Heartworms in Dogs

What Is Heartworm In Dogs?

Heartworm (Dirofilaria immitis) is a small thread-like roundworm parasite that spreads from host to host through the bite of mosquitoes. The definite host is the dog. The parasite is commonly called heartworm. The adult heartworms mostly reside in the pulmonary arterial system or lungs, arteries and the heart. The damage to the lungs, vessels and tissues are major causes of ill health in dogs. Sometimes, during heavy infections, the adult heartworms migrate to the right heart and even the great veins. Heartworm infection can lead to serious health issues or even death if left untreated.

The article will answer your questions related to heartworm infection such as, what causes heartworm infections in dogs? What are the four life stages of heartworm? What are the symptoms and treatment for affected dogs? Are there any side effects of medications? And lastly the natural remedies to cure heartworm in dogs.

GI CleanUp Gold For Heartworm
The symptoms of heartworm disease are initially quite mild and difficult to identify and when left untreated will prove fatal for your pet.

What Causes Heartworm Infections In Dogs?

The dog is easy victim to heartworm disease. With just a single bite from a mosquito with the infectious heartworm larvae inject heartworm infection in your dog. Mosquitoes are the only means of transmission for heartworms to dogs. Without mosquitoes, heartworms cannot grow to adulthood within dogs. It is the adult stage of the heartworm that causes the most health problems.

Mosquitoes are hard to avoid. Heartworm disease is reported from every state of America. Vets suggest that all dogs, regardless of the place they reside in, all the year round preventative measures should be taken to ensure that no stray mosquito can pass heartworm infections.

Heartworms cannot travel from host to host; mosquitoes are the means to spread the parasite. Mosquitoes bite the infected dog and ingest larvae (L1) i.e. microfilaria, or baby heartworms. Within the mosquito the larvae matures from L1 into L3. This infected mosquito bites your healthy dog and transmits larvae L3 into the dog’s bloodstream. In this way they pass along microfilaria to your loved pet.

What Are The Four Life Stages Of Heartworm?

You should understand the heartworms’ life cycle to know how they affect your pet’s health. This will make you realize why it is important to prevent a heartworm infection rather than wait and treat the worm later on.

The heartworm undergoes a total of four life stages to mature into an adult worm. The first two stages occur inside the mosquito and the next two occur inside the final host i.e. your dog.

Heartworm disease starts with an infected dog, which you can call as the source that contains microfilaria in its blood. A mosquito bites the infected dog and inadvertently sucks up a number of circulating microfilaria from its bloodstream. Inside the mosquito’s body, the microfilaria goes through to complete two life stages over a period of 14 days or longer depending upon the surrounding temperature. They go through their first two stages and change from an L1 to an L2 and then an L2 to an L3, L3 is the third stage of development of the larva.

It is the L3 larvae that the mosquito transmits to your pet via a small bite. This larva continuously develops, and the heartworm takes minimum 6 to 7 months to complete the last two life stages and become sexually mature to reproduce. It is only at this point of time, that the infection can be detected by a Heartworm test.

The L3 larva goes to the L4 just within the first 15 days or even as soon as 2-5 days after infection. The second shift from the L4 to the L5 occurs within the next 2 months. The L5 larva can be called a juvenile adult. It enters the host’s tissues and the heart within 70 days after first entering the dog. The L5 heartworm larvae reach the heart within 90 days. In the heart they stay and rapidly grow in length and size. If left untreated it can continue to live in the heart until your dog dies i.e. normally between 5-7 years.

In fact the heartworms continue to grow in size only after reaching sexual maturity i.e. about three months after entering your dog. The females produce many small microfilarias that pass into the dog’s blood. Hence, the infected dog has numerous worms. The mass of these heartworms in dogs are responsible for severe blockage to the normal flow of blood and the right ventricle of dog’s heart and blood vessels. Actually, adult female worms can grow up to 14 inches long whereas the males are normally shorter.

The adult heartworm will continue to produce young heartworms for several years in the dog, around 7 years. This completes the normal life cycle of the heartworm.

What Are The Symptoms Of Heartworm?

The symptoms of heartworm disease are initially quite mild and difficult to identify and when left untreated will prove fatal for your pet. The disease progression in the early stage merely displays symptoms to recognize heartworm and it is only in the later stages that the disease is diagnosed.

The dog suffers from mild cough during the first two stages and later as the infection progresses the cough is persistent in the third and fourth stages. Without treatment, the symptoms becomes very severe and negatively affects the dog’s lungs and heart. The dog’s stage of heartworm disease, its age and health will help the vet determine the approach for treatment. The major symptoms of the disease are:

  • Persistent Cough
  • Difficulty In Breathing
  • Fatigue And Tiredness
  • Reluctance To Work Or Weakness

Below mentioned are the stage-wise symptoms that displays the progress of the infection

Stage 1

In the first stage of heartworm disease, the dog will generally show no symptoms at all apart from mild cough. With this mild cough the dogs will appear happy and healthy, making it almost difficult to identify the heartworm infection. Even the blood test reports may also come back with a negative result for heartworm disease.

Stage 2

In stage two of heartworm infection the moderate symptoms like lingering cough or fatigue after exercise can be noticed. The symptoms at this stage are now advanced that can detect heartworm infection via blood test.

Stage 3

During third stage your dog’s health will be severely affected and the symptoms are more noticeable. Dogs will continue to cough, may experience fatigue after exercise or reluctance to exercise i.e. weakness and difficulty in breathing. Dogs might cough out blood and the infection gets more evident on x-rays.

