Why Heartworm Prevention is Critical in AZ Right Now
- Oct 17
- 3 min read
By: Dr. Geoff McGee, Veterinarian
October 17, 2025
Recent rains in Maricopa County have brought more than just cooler temperatures. They've also led to a surge in mosquitoes, making this the perfect time to talk about one of the most serious threats to your pet's health: Heartworm Disease.
Heartworm disease is a severe, progressive illness caused by foot-long worms (Dirofilaria immitis) that live in the heart, lungs, and associated blood vessels of affected pets, leading to severe lung disease, heart failure, and damage to other organs. The medication used to treat heartworms in dogs cannot be used in cats, so prevention is the only way to protect your cat from the effects of heartworms.
The Mosquito-Heartworm Connection
Heartworms are transmitted through mosquito bites, and it only takes one bite from an infected mosquito for your pet to get heartworms. When a mosquito bites an infected animal, it picks up baby heartworms (microfilariae). When that same mosquito bites your pet, it deposits the larvae, which then mature into adult worms over several months.
Because we have an extended mosquito season and these pests don't need standing water for long to reproduce, prevention must be year-round, even in the drier months. The recent rain simply means the immediate risk is even higher.
Why Annual Heartworm Tests are Necessary
It may seem counterintuitive to test when your pet is already on prevention, but this annual test is a crucial safety net for two main reasons:
Testing Confirms Safety: Giving a heartworm preventative to a dog that already has adult heartworms can be dangerous. It causes a sudden die-off of microfilariae, which can trigger a severe reaction. The heartworm test ensures your pet is heartworm-free before you continue or start monthly medication.
It Catches "Breakthrough" Infections: No matter how diligent you are, things happen: a forgotten dose, a pet spitting out a pill, or delayed administration. If an infection occurs, heartworm testing is the only way to catch it early enough to begin effective, potentially life-saving treatment before the disease causes irreversible organ damage.
A negative heartworm test doesn’t mean that you can skip heartworm prevention. A negative test simply means your pet wasn't infected six months ago (the minimum time it takes for an infection to show up on a test). Prevention is what ensures the next test will also be negative.
Prevention is Simple, Treatment is Not
Heartworm prevention is one of the easiest parts of your pet's wellness plan, often involving a chewable tablet given once a month. Our TREATment manager, Georgia, loves getting her “monthly treats” each month, and happily shows off her best tricks for them.
Cost: Heartworm prevention costs significantly less than heartworm treatment.
Safety: Preventatives are extremely safe and effective.
Peace of Mind: Knowing you've protected your pet against this painful and serious disease is invaluable.
If you have missed a dose or are behind on your pet's annual exam and heartworm test, please call McGee Veterinary Service at 623-396-9185! We can come to your home to perform the necessary blood draw for heartworm testing and send the sample to a lab for quick, accurate results. Protect your pet today! 🐾
McGee Veterinary Service offers in-home veterinary care and peaceful at-home pet euthanasia to Phoenix, Scottsdale, Paradise Valley, Cave Creek, Carefree, New River, Anthem, Peoria, Glendale, Litchfield Park, Surprise, Sun City, and Sun City West. To see if we cover your neighborhood, view our detailed Service Area Map.
ABOUT THE AUTHOR
Dr. Geoff McGee is the owner of McGee Veterinary Service in Phoenix, AZ. He graduated from WSU College of Veterinary Medicine in 2017, completed a surgical internship, and founded his mobile in-home veterinary service in 2024 driven by his desire to better care for his senior dog. When not serving the community's pets, Dr. McGee enjoys hiking, camping, and spending quality time with his family.
