By: Dr. Rachel Sparling DVM from Lake Panasoffkee Animal Clinic
Mosquitoes, Spaghetti, and Your Pet’s Heart: Let’s Talk Heartworm
If you live in Florida, you already know two things are inevitable: humidity… and mosquitoes. Lots of mosquitoes. The kind that shows up to a barbecue uninvited and never leave. Unfortunately, mosquitoes don’t just ruin backyard evenings—they can also transmit one of the most serious parasites our pets face: heartworm disease. Heartworms are exactly what they sound like: long, spaghetti-like worms that live inside the heart and major blood vessels of dogs (and occasionally cats). Once they’re there, they can cause serious, often irreversible damage. The good news? Heartworm disease is almost completely preventable. Let’s break it down.
First Things First: What Are the Signs of Heartworm?
One of the tricky things about heartworm disease is that many pets show few or no symptoms early on. As the worms grow and multiply, dogs may develop:
• A persistent cough
• Exercise intolerance or tiring easily
• Lethargy
• Weight loss
• Difficulty breathing
• A swollen abdomen (in severe cases)
By the time these symptoms appear, the disease may already be causing damage to the heart and lungs. Cats are even trickier. Many cats with heartworm show vague symptoms or sudden illness, including:
• Coughing or asthma-like symptoms
• Vomiting
• Lethargy
• Difficulty breathing
• Sudden collapse or death in severe cases
Unlike dogs, cats unfortunately do not have an approved treatment for heartworm disease, which makes prevention absolutely critical.
The Heartworm Life Cycle (AKA: The Mosquito Delivery System)
Heartworms rely on mosquitoes to spread from animal to animal. Here’s how it works:
A mosquito bites an infected dog and picks up microscopic baby heartworms (called microfilariae) circulating in the bloodstream. Inside the mosquito, those baby worms develop into an infectious stage. When that mosquito bites another dog or cat, it deposits the immature larvae under the skin. The larvae migrate through the body over the next several months. Eventually they reach the heart and lungs, where they mature into adult worms. Adult worms can grow 10–12 inches long and live for years in the heart and pulmonary arteries. From the time a pet is infected, it can take up to six months before heartworms mature enough to be detected on a blood test. That’s why testing timelines matter.
Why Your Vet Tests for Heartworm
The most common screening test is a heartworm antigen test (often called a SNAP test). This test detects proteins from adult female heartworms. Because of the heartworm life cycle:
• It can take up to six months after infection before a dog test positive.
• If a pet misses prevention, we recommend retesting six months later.
• This also applies to newly adopted pets with unknown prevention history.
Testing ensures prevention is still working and catches infections as early as possible.
Florida + Mosquitoes = Year-Round Risk
In some parts of the country, winter helps reduce mosquito populations. Florida…not so much. We may get a few cold days each year, but mosquitoes are active nearly year-round. That means heartworm prevention should be given every single month without exception. Skipping even one month can leave a window for infection.
Prevention Is the Real Hero
Here’s the most important takeaway: Heartworm prevention is far easier, safer, and less expensive than treating the disease. Most preventives work by eliminating immature heartworm larvae before they can grow into adults. Many products also protect against other parasites that Florida pets commonly encounter, including:
• Roundworms
• Hookworms
• Whipworms
• Fleas
• Ticks
There are even combination products that protect against several parasites at once. Your veterinarian can help determine which product is safest and most appropriate for your pet.
Heartworm Prevention Options for Dogs
Dogs have several prevention options, including monthly oral or topical medications and longer-acting products like ProHeart, an injectable heartworm preventive that protects dogs for up to 12 months with a single injection. Other monthly preventives may also provide protection against intestinal parasites, fleas, or ticks. The best choice depends on your dog’s health, lifestyle, and parasite risk.
What If a Dog Tests Positive?
The good news is that dogs can be treated for heartworm disease. Many veterinarians follow the treatment protocol recommended by the American Heartworm Society. In simple terms, the process typically includes:
- Stabilization and rest to reduce stress on the heart and lungs
- Pre-treatment medications, often including doxycycline and anti-inflammatory medications
- A series of injections that kill the adult heartworms
- Strict exercise restriction for several weeks to reduce the risk of complications as the worms die and break down
Treatment is effective but can be lengthy, expensive and requires careful monitoring.
This is another reason prevention is so important—treatment is much harder on pets than prevention is.
What About Cats?
Cats are less commonly infected than dogs, but heartworm infection in cats can be much more dangerous. Even a small number of worms can cause severe lung inflammation. Because there is no approved treatment to eliminate adult heartworms in cats. Veterinarians focus on supportive care if infection occurs. This is why prevention is essential for cats too, even indoor cats. Common heartworm preventives for cats include:
• Bravecto Plus
• Revolution / Revolution Plus
• Advantage Multi
These products often also protect against fleas, mites, and intestinal parasites.
The Bottom Line
Heartworm disease is serious, but it’s also one of the most preventable diseases we see in veterinary medicine. All it takes is:
• Regular prevention
• Annual testing for dogs
• Staying on schedule with your veterinarian’s recommendations
Your pet’s heart works hard every day—through zoomies, walks, naps, and begging for snacks. Keeping them protected from heartworms is one of the best ways we can return the favor. And remember: when it comes to mosquitoes in Florida, it’s always heartworm season.
