Heartworm Disease in Dogs: Causes, Symptoms and Treatment

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Heartworm disease in dogs is one of the most common diseases contracted by dogs. In the old times, the veterinaries developed a vaccine prescribed only to pet owners living in places where mosquitoes were found dominant, but in these present times, the heartworm disease is a global problem.

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Some dogs may be asymptomatic even after testing positive for heartworm disease. Therefore, It is vital to test for heartworm disease in your dog regularly because if this condition is left untreated, it is most likely lead to the death of your dog.

What Is Heartworm Disease?

Heartworm is a possibly dangerous parasitic disease in dogs which are transmitted by a vector mosquito. The larvae develop within the mosquito for up to a month. Larvae are injected into an infected dog when the female mosquito bites.

At this point, the larvae develop in the skin, and after some months they get in the bloodstream and are conveyed into the pulmonary arteries, the large blood vessels leaving the heart, where they develop and mature into adults.

More or less than six to seven months after the first inoculation, the adult worms procreate and start to shed larvae into the bloodstream. The cycle is repeated when a female mosquito bites the septic dog and habituate the freshly formed larvae.

Complications of heartworm disease can cause the heartworms to block the blood vessels around the heart. The heartworms fill the whole right side of the heart and the vena cava.

This is a severe form of heartworm disease called Caval syndrome.

Signs of Heartworm Disease in Dogs

The symptoms shown by the infected dog depends on what stage it is in. There are four main stages of canine heartworm disease.

Stage 1: At this stage, dogs are usually asymptomatic to the disease, or they only have a mild cough, which could be tossed out as negligible by not so caring pet owners.

During this stage, there are possibilities that the dogs that have this disease may test positive for heartworm or may not. At this stage,  there may be no abnormal, laboratory, radiographic, or clinical symptoms that a dog in this stage may have this disease.


Stage two: At this stage, the dog may show symptoms like a persistent cough, exercise intolerance, and fatigue.

Stage three: At this stage, the health of the dog becomes highly affected. The symptoms of cough,  fatigue, and exercise intolerance may continue, but the dog would get to a point where it might cough out blood. X-rays are carried out on the dog at this stage will show evidential signs of the heartworm disease.

Stage four: This stage is the final and last stage of this disease.  If this disease is left untreated at this stage, it may result in heart failure or damage to the other organs. The worst that may come from this disease is death.

Causes of Heartworm Disease

The heartworm disease is contracted when an infected mosquito bites a dog. The larvae ingested causes an innovative blockage of the pulmonary artery, which results in the inflammation of the lungs and pulmonary hypertension.

Adding to this, the growth of these changes leads to heart enlargement and heart failure. Heartworm disease can also cause kidney and liver damage.


The treatment of heartworm disease in dogs includes getting rid of adult worms that inhabit the heart and pulmonary arteries. This also means killing those in larval stages, which are also referred to as microfilaria that lives in the bloodstream.

Just like every other disease, building a treatment plan starts with examining the dog’s general condition thoroughly. As with any other disease, formulating a treatment plan begins with a thorough examination of the dog’s overall health and condition.

In treating heartworm disease, two medications are used, and they include:

  1. Melarsomine: This medication is administered to kill the adult worms in order to destroy the final stage of the worm’s life cycle. It is given to the dog through a series of injections. The injection site of this medication on the back, and when it is injected into the back muscles, pain killers are usually administered simultaneously in order to reduce pain for the dog.

In the administration of this medication, two distinct protocols are used. And they are;

  • The first protocol: This protocol is specially set aside for dogs that seem healthy and are not exhibiting significant symptoms relating to heartworm infection. This protocol involves two injections, which are given about 24 hours apart.
  • The second protocol: In this protocol, three injections are given. A month after the administration of the first injection given, two extra injections are given 24 hours apart. The second protocol has reduced risks of complications, and it is relatively safer when compared with the first protocol.
  1. Ivermectin: This medication is administered to destroy the larval stage of the heartworm, disrupting the completion of the larva life cycle.

Ivermectin-based medication is administered monthly and is used as a preventive method of dealing with heartworm disease. This is a method called “slow kill” because it works by allowing the adult worms to die of natural cause.


Adult worms’ lifespan is only two years before they die, but they are dangerous enough to cause heart damage as well as lung damage at that period.

This method of treating heartworm disease involves the administration of preventive treatment monthly. Additionally, a veterinarian may have antibiotics or steroids prescribed for the infected dog according to the stage of the disease and how bad the disease has gotten.

Home Care

In home care, the most important thing needed by your dog for its full recovery from this medical condition is rest. As a pet owner, your veterinarian must have told you about embolism on the course of treating your dog of heartworm disease.

In case you have never heard of the word “embolism,” it is when the blood vessels are being blocked by dying or dead worm.

That is why during the period of heartworm disease recovery, you are advised to let your dog have complete rest because exercises and other hyperactive activities increase the risk of embolism. Therefore the risk of complications and death is increased as well.

So for the sake of your dog, you must enforce strict confinement during this period for at least four weeks after the last injection of the medications. Furthermore, proper ventilation and adequate diet to generate an inactive state.

As a pet owner, when having your dog treated for any infection, including heartworm infection, you should provide an adequate diet and enough water while carefully following instructions on any medication prescribed or treatment recommended strictly.

Once the treatment is proven successful evident in your dog being health, heartworm preventive medications are adopted and ensured strictly.

Prevention of Heartworm Disease

Flea and tick collars are known to repel mosquitoes, but the truth is that they do not prevent mosquitoes from biting your dog, which can get your pet infected.

Moreover, preventive medications can be used to stop the larva’s life cycle completion inside the host. Additionally, as a pet owner, It is recommended that the health status of your dog be monitored using blood tests while administering preventative methods.


In tropical or warmer areas, heartworm medicine is recommended to be administered year-round due to the way mosquitoes breed more in such areas. As a pet owner, when the suspicious of your pet being unwell kicks in, you have to instinctively call your veterinarian as soon as possible.

You are advised to consult your veterinarian whenever you have questions regarding the health of your pet. It is good to establish a good doctor-patient relationship with your veterinarian for the sake of your pet as they have your pet examined while taking the health history of your pet in order to establish the best for your pet.

Do you have a dog for a pet? Is your dog suffering from heartworm disease? If yes, what steps have you taken to manage the condition? Kindly share it with us in the comments below.

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