Loiasis

What is loiasis?

Loiasis, commonly called African eye worm, is an infection caused by the Loa loa roundworm. Loiasis is a type of filariasis, an infection from a filarial worm (parasitic roundworm).

People can get loiasis if they're bitten by deerflies (also called mango or mangrove flies) that carry the parasite. Deerflies live and reproduce in some rainforests in West and Central Africa.

Loa loa worms are parasites that can reproduce and live inside you. When they enter your body, they usually live in your:

• Blood.
• Lungs.
• Lymphatic system (part of your immune system where certain blood cells are made).
• Subcutaneous tissues (tissues under your skin).

Who does loiasis affect?

Over 29 million people in affected parts of West and Central Africa may be at risk of getting loiasis.

Can loiasis cause blindness?

Seeing a worm in your eye can be unsettling and uncomfortable. But Loa loa worms, which are 1 to 3 inches long, don’t cause blindness and usually don’t damage your eyes. The worm usually moves across your eye and back into your body. Your provider can safely remove a visible worm with a minor procedure, but this will not cure the infection.

What are the symptoms of loiasis?

Many people who have loiasis don’t have symptoms, but you may experience:

• Fatigue.
• Itching all over your body.
• Itchy, swollen areas or sores on your body, especially near joints like your knees or elbows. These are called Calabar swellings. The swelling may go away after a few days and come back again days or weeks later.
• Muscle or joint pain.
• Worm that you can see crawling under your skin.
• Worm that crawls across your eye’s conjunctiva, the lining on the surface of your eye and inside your eyelid.

What causes loiasis?

Loiasis spreads when an infected fly bites your skin. The biting flies that carry the Loa loa infection are deer flies and mangrove flies found only in Africa. When these flies bite an infected person, they can spread the infection to the next person they bite.

Once the microfilariae (microscopic worms) are in your body, it takes several months for them to become adult worms. As they grow, the microfilariae can move to your body’s tissues and certain organs, like your lungs. Once the adult worms are inside you, you might see them moving under your skin or in your eye.

If you take a short trip to Africa, your chances of getting loiasis are small. People who contract this infection are usually bitten by infected flies many times over a period of several months.

Is loiasis contagious?

No, loiasis infections aren’t spread from person to person.

How is loiasis diagnosed?

If you traveled to or live in affected areas of Africa and you have loiasis symptoms, your provider may order a blood test. This test can show whether you have the Loa loa microfilariae in your blood. Your provider may also perform a physical exam and look for signs of loiasis, such as itchy, swollen areas on your body.

How is loiasis treated?

Antiparasitic medications, like ivermectin and diethylcarbamazine (DEC), treat loiasis. But people with high levels of Loa loa microfilariae in their blood can have life-threatening reactions to these medications. Your provider may order a test to measure the number of microfilariae in your blood before giving you ivermectin or DEC.

If you have more than 8,000 microfilariae per milliliter of blood, ivermectin and DEC may not be safe for you. Your provider may recommend a medication called albendazole or a blood filtering procedure first. Albendazole and blood filtering lower the number of microfilariae in your blood. Then, ivermectin or DEC may be safe for you to take.

Because loiasis is rare in the U.S., your provider may consult with an expert in tropical medicine to treat the infection. If you have a severe infection, you’ll need to see an experienced specialist.

How can I reduce my risk of getting loiasis?

There aren't any vaccines that prevent loiasis.

If you're traveling to West or Central Africa and planning to stay for a long period of time, you can reduce your risk of loiasis infection by:

• Taking 300 milligrams (mg) of diethylcarbamazine (DEC) once a week.
• Wearing insect repellants with DEET (N,N-Diethyl-meta-toluamide).
• Wearing long pants and long-sleeved shirts to keep flies off your skin.
• Applying an insecticide called permethrin to your clothes.

What can I expect if I have loiasis?

Many people who have loiasis don’t know they have it, and may not have serious health problems from it. If you have symptoms or suspect you have loiasis, talk to your provider. Medications can treat the infection and prevent possible complications.

When should I see my healthcare provider?

See your provider if you:

• Have symptoms of loiasis after traveling to West or Central Africa.
• Plan to travel to West or Central Africa and may need preventive DEC treatment. It can take several weeks to get DEC, so see your provider as early as possible before your trip.

A note from Cleveland Clinic

Loiasis (African eye worm) is a parasitic infection that can cause various symptoms, or may cause no symptoms at all. Finding a worm in your eye can be frightening, but the worm usually moves across your eye within a few hours and disappears. Your provider can also remove it with a minor surgical procedure.

You can take steps to prevent loiasis if you’re traveling to affected areas of Africa. And if you do get the infection, your provider can treat it with antiparasitic medications.