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Lungs affected by heartworms
Lungs affected by heartworms

My Dog Tested Positive For Heartworms. Now What?

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Heartworms are devastating parasites in dogs, responsible for thousands of deaths each year. Most of these occur due to the destruction that heartworms cause not just to the heart, but the lungs, liver, and kidneys as well. In some cases, the number of heartworms can become so great that blood circulation is actually compromised by the heartworms, resulting in sudden death. Other dogs infected with heartworms can go years without showing any signs of disease, seemingly forming a symbiotic relationship with the heartworms themselves.

Heartworms place a tremendous burden on the body's organs and immune system. If your dog is diagnosed with heartworms, there are two treatment options available to you: 1) Fast Kill; and 2) Slow Kill. Let's take a quick look at both methods of treating heartworms.



The fast kill, or standard treatment for heartworms uses melarsomine, a compound that is lethal to most heartworms when injected directly into the dog. In most cases, it will eliminate all adult heartworms within four to six weeks.

Prior to treating a dog for heartworms, a complete laboratory work-up, including X-rays and/or ultrasound, should be performed to determine the status of the internal organs, especially the heart, lungs, liver, and kidneys. If potential problems do exist because of the heartworms, a "priming" dose of medication may be administered to allow the body to adjust to the drug and to weaken the heartworms. Then in a month or so, if all looks well, the standard treatment for the heartworms is often attempted. Ironically, because of the effectiveness of melarsomine, complications can arise as the heartworms die, prompting immediate cessation of the treatment series.

Remember: When heartworms die, they aren't simply passed from the body like intestinal worms are. Dead heartworms must be processed and dissolved by the dog's body just like any other type of internal "infection". Complications that can arise as heartworms die can include loss of appetite, vomiting, and/or the development of icterus, indicating liver inflammation. Pieces of dead heartworms can lodge within the blood vessels of the lungs, and if the number of dead heartworms is extensive, clots can form in the lung vessels, causing severe coughing and lung hemorrhage.

If all goes well, patients are discharged from the hospital to begin a four to six week convalescence at home. Preventive medications for heartworms will be given either during or after this time to kill any microfilaria (baby heartworms) still circulating in the blood. Exercise and activity MUST be restricted during this convalescent period, since the heartworms are still dying and clots could form if a dog gets its pulse or blood pressure up too high.

Advantages of the Fast Kill Treatment for Heartworms:

1. Quick kill, reducing ongoing organ damage caused by the presence of heartworms.

2. Prevents new infestations of heartworms(when employed with preventative).

3. Can exhibit up to 100% killing efficacy against all ages of heartworms.

4. Dogs can generally resume normal activities within 45 days of treatment without fear of sudden clots from dying heartworms damaging the lungs.

Disadvantages of the Fast Kill Treatment for Heartworms:

1. Expensive ($500 to $1500)

2. Multiple clots in the lungs could form as a result of the massive die-off of heartworms following the injections, sometimes with fatal consequences.

3. Convalescent period following the treatment for heartworms is critical; dogs often must be kept in strict confinement to limit activity.

4. Some dogs may have a reaction to the melarsomine itself in addition to the heartworms, with severe reaction resulting in organ damage.

5. The injections to kill the heartworms are painful.



Heartgard Plus (ivermectin) or a similar generic product given monthly at the normal preventive dose will, in most instances, eventually kill heartworms, although it can take up to 30 months for this "slow kill" approach to work. Although this method of treating heartworms is frowned upon by many veterinarians, others feel it remains a viable options in those instances where finances are a concern or where the fast kill treatment for heartworms is deemed too risky for the pet (including dogs with extra large burdens of heartworms, dogs under 20 pounds, and dogs exhibiting clinical signs from the heartworms at the time of diagnosis).

Advantages of the Slow Kill Treatment for Heartworms:

1. Inexpensive.

2. Prevents infestations by new heartworms.

3. Weakens existing heartworms, improving the efficacy of the fast kill treatment for heartworms if that mode of treatment is desired later on.

4. Avoids the safety concerns associated with the fast kill treatment for heartworms.

5. Can exhibit up to 100% killing efficacy against immature and young heartworms.

Disadvantages of the Slow Kill Treatment for Heartworms:

1. Clot in the lungs caused by dead heartworms could occur suddenly at any time during the prolonged treatment period, especially during exercise or rigorous activity.

2. As long as living heartworms are present inside the heart and vessels, ongoing damage to the heart, lungs, and other organs can occur.

3. May not work well against older heartworms, especially older female heartworms.

Regardless of which approach to treating heartworms you ultimately select for your dog, either one is better than doing nothing at all. And once your furry friend is finally free of heartworms, be sure to keep him/her on the medication to prevent heartworms each and every month. Its cheap protection against heartworms and so worth it!

So is your pet.

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