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Heartworm: Symptoms and Treatment

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The thought of your beloved dog suffering from Heartworm Disease can certainly make you cringe. Those horrid spaghetti-like worms can cause serious health issues and may even be fatal for your dog.

The Basics: How Is Heartworm Spread?

As the name suggests, heartworms are worms that live in the heart and lungs of their hosts. Dogs are the most common hosts for these worms, but other mammals (such as felines, ferrets, and wild canids) have contracted these parasites. Humans are not a natural host for heartworms, so you don’t have to worry about contracting them. However, household cats are at risk, which we’ll cover more later in this article.

Heartworms are not directly contagious to other dogs since the parasites transmit through mosquito bites. Here’s how it works:

A mosquito bites an infected animal and picks up microscopic heartworm larvae, called microfilariae. When this mosquito bites another animal, it passes the microfilariae into the bloodstream of the new host.

The microfilariae then migrate through the bloodstream toward the host’s heart and lungs. It can take up to six months for the microfilariae to reach these organs, so detecting this disease early in the course of the infestation is challenging.

Once in the heart and lungs, the microfilariae mature into adult heartworms and can grow to over a foot in length.

Heartworm Risk Factors

From teacup-sized Terriers to large Labrador Retrievers, dogs of any age or breed can contract heartworms from the bite of a mosquito carrying microfilariae.

Breeds with very heavy coats are also susceptible to this disease. Dogs who are older or have existing medical conditions, such as heart or respiratory problems, may be more severely damaged by this parasite.

Cases of heartworms have been found in every state across the country. Areas with hot and humid climates, such as the Ohio and Mississippi river basins and the Atlantic and Gulf Coasts, are especially endemic. That’s because they are good breeding grounds for the mosquitos that transmit the disease.

While all dogs are susceptible to Heartworm Disease, the greatest risk for transmission in dogs is during mosquito season, even for dogs that live primarily indoors. Besides protecting your pup from mosquitos, learn some additional ways to keep your pal safe while they are outdoors.

How long can a dog live with heartworms?

Dogs are able to live for years with this parasite, however, their condition will continuously worsen. It’s a dangerous disease overall, which is why some people have even described untreated heartworms as the “slow kill.”

Heartworm Symptoms

How do you know if your dog has heartworms? Understandably, this is a question that most dog parents worry about. In its early stages, when the microfilariae are migrating through the body, this disease may be difficult to detect. However, later in the disease, when the adult worms are invading the heart and lungs, dog parents may notice symptoms such as:

  • Mild or persistent coughing
  • Shortness of breath
  • Nosebleeds
  • Tiring easily during exercise
  • Lethargy
  • Fainting spells
  • Decrease in appetite leading to weight loss

If a large number of heartworms develop in the same blood vessel, they can block the blood flow and cause Caval Syndrome (also called Vena Cava Syndrome). This is a life-threatening situation that can be marked by severe difficulty in breathing and collapse. Caval Syndrome requires immediate emergency medical and surgical intervention to try and remove the blockage. 

Heartworm Disease is a complex and life-threatening health issue, especially as it progresses. Remember that we are talking about parasites that are up to a foot long, causing severe damage to the heart, lungs, liver, and kidneys.

jack Russell terrier asleep on a colorful blanket

Heartworm Treatment: Can Heartworm Be Cured?

If your dog tests positive for Heartworm Disease, your veterinarian will determine the best course of treatment.

The American Heartworm Society (AHS) recommends treating infected dogs with an antibiotic and heartworm preventative medication. This helps combat any secondary infections and begins to eradicate the heartworm larvae. You can download the guidelines at the AHS’s website.

Dogs with significant clinical signs of this condition should also be “normalized” as much as possible before moving onto the next step, which is therapy for the adult worms. During this portion of the treatment, the AHS calls for a three-dose regimen of an adulticide drug given by injection to kill off the adult heartworms.

Your veterinarian will administer these three injections over a period of time. The second injection is usually administered approximately one month after the first. The second and third injections are given about 24 hours apart.

