The Importance of Heartworm Testing and Prevention

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If you watch late-night television, on any given night you’re bound to see at least one commercial for a heartworm prevention product. Most pet owners know that monthly heartworm prevention is important, but may not understand just how serious heartworm disease is and why preventing it is so critical.

What is Heartworm Disease?

Heartworm disease is caused by a parasite called “Dirofilaria immitis” that can be transmitted to your pet through the bite of an infected mosquito. It’s seen mostly in dogs, but cats and ferrets can also be affected.

Heartworms can cause extensive damage inside your pet’s body. These nasty worms clog blood vessels in the lungs and, once inside the heart, can cause congestive heart failure.

Heartworm disease is widespread…cases have been reported in all 50 states in the U.S., as well as numerous other countries.

Heartworm Life Cycle

Heartworms need a mosquito to complete their life cycle. The cycle plays out like this:

• A mosquito bites a heartworm-infected dog who has circulating microfilariae (microscopic baby worms) in his blood.
• The microfilariae are ingested by the mosquito, which grow inside the mosquito’s body and become larvae.
• When this mosquito then bites a healthy dog, the larvae are deposited on the dog’s skin, where they migrate through the skin and into the dog’s bloodstream.
• Once in the bloodstream, the larvae grow into adult worms (which can take up to 6 months).
• The adult worms finally make themselves at home in the blood vessels of the dog’s lungs and the right side of his heart.

Heartworm Testing

All adult dogs need to have an annual heartworm test. The heartworm screen for dogs is a simple blood test, which most veterinarians (or technicians) can perform right in the clinic. Results can be provided in as little as 24 hours.

Although in rare cases cats are able to become infected with heartworm, the worms are not able to reproduce well in cats. This causes heartworms in cats to eventually die off. Unfortunately, an accurate screening test for cats does not exist, so most veterinarians usually don’t perform an annual heartworm screen on our feline friends. If for any reason your vet suspects a heartworm infection in your cat, it can be diagnosed with a series of specialized blood tests, combined with x-rays or an echocardiogram (ultrasound of the heart).

How to Prevent Heartworm Disease

Once your dog tests negative for heartworm, you can begin giving monthly heartworm prevention as prescribed by your veterinarian. Preventive medication works by killing the worms in the larval stage.

I recommend giving heartworm preventive on the first day of each month, since that’s easy for most people to remember. Most forms are chewable and dogs seem to love the taste, so no need to do the “coat it in peanut butter and cross your fingers” trick!

Years ago, in cold weather climates (like Ohio, where I grew up), veterinarians used to recommend only giving heartworm preventive 9 months out of the year and skipping the winter months. However, mosquitos are hardy little critters, and since live mosquitos can be found even in the middle of winter, most veterinarians now recommend giving preventive year round.

If heartworm prevention is given as directed, the chance of your pet developing heartworm disease is extremely low. And BONUS! Many heartworm preventives also protect against other forms of parasites like roundworms, hookworms, and whipworms…and some even protect against fleas as well.

Heartworm disease is much easier to prevent than to treat, so always follow your veterinarian’s instructions to the letter regarding heartworm testing and prevention!

What type of heartworm prevention do you prefer for your pet? Tell us about it in the comments section below!