Heartworm Life Cycle


In order to understand how to prevent the infestation of heartworms in your dog, you need to be aware of how the heartworm life cycle actually works.

Understanding the Life Cycle of a Heartworm

While most people understand that heartworms are caused by a mosquito bite, many pet owners don't understand the heartworm life cycle. Understanding the life cycle of this parasite will help you see the importance of preventative treatment for your beloved pet. The cycle of a heartworm is as follows:

  1. A mosquito bites an infected animal, such as a dog, fox, cat, wolf, coyote or some other animal.
  2. As the mosquito feeds off the host animal, it ingests the heartworm microfilaria.
  3. The microfilaria mature for approximately two weeks depending on the temperature. Colder temperatures will slow down the maturation of the larvae.
  4. The microfilaria continue to develop into an infective stage larvae while still in the mosquito.
  5. The mosquito bites an animal and transfers the larvae that then travels into the bloodstream as it matures.
  6. As the heartworm works its way towards the heart, it continues to develop. This typically takes several months and until a heartworm reaches its adult stage, it can be difficult to detect.
  7. If the heartworms aren't treated, the adult worms can live in a host animal for several years, reproducing and seriously affecting the animal's heart and lungs.

Important Heartworm Life Cycle Facts

  • Heartworms can reach sexual maturity in as little as three months, and they can continue to reproduce for several years in the host animal.
  • Adult heartworms are typically found in the right ventricle of the heart, as well as in the host animal's blood supply.
  • The number of the microfilaria isn't directly related to the number of heartworms in an animal since sexually mature heartworms continue to reproduce.
  • Heartworms have been found to grow as long as a foot or even longer!
  • In some cases, infected animals have been known to harbor more than 100 heartworms.
  • Besides the heart and lungs, heartworms can also infect other areas of the body, such as the stomach, brain, liver, spinal cord and even the eyes.
  • Heartworms are only transmitted by female mosquitoes.
  • The concentration of microfilaria in the blood can vary depending upon the season, with the summer months registering a higher concentration than the winter months.

What this Means for You

Once you understand the heartworm life cycle, it is easy to see how important heartworm prevention medicine is for your dog's health. Before you can begin your dog on any heartworm medicine. However, your vet will need to check your dog for the presence of heartworms. Once you've begun a preventative regimen on your pet, keep him on it year round for the best protection.

Heartworm Life Cycle