Loa loa

Loa loa is the filarial nematode (roundworm) species that causes Loa loa filariasis. It is commonly known as the "eye worm". Its geographic distribution includes Africa and India.

L. loa is one of three parasitic filarial nematodes that cause subcutaneous filariasis in humans. The two other filarial nematodes are Mansonella streptocerca and Onchocerca volvulus (causes river blindness).

Maturing larvae and adults of the "eye worm" occupy the subcutaneous layer of the skin – the fat layer – of humans, causing disease. The young larvae develop in horseflies of the genus Chrysops (deer flies, yellow flies), including the species C. dimidiata and C. silacea, which infect humans by biting them.

Biology

Morphology

Loa loa worms have a simple body including a head, body, and tail. Males range from 20mm to 34mm long and 350μm to 430μm wide. Females range from 20mm to 70mm long and are about 425μm wide. They have varying colors.

Life cycle

Three species involved in the life cycle include the parasite Loa loa, the fly vector, and the human host:

Loa loa filariasis

Loa loa filariasis (also known as loiasis, loaiasis, Calabar swellings, fugitive swelling, tropical swelling and African eyeworm) is a skin and eye disease caused by the nematode worm Loa loa. Humans contract this disease through the bite of a deer fly or mango fly (Chrysops spp), the vectors for Loa loa. The adult Loa loa filarial worm migrates throughout the subcutaneous tissues of humans, occasionally crossing into subconjunctival tissues of the eye where it can be easily observed. Loa loa does not normally affect one's vision but can be painful when moving about the eyeball or across the bridge of the nose. The disease can cause red itchy swellings below the skin called "Calabar swellings". The disease is treated with the drug diethylcarbamazine (DEC), and when appropriate, surgical methods may be employed to remove adult worms from the conjunctiva.

Signs and symptoms