About loa loa worms in humans

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About loa loa worms in humans
(Loa Loa worm in the subconjunctival eye tissues/JD McLean/Wikimedia.org)

According to the Centers for Disease Control, the Loa loa worm is one of eight species of filarial worms that can cause complications in humans. Loa loa worms, which affect primarily the subcutaneous tissues, won't be found in your back yard, and in fact, filariasis in the U.S. was last noted in the late 1920s. However, in other parts of the world, the Loa loa worm is still endemic to native populations and poses a hazard to travellers.

Loa Loa Worms: Where They're Found

The Loa loa worm, also called the "African eye worm," is specific to African rainforests, particularly those in Central Africa. However, other types of filial worms are found in other parts of the world, including India, Turkey, Southeast Asia, Australia, South America and the Philippines. The carrier of the Loa loa worm is the deer fly, which ingests the worm's larvae during the course of a blood meal.

How Loa Loa Worms Infect Humans

According to the CDC, Loa loa worm larvae are transmitted to humans through a bite from an infected deer fly. Adult Loa loa worms then migrate through the subcutaneous tissue--and sometimes across the human eye. Adult worms produce microfilariae that can be noted in the blood, spinal fluid, urine and saliva.

Symptoms of Loiasis

A Loa loa worm infection results in loiasis, a specific type of filariasis. Symptoms include angioedema (swelling) noted primarily in the extremities. According to Merck.com, this is possibly a type of reaction to the allergens produced by adult Loa loa worms. Sometimes, the worms may wander across the eye, which is a more disconcerting symptom. Natives usually experience swelling for only one to three days, but travellers may note more pronounced symptoms.


According to Merck.com, the optimal time to test for a Loa loa worm infection is to draw blood at noon, when microfilaremia levels are particularly high. This type of blood testing won't differentiate an infection due to the Loa loa worm from any other type of filarial worm.

Treating Loa Loa Worms

The first-line treatment for a Loa loa worm infection is usually Diethylcarbamazine (DEC), which kills both worms and their microfilariae. Allergic reactions can be treated with oral antihistamines. Other treatments for Loa loa worms may include albendazole and ivermectin. These drugs work more slowly, but may result in fewer side-effects.

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