Boston Pet Owners: 8 Symptoms of Heartworms in Dogs

Heartworm disease is a serious and potentially deadly disease that can affect dogs, cats and ferrets, as well as wild canine species.  In the US, cases of heartworm disease have been reported in all 50 states, as well as in other parts of the world.

In this article, we’ll go over the common symptoms of heartworms in dogs and what you need to do next as a pet owner in Boston, MA.

What is Heartworm Disease?

Heartworm disease is caused by parasitic worms called heartworms.  The reason that they’re called heartworms is that they live in the heart, more specifically the pulmonary artery of the heart.  These worms can also infiltrate other parts of the heart and lungs, and if untreated, can cause severe lung disease, blockages of the valves of the heart, as well as damage to other vital organs in the body.

In severely affected dogs, you may see a swollen abdomen due to fluid buildup because the heart cannot effectively circulate blood, or notice a cough, or other signs such as respiratory distress.  Heartworm disease in dogs is known as a silent killer, because it can take months before your dog shows symptoms.

Heartworms are transmitted by mosquitos, which act as vectors and play an important part in the transmission of heartworms to your dog.  Adult female heartworms create infant worms called microfilaria that circulate in the bloodstream of the body.

When a mosquito bites a dog or other canine that has heartworm disease and takes a blood meal, the mosquito ingests the baby worms, which develop and mature into the infective stage of larvae over a period of 10 to 14 days. When the infected mosquito, the vector, bites another dog, cat, or other animal, the infective larvae are injected into the new host through the mosquito’s bite.

Once inside the new host, it takes about six months for the larvae to mature into adult heartworms. Once mature, heartworms can live for five to seven years in dogs, and up to two or three years in cats.

Heartworms can live a long time in your pet, and it’s important to note that with each new mosquito season, more heartworm larvae can be transmitted to your dog.  When veterinarians diagnose heartworm disease, a blood test is run, and this test can detect heartworm antibodies in the blood.  A blood smear can also show microfilaria moving in the blood sample on a slide.

What are the Symptoms of Heartworm Disease in Dogs?

In the early stages of the disease, dogs may not show any symptoms at all, but the longer the dog goes without diagnosis or treatment, the more likely symptoms will develop.  Young dogs, or dogs that are normally active, or those with health issues may show more obvious signs that other dogs.

If you are a dog owner, you have probably discussed heartworm prevention with your veterinarian, and know that your dog should be on medication.  Heartworm medications can either be a once-a-month chewable tablet, or an injectable form that can last up to 6 months.

You and your veterinarian can decide which medication is best for you and your dog.  If your dog is diagnosed with heartworm disease, early treatment is essential and can really improve your dog’s chances of recovery.

However, as a dog owner it is still important to recognize the signs and symptoms of heartworm disease.  According to the FDA, there are four stages of heartworm disease, and symptoms appear differently in each stage.

Class 1:

Light, Dry Cough

When heartworms infiltrate the lungs and start reproducing in the lungs and in the surrounding vessels, your dog may start to cough.  This is usually a dry, unproductive cough that can be more obvious after exercise.  Sometimes dogs may have “coughing fits,” that may even cause fainting.

Class 2:

Lethargy, Inactivity, More Frequent Coughing

One of the first signs of heartworm disease in dogs is lethargy, or acting tired and “lazy.”  If your dog doesn’t want to run, or hike or be as physically active as he usually is, contact your veterinarian for an exam.

Dogs with heartworm disease often feel weaker, and low-energy because the worms are putting an extra load on the heart and lungs, and that can affect energy levels and the movement of oxygen throughout the body.

Weight Loss, No Appetite

As heartworm disease advances, your dog may not feel like eating as much, and you may notice some weight loss.  If you notice these signs, make an appointment with your local veterinarian as soon as you can to rule out heartworm disease or other illnesses.

Class 3:

Panting, Shallow Breathing

As heartworms spread through the heart and lungs, your dog will have a harder time moving blood and oxygen around his body.  Also, as the heartworms block vessels, the areas around these vessels will see fluid build-up, making it even harder for your dog to breathe and get oxygen, causing him to take more shallow, rapid breaths.

Distended Abdomen and/or Chest

In advanced cases, dogs with heartworms may exhibit a swollen abdomen, or a distended chest.  This is caused by the heartworms backing up the vessels of the heart and lungs, causing a sort of pinched garden hose effect where fluid collects in the belly and in the tissues around the heart and lungs because it can’t circulate properly through the heart.

Seizures or Blindness

Heartworms can reach other places beside the heart, and can migrate to the brain and eyes, causing potential seizures and blindness.  Although these symptoms are rare in heartworm disease, they are still a consideration.

High Blood Pressure

Dogs with heartworm disease can also experience high blood pressure that results from the heart having to work harder to pump blood through vessels that are partially blocked by heartworms.

Class 4:

Caval Syndrome, Fainting

As heartworms infect the heart, blood flow is blocked, and this is known as “vena cava syndrome.”  Known as CS, vena cava syndrome happens when heartworms block the right atrium of the heart, the right ventricle and the vena cava (the large blood vessel responsible for bringing blood back and forth to the heart).

As a result, the blockage of worms interfere with the functions of the tricuspid valve, reducing blood flow through the right side of the heart, leading to heart failure and cardiovascular collapse.

When this happens, a dog will faint because of reduced blood flow to the brain, and may become shocky.  At this late stage, the disease has progressed so far that the prognosis for survival is very grave.

When Should I Have My Dog Tested for Heartworms?

If you have questions about heartworm testing in your dog, contact your local veterinarian for recommendations.  The American Heartworm Society suggests that dogs be routinely tested for heartworm disease, and make the following recommendations:  Puppies under six months can get their first heartworm prevention medication without a heartworm test (because it takes six months for a dog to test positive after being infected).

At six months you can have your puppy tested, and each year after that.  Adult dogs over the age of six months that haven’t been on heartworm medication before should be tested, then retested six months later, then once a year thereafter.  If you miss a dose, your veterinarian may suggest a heartworm test.

Year-round testing is important to make sure that the medication is working, and while heartworm medications are successful, there is still a chance that your dog could become infected due to things like spitting up a pill or not getting a correct dose.

If you’re ever concerned that your dog is experiencing any heartworm symptoms, contact your veterinarian immediately.  Your veterinarian can do a simple blood draw to check for the presence of a heartworms, and if your dog is infected, your veterinarian can make recommendations and come up with a treatment regimen for your dog, depending on how ill your dog is.