Disease Focus: Heartworm disease

It’s that time of year again.  The sun is shining, the flowers are blooming, and it means that mosquitos are going to start breeding and emerging as well.  Mid to late March is the time where veterinarians urge pet owners to get back into the routine of monthly heartworm prevention prior to the onset of mosquito season.  (We really recommend year round prevention).  I am surprised by how many clients are unaware of the true risk of heartworm disease, or the importance of monthly heartworm prevention given consistently.

What is Heartworm Disease?

Heartworm disease is a worm, an actual worm, that your pet can get from a mosquito bite.  When an infected mosquito bites your pet, it can inject baby heartworms, called microfilariae, into your pet’s blood stream with that bite.  These microfilariae go through several stages of maturation, and end up in the vessels of the heart and lungs as adult heartworms.  Heartworms don’t just stay put once they get there, and can cause a lot of damage migrating around your pet’s lungs.  As the amount of worms living in there gets larger and larger, they cause problems with blood flow.  Heartworm disease can cause lung damage and can ultimately lead to heart failure as well.

How does heartworm prevention work?

Regardless of what monthly heartworm prevention your pet is on, the heartworm prevention is meant to kill the microfilariae that your pet may have picked up by mosquito bites over the past month.  The medication does not stay in your pet’s system for a month, and can ONLY kill the “baby” stage of the worm, which is why the “monthly” timing is so crucial.

If you have missed a dose of heartworm prevention, but then resume it after that missed dose, your pet can STILL get heartworm disease, because that worm will mature past a stage the medication can kill, and keep maturing.  This is why your veterinarian will recommend yearly heartworm testing, even if your pet takes preventatives.

If you pet gets a heartworm, it can take six months before the test will show a positive result, because the heartworm testing can only detect adult heartworms.  So sometimes you can have a negative heartworm test one year, start prevention, and have a positive result the next year.

My pet stays inside, can he still get heartworms?

Indoor pets, and mostly indoor pets are still at risk.  We have all gotten mosquito bites while sleeping because a mosquito slipped inside.  Obviously the exposure to mosquitoes is reduced, but the potential is still there.  If you have chosen not to use heartworm prevention on your mostly indoor dog, a yearly heartworm test is even more crucial to try and catch any disease as early as possible.  Cats, indoor and outdoor, are also at risk, and are recommended to be on heartworm prevention.

What if my pet becomes infected with heartworms?

Pets that contract heartworms can be treated, but heartworms are really bad.  They can cause a lot of damage to your pet’s organs, and they are hard to kill.  Worse, is that the treatment is risky, and very costly, where the preventatives are not.  Your pet will need to go on a series of medications, and injections, and may require a few hospital stays in order to clear the disease.