Dirofilaria repens life cycle

During a blood meal, an infected mosquito (Aedes, Anopheles, Culex, Mansonia) introduces third-stage filarial larvae of Dirofilaria repens onto the skin of the canine definitive host (but also occasionally humans, especially in Europe), where they penetrate into the bite wound (1). In the definitive host, the L3 larvae undergo two more molts into L4 and adults, the latter of which resides in subcutaneous tissues (2). Adult females are usually 100 to 170 mm long by 460 to 650 micrometers wide; males are usually 50 to 70 mm long by 370 to 450 micrometers wide. Adults can live for 5 to 10 years. In subcutaneous tissue, the female worms are capable of producing microfilariae over their lifespan. The microfilariae are found in peripheral blood (3). A mosquito ingests the microfilariae during a blood meal (4). After ingestion, the microfilariae migrate from the mosquito's midgut through the hemocoel to the Malpighian tubules in the abdomen (5). There the microfilariae develop into first-stage larvae (6) and subsequently into third-stage infective larvae (7). The third-stage infective larvae migrate to the mosquito's proboscis (8) and can infect another definitive host when it takes a blood meal (1). In humans (9), D. repens usually manifests as either a wandering worm in the subcutaneous tissue or a granulomatous nodule, although there are reports of pulmonary dirofilariasis with this species.