Parasitological and entomological aspects of loiasis

Loa loa is a filarial pathogen transmitted by the blood-sucking flies Chrysops silacea and Chrysops dimidiata. Humans are the final host where adult worms migrating through the soft tissue reproduce. Microfilariae are found in peripheral blood with a peak during the hot hours of the day. Taken up by a Chrysops fly, larvae develop stepwise to infectious L3 larvae. These are actively migrating into the bite wound to infect the next human host and closing the transmission cycle.

The Chrysops fly’s habitat is the canopy of the rainforest. It is therefore exclusively found in rural regions characterized by forest or adjacent savannah. It bites during the daytime preferentially at the lower limbs. Chrysops silacea and C. dimidiata breed in muddy soil of the rainforest and are anthropophilic. The flies are attracted by moving individuals, blue colours of cloths and woodfire

References:

The African eye worm: current understanding of the epidemiology, clinical disease, and treatment of loiasis.

Ramharter M, Butler J, Mombo-Ngoma G, Nordmann T, Davi SD, Zoleko Manego R. Lancet Infect Dis. 2024 Mar;24(3):e165-e178. doi: 10.1016/S1473-3099(23)00438-3.

Loa loa vectors Chrysops spp.: perspectives on research, distribution, bionomics, and implications for elimination of lymphatic filariasis and onchocerciasis.

Kelly-Hope L, Paulo R, Thomas B, Brito M, Unnasch TR, Molyneux D. Parasit Vectors. 2017 Apr 5;10(1):172. doi: 10.1186/s13071-017-2103-y.