Heartworm in Dogs: What Pet Parents Should Know

Heartworms are dangerous parasites that can invade your dog’s heart, lungs, and blood vessels, leading to a serious condition known as heartworm disease. Over time, this can lead to organ damage and even death if untreated.¹

Recognizing the signs of heartworm in dogs can be difficult, so prevention is key to keeping your pup protected. Let’s take a closer look at dog heartworm symptoms, causes, and treatment. Then, we’ll explore how dog insurance could help cover the cost of treating or preventing heartworm in dogs.

What Is Heartworm in Dogs?

Heartworm in dogs refers to the presence of pale, thin worms named Dirofilaria immitis.¹ These worms are parasites, and the dog is their host. The heartworms grow, mate, and produce offspring within the dog’s body.

The disease is so named because the worms usually reside in a dog’s heart, along with nearby blood vessels and the lungs. Over time, these worms can cause critical damage to these vital organs, potentially even leading to the dog’s death.¹

How Do Dogs Get Heartworms?

Heartworms are typically transmitted through mosquito bites. When a mosquito bites a dog or other animal already infected with heartworm, it picks up the larvae (known as microfilaria) that are present in the animal’s bloodstream.

The next time the infected mosquito bites an animal, the microfilariae are deposited into the circulatory system of the new host. These larvae get dispersed throughout the body and mature over a period of 6 months. Once heartworm larvae mature, they can remain in the host for up to 7 years.¹

Which dogs are most at risk?

It’s tempting to think that heartworm is only a problem in regions with a heavy mosquito population. However, heartworm disease has been recorded in all 50 states — even in northern states where the weather is colder.² That said, here are additional risk factors to consider:

• Time outdoors: Pets who spend a lot of time outdoors are typically at a higher risk of infection, but that doesn’t mean indoor pets are completely safe. Mosquitoes can easily get inside your home and target your dog.²
• Geography: While dogs everywhere are susceptible to heartworm, cases in the U.S. are more common along the Atlantic and Gulf coasts and along the Mississippi River.¹
• Shelter animals: They tend to be at a higher risk for heartworm since they’ve often spent time outdoors without vet care and preventive medication.³

If you adopt a dog from a shelter, be sure to have them tested and ask your vet about a prevention plan as soon as possible. If your newly adopted pup already has heartworm, be prepared to give them the treatment they need.

Heartworm Symptoms in Dogs

Early heartworm disease often doesn’t present symptoms, which is why it can be so difficult to diagnose.¹ As the larvae mature, symptoms will become more apparent.

What are the first signs of heartworms?

Early infection is virtually undetectable. This is the time between the initial mosquito bite and the worms reproducing. It’s not until the worms mature in the heart and lungs that your dog may begin to exhibit:²

• Persistent cough
• Fatigue
• Loss of appetite
• Weight loss

Symptoms of mid-stage heartworm

This is when the mature heartworms begin to clog your dog’s blood vessels, heart, and lungs. At this point, heartworm symptoms become more obvious:²

• Swollen abdomen
• Heart failure

Symptoms of late-stage heartworm

This is the most dangerous stage of heartworm disease in dogs because the abundance of worms causes organ failure. Blood flow is blocked by the sheer volume of worms in the heart and circulatory system, a condition known as caval syndrome. Hallmarks of this condition include:²

• Pale gums
• Blood in urine
• Dark urine color
• Difficulty breathing

If dogs at this stage don’t receive immediate veterinary care, the prognosis is often fatal. Surgery may be required to remove the mass of heartworms from the heart and lungs.²

Heartworm Prevention for Dogs

The good news is heartworm is entirely preventable. Furthermore, taking steps to prevent heartworms isn’t just the safe option; it’s also the most cost-effective one. A monthly prescription for heartworm tablets can range from $6 – $18 per month.⁴

Heartworm tests are often conducted as part of wellness exams. The most common test is referred to as an antigen test and usually costs between $35 – $75.⁴ MetLife Pet Insurance offers an optional Preventive Care plan that can help you cover heartworm prevention expenses.

Diagnosing Heartworm in Dogs

Another reason heartworm prevention is so critical is that the condition is almost impossible to detect for months. If your dog does begin exhibiting symptoms of heartworms, bring them to the vet even if they’re already on preventive medication.

Vets can use an antigen blood test to check for proteins produced by heartworms, although these can only be detected 5 months after the initial infestation.¹ After 6 months, vets can also test for the presence of the microfilariae in your dog’s blood.³ An X-ray may also be recommended to image the mass of worms in your dog’s heart or lungs.¹

When to test for heartworm in dogs

The American Heartworm Society advises pet owners to get their pets tested for heartworms every 12 months and give them a heartworm preventative each month.² It’s generally recommended not to test dogs for heartworms until they are 7 months old.¹

It’s important to test your pup before starting them on a heartworm preventative. If your dog already has an adult heartworm infestation, the preventative could kill off the worms. While this might sound like a good thing, the downside is it can trigger systemic shock in your dog, which could endanger their life.¹

Treatment for Heartworm in Dogs

Even after it progresses, heartworm disease in dogs is treatable. However, as the disease progresses, the possibility of complications rises. Keep in mind that the severity of the disease isn’t necessarily correlated with the severity of the symptoms.⁵ Treatment can get expensive, and it may take months before the infection clears up completely.

During the first 2 months, your vet may begin by putting your dog on a regimen of steroids and an antibiotic known as doxycycline. These help reduce inflammation and weaken the heartworms. Combined, these medications can cost nearly $200.⁴

Preventative medication may also be administered for the first 30 days. This is intended to get rid of any larvae lingering in your dog’s body. A waiting period of another 30 days follows, after which your dog will begin treatment to kill the adult worms. This involves a series of injections of a drug called melarsomine, which can run you between $500 and $1,500 per dose.^4,6 Additional rounds of steroid treatment may also be recommended during this stage.⁴

What is the recovery time for a dog infected with heartworms?

Most cases of heartworm clear up after 1 – 3 months of treatment. A dog’s life expectancy after heartworm treatment is generally favorable, so long as they respond well to the treatment and no permanent damage is caused.

Melarsomine as a treatment is known to have side effects, however, including:⁶

• Most common: Pain and swelling at the injection site
• Less common: Lethargy, vomiting, loss of appetite, depression
• Rare: Diarrhea, coughing up blood, excessive panting, death

Your vet will monitor your dog’s progress for these side effects or any other complications. Additional steps, such as limiting exercise, can help mitigate the likelihood of complications and may reduce overall recovery time.⁵

Pet Insurance Could Help You Prevent Heartworm

The cost of heartworm prevention is minimal when compared to the high price tag for treatment and recovery from this dangerous parasite. Protecting your dog also saves them from having to go through the trauma and pain of extensive treatment.

While you protect your dog, let MetLife Pet Insurance help protect your wallet. A standard dog insurance policy could reimburse⁷ you for the cost of heartworm treatment, while our Preventive Care add-on can help cover the cost of parasite prevention.

Ready to take the next step? Fetch a free quote to see exactly how much you could save while keeping your pup safe!