As the embryo elongates, the surrounding membrane stretches to conform as an enclosing sheath. At birth, the membrane is lost and the embryo appears in the blood as a sheathless microfilaria. Microfilariae are deposited in the blood of the chambers of the right side of the heart and pulmonary artery. They are carried through the lungs, into the left chambers of the heart, and into the systemic circulation. There is marked nocturnal periodicity in the peripheral blood.
Mosquitoes serve as vectors.
After microfilariae are ingested durding bloodfeeding, they migrate from the intestine within 24 to 36 hours into the Malpighian tubules, where further development and a molt from the first to the second stage juvenile occurs. After 9 days they enter the abdominal hemocoel, where the second molt occurs. Third stage larvae are about 900 um long and appear 10 to 20 days after entering the mosquito. The third stage juveniles migrate to the mouthparts of the moquito. Infection of dogs occurs while mosquitoes are feeding.