How they get into the Heart

The spread of heartworms starts when a mosquito feeds on an infected animal. When it does, it consumes a number of microfilaria contained in the animal’s blood. Microfilaria is the microscopic, worm-like larval offspring of the adult heartworm. Once in the mosquito, over the next 14 days or so depending on the environment’s temperature, they molt into their second larva stage, and then into their third larva stage.

At this stage, the heartworm larvae are ready to find a host. They migrate through the mosquito’s body to the saliva glands. When the mosquito feeds on a dog, the larvae transfer to the bit wound and burrow into the skin.

Once in the host’s skin, the larvae migrate toward the heart and lungs. Also, within the first 14 days, they molt into their fourth stage. Before 60 day they continue maturing and molt into their fifth stage at which they become juvenile adults. By 90 days, most of the larvae will have reached the right ventricle of the heart and lungs, where they will continue to grow and stay for the duration of their 5 to 7 year life spans. From the time they enter the host, the heartworm will take 6 to 7 months to become fully mature and able to produce its own young.

Young are born into the first larva stage, microfilaria. The microfilaria will swim around in the blood waiting to be sucked up by a mosquito and infect another host.