints. Adult worms that migrate across the eye or under the skin can cause itchiness or irritation. Less common symptoms include generalized itching, muscle pain, joint pain, and fatigue. Infected persons may not have any symptoms at all.

What is the treatment?

Decisions about treatment of loaisis are sometimes difficult and should be made in consultation with an expert in infectious diseases or tropical medicine. Adult worms visible on the surface of the eye or under the skin can be surgically removed under local anesthesia to provide relief of localized symptoms. Persons who undergo surgical removal of a worm may still have larvae in their blood and often receive treatment with an anti-parasitic drug in addition to surgery. Treatments to kill the parasite in the body are available. The treatment of choice is a medication called diethylcarbamazine or DEC, though there is a small risk of serious side effects of treatment. Your doctor will do tests to be sure that it is safe to treat your condition. Sometimes, other medical conditions or infections that might be present will need to be addressed first to make it safer to use DEC. In some instances, treatment is not recommended.

How can I prevent loiasis?

Taking precautions to avoid insect bites and to avoid the smoke of wood fires should reduce your risk of infection. Additionally, loiasis can be prevented by taking DEC weekly when visiting areas affect by Loa loa in West and Central Africa. You should consult an infectious disease expert to determine whether using DEC to prevent infection is appropriate for you.

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This information is not meant to be used for self-diagnosis or as a substitute for consultation with a health care provider. If you have any questions about the parasites described above or think that you may have a parasitic infection, consult a health care provider.

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  • Page last reviewed: November 2, 2010
  • Page last updated: November 2, 2010 The U.S. Government's Official Web PortalDepartment of Health and Human Services
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