The final host for the dirofilaria immitis is usually a domesticated dog. However, they can also infect other animals: coyotes, humans, horses, and even beavers. This is just a small list of the animals these worms can infest. The grown larva comes in from a mosquito bite, and then go into the bloodstream. The grown worms then feed on the host’s blood, finding all the nutrients they need from that.
The cycle starts all over again when another mosquito bites the host. The eggs of the worm are sucked up via the blood meal that the mosquito has. From there, the eggs might be taken to a host of the same species of the previous host, or it might be taken to a different species of host all together.