Loiasis FAQs


What is loiasis?

Loiasis is an infection caused by the parasitic worm Loa loa.

What are the signs and symptoms?

Many people do not develop any symptoms, and symptoms usually do not show up for many months after infection. If you have loiasis, you may have itchy, non-painful swellings of the body that come and go. The swellings can show up anywhere though they are more common near joints. You may develop an eye worm that crawls across the surface of your eye. Sometimes you may see a worm that crawls under your skin. Less common symptoms include itching all over your body, muscle pain, joint pain, and fatigue. Blood tests may show high counts of eosinophils, which are a type of blood cell that can be associated with parasitic infections.

How do you get infected?

You get infected by being bitten by an infected deerfly of the genus Chrysops. Deerflies become infected when they eat blood from an infected person. Travelers are more likely to become infected if they are in areas where they are bitten by deerflies for many months, though occasionally they get infected even if they are in the area for less than 30 days.

Where in the world can one get infected?

The parasite is passed from deerflies to humans in certain rain forests of West and Central Africa. The deerflies usually 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 may be an area where many deerflies are found. Your health care provider can help you determine if you are going to or have been to an area where loiasis is found.

Can loiasis be spread person to person?

No. If you are infected you cannot pass the infection on to other people.

How is it diagnosed?

If you have traveled to an area where infected flies are found and you develop symptoms, your health care provider may order a blood smear.  Blood is put on a microscope slide and examined for the larvae of the parasite.  Additionally, loaisis can be diagnosed by a health care provider if they see an adult worm on the surface of your eye.  Sometimes, if your health care provider is concerned that you may be infected but your tests are normal, he or she may order a specialized blood test.

What is the treatment?

Sometimes treatment of loiasis can be dangerous, so your health care provider may want to talk to an expert in tropical medicine before giving you any medication to treat loiasis. If you have an eye worm, the worm can be surgically removed to provide immediate relief while your health care provider determines if it is safe to treat you with medication to kill the parasite. Removing the worm from your eye does not cure the infection, as the parasite is often found in other parts of your body. A medication called diethylcarbamazine, or DEC, can be used to kill the parasites in your body. Because there is a small risk of serious side effects related to killing the parasites, your health care provider will do tests to be sure that it is safe to treat you. Sometimes people need special treatments before it is safe to give medication and sometimes treatment with medications is not recommended.

How can I prevent loiasis?

Avoid insect bites by wearing long pants and long-sleeved shirts and avoid the smoke of wood fires to reduce your risk of infection. If you are going to stay in an area affected by Loa loa in West and Central Africa for a long period of time, you can reduce your risk of getting loiasis by taking DEC weekly. You should consult a tropical medicine expert to determine whether using DEC to prevent loiasis is right for you. It can take time to get DEC, so do not wait until the last minute.

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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.

Page last reviewed: September 17, 2020