When to Start a Puppy on Heartworm Prevention

Medical Articles

What are heartworms?

Heartworms are parasitic worms that live in the heart and surrounding blood vessels of an infected dog. They can grow up to one foot in length. It is common for many worms to be living in the heart at one time, which can cause damage to the heart and lungs and prevent the heart from pumping blood correctly throughout the body.

What is heartworm disease?

Heartworm disease is the illness associated with heartworm infection. Damage to the heart and lungs can lead to heart failure and severe lung disease. Symptoms include cough, trouble breathing, trouble exercising, and a distended belly from backflow pressure of the failing heart. Death can occur if the pet is not treated.

How do dogs get heartworms?

Adult heartworms inside the dog produce baby worms, called microfilaria, that live in the dog’s bloodstream. Mosquitoes pick up these microfilariae when they bite dogs for a blood meal. The microfilariae grow and mature in the mosquito for about two weeks to become infective larvae and are then transferred to another dog during another blood meal by the mosquito.

Can puppies get heartworms?

Yes. If a mosquito with infective larvae bites a puppy, he or she will likely develop heartworms. Once infected, it takes about six months for heartworm larvae to become an adult heartworm.

Is heartworm disease common in puppies?

Heartworm disease is rare in puppies because it takes such a long time for the infective larvae to develop into adults. That being said, heartworms live for 5-7 years once they reach adulthood, so once your puppy is infected, heartworm disease is likely with time if he or she is not treated.

How do I prevent heartworms in my pet?

Heartworm prevention medications are available for adult dogs and puppies. These prevent heartworms by killing the infective larvae in the dog’s body before they can become adult worms (also known as molting).

Can I use heartworm prevention to treat my dog if he is already infected?

No. Heartworm prevention medication only works on the infective larvae. In as early as 51 days, those larvae can develop past the point that prevention will kill them, and they will develop into an adult. After this, your dog will need to be treated with a more costly and extensive adulticide regimen to kill the adult worms.

What will happen if I don’t use heartworm prevention?

Your puppy could develop heartworms and heartworm disease. All it takes is one bite from a mosquito carrying infective larvae for your dog to become infected with heartworms.

What types of heartworm medicine are available for puppies?

Numerous types of heartworm preventives are available. Most are used monthly. Some kinds of heartworm prevention are chewable or oral medications, while others are topical and applied between the shoulder blades. There is also an injectable form that can be used every six months. Be sure that you are using the heartworm medication that is labelled for heartworms. Flea or tick medications do not prevent heartworms, although some will have heartworm prevention medication included in the product.

Does my puppy need a prescription for heartworm prevention?

Yes. Heartworm prevention medication must have a prescription to be purchased. Your puppy’s regular veterinarian will be able to assist you with obtaining a prescription. He or she will also be able to help you decide which heartworm prevention will work best for your pet.

When should a puppy get heartworm medicine?

You should start a puppy on heartworm prevention (i.e., heartworm medicine) as soon as possible. The American Heartworm Society recommends starting a puppy on heartworm prevention no later than eight weeks of age. Each heartworm prevention product will have different ages and weights in which it is safe to start a puppy on heartworm prevention. Your veterinarian will be able to help you determine which heartworm medicine is safest for your puppy’s age and weight.

My puppy is older than eight weeks and has not been on heartworm prevention. Does he need a heartworm test first?

If your puppy is less than seven months of age, he can be started on heartworm prevention without having a heartworm test. It will take at least six months for heartworms to mature enough for a heartworm test to be positive if your puppy was infected while not on prevention. Your veterinarian will be able to help you choose a safe heartworm prevention product to start him on, as well as your puppy’s heartworm schedule. You should have your dog tested six months after this visit and again six months later to ensure your puppy has not developed a heartworm infection while not on prevention. Your dog should be tested yearly after this to ensure he continues to remain heartworm negative or free of heartworms.

Does an all-natural heartworm prevention exist?

No. Labelled heartworm prevention medications are the only US Food and Drug Administration (FDA) approved methods to prevent heartworm infections in puppies and dogs.