Brookside Barkery

Facts About Heartworm

“To judge by your local veterinarian’s stern insistence on regular heartworm pills for your dog, you’d think we’re in the midst of a brutal epidemic, leaving piles of the dead in its wake. I think there’s an epidemic too, but of a different sort: of disease-causing toxicity instilled in our pets by heartworm preventative pills.” – The Nature of Animal Healing by Martin Goldstein, DVM

Every spring, vet clinics put up heartworm signs and insist on testing and preventative treatment. This article from Dogs Naturally Magazine takes a closer look at heartworm disease to guide you in determining whether the risk for heartworm is worth all the hype, or is it just about the money?

What Is Heartworm Disease?

Heartworm is a parasite transmitted by some types of mosquitos. Once they enter the host, these worms circulate in the bloodstream and can grow up to 14 inches long. When the worms reach maturity, they migrate to the heart and pulmonary arteries, where they can cause lung, heart, and organ damage. This serious disease can cause a dog to suffer from:

  • Aneurysms
  • Blood clots (embolism)
  • Fluid accumulation in the lungs
  • Lack of oxygen in the blood
  • Heart failure
  • Exercise intolerance
  • Coughing
  • Nose bleeds
  • Pneumonia

The Heartworm Life Cycle

Heartworms go through 5 larval stages of growth (L1-L5). Each stage requires different environments and conditions. Heartworms reproduce when adult male and female heartworms mate and create live baby worms called microfilariae. If a dog is bitten by a pregnant female mosquito, her microfilariae are released into the circulatory system and they wait their for a new mosquito to bite the dog again.

This is the only way microfilariae can begin to develop into adult heartworms. They must be picked up by a second mosquito to develop into the second and third larval stages of growth. They do this while they’re in the mosquito’s body and this can take a few weeks to occur. If the temperature falls beneath 57°F, they’ll die off.

How Dogs are Affected

If the microfilariae are lucky enough to be hanging around an area that the dog is bitten by a second mosquito, and that mosquito lives long enough with a high temperature, the microfilariae can develop into L3 larvae. If the L3 makes it into the dog, they can develop into L4 and this takes up to two weeks to happen – if the dog’s immune system doesn’t find and destroy the L3 first. Special white blood cells can seek out and destroy heartworms and their larvae.

If the L3 and L4 survive the immune system, L4 will reside in the dog’s skin for about 3 months while it develops into L5 or adult heartworm. At that point, the heartworm leaves the skin and moves to the circulatory system, and eventually into heart and arteries. Adult heartworms can reproduce there and create microfilariae that can develop into adult heartworms in about 6 months.

What is the Real Risk For My Dog?

The American Heartworm Society is an organization that keeps track of heartworm cases. Keep in mind who sponsors the Society (a bunch of pharmaceutical companies who sell heartworm drugs).

Here is the incidence of US heartworm cases for the last 5 years:

As you can see, the nationwide average (which includes high and low prevalence states) is 1.19%. Data taken from

Most pets infected with heartworm are homeless for some period. Therefore, they are often also dealing with other immune-compromising issues such as poor diet, mange, group diseases or infection.

Heartworm Prevention

Conventional heartworm drugs are usually advised by your vet all summer, or all year round. Those drugs don’t actually “prevent” anything, they just kill any heartworm microfilariae or larvae that may already be in your dog by paralyzing the heartworm larvae.

If they can kill the heartworm larvae, they can also harm your dog. There are many reports of dogs suffering adverse reactions after taking heartworm meds, including:

  • Depression/lethargy
  • Vomiting
  • Diarrhea
  • Weakness
  • Convulsions
  • Allergic reactions
  • Difficulty breathing

How Often To Give Heartworm Drugs

If you choose to give your dog heartworm meds, it’s important to know when and how often. Since heartworm can only be transmitted by mosquitos, the first meds should be given 30 to 45 days after weather warms up enough for mosquitos to appear. You can stop giving them after the first frost.

Most heartworm drugs come with instructions to give them every 30 days. But according to many holistic vets, the monthly drugs are just as effective if you give them every 45 days, and 99 percent as effective if given every 60 days.

Preventing Heartworms Naturally

The foundation of protecting your dog from heartworm lies in a healthy immune system. Your dog’s immune system is his first defense against any kind of disease, including heartworm. Taking these steps will help strengthen your dog’s immune system:

  1. Feed a fresh, whole food diet
  2. Minimize vaccines
  3. Avoid commonly prescribed drugs like antibiotics or non-steroidal anti-inflammatories (NSAIDs)
  4. Avoid chemical pest control products (like spot-on products) and dewormers
  5. Don’t use pesticides or herbicides on your lawn
  6. Use natural cleaning products in your home

Regular testing for heartworm disease is a good idea for any dog – at least once or twice a year. To learn more about heartworm and treatment options, visit Dogs Naturally Magazine.