Loa loa
By Thuy-tien Huynh


Phylum: Nematode

    Class: Secernetea

        Subclass: Spiruria

            Order: Spirutida

                Superfamily: Filarioidea

                    Family: Filariidae

                        Genus and species: Loa Loa


Loa Loa: is the "eye worm" of Africa, which produces loiasis, or fugitive or Calabar swelling. The Loiasis is the disease caused by the filarial parasite Loa loa. Transient localized swelling as the adult worm migrates in the subcutaneous tissues characterizes it. The worm may also transit the eye beneath the conjunctiva (Fig).

Definitive Host: Humans

Intermediate Host: Deerfly genus Chrysops

* Some times the definitive host can be considered the deerfly and intermediate host can be human. It's dependent on how you define it. In this parasite, because it reproduces in humans, then humans are considered the definitive host.

Geographical Distrubution: Central and Western Africa.

Rain and swamp forest areas of West Africa.

Equatorial Sudan.

Especially common in Cameroon and on the Ogowe river.

West Indies, where it was first discovered during slavery. But it no longer exists there.

Morphology: L. loa is typical of the family: a simple head with no lips and eight cephalic papillae; a long, slender body; and a blunt tail. The cuticle is covered with irregular, small bosses, except at the head and tail. Males are 20-34 mm long by 350-430 um wide. Females are 20-70 mm long and about 425 um wide. The vulva is about 2.5 mm from the anterior end, and the tail is about 265-300 um long

Life Cycle: Adult live in subcutaneous tissue including back, chest, axilla, groin, scalp, and eyes of the humans. Loa loa is transmitted to humans by day-biting deerfly. Once inside the body the infective larvae develop slowly into a mature adult. During this period it lives and moves around the facial layers of the skin. In development period, Loa loa often makes frequent excursions through the subdermal connective tissues. Once they reach maturity, the adults mate and produce sheathed microfilariae. The microfilarae are diurnally periodic in synchrony with their vector and one they reinfect a fly they undergo two stages of growth into infective larvae, which can then be transmitted back to humans.

Pathogenesis: Slowly developing swelling of specific areas often a hand or foot. Adult worm may occasionally be seen moving slowly across the surface of the eyes or the bridge of the nose. These worms have a tendency to wander through the subcutaneous connective tissues, provoking inflammatory responses as they go. When they remain in one spot for a short time, the host reaction results in localized Calabar swellings, especially in the wrist and ankles, which disappear when the worm moves on. Adult worm migrates through the conjunctiva and cornea with swelling of the orbit and psychosomatic results to the host. There is also intense itching, joint pain and fatigue. When the migrating adult worms appear on the surface of skin, the worms often appear around the eye where they can damage the conjunctiva. The migrating worms can cause the calabar swilling in the arms and legs. These swelling is extremely painful when it moving. The Dying worm can also cause chronic abscesses followed by granulomatous reactions and fibrosis.

Diagnosis: Surgical removal is simple and effective, providing the worm is properly located, but most of the worms are inapparent. Transient swelling of the skin are suspect.

Treatment: Specific anti-protozoal drugs. The best choice drug is Diethylcarbamazine (DEC). Ivermectin seems to be effective. DEC and Ivermectin are also used as preventitive to heartworm disease

Control: Avoid the bites of deerflies.

Control of deer flies, which breed in swampy areas of the forest

Personal protective wearing long pants, and sleeping in well-screened areas. Use an effective repellent containing Deet.


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This page was last modified on January 26, 2004
Send questions and comments to Kim Bates