Heartworms in Dogs

icon July 17, 2023

What Is Heartworm Disease?

Heartworm disease in dogs, also known as canine heartworm disease, is a serious and potentially fatal condition caused by the parasitic worm Dirofilaria immitis. These worms primarily infect the heart, lungs, and associated blood vessels of dogs.

How Many Dogs Get Heartworm?

Heartworm disease is considered endemic in many parts of the world, including certain regions of the United States, Europe, Asia, and Australia. The U.S. Health Services estimates that more than one million pets are infected in the United States. The U.S. Institutes of Health notes that climate and environmental changes have also contributed to the spread of the disease.

Heartworm in dogs

Heartworm Life Cycle in Dogs

When an infected dog is bitten by a mosquito, the mosquito ingests the microfilariae along with the blood. Inside the mosquito, the microfilariae undergo further development and molt twice over a period of about two weeks, transforming into infective larvae (known as third-stage larvae or L3). When the mosquito bites another dog, the infective larvae are transmitted to the new host through the mosquito's saliva and enter the dog's bloodstream. The infective larvae migrate through the dog's tissues for several months, primarily targeting the blood vessels near the heart and lungs. The mature adult heartworms take up residence in the heart, lungs, and associated blood vessels of the infected dog. The female worms release microfilariae into the dog's bloodstream, completing the life cycle.

How to Know If Your Dog Has Heartworms?

There are several stages of heartworm symptoms in dogs. Heartworm disease progresses through different stages as the infection develops and the worms grow within the dog's body. The stages include:

The First Signs of Heartworms in Dogs

In the early stages of heartworm infection, dogs may not show any visible signs or symptoms. 

Stage 2 Heartworms in Dogs

As the infection progresses, dogs may start showing mild symptoms such as

  • coughing
  • occasional fatigue
  • lethargy
  • decreased appetite
  • weight loss

These symptoms can often be mistaken for other respiratory or gastrointestinal issues.

Stage 3 Heartworms in Dogs

In the moderate stage, dogs may exhibit more pronounced symptoms. These can include

  • persistent coughing
  • difficulty breathing
  • exercise intolerance
  • reduced activity level
  • weight loss

The dog's overall health and condition may begin to deteriorate.

Signs of Late-Stage Heartworms in Dogs

In the severe stage of heartworm disease, dogs may experience severe respiratory distress, coughing up blood, pale gums, fatigue, collapse, and even right-sided heart failure. Severe cases can lead to significant organ damage and can be life-threatening.

Heartworm Test for Dogs

Heartworm testing for dogs is an important diagnostic tool used to detect the presence of heartworm infection. There are two primary types of heartworm tests commonly used:

Microfilariae Test

The microfilariae test aims to identify the presence of heartworm offspring (microfilariae) in a dog's bloodstream. It involves examining a blood sample under a microscope to visually identify the microfilariae. This test is usually used in conjunction with the antigen test or when there is a suspicion of early-stage heartworm infection.

Antigen Test

The antigen test detects the presence of adult female heartworms. It looks for a specific protein (antigen) that is released by adult female heartworms into the bloodstream. This test can usually detect heartworm infections approximately 5 to 6 months after a dog has been bitten by an infected mosquito.

RelatedHeartworm Test for Dogs

How Much is a Heartworm Test for Dogs?

Generally, the cost falls within a range of $20 to $50.

It's important to note that the cost of the heartworm test may not include other associated expenses, such as a veterinary consultation fee or the cost of preventive medications. Additionally, if the test results are positive and further diagnostics or treatments are required, there may be additional costs involved.

How Often Do Dogs Need Heartworm Tests?

Annual heartworm testing is typically recommended for dogs that are on a regular heartworm preventive medication regimen.  
In regions where heartworm disease is more prevalent or in areas with a high mosquito population, more frequent testing may be recommended. Tested at three-month intervals.

How To Treat Heartworms in Dogs?

  • Before initiating treatment, your veterinarian will confirm the presence of heartworms through diagnostic tests. They will also assess the severity of the infection and evaluate your dog's overall health.
  • If your dog has severe heartworm disease or is experiencing significant symptoms, they may require stabilization before starting the actual treatment. This may involve managing any secondary health issues, such as heart or lung complications.
  • The primary medication used to kill adult heartworms is called melarsomine dihydrochloride, commonly known as Immiticide. It is administered through a series of injections given by a veterinarian. The injections are typically spaced out over several weeks to minimize the risk of complications.
  • Following the Immiticide treatment, your dog will need a period of rest and restricted activity to allow their body to absorb and eliminate the dead worms. Exercise restriction is crucial during this time to avoid complications and minimize the risk of thromboembolism (blockage of blood vessels).

How to Keep Dog Inactive During Heartworm Treatment?

Keeping a dog inactive during heartworm treatment is crucial to minimize the risk of complications, particularly after the administration of the medication that kills the adult heartworms.

