Heartworm: Your Questions Answered

Preventing Heartworm

Most pet owners are familiar with the term “heartworm”, yet there is still a great deal of misinformation out there regarding this potentially dangerous parasite. If you have questions about heartworm, never fear, that’s why we’re here!

Heartworm is a type of roundworm that resides in the heart, lungs, and surrounding blood vessels of a host animal, typically a dog (or other canid, such as coyote or fox), as well as cats and ferrets. Heartworms develop from microscopic larvae in the bloodstream to adult worms that can measure up to a foot in length. Let’s shed some light on this dangerous parasite by answering some of the most frequently-asked questions regarding heartworms.

Q. How do pets get heartworm?

A. Heartworm is transmitted through the bite of an infected mosquito. This parasite cannot be transmitted directly from dog to dog and requires a mosquito as an intermediate host. When a mosquito feeds on the blood of an infected dog it ingests heartworm larvae. These larvae develop inside the mosquito until they reach a stage where they can then be transmitted to another dog. While cats are not the preferred host for heartworms, they can also contract the parasite.

Heartworm is transmitted by the bite of an infected mosquito and has been documented in all 50 states.

Q. Is there a treatment?

A. Yes, there is a treatment for heartworm disease in dogs, but this treatment is lengthy, expensive, and carries risks. Treating heartworm disease once it develops should be avoided at all costs to prevent your pet from having to undergo months of medication, activity restriction, and painful intramuscular injections. Antibiotics are given to eliminate bacteria carried by the heartworms, while steroids are necessary to reduce inflammation in the lungs and blood vessels. A series of injections are administered to kill the adult heartworms, and exercise must be restricted from the time of diagnosis until about 8 weeks after the final injection. During this time, the adult heartworms are dying and being resorbed into the pet’s bloodstream. If a dog is too active, debris from the dead worms can obstruct blood vessels and cause serious complications, including death. There is no FDA-approved heartworm treatment for cats.

Cats can also contract heartworm, and there is currently no FDA-approved heartworm treatment for cats.

Q. How often do I really need to give heartworm prevention?

A. Heartworm prevention works by killing heartworm larvae in your pet’s blood before it can develop into the dangerous adult stage. It takes about 6 months for heartworms to transition from innocuous microfilaria, or larval stage, to adult heartworms. Skipping even one dose of heartworm prevention can allow the microfilaria to mature to a point that preventatives are no longer effective in killing the parasite at its larval stage. Heartworm disease has been documented in all 50 states and mosquitos can emerge any time the temperature reaches 50 degrees F, so year-round prevention is essential no matter where you live.

Year-round heartworm prevention is essential. Fortunately, there are many options for safe and effective preventives available.

Q. Why do I need to test for heartworm every year if my pet is on prevention?

A. While heartworm prevention is very effective, there is still a possibility that your pet can become infected while on prevention. If your pet does contract heartworm, early detection is key to avoid serious damage to the heart and lungs. It can also be potentially dangerous, even lethal, to give some types of heartworm prevention if a pet is heartworm positive. Puppies can generally begin heartworm prevention around 8 weeks of age, and should be tested for the first time around 6-7 months old and annually thereafter.

For more information on heartworm disease and prevention, visit The American Heartworm Association or schedule an appointment to speak with one of our knowledgeable veterinarians. We understand that heartworm disease can be scary for pet parents, but armed with accurate information and regular prevention and veterinary care, you can keep your pet safe.

Visit our website for further information on services offered by SPCA Tampa Bay Veterinary Center, or to schedule an appointment call 727-220-1770. 

Blog by SPCA Tampa Bay Veterinary Center