Stage 4

The symptoms of heartworm infection in stage four are very visible that accompanies long-term problems for the dog’s health. The symptoms of the first three stages will continue and become more serious. Conducting tests will reveal the impact of the infection in the dog. The spread of infection on the dog’s lungs, liver, and heart will be known from the test results. This stage of heartworm disease if left untreated can lead to the death of your pet.

As the stages of infection progresses, the treatment methods becomes more severe and persistent. Be careful to notice your dog’s typical behavior, and don’t overlook the potential symptoms of heartworm like reluctance to exercise, lethargy or weakness. Taking heartworm medication before the heartworm matures into adults can easily be cured so annual heartworm tests are recommended to detect early signs of infection.

What Is The Treatment Of Heartworm?

There are three conventional methods of treating heartworm, namely the fast kill method using Immiticide (melarsomine), the slow kill method using Heartgard (ivermectin); and the surgical method (the worms are surgically removed from the arteries). In addition, there are also some holistic treatments, such as homeopathic or herbal remedies.

Fast Kill or Immiticide

Fast kill is preferred after stage one, it consists of giving two injections 24 hours apart and then keeping the dog strictly confined for the next four to six weeks. The injections are normally given in a painful location like the muscle near to the dog’s spine in the lower back. The worms are easy target here and start to die immediately. As the worms bodies get decomposed, they pass into the dog’s bloodstream and later filters out through the dog’s lungs. This can cause the dog to cough or it remains in silence or can lead to a fatal lungs embolism.

Slow Kill or Heartgard

Slow kill method is preferred for dogs in Stage one of the infection. It consists of giving the dog Heartgard on a monthly basis. This heartworm preventative medication is effective against the adult worms and gradually eliminates them from the dog over a period of one to two years. Without treatment, the worms can live up to five years. The simple rule; earlier the treatment is started after infection, the quicker the adult worms gets eliminated. Other medication like Revolution (selamectin) affects very less adult worms, Interceptor (milbemycin oxime) is not effective to all so only Heartgard (ivermectin) should be used. This method is gentler then fast kills but the danger from the dying worms lasts for a longer period.

Surgical Methods

Surgical methods of heartworm elimination require specialized training and instrumentation. This method is normally reserved for high-risk patients that are not expected to survive. The surgery is performed only after following any or all of the standard treatments methods. It is done a few weeks after the standard treatment to kill any remaining worms.

Is There Any Natural Remedy To Cure Heartworms?

One of the prevention and treatment methods is to use a medication that consists of natural ingredients that is beneficial to the general health of your dog while also curing heartworm infection. These natural ingredients mix syrup to keep the mosquitoes away from your dog so the risk of infection reduces. However, if the dog is affected, then it works to kill the heartworms and then expel them from the dog’s body. If the infection is the last or severe stage than consult veterinarian to further get assistance and follow his instructions. The natural product contains ingredients as mentioned below that helps the dog’s body to gradually expel existing heartworms.

  • Garlic
  • Black seed
  • Hawthorn
  • Licorice
  • Sorrel
  • Hops
  • Grapefruit seed extract
  • Apricot pits
  • Flavorings
  • Distilled water
  • Alcohol

Many people believe that the alternative methods to kill heartworms, like Paratox, are no longer safe to use as compared to conventional drugs. These alternative methods also rely on the same concept as conventional methods i.e. they kill the larvae or heartworms within the dog from its bloodstream. The greatest risk or danger during treatment is the death of the worms that decomposes and the mass that accumulates and creates blockage.

Besides, no studies are conducted to show that these alternate treatments are effective. Hence, they are similar to the slow kill method, with the same drawback of continued damage to the body as the worms remain present. Finally, some of the herbs used to treat heartworm are considered dangerous and may prove toxic in the amounts used to kill the worms.

The natural home remedies tend to work towards killing and expelling heartworms without any side effect. However, heartworm is a risky infection that can be deadly for your pet so it is suggested to consult the vet and not just rely on natural cure as it may not prove as effective as conventional methods.

Is There Any Side Effects From Medications Of Heartworms?

The most serious side effects usually occur with the treatment of the adult heartworms. As the worms die, they house in the lung arteries and severely blocks the blood vessels. In addition to the usual inflammation caused, just the presence of the worms is now greater than before due to the decomposing worms within the blood vessels.

The prescription medications used to treat the adult heartworms are called adulticides. These medications can prove toxic to the liver, kidneys, or may cause severe irritation if the solution spreads outside the vein. The major side effect is destruction of the adult worms and the resulting blood vessel blockage and inflammation.

After the adulticide treatment and its side effects are resolved that can last for about 1 month post treatment, the microfilaria are then eliminated. After about four months completing the adulticide therapy, the dogs are retested for the presence of heartworms, to determine if any additional treatment is needed or not. The infection is very risky and so are the side effects associated with its medications.


Heartworms and the treatment, killing them when they are present in your pet’s system is quite a dangerous process. Constantly involve the veterinarian in the treatment of heartworm infection of your dog even if you have decided to use natural and home remedies. Look for early signs of heartworm infection in your pet so that preventive steps are taken and it does not go to the last stages that are critical. Regular visit to a vet is the only preventive measure that can help you to correctly identify heartworm infection in early stages.

External Link References

1. http://www.petrescuebyjudy.com/info/display?PageID=5811
2. http://www.petcarerx.com/article/dont-let-heartworm-get-your-pets-heart/219
3. http://www.petmd.com/dog/general-health/evr_dg_heartworm_disease
4. http://en.wikipedia.org/wiki/Dirofilaria_immitis
5. http://dogaware.com/articles/wdjheartwormtreatment.html#other