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Heartworm in Dogs

Copywriter, mini schnauzer mom, cat lover | + posts

Ali is a copywriter with a passion for grammar. She's also mom to Ziggy, the mini schnauzer.

Heartworm is unsettling and painful for dogs, and perhaps equally so for the humans that care for them. The condition is a serious one, but thankfully it’s preventable – so, you can rest easy if you’re well informed and on your pup-parent game. Here’s everything you need to know about heartworm in dogs, including prevention, symptoms, treatments, and more.

First and foremost: What is heartworm disease?

Heartworm disease is an illness caused by – you guessed it – the parasitical monsters known as heartworms. Heartworms can be up to 12 inches in length and take up residence in your dog’s heart, blood vessels, and other organs, causing dangerous blockages and damage. The parasite’s official scientific name is Dirofilaria immitis but are commonly called “heartworms” because of the damage they can do to pets’ cardiovascular health when they create a home in their hearts, lungs, and blood vessels.

What do heartworms look like?

Imagine the nastiest spaghetti squash you’ve ever seen. Take the stringy part out, bleach it, and stretch each “spaghetti” to about a foot in length. Not something you want to see in real life.

What are the first signs of heartworm in dogs?

According to veterinarian and author Dr. Margit Muller, many dogs don’t actually show any symptoms for the first few months of heartworm infection, though active dogs are most likely to suffer from symptoms the soonest. That said, the earliest signs of heartworm disease in dogs can include:

  • Persistent cough
  • Difficulty breathing
  • Loss of appetite
  • Weight loss
  • Lethargy and fatigue
  • Bulging ribs

The problem with heartworm disease symptoms is that they overlap with any number of potential other conditions. If you suspect your dog is ill and exhibiting them, be sure to take them to your veterinarian for proper diagnosis and treatment.

How can I prevent my dog from getting heartworm?

Year-round preventative treatment is a must, as well as application of FDA-approved mosquito repellents. You can also take steps within your environment to reduce the likelihood of mosquito bites, including eliminating any standing water outdoors, using mosquito traps, and timing your dog’s outdoor activity to exclude dusk and dawn, when mosquitoes are most active.

Regular heartworm testing, as well as preventative medication, are crucial to preventing your dog from contracting heartworms. There are monthly oral doses your pet can take to prevent heartworm, as well as topical treatments to repel the parasites and the mosquitoes that carry them. Some insurance companies will even cover a portion of the costs. For instance, Pumpkin’s Preventive Essentials Pack for dogs fully refunds a yearly heartworm test for dogs each year.

How should I get a heartworm test for my dog?

If your dog exhibits any of the symptoms mentioned above, visit your veterinarian immediately for heartworm testing. Got a healthy pooch? Great! Your dog should be tested for heartworms annually, even if they’re on preventative medication and you have no reason to suspect infection. Your vet will likely perform the test at your dog’s annual wellness exam.

If your dog misses a dose of their preventative heartworm medication, or if they spit it out or vomit after taking it, you should have them tested for heartworm, as missing even a single dose can put your dog at risk of the parasitical infection. If you use a topical medication, be sure your dog doesn’t rub it off, and if they do, take them to the vet.

Dogs aged seven months and younger can start a heartworm preventative without testing; vets typically begin heartworm testing in dogs annually once they reach seven months old. This is because it can take up six months to detect heartworms.

What are long-term symptoms of heartworm in dogs?

“Long-term symptoms occur when the adult worms cause inflammation of the blood vessels and can block blood flow,” Dr. Muller tells Pumpkin. “This leads to clots in the lungs and heart failure. Heartworm disease can also lead to liver or kidney failure.”

In terms of symptoms you can see with the naked eye, your dog may also develop a swollen abdomen due to fluid buildup. If you notice your dog has trouble breathing, dark urine, and/or pale gums, seek medical attention for them immediately, as they may have developed caval syndrome – a potentially deadly cardiovascular issue that requires immediate surgery for your furbaby’s survival.

How is heartworm diagnosed?

Because heartworm disease shares symptoms with so many other health conditions dogs may face – and because your dog may not exhibit any symptoms at all for months – special tests are necessary for diagnosis to rule out other causes for their discomfort. Your veterinarian will simply have to take a small blood sample from your dog, the American Heartworm Society notes, in order to check for heartworm proteins. If your dog tests positive for heartworm proteins, your vet may order more tests, including X-rays, ultrasounds or echocardiography, or opt to start treatment immediately. The good news is some pet insurances like Pumpkin may help cover these costly heartworm disease treatments and reimburse 90% of eligible costs.

Can heartworm in dogs be cured?

Thankfully, there is a cure for heartworm in dogs, but know that it’s a bit of a lengthy, complex, and expensive process. “There are injections available to treat heartworm,” Dr. Muller says, “but they have to be given repeatedly, usually two or three times.” Of course, all dogs vary and it may depend on the severity of your pet’s particular case. It’s also important to note that dogs who have a lot of heartworms may not exhibit any more symptoms than dogs with fewer heartworms. However, the less severe the symptoms, the more likely they’ll respond positively to heartworm treatment with minimal complications.

