10 facts about Heartworm Disease


Transmitted by mosquitoes, heartworm disease is deadly, yet completely preventable.  I’m sure you've heard your veterinarian tell you about Heartworm prevention, you know it's a pill you are supposed to give every month, but what else do you know?


April is Heartworm Disease Awareness month and to bring some knowledge your way I've gathered a few facts about Heartworm Disease that may be new to you.  Hopefully you learn something new and are even more encouraged not to forget that once-a-month prevention!


1.  Heartworm is an actual heart worm. It lives in the chambers and vessels of the animal’s heart and lungs.  Did you know these worms can grow to be up to 1 foot long?  They can live for 5-7 years and canines can host 100-200+ worms in their heart. Fecal (stool) testing does nothing to detect this parasite.


2.  Your dog and cat contract heartworms from the bite of an infected mosquito. The mosquito injects the immature worms into the bloodstream of your pet.  If your fur baby is on monthly prevention, the worms die.  If they are not on prevention, the worms migrate to the heart and lungs to settle in and grow.


3.  It takes 6-8 months for the worm to mature and grow into an adult.  The test to detect heartworms in dogs only tests for adults so it takes 6-8 months from the time your dog is bitten before we will know if he is infected.


4.  Many animals have no signs of disease.  Dogs can live a fairly symptom-free life with a good number of worms in their heart.  Or they may have an occasional cough or be a little slower on your morning run: signs many owners wouldn't really notice.


5.  There is no treatment for cats. Cats metabolize many medications into toxic compounds, and the medical treatment for Heartworm disease is hard even on some of our canine companions causing heart failure and even death. Prevention is the best medicine.


6.  Cats can die from hosting just 1 single heartworm.  The only way to protect your cat is monthly prevention.


7.  Heartworm disease is not contagious.  Your pet can only develop heartworm disease if he is bitten by an infected mosquito.


8.  Heartworms are in all 50 states.  Some states have a larger mosquito burden than others (ex: South Carolina vs. Colorado), but the disease has been diagnosed and confirmed all over the USA.


9.  Heartworm disease can affect dogs, cats, ferrets, foxes, coyotes, wolves, sea lions (yup!), and even (although very rare) humans.


10.  The American Heartworm Society recommends every dog be given prevention year-round and tested for heartworms every 12 months.



My clients often want to know why I recommend having their dog tested for heartworms yearly when they give them a pill every single month to prevent the disease.  Well, let me tell you about Cooper.  Cooper was a golden retriever with a skin infection.  I performed a culture on his skin to determine exactly which antibiotic I needed to use.  Cooper’s mom gave him the pills every 12 hours for 2 weeks like clockwork.  When I saw him at his recheck appointment his skin was awful.  I was flabbergasted.  There is no way he was getting his medication despite his mom telling me she gave it every morning and evening.  After a short Q&A I realized she never actually SAW him swallow the pills.  She went home and found a large collection of capsules in the corner of her garden.  She let Cooper out after his meals and he had spit out every single dose of his medication.  So, nothing in life is 100%.  We make mistakes, dogs will be dogs, so we test once a year.


I hope you learned something new about Heartworm Disease!  Let's work together to keep our animals safe.  The American Heartworm Society recommends that in addition to administering heartworm prevention all year long, a topical repellant be used as well.  Talk with your veterinarian & decide which prevention works best for you and you fur baby.


Leigh Hofmeister, DVM, Blog Signature – Leigh Hofmeister, DVM

Source: American Heartworm Society (heartwormsociety.org)

Leigh Hofmeister