loiasis

Loiasis, also known as African eye worm disease, is a tropical parasitic infection caused by the filarial nematode Loa loa. The adult worms live in subcutaneous tissues and can migrate through the body, occasionally crossing the conjunctiva of the eye. Transmission occurs through bites of Chrysops deer flies, which inhabit forests of central and western Africa.

Loa loa microfilariae circulate in the peripheral blood with a diurnal pattern, being most abundant during the day. Humans acquire infection when bitten by an infected Chrysops fly, which transmits the larvae that develop into adult worms over time. Adults may live for many years in subcutaneous tissues and produce microfilariae that continue the life cycle.

Clinical features vary. Some people are asymptomatic, while others experience Calabar swellings—transient, localized angioedema near joints—and pruritus. The migrating eye worm can be seen in the conjunctiva, causing irritation and concern. In heavy infections, systemic symptoms such as fever, malaise, or headaches may occur.

Diagnosis relies on identifying microfilariae in daytime peripheral blood samples or observing an adult worm in subcutaneous tissue or the eye. Serology and imaging are less definitive. Microfilarial load helps guide treatment decisions due to the risk of hypersensitivity reactions.

Treatment centers on diethylcarbamazine (DEC), which targets both microfilariae and adults, though significant inflammatory reactions can occur in people with high microfilarial densities. Pre-treatment assessment of microfilaremia is advised. Albendazole is an alternative or adjunct; ivermectin is usually avoided in patients with high microfilarial loads due to the risk of severe adverse events. Prevention focuses on bite avoidance and protective measures in endemic areas.