Loaiasis is a filariasis in the connective tissue caused by Filaria loa. The main clinical manifestations are migratory masses in the connective tissue, conjunctivitis, and arthralgia.


The pathogen is Filaria loa, also known as Loa loa or eye worm.

The adults are white, linear, with a slightly thin head. Males are 30 - 34mm long and 0.35 -0.43mm wide, while females are 50 - 70mm long and 0.5mm wide. Microfilariae are white, 250 - 300μm long,6 - 8.5μm wide, and appear in the peripheral blood during daytime.

Adults parasitize the subcutaneous tissues of the human body, including the back, chest, limbs, underarms, groin, penis, scalp, and eyes. They can migrate freely in the deep connective tissues under the skin, forming migratory subcutaneous masses, and often periodically migrate under the conjunctiva. Females deliver microfilariae intermittently during migration. After reaching the blood, microfilariae can be sucked by the deerfies during daytime, and develop into infective larvae in about 9 - 10 days. If humans are bitten by the deerflies, the infective larvae develop into adults in about one year in the human body. Adult worms can survive for more than 15 years.

Patients are the only source of infection.

The media of transmission are deerflies, also known as mango flies or mangrove flies.

Signs and Symptoms

Adult worm migrates to the connective tissues under the skin. Under the action of the metabolites of Loa loa, allergic reactions occur in the subcutaneous tissues, forming migratory masses. There may be redness, swelling, fever, pain, and pruritus. The migratory masses are 5 - 10cm in diameter, indurated, and elastic. The swelling persists for 2 - 3 days and is more common in the limbs, trunk, interdigital areas, thenar muscles, and gastrocnemius muscles, as well as scrotum. After the worm leaves, the masses subside spontaneously. The peristaltic, funicular worm can be palpated under the skin on the affected area. Adult worms can infiltrate deep skin to deliver microfilariae.

Adult worms often migrate to the ocular conjunctiva, causing conjunctivitis. The main symptoms include conjunctival hyperemia and edema, photophobia, lacrimation, pruritus, foreign body sensation, and little discharge. There is not serious harm. The worm can cause funicular, migratory masses in the blepharal skin. Loa loa can migrate from one eye to the other from the subcutaneous tissue.

Figure 1 ocular loaiasis

The invasion of the heart can cause endocarditis, myocarditis, and pericarditis. In addition, microfilariae can block cerebral capillaries, causing cerebral hypoxia and central neuropathy, and can also cause peripheral neuritis.

Some patients develop anxiety due to visual inconvenience caused by ocular symptoms. There are arthralgia in the proximal extremities, local swelling, and impaired mobility in some patients. In addition, patients may present with fever, urticaria, and eosinophilia.

Adult worms can crawl out from subcutaneous tissues and invade various organs, such as stomach and bladder. Occasionally, the worms may invade the glottis or urethra, leading to severe symptoms.


If there are a history of deerfly bites and clinical presentations, the disease should be suspected.

If there are microfilariae found in the peripheral blood, adult worm seen in the conjunctiva, or adult worm found in the migratory masses, the disease can be definitively diagnosed.


The adult worms in the conjunctiva and subcutaneous masses can be eliminated by surgery.

The medication regimen is diethylcarbamazine 2mg/(kg.d) orally in 3 divided doses for 3 weeks, if necessary, repeating with a withdrawal interval of 4 weeks.

Ivermectin and albendazole can also be administered.