According to the American Heartworm Society, heartworm treatment in dogs can take several months and methods:

  • You’ll have to restrict and minimize your dog’s activity. Active dogs are more likely to have heart and lung damage from heartworms. You’ll want to keep your pet crated or restricted to one room, and keep walks minimal and limited to just relieving themselves. If you have a particularly energetic dog, your veterinarian may prescribe a sedative to keep them calm and restful.
  • Your dog may require therapy to stabilize their condition before treatment, especially if they have severe heartworms or other serious medical issues that may pose complications.
  • Your vet will likely give your dog an injection of melarsomine dihydrochloride (brand names Immiticide and Diroban) to kill the worms, the American Kennel Club notes. Advantage Multi for Dogs (imidacloprid and moxidectin) is also often administered to rid your dog’s bloodstream of microscopic heartworm larvae.
  • Your veterinarian may also prescribe antibiotics or steroids.
  • In severe cases, your vet may perform surgery to physically remove heartworms from your dog’s body.
  • Your vet will continue testing for heartworms after treatment, often starting at about six months post-treatment’s end.

Why do I have to limit my dog’s activity and exercise if they’re heartworm positive?

No one wants to see their beloved pet bored and sad in a crate or kennel, or confined to a small space, but it’s imperative that you keep your dog at rest and as inactive as possible until they’ve completed their heartworm treatment, per the American Heartworm Society. When the treatment kills the worms in your dog’s body, the decomposing worms can cause blockages in blood vessels near the lungs. If your dog’s heart rate increases due to exercise or excitement, they’ll be at risk of a pulmonary embolism, which can be fatal at worst, and at best, cause an increased chance of serious complications.

How can I keep my dog entertained while limiting their activity during heartworm treatment?

Instead of playing fetch, roughhousing, or running with your dog, which can be harmful to their recovery after heartworm treatment, exercise their brain instead. The American Heartworm Society recommends investing in chewable toys (think Nylabones and squeakers) to keep your pup occupied, and to have them try their paws at games like puzzles and “casinos,” where they have to work to get a small treat. This will keep your pup mentally stimulated, even if they can’t move around much. You can also fill Kong toys with their food to extend mealtimes, and keep them close to you while you work from home, read, watch TV, or do anything else around the house, so they don’t feel lonely.

How much does it cost to treat heartworm in dogs?

Like almost anything else, there are a number of variables when it comes to the price of heartworm treatment for dogs, including the severity of the case, location, and the specific course of treatment given. That said, Dr. Muller advises, “The pure treatment might be around $500, but a complete examination and treatment including X-rays, blood tests, and proper follow-up testing might add up to $1,000 or more.”

What happens if heartworm in dogs goes untreated?

“If untreated, the heartworm numbers can increase up to several hundred worms in the dog’s bodies,” Dr. Muller told us. “Heartworm disease causes lasting damage to the heart, lungs, and arteries, and can negatively affect the dog’s health and quality of life.” If the organ damage from heartworms is severe enough, it may be fatal.

Are some breeds more or less prone to heartworm?

All dog breed types are susceptible to heartworm.

Does where I live impact the likelihood of my dog getting heartworms?

Make no mistake: Heartworms can infect dogs anywhere in the world, though they tend to be more concentrated in some areas than others, with geographical infection rates varying widely from year to year. As of 2020, the Southeast United States (North and South Carolina, Florida, Georgia), Louisiana, Mississippi, Alabama, Texas; parts of Illinois, Oklahoma, Missouri, and Minnesota; and California are more prone to heartworms and the mosquitoes that carry them. However, climate change, pets infected with heartworm relocating to other areas, migration of wild animals (like foxes, coyotes, and wolves) and stray dogs, and wind carrying mosquitoes long distances spreads the parasites all over. Long story short: Dogs everywhere are at risk of heartworms, so don’t take any chances.

What is the prognosis of heartworm in dogs?

According to Dr. Muller, the prognosis for heartworm in dogs depends on the stage and clinical manifestation of the disease. “Remember that the heartworm can stay alive up to six years in the dog,” she states. “In early stages without lung and heart failure, 98 percent of dogs will be cleared of heartworm with an intensive three-dose protocol. But the very best prognosis comes from regular prevention year-round.”

How do dogs get heartworms?

Heartworms are parasites, and unfortunately, dogs are natural hosts for them. This means immature heartworms can grow, mature, and procreate all in your dog’s body. When a mosquito bites a dog infected with heartworms, it can pick up microscopic baby heartworms from the dog’s blood. Over the course of 10 to 14 days, these worms can mature to what the American Heartworm Society dubs the “infective stage.” If an infected mosquito bites another dog, it can transmit the infective larvae to that animal (as if mosquito bites weren’t dreadful enough on their own, right?).

How long does it take for a dog with heartworms to show symptoms?

Some dogs live with heartworms for a long time with little to no symptoms or outside indicators of infection, especially if they don’t have many heartworms. That said, heartworms have a lifespan of five to seven years, so unfortunately, they have plenty of time to wreak havoc on your dog’s system. 

Is canine heartworm contagious?

Here’s some good news for pet owners: According to Dr. Muller, heartworm isn’t spread from dogs to other dogs, nor can you catch them from your canine (or vice versa). She explains, “No, heartworm isn’t contagious, as the heartworms are not transmitted from dog to dog. The bite of an infected mosquito is the only way heartworms are transmitted.”

Heartworms are a complicated issue that requires immediate medical attention and TLC for your infected dog. Still, as the FDA notes, the absolute best treatment is simply adequate heartworm prevention. Your dog (and your wallet) will thank you for keeping them healthy, safe, and free of creepy-crawlies.

Pets eat some crazy things.

Learn how Pumpkin Pet Insurance can help.


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