Loiasis

Loiasis is a disease caused by the filarial parasite Loa loa. It is characterized by transient localized swelling as the adult worm migrates in the subcutaneous tissues. The worms may also transit the eye beneath the conjunctiva. Humans and monkeys may be common hosts to certain species of the parasite.

Humans harboring microfilariae in the blood are the reservoir of loiasis (although non-human primates can be infected). Tabanid flies (deerflies, genus Chrysops, which breed in moist, muddy areas) bite the human and ingest blood containing the microfilariae. These develop into larvae in the fly (10-12 days) and are returned to man via the bite of the infective fly.

Clinical manifestations are often delayed for months or years and can continue for up to 17 years. They are caused by migration of the adult worm through the subcutaneous and deeper tissues of the body, leading to recurring or Calabar swellings. Allergic reactions, arthritis and neurological symptoms can occur. Diagnosis may be complicated by the presence of other filarial infections, especially onchocerciasis. The microfilarial have a day-time periodicity.

Loiasis is highly endemic in tropical (equatorial) west and central Africa. It is limited in distribution to forest areas in Central Africa from eastern Nigeria to Angola, extending into Congo, Zaire, Uganda and the Sudan. In Ethiopia a similar disease is called Kampala eye worm. In the Congo River basin, in particular, up to 90 percent of villagers in some areas are infected. In total it is believed that loiasis affects about one million people.