Top Dog Tips - Heartworm Prevention in DogsLast week my column was about buying pet store puppies and all the dangers that come with it. The reason so many pet store puppies become ill is because many of them come from irresponsible breeding. Poor genetics is not the only thing that leads to health conditions though. Some diseases are spread through insects and other pests. Heartworms are one of these issues that is passed from dog to dog, and it is important to protect your dog from becoming infected.

Many pet parents underestimate the importance of giving their dog a preventative treatment for heartworms. Both of my dogs take a heartworm preventative once a month (we use Sentinel), but I am passionate about educating other pet parents on the dangers of heartworms and helping to spread awareness. What better way to do that than to share some great information with all of you this week?

In order to understand the importance of prevention, you first need to understand what heartworms are how they are passed from one animals to another. Heartworm disease is spread by mosquitoes. The American Veterinary Medical Association explains very simply what this means for pet parents in this article.

  • All dogs, regardless of age, sex, or living environment, are susceptible to heartworm infection. Indoor, as well as outdoor, cats are also at risk for the disease. Because heartworms are spread by mosquitoes, any pet exposed to mosquitoes should be tested. This includes pets that only go outside occasionally.

In their very in depth booklet, entitled Current Canine Guidelines for the Prevention, Diagnosis, and Management of Heartworm (Dirofilaria immitis) Infection in Dogs, the American Heartworm Society (AHS) tells you everything you'll ever need to know about heartworms, heartworm disease and how to treat it. It's challenging to read and is full of veterinary and scientific jargon, but it will give you absolutuely all the information you will need.

  • When the mosquito takes a blood meal, the infective larvae rupture the end of the mosquito’s labrum and emerge within a droplet of hemolymph (mosquito blood) on the skin of the host. Immediately after the blood meal, these sexually differentiated larvae enter the animal’s body via the puncture wound made by the mosquito’s mouthparts.

The AHS has also created this easy-to-follow diagram that explains the life cycle of heartworms, when preventative measures are effective, and when treatment is required.

But what are heartworms and what will they do to your pet? Tufts University has created a very simple handout for pet parents with some basic information regarding heartworms. The information is really basic, but it's enough to understand the importance of preventative treatments.

  • When a mosquito sucks blood from an infected animal and then bites its next victim the larvae are transmitted through the skin. These larvae eventually make their way to the chambers of the heart or lungs where they grow into adults. They grow, some up to 10-12 inches in length, and can eventually wreak havoc on your pet’s organs.

Once you know what heartworms are and how they are transmitted, you need to understand exactly what they can do your dog and how they will be harmful to his body. has published a great article that explains all about heartworm disease in a very easy-to-understand way.

If you're just looking for a brief understanding of heartworms before you have a conversation with your vet, this is definitely the article for you.

  • Once in the heart, the worms can affect blood flow throughout the body. Heartworm infection can affect many different organs of the dog—heart, lungs, kidneys, and liver, for example—so symptoms may be varied.

The Veterinary Teaching Hospital at LSU answers some frequently asked questions about heartworm disease on their website. One of the most common questions asked by pet parents is ‘what are the symptoms of heartworm disease in dogs?' That's also the best question you can ask, because you need to know the symptoms in order to be able to recognize that their a problem.

The best thing you can do as a pet owner is to observe your dog on a daily basis. Keep his behavior, eating habits, bathroom habits and other common daily activities in mind. If you monitor your pet on a regular basis you will easily be able to pick up on signs when something is wrong. According to the Veterinary Teaching Hospital at LSU the symptoms that you should be looking for are:

  • Dogs with early heartworm infestation may not show any symptoms. Dogs with early symptoms may tire easily, especially during exercise, and might have a soft, deep cough. If not treated, this progresses to rapid breathing and weight loss. In severe cases dogs might have fainting spells. Sudden death is also possible.

