Spring is upon us and so are the bugs! Part III: Heartworm


Heartworm is a parasitic worm that lives, as an adult, in the heart and pulmonary arteries of the dog (and very rarely, the cat). The parasite is transmitted to a dog by a bite from an infected mosquito.

Simply stated, an infected mosquito injects larvae into a dog’s skin where these larvae (called L3) then spend the next week or two developing into the next larval stage (L4). The L4 stage lives in the skin for three months or so until it develops to a young adult stage (L5) and is ready to enter the dog’s circulatory system. The young adults, migrate to the heart and out into the pulmonary arteries (if there is room) where they will become adult heartworms and mate, approximately 5 to 7 months after first entering the new host.

There are many safe and effective heartworm preventives that act by killing the L3 and  L4 stages. The ivermectin products are also able to kill the younger L5.

Heartworm preventatives that we currently carry at our hospital include:

  • Heartgard Plus (dogs only)
  • Iverhart (dogs only)
  • Revolution (dogs and cats)
  • Proheart 6 (dogs only) – coming soon!

Testing for heartworm disease

Heartworm tests on the market do not detect infection with immature worms. This is why it takes 5 to 7 months from the time of exposure to get a valid heartworm test, therefore, there is no point in testing puppies less than 5 to 7 months of age. At that point, it is recommended that your dog be tested annually even if it is on heartworm protection year round.

For a further explanation of this and other information on heartworm disease, please click on the links below:

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