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Metropolitan Animal Specialty Hospital

Heartworms: What Are They and What Do They Do?

Owner Sitting with Dog at the Dock by the Lake

How do pets get heartworms?

Heartworms, also known by their technical name of Dirofilaria Immitis, is spread from animal to animal by infected mosquitoes. When a mosquito bites and begins to feed, it passes heartworm larvae into the tissue of their meal. Once heartworm larvae are inside the body, it will move through the tissue, arriving at the blood vessels around two months later. It takes the blood vessels to travel to the heart, where it prefers to live. As it is in the heart, the larvae will slowly grow and mature into adult heartworms.

What are the symptoms of heartworm infection?

One of the most difficult things about heartworm infections is that animals may not show any symptoms of an infection until adult worms grow and clog blood vessels in the heart. It can take as long as six months from the time of infection for symptoms to begin showing. However, there are some symptoms that may clue you in on an infection. As worms grow, blood flow will be blocked, and the symptoms you’ll see include:

  • Fainting

  • Heavy breathing

  • Quick to tire

  • Coughing, as well as coughing blood

  • Bloody noses

  • Unable or unwilling to exercise

  • A swollen stomach

Treating Heartworms

Heartworms are complicated and frustrating. There are different things that can complicate treating them, including:

  • If the animal is already unwell, they might be in the midst of heart failure. If this is the case, they have to be stabilized so they can handle the treatment they’re about to undergo.

  • Heartworms come with a bacteria which is released when they die. Antibiotics will be needed in addition to killing the heartworms.

  • Heartworm larvae have a two-month phase where medicine can’t treat them.

The veterinarian will put together an action plan for treatment which balances all of the pet’s needs. This action plan will typically include:

  • Stabilizing any heart failure that has come as a result of heartworm damage.

  • Beginning preventative treatment to kill heartworm larvae before they’re able to mature.

  • Waiting through the two-month phase when larvae are not affected by medicine.

  • A four-week course of antibiotics to protect organs against bacteria in the bloodstream.

  • Steroids are given as an anti-inflammatory, protecting against allergic reactions to dead or dying worms in the blood.

  • Begin a drug that kills adult worms. The final step of treatment.