It’s Summertime, and we know what that means…. longer days, warmer temps, picnics, and… mosquitos! Those dreaded invaders can darken anyone’s sunshine, put the kibosh on your party and leave your pet at risk for a life-threatening heartworm infection.

While yes, mosquitos are beneficial for the environment, providing a food source for many animals like birds, fish, and frogs, besides their irritating stings, they can also cause serious harm to our furry family members: their needle noses can inject tiny heartworm larvae into our pups’ skin, which then travel to the heart, where they can induce severe heart disease, heart failure, or death.

Heartworm disease affects 1 in 200 dogs annually, despite the monthly preventatives prescribed by vets nationwide making this one serious topic we must address! 

What Is Heartworm Disease?

Heartworm disease is a serious and potentially fatal disease of pets. It has been identified not only in domestic dogs, cats, and ferrets but also in wildlife such as foxes, coyote, wolves, and even in sea lions! Heartworms can cause heart failure, severe lung disease, and can even damage other bodily organs. In the US, it has been reported in all 50 states, most commonly along the Atlantic and Gulf coasts as well as along the Mississippi River and its main tributaries. 

What Causes Heartworms To Grow & Spread?

Heartworm disease is caused by mosquitoes that transmit the heartworm larvae through their bites. A mosquito carrying heartworm larvae bites your pup, injecting the larvae onto your pup’s skin. The larvae then enter the body through the bite and travel to your dog’s heart where they mature into adults.

This process takes about 6-7 months. Here, the heartworms mate and the females produce baby heartworms, called microfilaria, which enter the bloodstream of your dog. The microfilariae then circulate in your dog’s bloodstream until they are picked up by a mosquito feeding on your dog.

While they are in the mosquito, the microfilariae develop into the infective larvae. This takes about 10-14 days, under the right environmental conditions. The cycle starts all over again when the mosquito bites another dog, injecting the infective larvae. Therefore, dogs serve as the “primary host” and mosquitoes act to spread the disease. 

What Are Symptoms Of Heartworm Disease?

Some pets do not show any signs of being infected (which is worrisome because it means that, without testing, many infections go undetected). When pets do have clinical symptoms of heartworm disease it can look like-

  • A mild, persistent cough.
  • Easily fatigued.
  • Lethargy.
  • Reduced appetite.
  • Weight loss.

As the disease progresses, heart failure may ensue. Dogs that have a heavy worm burden may also experience acute cardiovascular collapse from worms blocking cardiac blood flow (called caval syndrome). Signs of this are pale gums, labored breathing, and/or dark bloody or coffee-colored urine. Caval syndrome is considered a medical emergency and few dogs survive without immediate surgery to remove the worms causing the obstruction. 

Testing For Heartworm Disease

Every year, when your pet has their annual exam, your vet should check a heartworm test, or a 4DX SNAP test, which screens for heartworm as well as exposure to bacteria transmitted by some ticks. If your vet is not doing this, please ask them to! Because some dogs do not show symptoms of the disease, annual heartworm testing is important, even if your dog is on monthly treatments as they can never be 100% guaranteed. 

If your pet is diagnosed with heartworm disease, your vet will likely recommend chest x-rays and bloodwork to help assess the level of disease and organ involvement. Once test results have been assessed, she will recommend treatment to eliminate the heartworms. 

Treatment for Heartworm Disease can be Toxic

Currently, there are two main therapeutic options for pets who are diagnosed with heartworm disease. Your vet will recommend one of the treatments depending on the presence and severity of your dog’s clinical signs. Additionally, she will likely prescribe an antibiotic to be given in addition to one of the below therapies. The antibiotic kills bacteria which live in the parasite and support its survival, allowing the other medications to work more efficiently.

The first treatment is considered the referred option. It involves 3 injections over the course of a month with melarsomine dihydrochloride, an arsenic-containing drug. Melarsomine is an “adulticide”, meaning it kills the adult heartworms. The drug is given by deep injection into the lower back muscles, which is painful. Some hospitals sedate dogs in order to administer the injection, due to the level of pain it causes. Dogs are then hospitalized for monitoring on the day of injection and are discharged with medication for pain and inflammation. Treatment with melarsomine is expensive and can cause serious side effects:

  • Depression, lethargy
  • Coughing, gagging
  • Reduced appetite/anorexia
  • Lung congestion
  • Vomiting
  • Elevated liver enzymes
  • Pain, injection site reaction/myositis
  • Pulmonary thromboembolism 
  • Weakness, paralysis, altered mentation

Slow Killing Heartworms-

The second option involves treatment with a heartworm preventative once a month, along with antibiotic therapy for 30 days every other month. This method kills the microfilaria only though, not the adults. Over time, the adults die off and, with no babies to grow into adults, the infection is eliminated. This option is referred to as the “slow kill method.”

