Just one mosquito bite is all it takes to infect your dog. But with consistent prevention, you can protect them from months of painful treatment and potentially life-threatening complications.
The risk is real, but prevention is simple, affordable and highly effective. In this comprehensive guide, we aim to provide you with the necessary information to protect your beloved canine companion from heartworm disease.
What is Heartworm Disease?
Heartworm disease is a serious and potentially life-threatening condition caused by a parasitic worm called Dirofilaria immitis. It spreads through mosquito bites and primarily affects dogs, although cats and other animals can be infected too.
Once inside the body, the larvae travel through the bloodstream and mature into long, thread-like worms over several months. These parasites are so dangerous because while they are reproducing and maturing, they are living in the hearts, blood vessels, and even lungs of our pets.
P.S. We do not recommend a Google search on heartworms unless you’re prepared for some stomach-turning image results.
Can Cats Get Heartworms?
Yes! Cats can get heartworms too, and a single adult heartworm can be fatal to a cat. However, because a cat is not an ideal host for heartworms, some infections resolve on their own, although these infections can leave cats with respiratory system damage.
Unfortunately, the approved treatment for heartworm infections in dogs cannot be used for cats, so prevention is the only means of protecting cats from the effects of heartworm disease.
Is Heartworm Contagious?
While heartworm disease is scary, thankfully, it is not contagious. Your dog can only contract heartworms through an infected mosquito bite, not through contact with a heartworm-positive animal. However, because mosquitoes don’t travel far in their lifetimes, a single positive dog (or coyote, wolf or fox) significantly increases the likelihood of heartworm carrying mosquitos in a local community.
Why Heartworm Prevention Matters
In 2023, only a third of dogs in the U.S. received even a single dose of heartworm prevention — leaving 67% unprotected.
If left untreated, heartworms can cause fatigue, breathing issues, organ damage and eventually heart failure. Heartworms are most dangerous to a dog if left untreated, as they can become fatal.
At the same time, heartworm treatment is incredibly expensive and can take a toll on your dog’s body through months of medication and strict activity restriction.
On the other hand, prevention is easy!
Essential Prevention Methods for Dogs
Once infected, the heartworm larvae stay in a dog’s tissue for 2 months (2½ for cats). The worms then mature into adults for the next 4-6 months in the bloodstream. Adult heartworms can live and reproduce in the bloodstream for 5-7 years in dogs and 2-3 years in cats. However, this can all be avoided with proper care.
Heartworm preventatives work by killing larvae before they grow into adult worms. While preventatives are only available by prescription, at least 20 different options are available, and all products are nearly 100% effective in preventing heartworms when used year-round and administered as directed.
Since mosquitoes are active year-round and commonly found in temperate climates of the United States, we as vets recommend year-round prevention, not just during the warmer months.
As with other pet-loving parasites, the only proven way to prevent heartworm disease is with a year-round, FDA-approved tablet, topical or injectable medication that kills heartworm larvae.
Monthly Oral Medications & Chewable Tablets
These are one of the most popular options because they are often flavored, making it easier for dogs to take them. Most are ivermectin-based and work well when given monthly without missing doses.
Simparica Trio is one (if not our most) common heartworm prescriptions for dogs. This monthly chewable serves as a 3-in-1 protection against heartworms, fleas, ticks, and some intestinal parasites. Simparica Trio is safe for puppies at 8 weeks old and is an easy chewable for your dog, especially if they are food motivated.
Topical Solutions
Topical preventatives are applied to the skin and absorbed into the bloodstream. They typically protect against heartworms and some options protect against external parasites like fleas and ticks.
Injectable Options
For busy pet parents — or dogs that won’t take pills — injections offer a “set-it-and-forget-it solution.” These shots are given by a veterinarian and provide constant protection for 6 or 12 months (depending on the product) and give dog parents peace of mind without monthly reminders.
As always, talk to your vet to determine the best heartworm preventive medication based on your dog’s risk factors and lifestyle.
Annual Testing
In addition to preventive medications, annual heartworm testing is crucial — even if your dog seems healthy. This helps detect any potential infection early on, allowing for immediate treatment if necessary. By combining preventive measures with regular testing, pet parents can safeguard their dogs’ health and well-being with the best defense against heartworm disease.
Recognizing Heartworm Signs
Identifying the signs of heartworm disease is key to early diagnosis and effective treatment. In the early stages of infection, dogs with heartworm disease may not show any visible symptoms. However, as the disease advances, common signs and symptoms may include:
- Labored breathing
- Lethargy or fatigue after activity
- Swollen belly
- Vomiting or dark-colored urine in severe cases
- Weight loss
- Decreased appetite
- Persistent coughing
- Difficulty breathing
- Pale gums
- Fainting
If you notice any symptoms or have concerns, contact your veterinarian right away.
Mosquito Control Tips
Since mosquitoes spread heartworms, reducing exposure helps lower your dog’s overall risk. This is especially important in areas where mosquitoes are active year-round — like Texas and Tennessee, which consistently rank among the top states for diagnosed heartworm incidents.
Here are simple preventive measures to help protect your dog from heartworms:
- Remove standing water from buckets, birdbaths and flowerpots
- Keep doors and windows closed or screened
- Use pet-safe mosquito repellents
- Avoid early morning or evening walks (midday is safer when mosquitoes are less active)
Protect Your Pet and Stay Stress-Free
At ReadiVet, we recommend year-round heartworm prevention paired with annual testing as the absolute best strategy to protect your pet from this serious and life-threatening disease.
Prevention is simple: monthly medication (available for dogs as young as 8-weeks), annual testing (for dogs 6-months and older), and basic mosquito control. With so many safe, effective options available, there’s no reason to leave your dog unprotected. Be sure to ask your veterinarian for advice because consistency matters, as does finding the right heartworm prevention for your specific dog.
For more information on heartworms, check out resources from the American Heartworm Society or the American Veterinary Medical Association.
