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What are the First Signs of Heartworms in Dogs?

Image of an Australian Cobberdog puppy lying face down

Heartworms: What are They and Why They’re so Harmful to Dogs

If you’ve brought your cat or dog to your Austin vet for a routine checkup, you’ve probably heard about heartworms. While heartworms can affect both cats and dogs, they appear to be more prevalent in dogs at roughly around 28% (with 4% in cats overall).

Heartworms, also known as Dirofilaria immitis, are thin, threadlike parasitic worms that can grow up to a foot long and take refuge in your pet’s lungs, blood vessels and even their heart, hence the name. While other worms seem focused on attacking your pet’s gastrointestinal tract, heartworms can cause even more harm, including lung disease, organ damage, and heart failure.

Heartworm Disease: How it Spreads

Contributing factors in heartworm disease can be related to an influx of mosquitoes, climate, including humidity and reservoir animals such as deer, bears and coyotes. Mosquitoes seem to be the major culprit for infection during their feeding season, when temperatures are over 50°F. Anywhere in the world where there are mosquitoes, you’re bound to find heartworm disease. Your pets can contract heartworm from a single mosquito bite.

While warmer parts of the country, such as Texas, tend to have a higher rate of infection, heartworm disease is pretty much everywhere. Even a designated heartworm-free region can contain pockets or hotspots of infection. This is why it’s important to take measures and prevent your pet from getting it at all costs. Once a mosquito bites your pet and then transmits the disease, it can take several years before major problems with your pet’s health start to appear.

Symptoms of Heartworm Disease in your Pets

Extreme cases of heartworm disease in dogs often depends on how many worms exist, your dog’s overall health and activity levels and the length of the infection. Initially, there may not be any symptoms that are noticeable, aside from maybe a small cough. More extreme symptoms of heartworm disease would be fatigue, excessive coughing, vomiting, breathing issues and even fainting.

However, it’s not just dogs that considered the host of choice for heartworms. As mentioned above, cats are also susceptible. While heartworm disease is very different among these different species, it can still be quite serious.

Cats are clearly smaller than dogs, so it may take fewer heartworms to make them quite sick. For cats, symptoms can be either very subtle to severe, with some unexpectedly collapsing and even dying. Be aware of their appetite, energy and their breathing. Keeping them on a year-long heartworm prevention program will also help them down the road.

How is Heartworm Disease diagnosed?

It usually takes one or more basic blood tests to diagnose heartworm disease. In some cases, additional diagnostic tests may be required in heartworm-positive dogs to decide if the dog is able to safely undergo any treatment. The following diagnostic procedures are usually recommended before treatment is started.

Serological test for antigens to adult heartworms: This test also known as enzyme-linked immunoassay or an ELISA, is a commonly used laboratory test that detects antibodies in the blood.

Chest X-rays: It’s highly recommended that dogs have x-rays or radiographs if they have heartworm disease, to determine any heart and lung damage exists before beginning treatment.

Bloodwork: Your Austin veterinarian may recommend blood tests before any treatment of heartworm disease. This will help determine the presence and extent of any heartworm-associated organ damage.

Preventing Heartworm Disease In My Pet?

If your dog needs treatment for heartworm disease, be advised that it can be extremely difficult for them. It’s a long process and there may be complications depending on how your dog reacts to all of it. In regards to cats, unfortunately no approved therapy for them exists at the moment; the treatment is mainly focused on keeping them stabile during the course of the illness.

The good news is that heartworm disease is actually preventable in both cats and dogs. Once your cat or dog reaches between 6 to 8 weeks old, they can begin preventative treatment against heartworm disease. Medicines such as Revolution or Heartguard are the most common and are available over the counter, or through your Austin vet.

Even if your pets are mainly indoors it’s wise to put them on heartworm prevention as well; mosquitoes are crafty creatures and can still find a way to get inside your house.
If you’re not sure what type of medication to use, speak to your Austin veterinarian. They can recommend the right type of product based on your pet’s condition and they can also provide regular testing to help keep them safe.