The American Heartworm Association does not recommend the slow-kill method as a primary treatment option, except in certain cases, because of the potential for further lung damage while waiting for the adults to die. Some cardiologists and vets do prefer this method because it is less toxic and the risk of serious side effects is lower. Many shelters are utilizing this option because it is less expensive than the melarsomine protocol.

How To Best Support Your Dog Through Heartworm Treatment-

Remember that 70-80% of your pet’s immune system resides in your pet’s gut, so a healthy GI system = a healthy immune system. Additionally, feeding your pet a whole food, minimally processed diet with probiotics added will help support their immune system. Essential fatty acids like fish oils can also help reduce inflammation in the arterioles traumatized by the heartworms. Adding a multivitamin/mineral supplement will help ensure your pet is receiving adequate levels of vitamins, amino acids, and minerals to support general body functions.

Although the treatments for heartworm disease are less than ideal, there are many natural ways to help your pet’s body process these chemical therapies.

Herbal, glandular, and nutritional supplements can be used to support your pup’s heart and lung function, liver detoxifying activities, and immune system during and after treatment. For example, heart-protective herbs, such as hawthorn, can be given to your pet throughout and after treatment. Antioxidants fight free-radical damage, reducing inflammation and protecting the heart and circulatory system. Herbs, such as milk thistle, dandelion root, beetroot, turmeric, and ginger can all assist the liver’s detoxifying action.

Because this topic can be so complex, our parent company Organic Bunny actually offers one-hour educational consults with our licensed Veterinarian to educate pet parents on how to keep a pet’s immune system as healthy and strong as possible throughout this process.

To book a consult for support on this topic, please head here.

How To Prevent Heartworm Disease-

So now, the most important part of the discussion, how can you, as a pet parent, prevent this infection from occurring in the first place? “An ounce of prevention is worth a pound of cure,” as they say, right?

Typically, conventional heartworm disease preventation involves giving your pet a monthly tablet, applying a topical every 1-3 months, or having your veterinarian administer an injection which lasts 6-12 months. Unfortunately, all of these options may cause adverse side effects such as-

Side Effects of Heartworm Preventatives-

  • Skin rashes
  • Depression, lethargy
  • Vomiting, diarrhea, reduced appetite, drooling
  • Staggering/ataxia, seizures
  • Death

There are also risks to humans, especially small children, associated with topical preventatives, which are combined with flea/tick control pesticides. Children touching pets treated with these products can absorb these chemicals thought their skin, and are more likely to place their hands in their mouths without washing them after playing with a pet. Such exposures have been linked to behavioral problems, cognitive issues, and problems with motor development.

Are There More Natural Alternatives to Heartworm Prevention?

There have not been many studies on the effectiveness of natural remedies for heartworm prevention which is important to understand before trying to shift to more natural routes of prevention. However, an example of a “less toxic” approach that some holistic veterinarians will suggest is administering monthly oral heartworm preventatives every 6 weeks, rather than every 4 weeks, based on the heartworm life cycle.

Brands like Heartgard or Interceptor do not add additional chemicals to kill fleas and ticks. Using products combined with flea/tick preventatives does seem to increase the risk of adverse events, as do the longer acting preventatives, which involve a higher initial dose which slowly deteriorates over time. Additionally, the oral monthly preventatives, such as mentioned above, act almost like single dose dewormers, meaning they exit your pet’s system quite rapidly.

Black walnut has been advocated as a heartworm preventative, but there has been no tradition for its use in ethnobotany and no scientific data proves its effectiveness. Safety with long term use is unknown. 

Some vets have successfully utilized herbal combinations as heartworm prevention. These may be Traditional Chinese Veterinary Medicine herbal combinations or western herbal combinations such as HWF Clean Heart. If a more natural treatment direction interests you, please bring it to the attention of your treating vet for their opinion or support.

Homeopathic nosodes have been used anecdotally, yet effectively, by some veterinary homeopaths. Use this link to find a vet certified in veterinary homeopathy near you.

Supplements To Support-

Oral supplements like Adored Beast’s Phytosynergy, Love Bugs, and Glacier Peak’s Daily Defense can help maintain healthy skin and immune balance so your pet can naturally fend off mosquitoes and other nasty little insects. Because heartworm disease can be fatal, it is critical to work with a holistic veterinarian that can help guide you best while properly monitoring your pet. 

Does Climate or Location Impact Heartworms?

