1. When an infected fly bites a person, it deposits Loa loa larvae onto the person's skin, and the larvae enter the bite wound.
2. The larvae mature into adults in tissues under the skin (in subcutaneous tissue).
3. Adults produce immature worm larvae (called microfilariae), which circulate in the bloodstream during the day and stay in the lungs at night. Microfilariae may be present in spinal fluid, urine, or sputum.
4. A fly ingests microfilariae when it bites the person.
5. In the fly, the microfilariae travel to the middle part of the fly's gut (midgut), then to muscles in its midsection (thoracic muscles).
6–7. There, the microfilariae develop into larvae.
8. Larvae travel to the fly's mouth parts (proboscis) and can be transmitted to other people when the fly bites them.
Image from the Centers for Disease Control and Prevention, Global Health, Division of Parasitic Diseases and Malaria.