In Spokane County, 1 out of every 106 dogs tested is positive for heartworm disease—higher than the state average of 1 in 169 heartworm-positive dogs. Despite the severity of heartworm disease and how frequently the condition is diagnosed, many pet owners have only a basic knowledge of this serious disease. Our answers to commonly asked questions will teach the ins and outs of heartworm transmission, prevention, and treatment. 

Question: How can my pet get heartworm disease?

Answer: Heartworms are tiny parasites transmitted to your pet through a mosquito bite. As the infected mosquito feeds, immature heartworms migrate into your pet, traveling to their blood vessels surrounding the heart and lungs. Without routine heartworm prevention, these immature heartworms develop into adults that create serious damage as they travel through your pet’s body to reach their ideal location. If immature heartworms are allowed to reach adulthood, they reproduce, and can cause life-threatening heartworm disease. 

Q: Can my pet give heartworms to me or my other pets?

A: Unlike other “worms,” such as roundworms and hookworms, your pet cannot directly transmit heartworms to another pet, or to you. Heartworm larvae can only be transmitted by mosquitoes, because they must go through a mosquito to advance their life cycle. However, if one of your pets is diagnosed with heartworm disease, that means the mosquitoes in your area are carrying the infective larvae, and all your pets need protection with a year-round heartworm prevention regimen.

Q: Can I see heartworms in my pet’s stool?

A: Again, heartworms are not like other worms, and are not visible in your pet’s stool. Roundworms and tapeworms, for example, are two worms commonly seen in feces, but they are intestinal parasites, whereas heartworms live in the blood vessels around the heart and lungs. 

Q: My dog goes outdoors only to go to the bathroom. Why is heartworm prevention still such a big deal?

A: In the height of summer, as you step outside to grab the mail, or walk to your car, at least one mosquito will likely bite you. Your pup may rush outside to do their business and come right back in, but they’re still at risk for a heartworm-carrying mosquito bite.

Q: My cat never goes outside, so why is year-round heartworm prevention recommended for house cats?

A: If you can honestly say you’ve never seen a single insect inside your home, you are fortunate. Mosquitoes are pros at slipping in open doors and through tiny tears in window screens, seeking a warm haven, and a warm meal. Your cat may never venture so much as a whisker outdoors, but they are still at risk for mosquito bites from those pesky pests who sneak indoors.

Q: Why doesn’t my pet only need heartworm prevention during warm months?

A: Mosquitoes are tough insects, and can find warm shelter that allows them to survive chilly winters. They can enter your home or garage any time, including the winter months, and zero in on your pet when they’re hungry. Plus, on an unexpectedly warm winter day, mosquitoes can emerge, and search for a hot meal. Rather than trying to predict the winter, keep your furry pal safe with year-round prevention. 

Q: What happens if I forget to give my pet a heartworm prevention dose?

A: Unlike flea and tick prevention, heartworm prevention works retroactively, meaning it purges the immature heartworm stages from your pet’s body, preventing the worms from developing into adults and causing heartworm disease. If you miss a monthly dose, the immature heartworms may be able to reach adulthood and cause disease. You can’t immediately test your pet for heartworm disease after a missed dose, because testing can detect only adult heartworms, and developing into adults takes five to six months. Additionally, the in-house test only tests for the presence of female heartworms, so false-negative results are possible. Contact your family veterinarian for advice, if you’ve missed a heartworm prevention dose. 

Q: What happens if my pet tests positive for heartworms?

A: If your dog tests positive for heartworms, treatment is available. However, treatment is costly, and can cause negative side effects. Your family veterinarian will explain the heartworm treatment protocol if your dog tests positive. If your cat tests heartworm-positive, no treatment is available, and managing their heartworm-associated respiratory illness is the only viable option. 

Q: What complications should I watch for if my pet is undergoing heartworm treatment?

A: Dogs undergoing heartworm treatment can experience negative side effects that require emergency treatment, which include:

  • Pulmonary emboli — As worms die, they decompose, and block blood flow in the pulmonary artery. The higher the parasite load, the greater risk for pulmonary emboli formation.
  • Rapid microfilarial death — The rapid death of the immature heartworms can cause mild illness, such as lethargy and inappetence, to more severe problems, like hypotension, rapid heart rate, and collapse.
  • Injection site reactions — Significant irritation can appear at the heartworm treatment’s injection site, causing pain, swelling, tenderness, and reluctance to move.

As your local Spokane animal emergency hospital, Pet Emergency Clinic and Referral Center is here to provide life-saving care for your beloved companion. Although all pets should be on year-round heartworm prevention, we understand that stray or rescue dogs may need heartworm treatment, which can cause negative side effects. If your dog is undergoing heartworm treatment, and experiences an adverse reaction, don’t delay. Contact your family veterinarian, or our after-hours team for emergency care.