Heartworm Prevention: Why Missing One Month Matters

You know heartworm prevention is important. Your vet has told you, the medication packaging reminds you, and you’ve probably seen the warnings at every pet store. But life gets busy, and it’s easy to think that missing one month — just one — isn’t a big deal. In Florida, that one missed dose could cost your dog everything.

How Heartworm Infection Actually Works

When an infected mosquito bites your dog, it deposits microscopic heartworm larvae into the skin. These larvae don’t immediately become adult worms — they go through several developmental stages over about six months. Monthly heartworm preventives work by killing larvae that entered your dog’s body during the previous 30 days, before they can mature into dangerous adults.

Here’s the critical part: the medication only works on larvae at specific developmental stages. If you miss a month, larvae from that window continue developing past the point where the preventive can kill them. By the time you resume treatment, those larvae are on their way to becoming foot-long adult worms that live in your dog’s heart and pulmonary arteries.

Florida’s Mosquito Reality

In many parts of the country, mosquito season is limited to summer months. In the Dunedin and North Pinellas area, mosquitoes are active virtually year-round. Our subtropical climate, combined with standing water from afternoon rainstorms, creates ideal breeding conditions from February through December — and even January isn’t truly safe.

The American Heartworm Society reports that Florida consistently ranks among the top states for heartworm cases. Every veterinary clinic in our area treats heartworm-positive dogs regularly. It’s not a theoretical risk here — it’s an everyday reality.

What Heartworm Treatment Looks Like

If prevention fails and your dog tests positive, treatment is lengthy, expensive, and hard on your dog. The standard protocol involves a series of injections with melarsomine, an arsenic-based drug that kills adult worms. During treatment — which spans several months — your dog must be strictly exercise-restricted. No walks, no playing, no excitement. The dying worms break apart and travel through the bloodstream, and physical activity increases the risk of a fatal pulmonary embolism.

Treatment typically costs between $1,000 and $3,000 depending on the severity of infection and your dog’s size. Compare that to roughly $100-150 per year for monthly prevention.

Getting Back on Track

If you’ve missed a dose or two, don’t panic — but do act quickly. Restart prevention immediately and call your veterinarian. We’ll likely recommend a heartworm test about six months after the gap in coverage, since that’s how long it takes for infection to become detectable.

At Dunedin Animal Medical Center, we carry multiple heartworm prevention options including monthly chewables and longer-acting injectable options like ProHeart. If you struggle with remembering monthly doses, ask us about ProHeart 12 — a single injection that protects your dog for an entire year.

Don’t gamble with heartworm. In Florida, the mosquitoes never stop, and neither should your prevention. Call (727) 738-2273 to check your dog’s heartworm status and get back on track.