Loiasis is an infection caused by the roundworm (nematode) Loa loa.
Loiasis is transmitted to people by infected flies.
Most people with loiasis have no symptoms, but itchy swellings may appear, mainly on the arms and legs.
Sometimes worms travel to the eye and move under the clear membrane that covers the eye (conjunctiva).
Doctors diagnose loiasis by identifying worm larvae (microfilaria) in a sample of blood or by seeing an adult worm moving across the eye.
The only medication that kills both adult worms and larvae is diethylcarbamazine.
Helminths are parasitic worms that can infect humans and animals. There are 3 types of helminths: flukes (trematodes), tapeworms (cestodes), and roundworms (nematodes). Loa loa is a type of roundworm called a filarial worm.
Loiasis occurs only in rain forest areas of western and central Africa.
(See also Overview of Parasitic Infections.)
Transmission of Loiasis
Loiasis is transmitted when an infected African deer fly bites a person and deposits larvae of the worm. The larvae enter through the bite wound and mature into adult worms in the tissues under the skin (subcutaneous tissues). The adult worms travel in tissues under the skin and under the clear mucous membrane that covers the eyes. Adult female worms are approximately 1 1/2 to 3 inches (4 to 7 1/2 centimeters) long.
The adult worms produce immature worm larvae (called microfilariae) that circulate in the bloodstream during the day and are found in the lungs at night. The infection is spread when the infected person is bitten by a fly during the day, when the microfilariae are in the bloodstream. The fly then transmits larvae of the worm when it bites another person.
Image from the Centers for Disease Control and Prevention, Global Health, Division of Parasitic Diseases and Malaria.
Symptoms of Loiasis
Most people with loiasis have no symptoms.
Itchy swellings (Calabar swellings) develop mainly on the arms and legs but can develop anywhere on the body. They are thought to be an allergic reaction to substances released by the traveling adult worms. Swellings usually last 1 to 3 days in people who live in areas where the infection is common but occur more often and are more severe in travelers to these areas.
The movement of adult worms across the eye may make the eyes itch or feel irritated. Although movement of adult worms across the eye is unsettling, it usually does not cause permanent damage.
Occasionally, loiasis affects the heart, kidneys, or brain, but symptoms are usually mild.
Urine may contain more protein than usual and a little blood.
Diagnosis of Loiasis
Examination or testing of a sample of blood
Observation of worms moving across the eye
Identification of worms removed from the eye or skin
Doctors suspect loiasis in people who have eye worms or swellings who have traveled to or emigrated from areas in western and central Africa where the infection occurs.
Doctors diagnose loiasis when they identify microfilariae in a sample of blood examined under a microscope. The sample is taken between 10 AM and 2 PM, when the most microfilariae are in the bloodstream.
Occasionally, doctors diagnose loiasis when they see worms traveling under the conjunctiva of the eye or when they identify worms removed from the eye or skin.
Treatment of Loiasis
Diethylcarbamazine
For heavy infections, albendazole or a procedure to filter the blood
The only medication that kills microfilariae and adult worms is diethylcarbamazine. It is taken by mouth for 21 days. Treatment may need to be repeated to eliminate the infection.
Before treating people with diethylcarbamazine, doctors check them for another filarial worm infection called onchocerciasis because diethylcarbamazine can cause serious side effects in people who have these loiasis and onchocerciasis at the same time. People who have both loiasis and onchocerciasis are given diethylcarbamazineand ivermectin, which is a medication that is used to treat worms.
Diethylcarbamazine can have serious, sometimes fatal side effects, especially if the infection is severe. Reducing the number of microfilariae in the bloodstream before using diethylcarbamazine can reduce this risk. So before treatment with diethylcarbamazine, doctors determine the number of microfilariae in the blood. If the number is high, they reduce the number of microfilariae by giving people another medication for worm infections called albendazole or by doing a procedure that filters the blood (apheresis). This approach reduces the risk of serious side effects. If the number is low, people are given diethylcarbamazine and also may be given albendazole if diethylcarbamazine does not work.
Prevention of Loiasis
People who are going to stay for a long time in an area affected by Loa loa can take diethylcarbamazine to help prevent loiasis.
To reduce the number of deer fly bites, people can
Use insect repellents.
Wear clothing that has been treated with the insecticide permethrin.
Wear loose-fitting, long-sleeved shirts and long pants.
Because the flies bite during the day, mosquito netting over beds does not help.
