Loiasis: African eye worm

Published on November 30, 2020   27 min

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My name is Louise Kelly-Hope. I'm a scientist at the Center for Neglected Tropical Diseases in the Department of Tropical Disease Biology at the Liverpool School of Tropical Medicine, UK. Today, I'll be talking to you about loiasis, also known as African eye worm.
The talk will include three main sections. First, I'll provide a brief overview of loiasis and then describe key factors about the biology, disease, infection, diagnosis, treatment and control before talking about the distributions, mapping procedures, environmental associations, and implications for filariasis elimination programmes.
Loiasis is caused by the filarial nematode Loa loa. It is transmitted by female tabanid flies of the genus Chrysops. It is largely confined to the tropical rainforest areas of Central and West Africa. An estimated 30 million people live in moderate to high risk areas, predominantly in Cameroon, Democratic Republic of Congo, Gabon, and Nigeria. It is currently not listed as a Neglected Tropical Disease by the World Health Organization or included in the Global Burden of Disease Studies. Its public health importance is related to the risk of serious adverse events or SAEs, associated with ivermectin-based treatment for onchocerciasis and lymphatic filariasis.
There are two main stages of the Loa loa life cycle, the human stage and the fly stage. Humans are infected during a blood meal of an infected fly, with third-stage larvae, which is commonly abbreviated to L3. In the human host, larvae develop into adult threadlike worms that live and migrate through the subcutaneous tissue, including the eye area. While in the human host, male and female adult worms mate and produce thousands of microfilariae which are found in the peripheral blood during the day. This is the time when microfilariae are ingested by a fly during a blood meal. In the fly, the microfilariae develop into third stage larvae, which takes between 10 and 12 days, then they migrate to the fly's proboscis where they can infect another human when they take a blood meal, and so this cycle continues.