How Heartworms Affect Dogs

As previously mentioned, heartworm disease affects dogs more often than cats, sometimes taking up to a few years before any signs of clinical infection appear. For dogs, the disease is usually diagnosed between the ages of 2 to 8 years. It’s rare in puppies before they reach their first year, as it takes around 5 to 7 months to transform into adult heartworms after the initial infection. Sadly, once the first clinical signs are diagnosed, heartworm disease may have greatly advanced.

Adult Heartworms

Once heartworms mature, they can advance the disease by attacking the heart and clogging major arteries, and blood vessels, including the pulmonary artery. Heartworms also can affect the function of heart valves. The clogged blood vessels affect the ability for blood to move to other organs in your dog’s body, especially the lungs, kidneys and liver. This lack of blood flow can cause their organs to malfunction.

The extent of the disease also depends greatly on how many adult worms are involved, where they’re located, how long they’ve been there and how much damage they’ve done to your dog’s organs. Again, the major signs to look out for are a dry cough, shortness of breath, weakness, listlessness, and loss of stamina. You may notice this after running around with your dog, and in some cases they may even faint or show signs of disorientation.

A veterinarian may be able to detect any lung or heart abnormalities by stethoscope. If the disease is rather advanced, your dog may experience congestive heart failure, which may cause their abdomen and legs to swell from accumulating fluid. You may also notice weight loss, and anemia, and if your dog is severely infected, he/she could very likely die while exercising.

Treatments to Stop Adult Heartworms

An injectable drug known as melarsomine (or Immiticide®), is available that is effective in killing adult heartworms in the heart and adjacent vessels. It’s administered in a series of injections; your veterinarian can determine the proper dosage and injection schedule based on your dog’s situation. It usually consists of an initial injection with a 30-day break, and then two more injections given 24 hours apart.

Some dogs may also be given doxycycline, an antibiotic to prevent infection with bacteria that can inhabit the heartworms.

Post Treatment: Complete Rest is Essential After Treatment

Once the treatment begins, your dog will require extensive rest. This period will allow adult heartworms to die and begin to decompose. Once the worms start to dissolve, they usually move to the lungs, where they wind up in the blood vessels and are then re-absorbed into the dog’s body.

This is a lengthy process that can take anywhere from a few weeks to a few months. These worm fragments can actually cause complications if a dog exerts itself in any way, especially after the final injection of the medication, so it’s very important to keep your dog quiet and allow them time to heal. The worms usually start to die off around one week after the initial injection. A dog might cough every now and then if they are extremely infected, but if the coughing worsens, then bring your dog to the vet for additional treatment.

Notify your veterinarian if your dog has symptoms such as shortness of breath, a loss of appetite, coughing up blood, fever, and even depression or extreme sadness. There is a chance your dog may need extra medications such as anti-inflammatories, antibiotics, and intravenous fluids to name a few.

Stopping the Spread of Microfilaria

In addition to melarsomine, a dog may receive an additional medication that kills microfilariae, or heartworm larvae. A stay in the hospital may be needed for observation, followed by a treatment with a heartworm preventative.

It’s best to consult with your Austin veterinarian, who can select the proper medication and administration schedule based on the severity of your dog’s illness.

Possible Extra Heartworm Treatments

If your dog has a severe case of heartworm disease, they may require additional medications such as antibiotics, pain relief medications, special food, diuretics to help alleviate fluid in the lungs, as well as additional medications to help with heart function. Dogs may require extra treatment for heart failure, such as ACE-inhibitors, beta-blockers or cardiac glycosides, and special low-salt diets, even if all the heartworms have been killed off.

Contact Us

This is a lot to absorb, but if you notice any of these symptoms, please bring your pets to your veterinarian right away. At ATX Animal Clinic, we offer Blood Parasite Screenings and carry the 4DX panel which tests for heartworms, but also tick-borne diseases such as Lyme Disease, Ehrlichia, and Anaplasma as well.