Heartworm is a deadly parasite that enters your pet’s bloodstream through the bite of an infected mosquito. Once it has taken up residence inside your dog, a heartworm can grow to be as much as a foot long and live up to seven years. Untreated heartworms interfere with blood flow and can be fatal to dogs.
Heartworms live and breed inside a host animal. When she’s ready to reproduce, a female heartworm releases her young, called microfilariae, into the host’s bloodstream. The next time a mosquito stops by for a snack, it sucks up both blood and a load of microfilariae before moving on. These microfilariae then live inside the mosquito, growing into larvae in 10 to 14 days. Then, when the mosquito feeds on another suitable host -- like your dog -- it releases some of the heartworm young, which move in and eventually become adults if not treated.
The mosquito is an essential part of the heartworm’s life cycle, and the parasite cannot be transmitted any other way. This means that even if a mother dog has the disease she can’t give it to directly her puppies. The only way the pups can get the parasite is if an infected mosquito containing mature larvae bites them.