Loiasis

Loiasis is caused by the African eye worm Loa loa and occurs in central and western Africa with an estimated 10-15 million people being infected.

Loa loa is transmitted by blood-feeding midges (Chrysops). The adult worms migrate through the subcutaneous tissues and may also migrate through the eye, giving it its common name “African eye worm”. Microfilariae are found during the day in the peripheral blood (diurnal periodicity). There are unspecific symptoms associated with the infection (urticaria, pruritus, exhaustion, etc.) and 50% of patients suffer from atypical chronic symptoms that can be of respiratory, cardiac, gastrointestinal, ophthalmological or renal nature.

Due to these chronic symptoms, loiasis causes comparable morbidity as other Neglected Tropical Diseases. Despite this, Loa loa is not yet listed by the WHO as a Neglected Tropical Disease and thus no loiasis control programs exist. Loiasis further handicaps elimination programmes for lymphatic filariasis and onchocerciasis because loiasis patients harbouring high microfilariae numbers are at risk of developing life-threatening adverse events following treatments used for filarial mass drug administration (DEC or ivermectin). Given that Loa loa does not harbour Wolbachia endosymbionts, individual therapy with doxycycline is not effective. Oxfendazole is the only drug candidate so far that has the potential to treat loiasis safely as it specifically targets adult filariae.