Please keep in mind that these are guidelines only. Your dog’s treatment is at the discretion of your veterinarian and based on your dog’s specific condition.

Just like medical professionals do for humans, veterinarians also use a lot of shorthand and abbreviations for common medical terms. Want to be in the loop on what all of these abbreviations mean? Learn about the most common acronyms in veterinary medicine.

Post Treatment

The most important responsibility of dog parents with dogs undergoing treatment for Heartworm Disease is to limit their exercise. A dog’s activity must be drastically restricted after treatment since exercise will increase blood flow and cause fragments of the dead heartworms to break off and migrate through the bloodstream. This can cause potentially dangerous blockages.

Keeping an active dog calm and resting can be tricky. If your dog is crate trained, the crate can come in handy as a safe resting space.

Approximately six months after treatment, the dog will need to be tested to ensure the heartworms have been successfully eliminated. If not, the treatment may need to be repeated.

Not being allowed to play and exercise as much, on top of not feeling their absolute best, your pup may feel down in the dumps while going through heartworm treatment—no need to worry, though. Check out these three pup-tastic dog treat recipes that will help lift your pal’s spirits.

Heartworm Prevention

Because treating this parasite is a long, costly, and risky process, the best approach is ALWAYS prevention. Talk to your veterinarian about which of the many available preventative medications is right for your dog. 

Heartworm preventative medications come in three forms:

  • Injections at your veterinarian’s office every six months
  • A topical gel that you apply monthly at home, which also works to prevent fleas, ear mites, and other parasites
  • Oral medication (tablets) given to your dog at home once a month

Monthly tablets may be the most convenient method for many dog parents, but that means you have to get your dog to swallow that pill. Wrapping it up in a bit of soft cheese or another treat can help the medicine go down. Get tips on giving your dog a pill.

Since heartworm larvae are passed to your dog by mosquitoes, look out for any standing water around your home and eliminate it as best as possible. Mosquitoes lay their eggs (often 300 at a time) in still or stagnate water. Keeping the mosquito population down will help keep your dog safer.

border collie chewing a kong toy atop a green couch

Heartworm Testing

Annual heartworm testing is just as important as using heartworm prevention for two main reasons:

1. Symptoms may be missed.

It can take up to six months after contracting the microfilariae before adult heartworms develop and cause noticeable symptoms.

2. Early detection is key.

It can help improve the odds of successfully treating an infected dog if the disease is caught early. As the disease progresses, more adult heartworms develop and increase the risk of treatment.

Heartworm testing is usually performed during your dog’s annual exam. It consists of a blood test that will either check for antigens left behind in the bloodstream by female heartworms or look for the presence of microfilariae. Your veterinarian will determine the correct test for your dog depending on local risk factors.

It can often be difficult for pet parents to tell when their dog isn’t feeling the best—some dogs can hide their condition better than others. To help you catch the problem earlier, it may be helpful to read up on six signs that your dog is sick.

Do Cats Get Heartworm Disease?

It’s a myth that cats can’t contract Heartworm Disease. They’re not a typical host for heartworms because the microfilariae (larvae) have difficulty maturing to adulthood in the heart and lungs. However, a large number of microfilariae can cause health problems, and even a very few adult worms can be fatal to your cat.

Like dogs, cats contract this disease from mosquito bites and may benefit from preventative medication. If you have a cat, you should discuss Heartworm Disease with your veterinarian and determine if preventive medicine would be appropriate for your feline friend.

To help keep your pet in tip-top shape, it’s essential that you continue their heartworm prevention medicine all year round, even if you live in a colder climate during the winter season.

While it may seem difficult to remember to give your pet a pill every month, it can be helpful to mark it on your calendar or set a reminder on your phone. And if you ever feel that paying for a preventive medicine every month may not be worth it, or you’re considering skipping a month or two, just remember the wise words of Benjamin Franklin: “An ounce of prevention is worth a pound of cure.”

The information presented in this article is for educational and informational purposes only and does not constitute or substitute for the advice of your veterinarian.

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