Your dog can have heartworms and show no symptoms at all. That is what makes this parasite so dangerous. By the time signs appear, the infection is often advanced and much harder to treat. Annual heartworm testing dogs is the simplest way to catch a problem early, before it becomes a crisis. A single blood test, done once a year, can protect your dog from a disease that attacks the heart and lungs and can be fatal if left undetected. This article explains how heartworm disease works, what warning signs to watch for, why yearly testing matters even for dogs on prevention, and what to expect if your dog tests positive. Whether your dog is a puppy or a senior, this information is important for every dog owner to understand.
What Heartworm Disease Does to Your Dog
Heartworm disease is caused by a parasitic worm called Dirofilaria immitis. It spreads through mosquito bites. When an infected mosquito bites your dog, it deposits microscopic larvae into the skin. Those larvae travel through the body and eventually reach the heart, lungs, and surrounding blood vessels, where they grow into adult worms. Adult heartworms can reach 12 inches in length and live for 5 to 7 years inside a dog.
An estimated 1 million dogs in the United States are currently infected with heartworms. The disease is present in all 50 states, not just warm southern climates. Mosquitoes are found wherever dogs spend time outdoors, including backyards, parks, and walking trails.
The real damage comes from long-term inflammation. As worms grow and multiply, they cause scarring in the lungs and strain on the heart. Dogs with heavy worm burdens face serious, sometimes permanent organ damage. Early detection through testing is the most effective way to prevent that damage from occurring.
Warning Signs of Heartworm Disease in Dogs
One of the most common questions we get from pet owners is, “How would I know if my dog had heartworms?” The honest answer is that early-stage heartworm disease often looks like nothing at all. Symptoms appear gradually as the infection progresses.
Watch for these signs of heartworm in dogs:
- Persistent cough: A dry, recurring cough is often one of the first signs. It is caused by worms settling in the pulmonary arteries near the lungs.
- Fatigue after mild activity: If your dog tires quickly on a short walk or seems reluctant to exercise, lung function may already be compromised.
- Reduced appetite: Dogs with advancing heartworm infections often eat less and lose weight over time.
- Swollen abdomen: Fluid accumulation in the belly can occur in more advanced cases due to heart strain.
- Labored or rapid breathing: Lung inflammation caused by heartworms makes breathing more difficult, especially after exertion.
In our experience, pet owners often notice these signs and attribute them to aging or the heat, not a parasite. That is exactly why a yearly blood test matters. Symptoms alone are not a reliable way to detect heartworm disease in its early stages. If you notice any of these signs, contact your veterinarian promptly.
How Often Should Dogs Be Tested for Heartworms?
Dogs should be tested for heartworms once every year, regardless of whether they are on a preventive medication. This is the standard recommended by veterinary professionals across the country.
Annual testing matters for several reasons. No preventive is 100% effective if doses are missed, given late, or vomited. Testing also catches any early infection that slipped through before the worms matured. A simple blood test at your dog’s yearly wellness visit is all it takes.
Heartworm prevention for dogs works by eliminating larvae in the early stages, not by killing adult worms. That distinction is important. If a dog misses even one monthly dose, larvae from a recent mosquito bite can mature undetected. Yearly testing closes that gap and gives your vet a clear picture of your dog’s health each year.
Puppies should be tested at 7 months of age and then annually after that. Dogs new to a household should be tested before starting any preventive medication.
Why Illinois Dogs Still Need Annual Testing
Some pet owners in cooler states assume heartworm is a southern problem. In Illinois, we see this misconception regularly. Mosquito season in the Midwest runs from spring through late fall, and that is enough time for heartworm transmission to occur.
Heartworm prevention for dogs is recommended year-round in Illinois because mosquito activity can continue longer than expected in mild autumns. Burr Ridge and surrounding areas are no exception. Dogs that spend any time outdoors, even briefly for bathroom breaks, are exposed.
Preventative care for dogs in the Midwest must account for parasite risks that are easy to underestimate. Heartworms are transmitted by dozens of mosquito species, and many of those species are common throughout the Chicago area. Thinking your dog is low-risk because the winters are cold is one of the most common mistakes we see in this region. Testing annually is the only way to know for certain.
What Happens If Your Dog Tests Positive
A positive heartworm result is serious, but it is treatable, especially when caught early. Your veterinarian will assess the severity of the infection before recommending a treatment plan.
Treatment for heartworm involves several stages:
- Confirm the diagnosis. A positive antigen test is followed by additional testing to evaluate heart and lung health and confirm the extent of the infection.
- Stabilize the dog. If symptoms are present, your vet may prescribe anti-inflammatory medication before treatment begins to reduce lung inflammation.
- Restrict activity. Exercise must be limited throughout treatment because physical exertion increases the rate at which damaged heart and lung tissue deteriorates.
- Administer treatment. Dog heartworm treatment options include an injectable medication given in a series of doses, typically over one to two months, to kill adult worms.
- Monitor recovery. Follow-up testing is done 6 months after treatment to confirm the infection has cleared.
Many dogs we treat for heartworm recover fully when the infection is caught in the early or mid-stage. Dogs diagnosed in the later stages face a longer recovery and a higher risk of complications. This is why annual testing is not optional. It is the safeguard that keeps treatment manageable.
Harvester Veterinary Hospital of Burr Ridge provides annual heartworm testing as part of our comprehensive preventative care for dogs. Early detection gives your dog the best possible outcome.
Keeping Your Dog Protected All Year Long
Annual heartworm testing for dogs is one of the most important things you can do to protect your dog’s long-term health. Heartworm disease is silent in its early stages, serious in its later ones, and entirely preventable with the right care. Testing once a year, maintaining consistent preventive medication, and scheduling regular wellness visits are the three pillars of heartworm protection.
At Harvester Veterinary Hospital of Burr Ridge, our team is ready to help keep your dog safe, healthy, and heartworm-free year after year. Book an appointment today.
Frequently Asked Questions
Q: How often should dogs be tested for heartworms?
Ans: Dogs should be tested for heartworms once a year. Annual testing is recommended even for dogs on year-round preventive medication, because no prevention is completely foolproof if doses are missed or given late.
Q: Can a dog on heartworm prevention still get heartworms?
Ans: Yes, it is possible. Preventive medications eliminate larvae in the early stages but do not kill adult worms. If a dose is missed or late, larvae from a mosquito bite can mature undetected. Yearly testing confirms your dog remains infection-free.
Q: What are the signs of heartworm in dogs?
Ans: Early heartworm infection often shows no symptoms at all. As the disease progresses, signs can include a persistent cough, fatigue after light activity, reduced appetite, swollen abdomen, and labored breathing. A blood test is the only reliable way to detect the infection early.
Q: Are heartworms a risk for dogs in Illinois?
Ans: Yes. Heartworm disease is present in all 50 states, including Illinois. Mosquito season in the Midwest runs from spring through late fall, which is sufficient time for heartworm transmission. Dogs should remain on preventive medication year-round.
Q: What is the treatment for heartworm disease in dogs?
Ans: Treatment involves a series of injectable medications to eliminate adult worms, combined with strict activity restriction and monitoring. Dogs diagnosed in early stages generally respond well to treatment. Your veterinarian will create a plan based on the severity of the infection.
