Dirofilaria immitis life cycle

During a blood meal, an infected mosquito (Aedes, Culex, Anopheles, Mansonia) introduces third-stage filarial larvae of Dirofilaria immitis into the skin of the definitive host, which is usually a domestic dog or coyote in the United States (although a wide variety of other animals can also be infected, including felids, mustelids, pinnipeds, beaver, horses, and humans), where they penetrate into the bite wound (1). In the definitive host, the L3 larvae undergo two more molts into L4 and adults. Adults reside in pulmonary arteries and are occasionally found in the right ventricle of the heart (2). Adult females are usually 230 to 310 mm long by 350 mcm wide; males are usually 120 to 190 mm long by 300 mcm wide. Adults can live for 5 to 10 years. In the heart, 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. immitis larvae tend to follow the same migratory pathway as in the canine host, ending up in the lungs, where they often lodge in small-caliber vessels, causing infarcts and typical "coin lesions" visible on radiographs.