  • Restrict your dog's exercise to short, leashed walks for bathroom breaks only. 
  • Provide your dog with plenty of mental stimulation, such as puzzle toys, treat-dispensing toys, and supervised chew toys, to keep them entertained and prevent boredom.
  • When your dog needs to be outside, ensure it is in a controlled environment where they cannot engage in excessive activity. Use a leash or secure, enclosed area to restrict movement.

What to Feed a Dog with Heartworms?

When a dog is undergoing treatment for heartworm disease, it's important to provide them with a balanced and nutritious diet to support their overall health and recovery. 

Provide a diet that is rich in high-quality proteins, healthy fats, and essential nutrients. These can support your dog's immune system, muscle maintenance, and overall well-being. Ensure the food is well-balanced and provides adequate levels of vitamins, minerals, and antioxidants.

Encourage your dog to stay hydrated by providing fresh, clean water at all times. Ensure they have easy access to water and monitor their water intake, as increased urination may be a side effect of heartworm treatment.

When Do Dogs Start Heartworm Prevention?

Dogs should start heartworm prevention as early as possible, ideally when they are puppies. Heartworm preventive medications are safe and effective when administered to puppies as young as 6-8 weeks old. 
Once you start your dog on heartworm prevention, it's important to maintain consistent administration throughout their life. Heartworm preventives are typically administered monthly, and it's essential to follow the recommended dosage and schedule provided by your veterinarian.
Alongside regular heartworm prevention, annual heartworm testing is generally recommended for dogs.  

Annual testing helps ensure early detection and timely treatment if needed.

Recommended medications to prevent heartworm.

  • Heartgard ®Plus for Dogs (chewable, ivermectin/pyrantel)
  • Tri-Heart®Plus for Dogs (chewable, ivermectin/pyrantel)
  • Iverhart Max® for Dogs (chewable, ivermectin/pyrantel permeate/prziquantel)
  • Sentinel® for Dogs (chewable, milbemycin oxime/lufenuron/praziquantel)
  • Puainta® Abamectin B1 (Topical application)

Puainta® Topical Deworming Drops to Kill Fleas & Ticks in Dogs/Cats

What is the Life Expectancy of a Dog After Heartworm Treatment?

Early detection and timely treatment of heartworm disease can increase the chances of a positive outcome and longer life expectancy for the dog. If the disease is detected in the early stages before significant damage to the heart and lungs has occurred, the prognosis is generally better.

If dogs with severe or advanced heartworm disease may have a more guarded prognosis. The extent of damage to the heart, lungs, and blood vessels can impact the long-term outlook and overall life expectancy.


Can Heartworms Cause Seizures in Dogs?

Yes, it is possible for heartworms to cause seizures in dogs. When a large number of adult heartworms are present, they can potentially migrate to other parts of the body, including the brain. This migration can cause inflammation and affect the normal functioning of the brain, leading to seizures.

Can Dogs Get Heartworms from Fleas?

No, dogs cannot get heartworms directly from fleas. Heartworm disease is primarily transmitted through infected mosquitoes. The life cycle of heartworms requires mosquitoes as an intermediate host to transmit the infective larvae to dogs.

Why Do Dogs Need Heartworm Test Before Medication?

The primary reason for this is that if heartworm preventive medication is administered to a dog with a heartworm infection, it can have serious consequences. This is because the drug can quickly kill the worms, leading to a potentially life-threatening condition called pulmonary thromboembolism.

Is Heartworm Contagious to Other Dogs?

Heartworm disease itself is not directly contagious from one dog to another. It requires an intermediate host, mosquitoes, to transmit the infection. But if an infected dog is bitten by a mosquito and that mosquito then bites another dog, the infective larvae can be transmitted to the second dog. 

How Much Does It Cost to Treat Dogs for Heartworm?

On average, heartworm treatment for dogs can range from $500 to $2,000 or more. However, it's important to note that this is just a general estimate, and the actual cost can vary widely.

Why Dogs Cough After Heartworm Treatment?

Coughing in dogs after heartworm treatment is not uncommon and can occur for several reasons.

Pulmonary Thromboembolism
In some cases, the presence of dead worms and the resulting inflammatory response can cause the formation of small blood clots in the lungs. These clots can partially obstruct the blood vessels, leading to a condition called pulmonary thromboembolism. Coughing can be a symptom of this condition.

Allergic Reaction
Dogs may develop allergic reactions to the medications used in heartworm treatment. This can lead to respiratory inflammation, coughing, and other respiratory symptoms.

Can My Dog Jump on the Couch After Heartworm Treatment?

No, after heartworm treatment, it is generally recommended to restrict your dog's activity and prevent them from jumping on furniture, including the couch. This restriction is essential to allow for proper healing and reduce the risk of complications during the recovery period.



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