Most veterinarians will do a test for heartworm every year during your dog's annual exam. What happens if your dog tests positive for heartworm? As you could probably guess, you can find everything that you need to know about heartworm disease on the website for the American Heartworm Society.

Along with the booklet that I mentioned earlier, the organization also has a very detailed article on their site that offers some great information to pet parents. Of course, you should consult with your veterinarian to discuss your dog's condition, but if you would like some information beforehand, this is a great read.

  • No one wants to hear that their dog has heartworm, but the good news is that most infected dogs can be successfully treated. The goal is to first stabilize your dog if he is showing signs of disease, then kill all adult and immature worms while keeping the side effects of treatment to a minimum.

Now that you have a better understanding of what exactly heartworms are and how they can effect your pet, I hope you are beginning to understand the importance of keeping your pet on a preventative heartworm medication. Whether you have mosquitoes in your region during the winter months or not, your pet should be on heartworm preventatives all year long.

This article, written by Dr. Dwight D. Bowman, explains why all pets should be treated year round.

  • CAPC recommends year-round heartworm prevention with internal and external parasite control for dogs and cats. It is difficult to comprehend why there is resistance from so many practitioners and their clients as to the need for such control, as this seems the logical means of easily preventing a number of pathogens from dwelling in or on a pet or feeding on a pet and inoculating it with dangerous microbes. The cost is minimal compared to the cost of treating the diseases and the morbidity (and sometimes mortality) induced, the concern of clients faced with an infected pet, and the potential of pets being the reservoir of zoonotic agents.

Heartworm preventatives don't prevent the mosquitoes from biting your dog. Think of using bug repellent on yourself. It may work to keep most of the pests from biting you, but it won't keep them all away. It works the same with dogs. No matter what type of substance you use to keep mosquitoes away from your pet, he is still sure to get bitten at least a few times.

That's why heartworm preventatives kill the heartworm larvae instead of trying to prevent the bite in the first place. Jessica Maloney wrote a brief article for Purdue University's College of Veterinary Medicine that answers some common questions about heartworm preventatives.

  • Heartworm preventatives do not actually prevent mosquitoes from infecting your dog with heartworm larvae. These preventatives actually kill different stages of heartworm larvae that already have infected your dog. Different types of heartworm preventatives kill different stages of heartworm larvae. Therefore heartworm preventatives can have different schedules of administration (monthly or every 6 months). 

You can also find some great information about heartworm disease on the United States Food and Drug Administration's (FDA) website. Of course, you should always use medications that have been approved by the FDA. Their website has information on preventative products as well as the two treatments that they have approved.

  • There are many FDA-approved products that prevent heartworm disease in dogs.  All require a veterinarian’s prescription.  Most products are given monthly, either as a topical liquid applied on the skin or as an oral tablet.  Both chewable and non-chewable oral tablets are available.  One product is injected under the skin every six months, and only a veterinarian can give the injection.

One last piece of advice before I go: make sure to get your pet's medication from your veterinarian. Not all online pet medication websites sell reliable medications. The FDA has a great article that warns of these dangers. It would be better to pay a little more at your vet's office than end up causing more problems by giving your dog the wrong medication.

  • FDA has found companies that sell unapproved pet drugs and counterfeit pet products, make fraudulent claims, dispense prescription drugs without requiring a prescription, and sell expired drugs. Pet owners who purchase drugs from these companies may think they are saving money, says Hartogensis, but in reality, they may be short-changing their pet's health and putting its life at risk.

If you've had experience with heartworm disease in pets, please share your advice in the comments below. It may help other pet parents to hear about what you and your dog went through. Please take the time to talk with your veterinarian about dog heartworm disease and learn about the importance of preventative medications.

Samantha’s biggest passion in life is spending time with her Boxer dogs. After she rescued her first Boxer in 2004, Samantha fell in love with the breed and has continued to rescue three other Boxers since then. She enjoys hiking and swimming with her Boxers, Maddie and Chloe.