Loiasis

• Infection by the african eye worm, loa loa.
• Loiasis is caused by the parasitic worm Loa loa.

It is passed on to humans through the repeated bites of deerflies (also known as mango flies or mangrove flies) of the genus Chrysops. The flies that pass on the parasite breed in certain rain forests of West and Central Africa. Infection with the parasite can also cause repeated episodes of itchy swellings of the body known as Calabar swellings.

Loa Loa Life Cycle

Incidence

• Knowing whether someone has a Loa loa infection has become more important in Africa because the presence of people with Loa loa infection has limited programs to control or eliminate onchocerciasis (river blindness) and lymphatic filariasis (elephantiasis).
• There may be more than 29 million people who are at risk of getting loaisis in affected areas of Central and West Africa.

Transmission

• 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.

Loa loa - microfilaria

Epidemiology

• 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.
• No person to person contact was described.

Loa loa microfilaria

Cause

• Loiasis is caused by the nematodes (roundworm) Loa loa that can inhabit the lymphatics and subcutaneous tissues of humans.

Life Cycle

• The vector for Loa loa filariasis are flies from two species of the genus Chrysops, C. silacea and C. dimidiata.

During a blood meal, an infected fly (genus Chrysops, day-biting flies) introduces third-stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound The number

1. The larvae develop into adults that commonly reside in subcutaneous tissue The number
2. The female worms measure 40 to 70 mm in length and 0.5 mm in diameter, while the males measure 30 to 34 mm in length and 0.35 to 0.43 mm in diameter. Adults produce microfilariae measuring 250 to 300 μm by 6 to 8 μm, which are sheathed and have diurnal periodicity. Microfilariae have been recovered from spinal fluids, urine, and sputum. During the day they are found in peripheral blood, but during the non-circulation phase, they are found in the lungs The number
3. The fly ingests microfilariae during a blood meal The number
4. After ingestion, the microfilariae lose their sheaths and migrate from the fly’s midgut through the hemocoel to the thoracic muscles of the arthropod The number
5. There the microfilariae develop into first-stage larvae The number
6. and subsequently into third-stage infective larvae The number
7. The third-stage infective larvae migrate to the fly’s proboscis The number 8 and can infect another human when the fly takes a blood meal

Loa loa

Diagnosis

• In people who have been bitten by the flies that carry Loa loa in areas where Loa loa is known to exist, the diagnosis can be made in the following ways:

• Identification of the adult worm by a microbiologist or pathologist after its removal from under the skin or eye
• Identification of an adult worm in the eye by a health care provider
• Identification of the microfilariae on a blood smear made from blood taken from the patient between 10AM and 2PM
• Identification of antibodies against L. loa on specialized blood test
• Diagnosis of loiasis can be difficult, especially in light infections where there are very few microfilariae in the blood. The specialized blood test is not widely available in the United States. A positive antibody blood test in someone with no symptoms means only that the person was infected sometime in his/her life. It does not mean that the person still has living parasites in his/her body.

Treatment

• Decisions about treatment of loiasis can be difficult and often require advice from an expert in infectious diseases or tropical medicine.
• Although surgical removal of adult worms moving under the skin or across the eye can be done to relieve anxiety, loiasis is not cured by surgery alone.
• There are two medications that can be used to treat the infection and manage the symptoms.
• The treatment of choice is diethylcarbamazine (DEC), which kills the microfilariae and adult worms.
• Albendazole is sometimes used in patients who are not cured with multiple DEC treatments.
• It is thought to kill adult worms.

Filariasis Microfilariae of Loa loa (right) and Mansonella perstans

Prevention & Control

• There are no programs to control or eliminate loiasis in affected areas. Your risk of infection may be less in areas where communities receive regular treatment for onchocerciasis or lymphatic filariasis.

Vaccine

• There are no vaccines that protect you from loiasis.

Preventive medication

• If you are going to be in an area with loiasis for a long period of time, diethylcarbamazine (DEC)—300mg taken once a week—can reduce your risk of infection.

Precautions

• Avoiding areas where the deerflies are found, such as muddy, shaded areas along rivers or around wood fires, may also reduce your risk of infection.
• You may reduce your risk of bites by using insect repellants that contain DEET (N,N-Diethyl-meta-toluamide) and wearing long sleeves and long pants during the day, which is when deerflies bite.
• Treating your clothes with permethrin may also help.

Loiasis Resources
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