Heartworms: A Hidden, Yet Deadly Disease

Heartworms are a very serious and deadly disease caused by a parasitic roundworm called Dirofilaria immitis that attack a dog’s vital organs and eventually cause organ failures and death.

How is it Transmitted?

Heartworm eggs are carried by mosquitoes, and when an infected mosquito bites a dog, the eggs are transmitted into the animal’s bloodstream. Once there, they hatch and grow into baby heartworms, which are a type of filaria, a small thread-like worm. Eventually, they grow from microscopic size into long white worms up to 16 inches long that clog the dog’s heart, lungs and other vital organs.

The worms can take up to six or seven months to reach maturity and can live between five and seven years inside their host. Dogs can have up to 300 or so adult worms and thousands of the filaria in their systems.

Heartworms exist all over the U.S., World

The scary thing is that heartworm parasites are very commonly carried in mosquitoes in all 50 states in the U.S. It’s also been found in South America, Southern Europe, Southeast Asia, the Middle East, Australian and Japan.

Symptoms of Heartworms

When a dog is first infected, he won’t show symptoms for several months, but once he does it can manifest in several ways:

  • Severe coughing
  • Coughing up blood
  • Chest pain
  • Abnormal lung sounds
  • Weight loss
  • Fainting
  • Heart failure

And in rare cases when the worms end up in an unusual part of the dog’s body like the eyes or the brain, or a leg artery, the dog can show symptoms of:

  • Blindness
  • Seizures
  • Lameness

Prevention of Heartworms

It only takes one tiny mosquito bite to transmit the parasite eggs, and that’s why it is important that owners need to protect their pets from these deadly pests.

Heartworms can be easily prevented in several ways, including a variety of monthly medications. These are formed into tasty treats to make them more palatable to dogs. The drugs approved in the US are ivermectin (HeartgardIverhart, and several other generic versions; milbemycin (Interceptor Flavor Tabs and Sentinel Flavor Tabs) and moxidectin (ProHeart). Collies and collie mix dogs can’t take any form of invermectin, so be sure to talk to your veterinarian before starting your pet on one of these medications.

Moxidectin also comes in a shot form called ProHeart 6 and ProHeart 12 that can be given either once or twice a year. The latter was removed from the market in 2004 due to safety concerns, but the FDA approved a new version of the ProHeart 6 in 2008, which is used in Canada and Japan. Proheart 12 is still used in Australia and Asia.

In recent years, topical treatments have been introduced that also kill other pests like round worms, hook worms, tapeworms, fleas, ticks and mites. Some of these solutions include Advantage Multi (imidacloprid + moxidectin), Topical Solution, and Selamectin (Revolution). You should discuss with your veterinarian which preventative is best for your pet.

Before your dog goes on any of these monthly preventatives, he should have a blood test to see if he is already carrying the disease, as a dog can’t take the monthly meds if he already has heartworms.

Treatment of Heartworms

While these preventatives are relatively inexpensive, it’s very expensive, as well as dangerous to treat a dog that already is infested with heartworms. The reason is that you have to actually poison the worms and when they die, the dog expels them and has to be strong enough to handle it.

The drug that’s used is a form of the poison arsenic called Immiticide. Infected dogs are given two or three shots of it to kill all the worms in their body and the treatment takes several weeks to complete.

The whole process usually costs several hundred dollars and there is no guarantee the dog will survive the treatment. When a dog is treated, the worms die and break up, which can sometimes cause the lungs to be clogged up. For this reason, dogs have to be kept very still and quiet during treatment.

In severe cases, surgery is used to remove the worms from the dog’s body, but this is rarely used.

If your dog has heartworms and is treated, about 96 percent end up being cured.

All in all, heartworms are a very serious and potentially deadly disease that can easily kill your pet. That’s why the American Heartworm Society recommends you give your dog a preventative all year long. So, if you don’t want your best friend to get heartworms, be sure to have him tested at the vet and then put on a heartworm preventative.


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