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For many years, heartworm disease was thought of as a problem for dogs living in the southern United States. Here in Wisconsin, it was easy to assume that our colder winters protected our pets from this potentially life-threatening disease.
Unfortunately, that assumption is no longer true.
Recent national data, combined with what veterinarians are seeing in practice, confirms that heartworm disease is becoming more widespread, even in areas that were once considered low risk. Mosquitoes do not recognize state lines, and neither does heartworm.
Heartworm disease is caused by Dirofilaria immitis, a parasite transmitted through the bite of an infected mosquito. After transmission, microscopic larvae migrate through the body over several months before developing into adult worms that live primarily in the heart, lungs, and major blood vessels.
By the time clinical signs appear, permanent damage may have already occurred.
Dogs may develop:
Cats are also susceptible to heartworm disease, although they often develop different clinical signs, including coughing, asthma-like symptoms, vomiting, difficulty breathing, or sudden death.
Mosquito season has changed.
Warmer temperatures, milder winters, increased travel with pets, relocation of infected dogs, and expanding mosquito populations have all contributed to heartworm appearing in areas where it was once considered uncommon.
The American Heartworm Society now reports heartworm disease in every state.
That means Wisconsin is no longer considered low risk.
As veterinarians, we’ve shifted our recommendations to reflect today’s reality, not the epidemiology from twenty years ago.
“One of the biggest misconceptions I hear is, ‘We live in Wisconsin, so my dog doesn’t need heartworm prevention year-round.’ Unfortunately, heartworm has become a nationwide disease. Mosquitoes travel, infected dogs travel, and our seasons are changing. Heartworm prevention is one of the simplest and most effective ways we can protect our pets from a disease that is almost entirely preventable.”
Nicole Azene, DVM, MS, MPH
Heartworm prevention does much more than prevent disease.
Monthly preventives eliminate immature heartworms before they become adults capable of causing irreversible damage.
Treatment for an infected dog is:
Dogs undergoing treatment require months of strict exercise restriction because dying worms can obstruct blood vessels in the lungs, creating life-threatening complications.
Cats have no approved treatment to eliminate adult heartworms.
For them, prevention truly is the best medicine.
“But my dog hardly goes outside…”
This is one of the most common statements we hear.
Unfortunately, mosquitoes do not stay outdoors.
They routinely enter homes, garages, screened porches, barns, and apartment buildings. Even pets that spend most of their time indoors are still at risk.
Another common misconception is that heartworm prevention is only necessary during the summer. Mosquito activity has become increasingly unpredictable, and missing doses creates gaps in protection that allow infection to occur.
At Onalaska Animal Hospital, we recommend year-round heartworm prevention for virtually every dog.
Consistent monthly prevention:
Annual heartworm testing remains important, even for pets receiving prevention, because no medication is 100 percent effective if doses are delayed, missed, or not fully absorbed.
Heartworm disease is largely preventable.
Treatment can cost thousands of dollars, requires months of restricted activity, and carries significant risks. Prevention costs only a fraction of that while protecting your pet from unnecessary suffering.
As veterinarians, we would much rather help you prevent heartworm than treat it.
Your pet deserves that opportunity.
If you have questions about heartworm prevention or are unsure whether your pet is due for testing, our team is happy to help. Together, we can build a prevention plan that keeps your pet healthy all year long.
