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Do I Need To Give My Dog Heartworm Medication?

Heartworm medication

Heartworms are dangerous internal parasites that infect dogs and cats (and even ferrets) by a simple bite of a mosquito. While heartworm disease is not contagious (meaning one dog cannot transfer heartworm to another dog), it is severe and can cause lung disease, heart failure and other organ damage. In some cases, heartworms can be fatal. 

Continue reading to learn everything you need to know about heartworms, including:

  • What are heartworms?
  • How do veterinarians test for heartworms?
  • How to prevent heartworm disease in dogs

Let’s dive right in.

What are heartworms?

Heartworms are a parasitic worm called Dirofilaria immitis. When your pet is bitten by a mosquito carrying the parasites, they are transferred into your pet where they mature, mate and multiply—heartworm offspring are called microfilariae—within your pet’s bloodstream. After about 6 or 7 months, infective larvae (microfilariae) mature into adult heartworms and set up shop in your pet’s heart, lungs and associated blood vessels.

What do heartworms look like?

Resembling a strand of cooked spaghetti, heartworms can live approximately 5 to 7 years inside your pet. Male heartworms grow 4 to 6 inches in length, while the females can grow up to 12 inches in length.

How many heartworms can infect my dog?

The number of heartworms inside your pet is called the “worm burden.” The average worm burden in dogs is 15, but can range anywhere from 1 to 250.

How do veterinarians test for heartworm disease?

Your vet will draw blood from your dog and perform two tests:

  1. An antigen test that detects heartworm protein release by adult female heartworms. The earliest that the protein can be detected in your dog is roughly 5 months after it was bitten by an infected mosquito.
  2. The second test detects microfilariae (which is produced when adult heartworms mate and produce offspring) in your dog’s bloodstream. The earliest microfilariae can be detected is roughly 6 months after your dog has been bitten by an infected mosquito (because only adult heartworms can multiply to produce offspring).

When should you test your dog for heartworms?

The timing and frequency of heartwarming testing will depend on several factors, including:

  • When you first gave heartworm prevention medication to your dog
  • If and when you forgot to give your dog heartworm prevention medication
  • If you’ve recently switched your dog’s heartworm prevention medication
  • The duration of mosquito season in your area
  • If you’ve moved your dog to a new area where heartworm disease is more prominent

Prevention of Heartworm Disease in Dogs

Fortunately, you can prevent heartworms from developing in your dog’s body. However, before giving preventative heartworm medication to your dog, your vet will test to make sure that there are no existing traces of the worm. If your dog does have heartworms, your vet will prescribe medication to eliminate them. Only then can you think about preventing future infestations.

There are several types of preventative heartworm medications, most of which are given orally (as a pill) on a monthly basis, however, sometimes topical treatments may be given to prevent your pet from being bitten by mosquitos. 

Types of Heartworm Prevention Medication

Here are some of the most popular heartworm prevention medications for dogs:

HeartGard Plus for dogs up to 25 lbs is usually prescribed for small dog breeds. It contains Pyrantel and Ivermectin, which completely destroys heartworm larvae before they mature into adult worms. Heartgard Plus also protects your dog from two types of roundworms and three types of hookworms, and it has proven effective in the treatment of mange and lice

Tri-Heart Plus is a budget-friendly alternative to its closest competitor, HeartGard Plus. Tri-Heart Plus contains Ivermectin and Pyrantel, the same ingredients found in HeartGard Plus, but typically costs about 20% less.

Interceptor Plus is a chewable monthly anti-heartworm medication that contains Milbemycin Oxime, which also protects your dog from hookworms, whipworms, roundworms and tapeworms.

ProHeart 6 is the only FDA-approved injectable preventative heartworm medication for dogs, and can protect your pet for up to six months at a time. It must be administered by your vet, and is proven to safeguard your dog from not only heartworm disease, but sarcoptic mange, and other worms including whipworm, hookworm and roundworm.

Advantage Multi is a monthly topical application that contains Moxidectin, which protects dogs from whipworms, hookworms, heartworms, and roundworms, in addition to sarcoptic mange and fleas. 

The Bottom Line

Heartworm disease is serious, and can be fatal to your canine companions. Prevention is the best way to keep your pets safe from not only heartworms, but other types of internal parasites. Talk to your vet about the best way to prevent your dog from contracting heartworm disease.