Life cycle of Loa loa
The vectors for Loa loa filariasis are two day-biting Chrysops deerflies, C. silacea and C. dimidiata. During a blood meal, an infected fly introduces third-stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound (1). The larvae develop into adults that commonly reside in subcutaneous tissue (2), where they can live for several years. The female worms measure 40 to 70 mm in length and 0.5 mm in diameter, whereas the males measure 30 to 34 mm in length and 0.35 to 0.43 mm in diameter. Adults produce microfilariae measuring 250 to 300 μm by 6 to 8 μm, which are sheathed and have diurnal periodicity. Microfilariae have been recovered from spinal fluids, urine, and sputum. During the day they are found in peripheral blood, but during the noncirculation phase, they are found in the lungs (3). The fly ingests microfilariae during a blood meal (4). After ingestion, the microfilariae lose their sheaths and migrate from the fly's midgut through the hemocoel to the thoracic muscles of the arthropod (5). There the microfilariae develop into first-stage larvae (6) and subsequently into third-stage infective filariform larvae (7). The third-stage infective larvae migrate to the fly's proboscis (8) and, just a few weeks after the microfilariae were ingested by the fly, can infect another human when the fly takes a blood meal (9).
From Centers for Disease Control Parasites and Health website.