Why don't humans get heartworm like our canine friends?

This week's question comes from Brent Rogers in Toronto, who asks 'what is the difference between human and canine physiology that makes us immune to the heartworm parasite?'

Dr. Scott Heximer, a professor in the Department of Physiology at the University of Toronto and a cardiovacular researcher at the Ted Rogers Centre for Heart Research, explains that humans can actually get heartworm, but it is rare. The parasite is passed by mosquitos, who bite both dogs and humans. However, if we do get the parasite, the symptoms are much less severe than they are in dogs. The human immune system is better equipped to recognize the worms in their immature state.  The human body creates an inhosbitable place for the maturation and completeion of the heartworm cycle, unlike dogs. In the skin of an infected dog, heartoworm larvae can mature into adults, then enter the bloodstream and lodge in the arteries of the lungs. From there they continue to grow and move into arteries associated with the heart.  The can lead to heart failure and death in untreated animals. In the rare cases in which the parasite reaches the lungs of humans, the worms usually die quickly.