Heartworms are caused by the parasite Dirofilaria inmitis and are transmitted by the bite of the mosquito. When a dog or cat is bitten by a mosquito infected with heartworms, the immature larvae carried by the mosquito enter through the mosquito bite in the skin. From the site of the mosquito bite, the larvae continue to molt and travel through the pet’s body. Approximately six months after infection, the mature larvae enter the pet’s heart and pulmonary vessels in the lungs and finish their maturation into adult heartworms. In dogs, most of the worms reside in the pulmonary vessels of the lungs (except heavy infections, where the worms can live in pulmonary vessels, the heart and the vena cava); in cats, due to a lower number of worms, the heartworms are mostly likely to reside in the heart.

It is important to differentiate between heartworm infection and heartworm disease. A pet whose body contains heartworms is said to be infected with heartworms. Heartworm disease occurs when an infected pet shows clinical signs of infection, including difficulty breathing, fluid in the lungs or abdomen, vomiting, diarrhea, weight loss, or sudden collapse and death. In cats, chronic vomiting or asthmatic-like signs are often the only signs seen in cats with heartworm infection and heartworm disease. Most dogs infected with heartworms are not suffering from heartworm disease at the time of diagnosis.

Diagnosis of heartworm infection in dogs is by finding microfilaria (baby heartworms) on a concentration or filter test, or by finding antigen (foreign protein) from adult female worms on an occult test. Many dogs (40 percent or more) will not have microfilaria and will have an occult (adult-only) infection. Additionally, the microfilaria of a benign subcutaneous worm Diptalonema reconditum, can be confused with the microfilaria of Dirofilaria immitts. For these reasons, it is imperative that dogs are screened for heartworms have an occult test, especially before heartworm treatment in instituted. Dipetalonema reconditum is a nematode that is commonly found to be endemic in dogs’ subcutaneous tissues. Worldwide distribution includes the United States, Italy, and Africa.

Diagnosis of heartworm infections in cats is more difficult, as cats usually do not harbor microfilaria and have fewer worms in their bodies than dogs. In cats, diagnosis can be made through a combination of tests, including occult testing for antibody and antigen detection, chest radiographs (x-rays), CBC, blood chemistry profile, and cardiac ultrasound.


Here are some key differences in heartworm infection/ disease of dogs and cats.

Heartworm in Dogs

  • Heartworms live an average of three to five years before dying naturally.
  • A minimal number to many microfilaria are seen
  • The average number of adult heartworms is 15, and more are possible.
  • Clinical signs of heartworm disease are rare when few worms are present.
  • The incidence of infection/disease is high in endemic areas if preventative medicine is not use.

Heartworm in Cats

  • Heartworms lice live approximately two years.
  • Microfilaria are very rarely seen.
  • The average number of adult worms is one to three.
  • The incidence of infection/disease in endemic areas is lower than in dogs (25 percent).

There are several protocols listed in the holistic literature for the treatment of canine heartworm infection/disease. Unfortunately, no controlled studies, showing their effectiveness have been completed, although the veterinarians who use these protocols have reported success in some cases. Many of these cases have not been followed long-term, and many holistic practitioners do not recommend them due to their questionable effectiveness. In some protocols, the dogs were also placed on monthly heartworm preventative medication (Heartgard®), which has been shown to actually kill adult worms after continuous usage, making interpretation of results from alternative treatments difficult. Some protocols also make use of more toxic herbs such as wormwood and black walnut.

For owners who wish to try one of these protocols, they must be administered under strict veterinary supervision to minimize toxicity. Pets should receive regular follow-up testing (occult heartworm tests) to determine effectiveness (or lack of effectiveness) if an alternative protocol is used. For owners who wish to use the conventional medical therapy combined with some type of complementary therapy, patient support (of the heart and liver) can be accomplished by various nutritional supplements and herbal preparations. Support of the heart and liver with herbs and glandulars can be beneficial in supporting the patient during conventional treatment.

Diatomaceous earth, while reportedly effective for helping control some intestinal parasites, is not effective in preventing or treating heartworm infection/disease.

These protocols can be used in conjunction with conventional therapies as they are unlikely to be effective by themselves in most patients. The natural treatments are widely used with variable success but have not all been thoroughly investigated and proven at this time.

As with any condition, the most healthful natural diet will improve the pet’s overall health.

In the past, an arsenical (arsenic-containing) medication called Caparsolate was the only medication available for treating heartworm infection in dogs. While it is effective, there is very little difference in the treatment dose and the toxic dose, making it imperative that the medication be carefully administered. Additionally, the compound was very caustic and had to be given intravenously. If any of the four required doses of Caparsolate leaked out of the vein, severe damage to the surrounding tissue was possible.

While there are still some veterinarians who use Caparsolate, a newer product called Immiticide® is currently considered the treatment of choice. The medication is safer than Caparsolate, requires only two injections, and the medication is designed to be given intramuscularly rather than intravenously.

Heartworm treatment is safer in dogs that are infected but not suffering from heartworm disease. Pre-treatment diagnostic tests (chest radiographs, urinalysis, and blood profiles) are necessary prior to treating dogs infected with heartworms or showing signs of heartworm disease to minimize side effects from therapy.

When administered properly to dogs with heartworm infection, treatment is generally safe and without side effects (especially when Immiticide is used). Treatment is generally recommended due to the overall safety of treatment (when properly administered in selected patients) and the long life cycle of the parasite.

Treatment of cats with heartworm infection or disease presents some difficulty. Neither Caparsolate nor Immiticide is approved for use in cats. Additionally, cats with heartworm disease are likely to suffer potentially fatal pulmonary embolisms after treatment with Caparsolate (estimates are that 30 to 50 percent of cats treated for heartworm infection/disease are likely to experience life-threatening crisis within three weeks of treatment). Many doctors choose supportive care (usually corticosteroids) for the vomiting or asthmatic-like signs seen in cats with heartworm disease rather than treat cats with Caparsolate or Immiticide, due to the shortened life expectancy of heartworms in cats as compared to dogs and the potential for adverse reactions when using the conventional medications in cats.

Prevention of heartworm can be accomplished with daily (dog) or monthly (dog and cat) administration of heartworm preventative medications. Dogs showing evidence of microfilaria in their blood may react (severely) with the diethylcarbamazine in the daily preventative medications. Additionally, if an owner misses more than 24 to 48 hours (a short window when heartworm infection can occur) between dosing, the dog can become infected. Therefore, most, if not all, pets would have greater heartworm protection with minimal side effects using the monthly preventatives. The monthly preventatives contain extremely low doses of medications. These medications, while only given monthly, do not actually last in the body for an entire month but just for a few days. Therefore, the holistic pet owner can feel comfortable using them. Most holistic veterinarians would recommend that pet owners not use the combination products that contain both heartworm preventative medication and flea preventative medication (Sentinel). As a rule, if the pet doesn’t need additional chemicals (as in the case of flea preventative medication), it shouldn’t be used.

Homeopathic heartworm nosodes have been suggested as an alternative to conventional medication to prevent heartworm disease. No studies are available suggesting their effectiveness.