Heartworm in dogs. Symptoms, treatment and prevention
by Jennifer Hanlon. K9Einsteins Professional Dog Training

What are Heartworms?

Heartworms are parasitic worms that travel via the bloodstream and live in the arteries of the lungs as well as the right ventricle of the heart. While they can mature and replicate in over thirty host species, the most common pet owners who are aware of their existence tend to be dog owners.

What is Heartworm Disease?

Heartworm Disease is the condition caused by these worms. As mentioned, the worms migrate through the blood vessels until they settle in the lungs and or heart. They will cause severe damage and potentially death for your dog. The disease is easily preventable and not so easily treated. More information of prevention and treatment will be provided further in this article

Where is Heartworm Found?

Heartworm is found in many parts of the world where mosquitoes are present, including the US, Canada, South America, Europe, Africa, Asia and Australia. In the US, heartworm has been found in dogs in all 50 states.

How does my dog get heartworms?

Adult female heartworms give birth to babies, called microfilariae (micro-fill-air-ee-ya) and release them into the animal’s bloodstream. Microfilariae cannot mature on their own without an intermediate host. Enter the mosquito.

The mosquito bites the infected animal and sucks up the microfilariae along with their blood and kind of baby sits it for a while. The infants mature inside the mosquito for about ten to fourteen days and grow into the infective larval stage.

Next the mosquito goes and bites another animal, and deposits the larva into the new animal’s bloodstream. There they travel along and approximately six months later develop into adult spaghetti like worms, where they will begin this process all over again.

Male heartworms can be anywhere from four to six inches long and females range from ten to twelve inches. According to the American Heartworm Society, dogs can have anywhere from one to two hundred fifty worms.
 

As the heartworm disease progresses, symptoms become more severe. In addition to the above, the liver may become enlarged. Temporary loss of consciousness due to poor blood flow to the brain may occur. There may be fluid build up in the abdomen. Heart sounds will also become abnormal. Death of the dog may follow shortly.

Are Heartworms Preventable?

Yes they are, and it really is quite simple. There are several medications on the market that you can give your dog for the prevention of heartworms. No dog ever needs to suffer the treatment of heartworms, or the damage these parasites can cause. Since there are so many products to choose from and their individual parasite control spectrums vary, you must consult your veterinarian to see which one would be best for your dog.

What Are The Approved Products For Heartworm Prevention?

Heartgard and Heartgard plus are made by Merial. The prevention in both is ivermectin in a specific dose. Heartgard plus adds a de-wormer and is labeled for treatment and control of hookworms and roundworms as well.

Iverheart Plus and Iverheart Max are by Virbac. Iverheart plus contains the same ingredients as Heartgard Plus, while the Iverheart Max also contains a de-wormer for the control and treatment of tapeworms.

Tri-Heart Plus by Schering-Plough are chewable tablets with the same ingredients and spectrum of Heartgard Plus and Iverheart Plus

Interceptor and Sentinel are both made by Novartis. The heartworm preventative in these products is milbemycin. Sentinel adds a product for flea control that sterilizes adult fleas to prevent infestation, but does not kill them. They are labeled for the treatment and control of hookworms, roundworms and whipworms.

Revolution is put out by Pfizer and the medication is Selamectin. It is labeled for the prevention of Heartworms, fleas, some ticks, ear mites and certain skin mites. While not labeled effective for intestinal parasites, if purchased from a licensed veterinarian Pfizer will give free worming tablets that are effective against hookworms and roundworms. If you find you are getting ticks on your dog, Pfizer will also provide Preventic collars free of charge if purchased from a veterinarian.

Advantage Multi is manufactured by Bayer. Moxidectin is the heartworm medication and it also combines a flea control as well. This product does kill fleas. It is also labeled for treatment and control of hookworms, roundworms and whipworms.

Advantage Multi® for Dogs (imidacloprid + moxidectin) Once a month Topical Solution Treats and controls ear mite infestations. Prevents heartworm disease. Kills adult fleas and treats flea infestations. Treats and controls common intestinal parasites: roundworms, hookworms and whipworms.

Advocate is the same product as Advantage Multi as shown above It is marketed under Advantage Multi in the US, Canada and New Zealand. Treats and controls ear mite infestations. Prevents heartworm disease. Kills adult fleas and treats flea infestations. Treats and controls common intestinal parasites: roundworms, hookworms and whipworms.

Moxidectin has also been formulated into an injection called Pro-Heart6 and is manufactured by Fort Dodge Animal Health. It is a time release form and lasts in the dog’s system for six months. Pro-Heart6 was on the market several years ago and was recalled. It has been re-launched and is listed among the above mentioned preventatives on the website of the American Heartworm Society.

**NOTE** The American Heartworm Society does NOT endorse the use of injectable ivermectin for cattle/swine in dogs for heartworm prevention.

The preventatives listed above are not in order of recommendation by this author. They are listed in the same order as on the website of the American Heartworm Society.

Are Heartworms treatable?

Yes, heartworms are treatable, but it’s not a safe or comfortable treatment. The adult worms must be killed with an adulticide, which can be dangerous and painful injections for the dog.

The arsenic based injection is given into the muscle. The dog is kept for monitoring and comes back in thirty days for the next injection. A third injection is given the next morning. The dog is also given antibiotics and anti-inflammatory medications.

During treatment, you MUST crate the dog and only leash walk outside to go to the bathroom. Absolutely NO EXERCISE AT ALL. The treatment protocol is killing adult heartworms, of which there is no way of knowing the actual worm count inside the dog. Dead heartworms can block the flow of blood through the dog’s pulmonary arteries. So a dog with a few heartworms might do fine, whereas a dog with a very heavy worm burden could still die.

When Should I test my Dog for Heartworms?

A dog that is on a heartworm prevention regimen should be tested every year. Most vets will do this at their annual exam and vaccine appointment. A dog that has not been on prevention should not start on any prevention product prior to being tested. If on prevention but you missed some doses, check with your vet to see if your dog should be tested first. The amount of consecutive months off of prevention will determine that.

It is dangerous to give a heartworm preventative to a dog that already has heartworms. The prevention products kill certain life stages of heartworms and if the juvenile worms die off they can cause obstruction.

They dog must be monitored and rested during the dying process, so if you are unaware of your dog’s heartworm status before giving the prevention, the results could be disastrous. A positive dog can also have an anaphylactic reaction and die after being given a preventative.


Author: Jennifer Hanlon. K9Einsteins Professional Dog Training

Please note: The medical articles on this site have not been written by a veterinarian & should not be considered a replacement for a veterinarian visit. The articles are provided for informative purposes only. While great care has been made in the creation of these articles, we cannot guarantee the accuracy or omissions on these pages. If in any doubt whatsoever, seek professional medical advice