Traditionally, vets in colder climates that experience freezing Winters have recommended discontinuing heartworm prevention once the weather is cold and the mosquitoes are gone. In general, once temperatures stay consistently below 50 degrees Fahrenheit, mosquitoes shut down, some even entering hibernation! When Springtime brings warmer weather and mosquito populations resurge, heartworm tests are repeated and, if negative, heartworm prevention is restarted.

Why Keeping Your Yard Clean Can Help!

Because heartworms are spread by mosquitoes, control of these little buggars will help. Clear any areas in your yard which promote standing water, where mosquitoes love to breed. Mow your lawn regularly. Research beneficial nematodes, they can be purchased online and actually eat mosquito and flea larvae. 

You can also utilize more natural mosquito prevention for your pet. Essential oil-based sprays and collars are available and can be highly effective when chosen with care. Remember, some essential oils are not appropriate for pets. You can access our favorite bug repellant here!

Some people have also utilized amber collars effectively, but there has been no research to support this to date. Finally, manage your pet’s activity outdoors and avoid times when mosquitoes are most active – generally early morning and early evening.

Do Dogs Develop Immunity to Heartworm Disease?

We do know that wild animals are known to be resistant. This may be a result of a healthier immune system, one not weakened by processed diets, lack of activity, excessive vaccinations, and chronic exposure to toxic preventatives. Additionally, dogs in endemic areas have shown resistance, perhaps due to chronic, long term exposure. 

Making sure your pup has a healthy immune system by feeding a wholesome, non- or minimally processed diet, providing regular exercise outside in the fresh air, vaccinating responsibly, and minimizing exposure to pesticides will all help reduce your pet’s risk but nothing replaces a good discussion with your holistic vet who can advise you appropriately.

What About Our Feline Friends?

Cats can also get heartworms after being bitten by an infected mosquito, but they are not as susceptible to infection as dogs. Because cats are not a natural host of heartworms, the worms do not thrive as well inside a cat’s body.  

Diagnosing heartworm disease in cats is a little more difficult than in dogs. Your vet will usually rely on a combination of blood tests, your kitty’s symptoms, and the results of other tests such as x-rays and an ultrasound of the heart, to determine if she has heartworm disease.

Not all cats with heartworm disease show symptoms. Some cats can also spontaneously rid themselves of heartworms without having any symptoms. 

Non-specific Signs of Heartworm Disease in Cats Includes-

  • Vomiting, diarrhea
  • Decreased activity and appetite.
  • Weight loss
  • Sudden death, some infected cats die suddenly from heartworm disease without ever showing signs of being sick.
  • Cats with heartworm disease rarely show signs of heart failure.

When the adult heartworms die, they release toxins into the cat’s bloodstream which causes lung damage, leading to respiratory problems or sudden death. Even the death of one worm can be fatal for a cat.

Respiratory signs occur due to the lung damage caused by the heartworms.  This damage induces an inflammatory response causing the syndrome known as Heartworm Associated Respiratory Disease (HARD). Respiratory signs, such as trouble breathing, increased respiratory rate, and cough, are the most obvious. It may be difficult to distinguish HARD from feline asthma or feline bronchitis.

There is no drug approved by the FDA available to treat heartworm disease in cats. Sometimes surgical removal of adult heartworms may be considered an option if the heartworms can be seen by ultrasound. This is not without risk; if the heartworms are not removed intact, there can be potentially serious complications, such as shock and death.

We generally manage symptoms with medications. Speak to your holistic vet about acupuncture, herbal or other therapies which can help improve your kitty’s comfort level and reduce her symptoms.

The Bottom Line…

Heartworm disease is serious and can be fatal. Preventatives are available and most effective but can have significant side effects. Treatment of heartworm disease can be painful and also produce serious adverse side effects.

There are no known proven natural alternatives to prevention. The best you can do for your pets is to feed them a minimally processed diet and provide supplements or utilize natural topicals which may discourage mosquitoes who might otherwise find your pets skin tasty. Consultation with a holistic regarding supportive options during administration of prevention and during treatment can be hugely beneficial.

Dr. Kristen

Comments 3

  1. September 2, 2020

    Cece Lewis

    Great article and thank you for taking the time to write it! Just one quick question. Is there a way to find what states HW is endemic to, and what states they are NOT? I am wondering, because I am about to travel and am not sure if I should worry about covering my dog for the state I will be in during the time we are gone, (when we do not currently live in a HW endemic state).

  2. September 2, 2020

    Lyn Shryock

    How do I sign up? I have an Italian mastiff that has tons of allergies and would like to follow your information, especially food, vaccines(he’s allergic to some), treatments, gut health, hot spots

  3. September 2, 2020


    You can just get your dog tested every 4 months since it takes 6 months for for the worms to get to adulthood. If they test positive, then nip it in the butt then with a heartwarming medicine killing the microfilaria.

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