Worldwide but most common in mild and warm climates. 37,000 asymptomatic dogs tested in California. Infection correlated with elevations of 152-1,000 meters and a 30 year mean annual rainfall of 65 cm or more. The most important filarioid parasite of domestic animals in North America. Nocturnally periodic in the peripheral blood.
Mosquitoes serve as vectors.
10-20 days in intermediate host. Enter definitive host through feeding wound. Spend 70-80 days in subcutaneous tissues and muscles. Then begin entering right side of heart and take several hundred days to mature. Up to 60 worms - circulatory difficulty.