Dirofilariasis

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 . 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 . Adult females are usually 230-310 mm long by 350 µm wide; males are usually 120-190 mm long by 300 µm wide. Adults can live for 5 - 10 years. In the heart, the female worms are capable of producing microfilariae over their lifespan. The microfilariae are found in peripheral blood . A mosquito ingests the microfilariae during a blood meal . After ingestion, the microfilariae migrate from the mosquito's midgut through the hemocoel to the Malpighian tubules in the abdomen . There the microfilariae develop into first-stage larvae and subsequently into third-stage infective larvae . The third-stage infective larvae migrate to the mosquito's proboscis and can infect another definitive host when it takes a blood meal . In humans , 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.

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 . In the definitive host, the L3 larvae undergo two more molts into L4 and adults, the latter of which resides in subcutaneous tissues . Adult females are usually 100-170 mm long by 460-650 µm wide; males are usually 50-70 mm long by 370-450 µm wide. Adults can live for 5 - 10 years. In subcutaneous tissue, the female worms are capable of producing microfilariae over their lifespan. The microfilariae are found in peripheral blood . A mosquito ingests the microfilariae during a blood meal . After ingestion, the microfilariae migrate from the mosquito's midgut through the hemocoel to the Malpighian tubules in the abdomen . There the microfilariae develop into first-stage larvae and subsequently into third-stage infective larvae . The third-stage infective larvae migrate to the mosquito's proboscis and can infect another definitive host when it takes a blood meal . In humans , 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 .

During a blood meal, an infected mosquito (Aedes, Anopheles, and possibly others) introduces third-stage filarial larvae of Dirofilaria tenuis onto the skin of the raccoon definitive host (but also occasionally humans), where they penetrate into the bite wound . In the definitive host, the L3 larvae undergo two more molts into L4 and adults, the latter of which resides in subcutaneous tissues . Adult females are usually 80-130 mm long by 260-360 µm wide; males are usually 40-50 mm long by 190-260 µm wide. Adults can live for 5 - 10 years. In subcutaneous tissue, the female worms are capable of producing microfilariae over their lifespan. The microfilariae are found in peripheral blood . A mosquito ingests the microfilariae during a blood meal . After ingestion, the microfilariae migrate from the mosquito's midgut through the hemocoel to the Malpighian tubules in the abdomen . There the microfilariae develop into first-stage larvae and subsequently into third-stage infective larvae . The third-stage infective larvae migrate to the mosquito's proboscis and can infect another definitive host when it takes a blood meal . In humans , D. tenuis may wander in the subcutaneous tissues for months, but finally is encapsulated in a granulomatous nodule, but may also be found around the eye or on the conjunctiva. Because of this, the infection in humans was first known as Dirofilaria conjunctivae.

During a blood meal, an infected black fly (genus Simulium) introduces third-stage filarial larvae of Dirofilaria ursi onto the skin of the ursine definitive host (although humans may also serve as hosts), where they penetrate into the bite wound . In subcutaneous tissues, the larvae develop into adults, which commonly reside in subcutaneous connective tissues . Adult females are usually 115-225 mm long by 460-700 µm wide; males are usually 50-90 mm long by 330-480 µm wide. Adults can live for 5 - 10 years. In the subcutaneous tissues, the female worms are capable of producing microfilariae over their lifespan. The microfilariae are found in peripheral blood . A black fly ingests the microfilariae during a blood meal . After ingestion, the microfilariae migrate from the black fly's midgut through the hemocoel to the Malpighian tubules in the abdomen . There the microfilariae develop into first-stage larvae and subsequently into third-stage infective larvae . The third-stage infective larvae migrate to the black fly's proboscis and can infect another definitive host when the fly takes a blood meal . Humans are not common hosts, but may become so after being fed upon by infected black flies .